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3rd Structural Integrity Conference and Exhibition – SICE2020

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Book of Abstracts

3rd Structural Integrity Conference

and Exhibition

(SICE 2020 e-Conference)

11-13 and 18-20 December 2020

Indian Institute of Technology Bombay, Mumbai, India

http://sice2020.in/


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Platinum Sponsor


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Platinum Sponsor


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Platinum Sponsor


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Gold Sponsor

Gold Sponsor


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Silver Sponsor


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Sr. No. Contents Page

No. 1. SICE2020 e-Conference Committees 8 2. Message from Indian Structural Integrity Society 9 3. ABOUT SICE 2020 10 4. Technical Theme and Symposia 11 5. Acknowledgements 12 6. Schedule 13-20 7. Plenary talks [PN] 21-27 10. Key note talks [TSXX_KNXX] 28-44

Themed symposium talks: Invited Talk [IN] Contributed[CN]

11. TS01 Structural Integrity of Additive Manufactured 45-47 12. TS02 Applications of Data Science 48-53 13. TS03 Creep and High Temperature Failure 54-62

14. TS04 Fracture and Fatigue in Materials and Structures 63-79 15. TS05 Fracture Mechanics at Multiple Length Scales 80-91 16. TS06 Fracture and Fatigue of Structural Adhesives 92-98 17. T07+TS26 Integrity of Concrete Structures Against Blast and Ballistic

Loading and Construction materials, and concrete and steel structures 99-101

18. TS09 Material Behaviour Characterization using Miniature Specimens 102-109

19. TS10 Material Behaviour Characterization Under High Strain Rate Loading 110-122

21. TS12 + TS16 Multiscale Modelling of Plasticity, Creep, Fracture, and Fatigue and Role in Material and Structural Integrity

123-140

22. TS13 Non-destructive Testing and Evaluation for Structural Integrity Assessment

141-143

23. TS14Nuclear Reactor Safety, Radiation and other Extreme Conditions 144-149

24. TS15+TS23 Reliability of coatings + Thin Film Deformation and Failure 150-158

25. TS17+ TS25-Reliability Aspects in Medical Devices and Implants Other - Biomechanics

159-165

26. TS20-Structural Integrity of Weldments and Welded Structures 166-169

27. TS21-Structural integrity of Gas Turbine Engine Materials 170-174

28. TS22-Damage and Failure modelling in Composite Materials 175-181


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SICE2020 e-Conference Committees

National Steering Committee:

• Dr. Ravi Chona, AFRL, USA

• Prof. Amol Gokhale, IIT Bombay, India

• Prof. Vikram Jayaram, IISc, India

• Dr. Vikas Kumar, DMRL, India

• Prof. Raghu Prakash, IIT Madras, India

• Dr. Karthik Prasad, DMRL, India

• Prof. Ashok Saxena, University of Arkansas, USA

• Dr. Ramasubbu Sunder, ITW-India, India

Local Organizing Committee – IIT Bombay

• Prof. Krishna Jonnalagadda (Convener)

• Prof. Alankar Alankar (Convener)

• Prof. Tanmay Bhandakkar (Convener)

• Prof. Nagamani Jaya Balila (Convener)

• Prof. Prasad Manepalli

• Prof. Prakash Nanthagopalan

• Prof. Anirban Patra

• Prof. Amber Shrivastava

• Prof. Parag Tandaiya


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Message from Indian Structural Integrity Society

Structural Integrity is at the core of any endeavor associated with safety critical engineering effort. The increasingly interdisciplinary nature of this discipline is well reflected in SICE2020, the third such Conference organized under the aegis of the Indian Structural Integrity Society and hosted by the Indian Institute of Technology, Bombay at Powai, Mumbai.

The first two meetings in 2016 in Bangalore and 2018 in Hyderabad were a resounding success, with more than 400 participants from over 15 countries between them. When IIT Bombay took up the organization of SICE2020, no one could have imagined the challenge that would be thrown up by a tiny virus that attacks structural integrity at the scale of human organism. Nevertheless, the dynamic team at IIT under the joint chairmanship of Profs. Krishna Jonnalagadda, Nagamani Jaya Balila, Alankar Alankar and Tanmay Bhandakkar have put together a rich conference programme.

SICE 2020 brings together well over a hundred participants from 7 countries, including 22 plenary speakers, over 40 invited speakers and close to 80 contributed papers. These will be presented across as many as 20 specialist symposia in line with the Conference theme aligned with Structural Integrity at Multiple Scales. Peer reviewed submissions will appear as a dedicated Springer publication.

To overcome the unforeseen challenge posed by COVID-19, SICE 2020 is organized across as many as five parallel on-line sessions spread across 6 days over the evening hours in India that should suit most global participants. And, to convert the unexpected problems posed by the pandemic into a virtual advantage, the Organizers have opened up the internet infrastructure to permit extended interaction between participants that extend beyond the formal sessions. All this at a Registration Fee that should be attractive to one and all.

SICE2020 may not have had the grandeur of its original venue, the Victor Menezes Convention Centre. But this appears more than made up by the eminent scientists from the world over and by a large number of participants from industry, academia and national laboratories, who have been brought together by the Indian Institute of Technology.

Please sign up if you haven’t done so, register, and enjoy SICE2020.

R. Sunder

President, Indian Structural Integrity Society


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ABOUT SICE 2020

The Structural Integrity Conference and Exhibition (SICE), is a flagship conference of the Indian Structural Integrity Society (InSIS). The 3rd edition of the regular conference was suppovsed to be conducted at IIT Bombay campus in December 2020. However, due to the existing COVID19 pandemic situation, it was decided to postpone the regular conference to a better time in near future. Considering that the 2nd SICE was conducted in 2018, the organizers at IIT Bombay in consultation with InSIS Executive Board (EB), have decided to conduct a ‘limited’ version of the conference, virtually, through video conferencing. Since, this decision, with the help of many colleagues and friends, the evolution of the conference has been interesting journey. The current program of the conference consisting of invited and contributory talks, and e-Posters, has come to fruition, due to the hard work and enthusiasm shown by Symposium Organizers, InSIS-EB members, Conference Organizers at IIT Bombay, and more importantly speakers and authors, who accepted our request at a short notice. In addition, the timely advice and support provided by Prof. Amol Gokhale (IIT Bombay), and InSIS-EB members, especially, Dr. R. Sunder (President, InSIS) and Prof. V. Jayaram (Vice-President, InSIS), has helped us shape this conference. Finally, the staff and student volunteers, have been working towards a smooth execution of this conference, and we hope that all the participants will have a great experience, in attending this virtual event, from the safety and comfort, of their respective locations. On a positive note, the advantage of this virtual conference is in its reach for those who cannot afford to attend and travel a regular conference.

We also take this opportunity, to thank all the members of the structural integrity community, who through their contributions have made this conference possible. We thank all the symposium organizers, InSIS international steering committee, IIT Bombay organizing members and authors, to make this conference a reality (albeit virtual!) in these unusual times. A few important names behind SICE2020 are listed below:

• Prof. Amol Gokhale – IIT Bombay

• Prof. Vikram Jayaram – Indian Institute of Science

• Dr. Ramasubbu Sunder – BISS, ITW

• Prof. Ashok Saxena – WireTech Cylinders LLC

• Dr. Vikas Saxena – Defense Metallurgical Research Laboratory

• Dr. Dheepa Srinivasan – Pratt & Whitney

• Prof. Raghu Prakash – IIT Madras Symposium Organizers:

• Dr. Dheepa Srinivasan

• Prof. Srikanth Gollapudi

• Prof. Ravishankar Kottada

• Prof. Viswanath Chintapenta

• Prof. Naresh Datla

• Prof. Prakash Nanthagopalan

• Prof. Manish Kumar

• Dr. Zafir Alam

• Prof. Eswar Korimilli

• Prof. Gaurav Tiwari

• Prof. Pritam Chakraborthy

• Prof. Anup Keshri

• Prof. Abhay Kumar Kuthe

• Prof. Amber Srivastava

• Prof. Anirban Patra

• Prof. Chandra Sekhar Yerramilli


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Technical Theme and Symposia

The technical theme of the conference for this edition is “Structural Integrity at Multiple Length Scales”. It is recognized that the integrity and failure are associated with the nucleation, growth and propagation of ‘defects’ in various materials and structures. The length scale at which these ‘defects’ dominate the response of a solid, small or large, determines its integrity. Therefore, the current conference includes, symposia that span a wide range of length scales from small crystal lattice to large structural components. Under such a broad theme, the conference includes the following symposia, which are ably led by our symposium organizers, listed next to the technical symposium name.

• Structural Integrity of Additive Manufactured Components – Dr. Dheepa Srinivasan

• Applications of Data Science – Prof. Alankar Alankar • Creep and High Temperature Failure – Prof. Srikanth Gollapudi • Fracture and Fatigue in Materials and Structures – Prof. Viswanath Chintapenta

• Fracture Mechanics at Multiple Length Scales – Prof. Nagamani Jaya Balila

• Fracture and Fatigue of Structural Adhesives – Prof. Naresh Datla

• Integrity of Concrete Structures Against Blast and Ballistic Loading AND

Construction materials, and concrete and steel structures – Prof. Prakash Nanthagopalan and Prof. Manish Kumar

• Material Behaviour Characterization using Miniature Specimens – Dr. Zafir Alam

• Material Behaviour Characterization Under High Strain Rate Loading – Prof. Eswar Korimilli, Prof. Krishna Jonnalagadda and Prof. Gaurav Tiwari

• Multi-scale Modelling of Creep, Fracture AND

Fatigue and Role of Multiscale Plasticity in Material and Structural Integrity Prof. Alankar Alankar and Prof. Pritam Chakraborty

• Non-destructive Testing and Evaluation for Structural Integrity Assessment - Prof. Krishna Jonnalagadda

• Nuclear Reactor Safety, Radiation and other Extreme Conditions – Prof. Alankar Alankar • Reliability of coatings – Prof. Anup Keshri • Reliability Aspects in Medical Devices and Implants and Biomechanics – Prof. Abhay Kumar

Kuthe

• Structural Integrity of Weldments and Welded Structures – Prof. Amber Shrivastava

• Structural integrity of Gas Turbine Engine Materials – Prof. Anirban Patra

• Damage and Failure modelling in Composite Materials – Prof. Chandra Sekhar Yerramalli

We hope that you enjoy the virtual talks and interactions, by speakers and participants.

From Conference Convenors:

Krishna Jonnalagadda Alankar Alankar Tanmay Bhandakkar Nagamani Jaya Balila


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Acknowledgements

We would like to take this opportunity to thank the president, vice-president and all the members of the

executive board of the Indian Structural Integrity Society for giving IIT Bombay the opportunity to host the

3rd Structural Integrity Conference and Exhibition-SICE 2020. They have constantly helped us with their inputs

and experience, in between their busy schedules for which we are grateful.

This conference would not be having the impressive list of invited speakers across more than 8 countries and

more than 100 contributed presentations/posters that we can boast of, without our symposium organizers.

We would like to thank them immensely for the time and resources that they have spared in bringing all the

people together, reviewing abstracts and conducting this conference smoothly, as well as being patient and

understanding with our lapses. We would like to express our sincere gratitude to all the Plenary, Keynote and

Invited speakers for taking time off their busy schedules to deliver their talks, while adjusting to the time

schedules of an online conference. Our students and colleagues will immensely benefit from their presence

and participation at SICE 2020.

We would like to thank all the authors who submitted their papers for consideration at SICE 2020.

Congratulations to those who were selected for full paper presentations as well as e-posters and we look

forward to listening to you all. No conference is a success without its attendees’ active participation. We would

like to thank all the participants for registering for SICE 2020 and joining us here.

No event can run without sufficient finances, not even an e-conference. While it has been a difficult year for

all, our industry friends have supported us immensely. In addition to best presentation and poster prizes, we

were able to offer free registrations to students for listening in to the conference talks. This is all because of

the generosity of our sponsors. We were also able to reach out to a larger audience because of them. They

have enriched our program by contributing technical talks and demonstrations in place of physical exhibits,

along with content on our webpage at: http://sice2020.in/exhibitors/. We would like to thank our Platinum

sponsors: Bruker Industron, Micro Materials, Dassault Systems, Gold sponsors: Zwick-Roell, BISS-ITW, Silver

Sponsors: DTS-Gleeble, for their generous contributions.

With the changed circumstances of this year and the entire conference going online, we could not have pulled

this through without an efficient team of website design and management. We would like to thank Mr Ulhas

Joshi, PowerSoft.Inc for providing us a platform for the same. We would also like to thank Mr Bansode and

SBI IITB for helping us with accounts. When the physical conference was being planned the IITB Administration

helped us in booking the venue and readying other logistics, which we unfortunately could not utilize.

Nevertheless, we are grateful for their support. We would also like to thank our publishing partner Springer, for

publishing the conference proceedings of SICE 2020. We are sure the authors will benefit immensely from this

opportunity.

While the planning for SICE 2020 started a while ago, it was the army of student volunteers who pitched in

during the last two weeks. This event would be an impossibility without them rising to the occasion and helping

us out with every task including registrations, scheduling, abstract booklets, poster lists and online session

coordination. We would like to thank each and every one of them here: Ashwini K Mishra, Soudip Basu,

Tanmayee More, Vaishali Garud, Mahavir Singh, Prakash Kumar Sahu, Pilla Kartheek, Deepesh Yadav, Tejas

Chaudhari and Hrushikesh Sahasrabuddhe.

On behalf of local organising committee, SICE 2020 Krishna Jonnalagadda Alankar Alankar Tanmay Bhandakkar Nagamani Jaya Balila

http://sice2020.in/exhibitors/


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Schedule


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Plenary talks

1. John Hutchinson 11th Dec 2020

2. Arun Shukla 12th Dec 2020

3. Huajian Gao 13th Dec 2020

4. K. Ravi-Chandar 18th Dec 2020

5. Rhys Jones 19th Dec 2020

6. Ioannis Chasiotis 20th Dec 2020


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Plenary Lecture-1

Dent imperfections in shell buckling: the role of geometry, residual stress

and plasticity

John W. Hutchinson

School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138

Departures of the geometry of the middle surface of a thin shell from the perfect shape have long

been regarded as the most deleterious imperfections responsible for reducing the shell’s buckling

capacity. Here systematic simulations are conducted for both cylindrical and spherical metal shells

whereby, in the first step, dimple-shaped dents are created by indenting a perfect shell into the

plastic range. In the second step, buckling of the dented shell is analyzed, in axial compression for

the cylindrical shells and under external pressure for the spherical shells. Three distinct buckling

analyzes are carried out: 1) elastic buckling accounting only for the geometry of the dent, 2) elastic

buckling accounting for both the dent geometry and the residual stresses, and 3) a full elastic-plastic

buckling analysis accounting for both the dent geometry and residual stresses. The three analyzes

reveal the relative importance of the dent geometry and the residual stress, and they suggest a clear

indicator of whether plasticity is important in establishing the buckling load of the dented shells.

This work has been performed in collaboration with Prof. Simos Gerasimidis, Civil and Environmental

Engineering Department, University of Massachusetts, Amherst, MA 01003.

John Hutchinson received his undergraduate education in engineering mechanics at Lehigh University and his graduate education in mechanical engineering at Harvard University. He joined the Harvard faculty in the School of Engineering and Applied Sciences in 1964 and is currently the Abbott and James Lawrence Professor of Engineering Emeritus. Hutchinson and his collaborators work on problems in solid mechanics concerned with engineering materials and structures. Buckling, structural stability, elasticity, plasticity, fracture and micro-mechanics are all relevant in their research. Examples of ongoing research activities are: (1) efforts to extend plasticity theory to small scales, (2) instabilities in soft materials and shell structures, (3) fracture mechanics of tough ductile alloys, and (4) the mechanics of thin films, coatings and multilayers. Hutchinson is a Fellow of the ASME, a member of the US National Academy of Engineering and the US National Academy of Sciences, and a foreign member of the Royal Society of London. Further information and publications can be downloaded at http://www.seas.harvard.edu/hutchinson .

http://www.seas.harvard.edu/hutchinson


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Plenary Lecture-2

Dynamic Instability and Fluid Interaction in Underwater Structures under

Complex Loading Conditions

Arun Shukla

Simon Ostrach Professor

Co-Director, National Institute for Undersea Vehicle Technology

Department of Mechanical, Industrial and Systems Engineering

University of Rhode Island, Kingston RI 02881, USA

[email protected]

This talk will present recent experimental results on the dynamic structural integrity of designed

composite cylinders under complex loading conditions. Experiments are conducted to study the

mechanics of implosion of single hull and double hull structures with and without confining

conditions. Experiments are also performed to investigate sympathetic implosions and interaction

of an imploding cylinder with a nearby structure. State of the art pressure vessel facilities are used

to study the implosion process. These pressure vessels are outfitted with several windows to allow

the use of the 3D Digital Image Correlation (DIC) technique. The pressure histories generated by the

implosion event are captured from dynamic pressure transducers mounted close to the specimen

in all the experiments. These pressure histories are then related to real time deformations and

velocities occurring on the shells. High speed images are captured for better understanding of the

deformation mechanisms and collapse modes of the structures during the experiments. 3D-DIC

technique is utilized in conjunction with high speed photography to get quantitative information on

the deformation of the collapsing cylinders. Displacements, velocities, and variations in the pressure

profile are correlated to key stages of the collapse event to improve understanding of the failure

process during the implosion of underwater structures.

Dr. Shukla was elected to the Russian Academy of Engineering in 2015 and the European Academy of Sciences and Arts in 2011. He is a Fellow of the American Society of Mechanical Engineers, American Academy of Mechanics, Society for Experimental Mechanics (SEM) and Fellow of the Society for Shock Wave, India. He has received the Murray, Taylor, Frocht, Lazan and Tatnall Awards from SEM. In 2003 he served as the President of SEM. He was the Technical Editor of the international journal Experimental Mechanics and currently serves on the Editorial Boards of key engineering journals. Dr. Shukla served on the National Research Council on the United States National Committee on Theoretical and Applied Mechanics for eight years. Recently, he also served as member and the Chair of the Executive Committee of the Applied Mechanics Division of ASME. Dr. Shukla has received the Distinguished Alumnus Award from his alma mater, IIT Kanpur. In 2011, he served as the Clark B. Millikan Visiting Professor at Caltech and in 2019 as the Satish Dhawan Visiting Professor at IISc Bangalore. Along with his many Ph.D. and M.S. students, he has published more

than 400 papers in refereed journals and proceedings. Dr. Shukla has

authored and edited 10 books and has delivered numerous plenary and

keynote lectures.


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Plenary Lecture -3

Engineer metals with internal interfaces for enhanced mechanical

performance Huajian Gao

Distinguished University Professor

Nanyang Technological University

Email: [email protected]

Gradient microstructures with internal interfaces exist ubiquitously in nature and are increasingly

being introduced in next generation engineering materials with unprecedented mechanical

properties. Here we discuss some recent studies on engineering metals with nature-inspired internal

interfaces and gradients. First, metals typically suffer from cumulative, irreversible damage to

microstructure during cyclic deformation, leading to limited fatigue life along with cyclic responses

that are unstable and history-dependent. Through atomistic simulations and variable-strain-

amplitude cyclic loading experiments at stress amplitudes lower than the tensile strength of the

metal, we report a history-independent and stable cyclic response in bulk copper samples with

microstructures mimicking the highly oriented nanoscale twin boundaries in conch shells. We

demonstrate that this unusual cyclic behaviour is governed by an unusual type of dislocations called

correlated ‘necklace’ dislocations (CNDs). Furthermore, we show that introducing gradient

nanotwinned structure in metals results in extra strengthening that defies the classical rule of

mixture theory. This phenomenon is attributed to another new type of dislocations called bundles of

concentrated dislocations(BCDs).

Huajian Gao received his B.S. degree from Xian Jiaotong University of China in 1982, and his M.S. and Ph.D. degrees in Engineering Science from Harvard University in 1984 and 1988, respectively. He served on the faculty of Stanford University between 1988 and 2002, where he was promoted to Associate Professor with tenure in 1994 and to Full Professor in 2000. He was recruited to become Director at the Max Planck Institute for Metals Research between 2001 and 2006, and then Walter H. Annenberg Professor of Engineering at Brown University from 2006-2019. At present, he is one of 6 Distinguished University Professors at Nanyang Technological University and Scientific Director of the Institute of High Performance Computing in Singapore.

Professor Gao’s research has been focused on the understanding of basic principles that control mechanical properties and behaviors of materials in both engineering and biological systems. He is the Editor-in-Chief of Journal of the Mechanics and Physics of Solids, the flagship journal of his field. He has been elected to US National Academy of Sciences, US National Academy of Engineering, American Academy of Arts and Sciences, German National Academy of Sciences, Chinese Academy of Sciences and Academia Europaea.

mailto:[email protected]


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Plenary Lecture-4

Exploring the mechanical behavior of materials through experiments Krishnaswamy Ravi-Chandar

M.C. (Bud) and Mary Beth Baird Chair

University of Texas at Austin

[email protected]

The most exciting role of experimental mechanics is in discovery – the uncovering and

understanding of phenomena. Such discovery experiments require careful attention both to

the design of experiments and to the development of appropriate tools for diagnostics. Of

course, the basic ideas go all the way back to Galileo. In this presentation, I will describe

three examples of this process through clean experiments related to constitutive and failure

behavior of materials: (i) dynamic strain localization and fragmentation under high strain-

rate loading in ductile materials; (ii) multiscale experiments on damage nucleation and

failure under quasistatic loading in polycrystalline metallic materials; (iii) nucleation and

growth of cavities and cracks in elastomers

Professor Krishnaswamy Ravi-Chandar holds the M.C. Bud and Mary

Beth Baird Endowed Chair at the Department of Aerospace Engineering

and Engineering Mechanics at the University of Texas at Austin. He is the

Editor-in-Chief of the International Journal of Fracture (2000 – present).

He served as President of the International Congress on Fracture (2005-

2009), and the American Academy of Mechanics (2011-2012), and as

Chair of the Applied Mechanics Division of the ASME, and the US National

Committee for Theoretical and Applied Mechanics (2019-2020). He

received the Murray Medal from the Society for Experimental Mechanics

in 2004, the Drucker Medal from the American Society of Mechanical

Engineers in 2015, and the Prager Medal from the Society of Engineering

Science in 2020. He is a Fellow of the American Society of Mechanical

Engineers, Society for Experimental Mechanics, the American Academy

of Mechanics, the International Congress on Fracture and the Indian

Structural Integrity Society



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Plenary Lecture-5

On the Mechanics and physics of AM and COLD spray build parts and their

use in limited life UAV structures and as airframe replacement parts Rhys Jones

Emeritus Professor

Department of Mechanical and Aerospace Engineering, Monash University, Clayton

[email protected]

One of the challenges in aircraft sustainment is to develop AM replacement parts for legacy

aircraft. This is particularly important to increase aircraft availability, to minimize logistics

problems, and for fixed and rotary wing aircraft that operate in aggressive environments, i.e.

in a marine environment, off carriers, etc. Such parts can be certified under the “limited life”

approach outlined in the US Joint Services Structural Guidelines JSSG2006, Structures

Bulletin EZ-19-01, and MIL-STD-1530D. The USAF have also adopted the concept of using

AM to rapidly deploy limited-life unmanned air platforms (attritable aircraft). Unfortunately,

crack growth in AM and cold spray built materials can be dependent on the build direction,

the fabrication process, and post processing. This paper reveals how to account for these

effects in a fashion that is consistent with both the fundamental physics of the problem and

with the governing crack tip parameter. We then illustrate how to perform the durability

analyses required in USAF Structures Bulletin EZ-19-01 for the airworthiness certification of

limited life parts. In this context, the damage tolerance and durability analyses presented in

this paper suggests that AM and cold spray built parts are attractive both for use as

replacement parts for legacy aircraft, and for attritable unmanned aerial vehicles (UAV’s).

The raises the potential for assessing the trade off between: Weight, cost of fabrication,

choice of AM process, choice of the post processing options, and their effects on the

economic life of the airframe.

Professor Rhys Jones AC is a Companion of the Order of Australia: “For eminent

service to mechanical and aerospace engineering, and to education as an

academic, researcher and author, particularly in the area of aircraft structural

mechanics, corrosion repair and airworthiness”. The Order of Australia replaced

a “Knighthood” in the Australian Honours systems. It is the highest honour that

can be given to an Australian Citizen. In 2008 his seminal paper on thermo-

elasticity was chosen as one of the Top Ten Defence Science publications in the

period 1907-200


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Plenary Lecture-6

Engineered Multifunctional Interfaces

Ioannis Chasiotis

Caterpillar Professor of Aerospace Engineering

Aerospace Engineering, University of Illinois at Urbana-Champaign

[email protected]

Engineered micro and nanostructured interfaces enable new forms of macroscale material

behavior, which are not possible through monolithic materials. For instance, compliant

interfaces comprised of nanowires or nanotubes alleviate thermal mismatch stresses while

introducing system-level functionalities, such as control of permittivity and impedance,

enhanced heat and charge transfer, energy storage, etc. In the context of microthermal

interfaces, films of dense and orderly arrays of Cu nanosprings provide tunable mechanical

compliance combined with high thermal conductivity. As a result, such nanoarchitected Cu

films, fabricated via Glancing Angle Deposition (GLAD), possess the compliance of

polymers but orders of magnitude higher thermal conductivity than polymers. This unique

combination of mechanical and thermal properties makes it possible to populate the largely

empty space in the materials selection chart of thermal conductivity vs. elastic modulus.

Control of the geometric features and materials comprising such discrete interfaces is an

effective means to design traction-separation laws of interfaces in a variety of applications.

For instance, the orientation and geometry of GLAD nanostructures in interlayers between

elastomeric substrates and hard coatings can be utilized to control surface wrinkling and

impart wrinkling anisotropy which is not attainable in isotropic material systems. Finally, the

application of Si-based GLAD nanospring layers as multifunctional films for embedded

power and stress control in high capacity Li+ anodes will be presented.

Ioannis Chasiotis is the Caterpillar Professor of Aerospace Engineering at the

University of Illinois at Urbana-Champaign and the editor-in-chief of Experimental

Mechanics. He received his Ph.D. and M.S. degrees in Aeronautics from the California

Institute of Technology, and his Diploma in Chemical Engineering from the Aristotle

University in Thessaloniki, Greece. His research focuses on mechanics of materials

and interfaces at small length scales. He is a recipient of the NSF Presidential Early

Career Award for Scientists and Engineers (PECASE), the Society of Engineering

Science Young Investigator Medal, the ASME Thomas J.R. Hughes Young

Investigator award, the Society for Experimental Mechanics A.J. Durelli award, etc.

He is a fellow of the American Society for Mechanical Engineers and the Society for

Experimental Mechanics.


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Keynote Talks

1. Michael Gorelik

11th Dec

2. Sunder Atre

11th Dec

3. Atul Chokshi

11th Dec

4. Raman Singh

12th Dec

5. Christoph Kirchlechner

13th Dec

6. Abass Bramiah

18th Dec

7. Vikas Tomar

11th Dec

8. Ghatu Subhash

12th Dec

9. C. S. Upadhyay

19th Dec

10. Ashok Saxena

12th Dec

11. B. K. Dutta

12th Dec

12. Sanjay Sampath

18th Dec

13. Vikram Deshpande

13th Dec

14. Sankara Narayanan

13th Dec

15. B. V. A. Patnaik

20th Dec

16. Anthony Waas

19th Dec


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TS01 Keynote Lecture

Lessons Learned” for Structural Alloys and Implications for Metal

Additive Manufacturing F&DT Considerations

Dr. Michael Gorelik

Chief Scientist, Fatigue and Damage Tolerance

Federal Aviation Administration, USA

[email protected]

Metal Additive Manufacturing (AM) is still a relatively new technology, with very limited

full-scale production and field experience in Aviation. The expanding use of AM, heading

towards the safety-critical applications, prompts F&DT considerations, both to ensure

product safety and to meet certification requirements. Most of the current “lessons

learned” for AM are based on either academic R&D, or industry development work (the

latter typically being proprietary). While such work is very important and helps with

identification of AM-specific properties and attributes and the means of addressing them

in the context of Q&C, it cannot replace decades of production and field experience for

more conventional forms of structural alloys, e.g. castings, wrought products, powder

metallurgy etc. Thus, examining some of the relevant lessons learned for such legacy

alloy systems can help with shaping the appropriate F&DT framework for metal AM

materials. These considerations, illustrated by specific examples, will be discussed in

the presentation.

As the Chief Scientist for Fatigue and Damage Tolerance at the FAA, Dr. Gorelik supports various certification programs, development of advisory materials and rule making activities across the Agency, training of FAA personnel, R&D and evaluation of new technologies, and engagement with aerospace industry, SDOs and government agencies. His prior industry positions included Engineering Fellow and Life Methods Manager at Honeywell Aerospace, and Six Sigma Master Black Belt at GE.

Dr. Gorelik has over 25 years of experience in the areas of fracture mechanics, fatigue, damage tolerance, additive manufacturing, characterization and modeling of material behavior, probabilistic methods, prognostics and health management. He currently serves as the Chair of the Structures and Dynamics Committee of IGTI (ASME) and Co-Chair of Emerging Technologies Task Group of MMDPS.



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Metal Fused Filament Fabrication of Ti-6Al-4V: Materials, Processing &

Design Sundar V. Atre

Endowed Chair of Manufacturing & Materials

University of Louisville

[email protected]

Building end-use functional metal parts from metal fused filament fabrication (MF3) is an

emerging extrusion process in additive manufacturing. MF3 involves extrusion of polymer

filaments that are highly filled with metal powder to print three-dimensional parts, followed by

debinding and sintering to eliminate polymer and get a fully dense metal part. Material properties, part design and processing conditions have a significant influence on the quality of printed MF3

parts. Part distortion and dimensional variations are significant quality challenges that hinder the

acceptance of printed parts in potential functional applications. However trial-and-error

experiments to find the best conditions for defect avoidance are time-consuming and expensive.

Hence, computational simulation and design solutions are required for MF3. This paper

investigates the quantitative influence of material properties on printed part quality using a

thermo-mechanical simulation platform for MF3. The simulation results of a Ti-6Al-4V filled

polymer were compared to experiments to effectively explore the material-process-geometry

space

Sundar V. Atre is the Endowed Chair of Manufacturing & Materials at the University of Louisville where he is Director of the Additive Manufacturing Institute of Science & Technology (AMIST). Sundar obtained his PhD degree in Materials Science and Engineering from the Penn State University, following a B.Tech. degree in Chemical Engineering from the Indian Institute of Technology, Madras. Sundar’s research focuses on the interactions between materials, manufacturing and design and has generated over 200 publications, 7 issued and licensed patents, and over 20 intellectual property filings. Sundar has led a start-up company and helped establish 8 other new businesses during the last 18 years. One company, Home Dialysis Plus, focusing on portable kidney dialysis, received over $185 million in private investment.


31


Current understanding of creep in polycrystals: Extension to advanced

ceramics, nanocrystals and high entropy alloys Atul H. Chokshi

Department of Materials Engineering, Indian Institute of Science, Bangalore 560 012

[email protected]

The time-dependent plastic deformation of materials, termed creep, is an important limitation for structural applications at high temperatures. The scientific studies on creep can be traced back to over a century. The phenomenological and micromechanisms based approaches have led to a good understanding of factors influencing creep. Experimental values of n, p and Q (the activation energy related to diffusion) are compared with those predicted by theoretical models to identify possible creep mechanisms, together with appropriate microstructural characterization. Diffusion creep mechanisms which depend on the grain size, such as Nabarro-Herring and Coble creep are associated with n=1, and p= 2 and 3, respectively. In contrast, intragranular deformation processes such as dislocation glide and climb involve p=0, and n=3 and 5, respectively. The general understanding of creep will then be extended to three different classes of advanced materials: ceramics, nanocrystals and high entropy alloys. In ceramics, the need to consider charge neutrality may involve the process of ambipolar diffusion, where diffusion creep is controlled by the slower moving species diffusing along the faster path. There is not much information available on creep in nanocrystals, with grain sizes below 100 nm, where potentially new mechanisms can be activated. High entropy alloys are a new class of multiple element concentrated solid solution alloys. Recent experimental results and possible new approaches to understanding creep in such materials will be discussed.

Prof. Atul Chokshi received his Bachelor of

Technology degree in Metallurgical Engineering

from Indian Institute of Technology, Madras, in

1980. Subsequently, he received M.S. and Ph.D.

degrees from University of Southern California, Los

Angeles in 1981 and 1984, respectively. He is

currently a Professor with the Department of

Materials Engineering, Indian Institute of Science,

Bangalore. His main research interests are in

engineering mechanical properties of materials

and he is well known for his pioneering research in

the area of mechanical behavior of nanocrystalline

materials, deformation mechanisms in

superplasticity and creep of ceramics.



32


Understanding Corrosion and Corrosion-assisted Cracking of Magnesium

Alloys for their Innovative Use as Bioimplants

Raman Singh (R.K. Singh Raman)

Department of Mechanical & Aerospace Engineering

Department of Chemical Engineering

Monash University (Melbourne), VIC 3800

[email protected]

Magnesium (Mg) alloys possess great potential for their use as temporary implants such as pins,

wires, screws, plates. Use of Mg alloys will completely avoid the cumbersome procedure of second

surgery (which is required when such implants are constructed out of traditional materials such as

titanium alloys or stainless steels). However, Mg also has limitations as a temporary implant

material, viz., their unacceptably high corrosion rates and concurrent hydrogen evolution, and stress

corrosion cracking (SCC) and/or corrosion fatigue (CF) under the simultaneous action of the

corrosive human-body-fluid and the mechanical loading. The presentation will provide an overview

of SCC and CF of different Mg alloys in simulated body fluid (SBF) and the associated fracture. The

presentation will also discuss the need of investigations under such mechano-chemical conditions

that appropriately simulate the actual human body conditions, and present new data generated

under such conditions in the presenter’s research group.

Professor Raman Singh’s primary research interests are in the relationship of

Nano-/microstructure and Environment-assisted degradation and fracture of

metallic and composite materials, and Nanotechnology for Advanced Mitigation

of such Degradations. He has also worked extensively on use of advanced

materials (e.g., graphene) for corrosion mitigation, stress corrosion cracking,

and corrosion and corrosion-mitigation of magnesium alloys. His professional

distinctions and recognitions include: Editor of a book on cracking of welds,

Editor-in-Chief of two journals, member the Editorial Boards of a few journals,

leader/chairperson of a few international conferences and regular

plenary/keynote lectures at international conferences, over 225 peer-reviewed

international journal publications, 15 book chapters/books. He has supervised

49 PhD students.


33

TS 05 Keynote Lecture

Why are nanotwinned systems damage tolerant? Insights from in situ

nanomechanics Christoph Kirchlechner

Professor – Head of the IAM-WBM

Institute for Applied Materials, Karlsruhe Institute of Technology (KIT), Germany

[email protected]

Nano twinned (NT) materials are known for their high strength and ductility, i.e. damage

tolerance. The fundamental origin of the damage tolerance of NT systems is yet not fully clear.

To shed light on the damage tolerance we (i) measured the stress for dislocation slip transfer

through a single coherent Σ3 twin boundary in copper (N Malyar et al. Acta Mater 2017) and (ii)

we extend this knowledge to multiple coherent Σ3 twin boundaries in Ag (MK Kini et al. Acta

Mater. 2020). While the slip transfer behaviour can explain the high strength, it is not suited to

explain the high ductility in NT materials. Hence, to understand this damage tolerance we (iii)

finally look into the role of dislocation nucleation from twin boundaries. The later study might

unravel the origin for damage tolerance in NT systems.

The talk will introduce experimental nano- and micromechanics comprising pillar compression

in the SEM, synchrotron Laue diffraction as well as pop-in statistics using spherical

nanoindentation

Christoph Kirchlechner studied material science

and received his PhD at the University of Leoben in

Austria. Subsequently, he held an Assistant

Professor position at the University of Leoben

(2012-1018) and was group leader for in situ nano-

and micromechanics at the Max-Planck-Institut für

Eisenforschung in Düsseldorf, Germany (2013-

2020). Since 2020, he is head of the Institute for

Applied Materials – Materials- and Biomechanics

(IAM-WBM) at the Karlsruhe Institute of

Technology. His research focusses on a

mechanism-based understanding of plasticity,

fatigue and fracture at the micron scale,

particularly at single interfaces. For this purpose,

he is using electron microscopy as well as

advanced synchrotron techniques. He was

awarded with a promotion sub auspiciis

praesidentis rei publicae (Austrian President) and a

Heinz Maier-Leibnitz prize (German Research

Foundation).



34


Contact Explosion Effects on Reinforced Concrete Columns. Abass Braimah

Vice Chancellor, Tamale Technical University, Ghana

The vulnerability of reinforced concrete columns to explosion effects and the attendant

likelihood of progressive collapse has seen increased research activity on the response of

columns to blast loading. Most of the research has however concentrated on the response of

columns to far-field explosion effects with many researchers investigating the effects of

explosions on columns through numerical modelling techniques.

This presentation will highlight the dearth of experimental research data on the response of

columns to near-field explosion effects and present an experimental and numerical modelling

program to investigate the response of reinforced concrete columns to contact explosion

effects.

Abass Braimah is the Vice Chancellor of Tamale Technical University in Ghana. Before his appointment as

Vice Chancellor he was a Professor of Blast Load Effects and Extremely Load effects on Critical

Infrastructure in the Department of Civil and Environmental Engineering (Infrastructure Protection and

international Security Program), Carleton University, Canada. He completed his PhD at Queen’s University

at Kingston and worked in Structural Engineering consulting and at the Canadian Explosives Research

Laboratory (CERL).

His research interest is in the area of critical infrastructure protection, especially extreme load effects on

structures. He is particularly interested in research on the response of reinforced concrete columns and

reinforced concrete walls to close-in explosions; blast risk assessment and vulnerability assessment of

critical infrastructure systems. He is also interested in the use of advanced composite materials in

structural engineering; especially the use of advanced composite materials for retrofit of structures

subjected to extreme loading.


35


Interface Level Shock Regime Rate Dependent Mechanical Properties and

Related Implications in Larger Material Architecture Settings

Abhijeet Dhiman1 and Vikas Tomar2 1Graduate Research Assistant, 2Lead Investigator

Purdue University, West Lafayette, IN-47907, USA [email protected], [email protected]

Role of interfaces at high strain rates approaching shock loading in materials is a challenging

problem to solve. Under shock loading one can use an equation of state to describe overall

homogeneous material behavior. At non-shock high strain rate loads one can use viscoplasticity

driven constitutive models to describe material behavior. However, as one dives deeper into

analyzing a material response to high strain rate loading, at the localized scale of interfaces local

strain rates and strains are significantly different from globally applied strain rates. As such

locally material can deform in significantly different and unexpected ways than what is expected

using a localized homogeneous equation of state or a viscoplasticity model. This issue bears

significant attention when one might want to change localized chemistry/chemical composition

of materials to change overall response to impact loading. Interfacial Multiphysics Lab (IML) at

Purdue has been performing time resolved interface level stress and thermal measurements

under impact loading using nanomechanical Raman spectroscopy coupled with numerical

advancements in the molecular simulations at experimental strain rates. This presentation

presents key insights obtained from interface level stress wave measurements during shock

loading of energetic materials. A new material viscosity model that considers shock level local

loading is Presented

Prof. Tomar started as an assistant professor in January 2006 after

graduating from Georgia Tech with PhD in mechanical Engineering in

December 2005. He was promoted to full professor in 2016 at Purdue

University.Professor Tomar has published 110 international journal

publications (h-index 28), filed 6 research patent/disclosures (awarded

2 patents), written 45 international reviewed proceeding articles and

book chapters. Professor Tomar’s excellence in research has been

recognized by a number of awards including VAJRA award from Govt of

India, AFoSR young investigator award for high temperature interface

thermomechanics, American Society of Mechanical Engineers (ASME)

Orr early career award for excellence in fracture and fatigue, The Mineral,

Metal, and Materials Societies (TMS) early career faculty fellow-

honorable mention award for materials research, inaugural Elsevier

Material Science and Engineering journals’ early career young researcher

award for interface mechanics, Purdue’s Seeds for Success Awards

(2017, 2018, 2020), Purdue’s CT Sun Research award, Purdue’s

University Faculty Scholar Award, and multiple other best paper awards.


36


Mechanics of Dynamic Tension, Compression and Shear Response of Visco-

Hyperelastic Materials

Ghatu Subhash*, Kshitiz Upadhyay**, and Douglas Spearot

Mechanical and Aerospace Engineering

University of Florida, Gainesville, FL 32611 USA

**Johns Hopkins University, USA

Soft materials such as biological tissues, elastomers and hydrogels, exhibit large elastic

deformations as well as nonlinear strain-rate dependent stress-strain response that is also

microstructure sensitive. In this research, a combined experimental and theoretical framework

based on fundamental continuum thermodynamics principles to study the constitutive behavior of

these materials is presented.

First, a generalized thermodynamic stability criterion is presented to formulate constitutive

inequalities for hyperelastic constitutive models. It is shown that all three primary deformation

modes (compression, tension and shear) should be considered to ensure a physically reasonable

model for 3D stress state. Quasi-static experiments in compression, tension, and shear on agarose

hydrogel at a range of gel concentrations are then conducted to formulate a concentration

dependent extended generalized Rivlin model. In the second step, we explore the time-dependent

mechanical behavior by conducting novel split-Hopkinson pressure bar (SHPB)-based experiments

for the shear and tensile characterization of soft materials under large deformations and in a wide

strain rate range. Full-field digital image correlation (DIC) and piezoelectric force sensing methods

are used to extract steady-state material response. Finally, a novel viscous dissipation potential is

proposed to model time-sensitivity using visco-hyperelastic framework, which can capture both

linear and nonlinear large deformation behaviors over a wide range of strain rates. By implementing

the proposed model to capture deformations of human patellar tendon and brain gray matter, a good

fitting accuracy in capturing 3D response is observed.

Professor Ghatu Subhash obtained his PhD from University of California San Diego in 1991 and conducted his post-doctoral research at

California Institute of Technology. He is currently the Newton C Ebaugh Professor in Mechanical and Aerospace Engineering at University

of Florida, Gainesvlle, FL. His research focusses on multiaxial behavior of advanced ceramics, metals, composites, gels and biological

materials. He has developed novel experimental methods which have been patented and widely used. He has co-authored 200 peer

reviewed journal articles (7800 citations in Google Scholar, h-index=47), 85 conference proceedings, 2-books, and 6 patents. He has given

numerous keynote and invited lectures at major international conferences. He has graduated 35-PhD students and is currently advising

6-PhD students and one post-doctoral fellow. Many of his students have received awards at student paper competitions from professional

societies and fellowships from NSF, DOD, and DOE. His former students are employed at major Universities in US and abroad, and national

laboratories including SNL, ORNL, PNNL and ARL. He is a Fellow of ASME, Society of Experimental Mechanics (SEM), and the American

Ceramic Society (ACerS). He is the Editor-in-Chief of Mechanics of Materials and Associate Editor of Journal of the American Ceramic

Society. He has received numerous awards, including the SEM Lazan Award (to receive in 2021) for innovative contributions to

experimental mechanics and development of in-depth understanding of multiaxial dynamic response of ceramics and soft materials, SEM

‘Frocht Award’ (2018) in recognition of outstanding achievements as an educator, ‘Best Paper’-Journal of Engineering Materials and

Technology (2016), ‘Significant Contribution Award’ for development rapid processing scheme of ceramic nuclear fuels, from the

American Nuclear Society. ‘Technology Innovator Award’ from University of Florida, ASME Student Section Advisor Award’, ‘SAE Ralph R.

Teetor Educational Award’, and ‘ASEE Outstanding New Mechanics Educator’ award. He has also served as the National Academies of

Engineering Panel Member.


37

TS12+TS16 Keynote Lecture

Towards predictive damage models – some recent experience

Chandra Shekhar Upadhyay

Professor

Department of Aerospace Engineering, IIT Kanpur

[email protected]

The need to predict onset and progression of failure mechanisms has inspired intense

investigation of micro-level behaviour of different materials. The seminal work of Kachanov-

Rabotnov on progressive continuum damage has led the way to creation of damage models,

over length-scales, representing the behaviour of different progressively damaging

materials. The GTN and Lemaitre models were successful in capturing damage in ductile

metals. All these models rely on a single damage variable. Extension of these ideas to

modelling progressive damage in composites has led to several phenomenological and

micro-mechanics inspired models. The progressive damage models in composites aim to

capture all the distinct underlying damage mechanisms through multiple damage variables

and appropriate stiffness reduction and damage evolution models.

The talk will present some micro-mechanics inspired damage models for both metals and

composites, emphasizing the need for a consistent thermodynamic frame-work. Further, the

modelling approach will seek to create models that are physically justifiable and robust.

Some examples from practical applications will also be discussed.

Professor CS Upadhyay is an Aerospace Engineer by training, with a B.Tech

degree from IIT Kharagpur (1991), MS (1993) and PhD (1997) from Texas A&M.

After a short-stint as a post-doctoral fellow at TICAM (now ICES) at UT Austin, he

joined the department of Aerospace Engineering at IIT Kanpur in 1997. At IIT

Kanpur he has developed and taught courses on continuum mechanics, linear and

nonlinear finite element method, composite structures, structural integrity and

solid mechanics. He researches in the domains of material modelling, damage,

design and numerical analysis, in which he has published more than 120 papers

in international journals and conferences


38


Integrity Assessment and Design of Pressure Vessels for Storing Hydrogen

Ashok Saxena

President

WireTough Cylinders, LLC

[email protected]

Cost-effective, pressure vessels for use in ground storage of hydrogen in refueling stations

require vessels that can safely store up to 750 liters of gaseous hydrogen at 875 bars or

87.5 MPa. This paper addresses fracture mechanics analysis to assist in the design and

structural integrity of a Type 2 pressure vessel to meet this need.

Metal cylinders have been used for storing hydrogen for several decades but are limited to

pressures of 55 MPa due to hardenability of the material and the ability to reliably inspect

for flaws. The designs must also meet safety requirements of standards such as the ASME

PVP Section VIII- Division 3 codes. Using the time-tested, metal cylinders as liners and

wrapping them with high strength steel wires that are 2 GPa or higher in strength is an

effective approach for increasing the pressure capability and fatigue life of these metal

composite cylinders. The wire-wrapped cylinders are further subjected to an autofrettage

process in which they are subjected to pressures high enough to plastically deform the inner

liner, but the wire jacket remains elastic. Upon release of the autofrettage pressure, the inner

liner is left with high residual compressive hoop stresses. This process decreases the

maximum tensile hoop stress in the liner under the operating pressure and can thus enhance

the fatigue life of the vessel very significantly. This paper will address several aspects of

design considerations such as materials selection, inspection capabilities and allowable

design stresses to meet the need of the users in the form of user design specifications in a

more wholesome design approach to ensure structural integrity.

Dr. Saxena currently serves as the President of WireTough Cylinders, LLC, a company located in Bristol,

VA, USA. He also serves as Emeritus Distinguished Professor and Dean in the Department of

Mechanical Engineering at the University of Arkansas and as an Adjunct Regents’ Professor at Georgia

Tech in Atlanta. In the past he served as the provost and vice-chancellor of academic affairs, dean of

engineering and the founding head of the Department of Biomedical Engineering at the University of

Arkansas. He also held the 21st Century Endowed Graduate Research Chair in Materials Science (2003-

2007), Irma and Raymond Giffels’ Endowed Chair in Engineering (2007-2012), and the George and

Boyce Billingsley Endowed Chair (2014-2015). Prior to University of Arkansas, he served as a Regents’

Professor and Chair of the School of Materials Science and Engineering at Georgia Institute of

Technology in Atlanta.

Dr. Saxena has primarily worked in linear and nonlinear fracture mechanics within the disciplines of

mechanical engineering and materials science and engineering.


39


Mechanical properties of irradiated two nuclear materials using small punch

test data

B.K.Dutta1 and S.R.Ghodke 1Institute Chair Professor

Homi Bhabha National Institute

[email protected]

The small punch test (SPT) is an alternative method to assess the mechanical properties of nuclear

materials where the limited quantity of available irradiated material is insufficient to conduct

conventional standard tests. SPT specimens of two nuclear materials, OFE copper and Titanium, are

irradiated in electron accelerator up to various levels of irradiation dose. These SPT specimens are

then tested to obtain load v/s displacement data. Using experimental data and existing correlations

from literature, yield stress, ultimate stress, bi-axial fracture strain, specimen energy at fracture and

fracture toughness are calculated as a function of irradiation dose. The yield and ultimate stresses

are also used to obtain complete stress-strain curves at different doses of irradiation.

Prof. B.K.Dutta, former Distinguished Scientist and Dean HBNI, contributed

significantly in basic and applied research in structural and material

mechanics. He has guided eight PhD students, fifteen MTech. students and

presently associated with the doctoral programs of six students. He is the

author of 300+ publications, which includes 125+ peer reviewed journal

papers. He has been associated with the Homi Bhabha National Institute

right from its inception and served the institute in various capacities. He was

president of International Association for Structural Mechanics of Reactor

Technology (USA) and presently lifetime advisory board member. He is a

fellow of Indian National Academy of Engineering.


40


Structurally Integrated, Damage Tolerant Coatings Sanjay Sampath

Distinguished Professor and Director

Center for Thermal Spray Research

Stony Brook University, Stony Brook, NY, USA

Thermal spray coatings are used extensively for the protection and life extension of

engineering components exposed to harsh wear and/or corrosion during service in

aerospace, energy, and heavy machinery sectors. Cermet coatings applied via high-velocity

thermal spray are used in aggressive wear situations almost always coupled with corrosive

environments. In several instances (e.g., landing gear), coatings are considered as part of

the structure requiring system-level considerations. In addition, spray based

remanufacturing of worn components is also expanding with the advent of high velocity

spray technology and here the integration of the restored and parent material from a

structural point of view is of importance. Despite their widespread use, the technology has

lacked generalized scientific principles for robust coating design, manufacturing, and

performance analysis. Advances in process and in situ diagnostics have provided

significant insights into the process–structure– property–performance correlations

providing a framework-enhanced design. In this overview, critical aspects of materials,

process, parametrics, and performance are discussed through exemplary studies on

relevant compositions. The underlying connective theme is understanding and controlling

residual stresses generation, which not only addresses process dynamics but also provides

linkage for process-property relationship for both the system (e.g., fatigue) and the surface

(wear and corrosion). The anisotropic microstructure also invokes the need for damage-

tolerant material design to meet future goals. This presentation will provide an overview of

emerging concepts of structurally integrated coating design and structural remanufacturing

of engineering components. In addition to traditional methods of coating evaluation, new

methods of integrated characterization of coating and structure is contemplated. Using

these principles approaches to enhancing applications will be presented.

Dr. Sanjay Sampath, is currently Distinguished Professor of Materials Science at Stony

Brook University (SUNY) and director of the Center for Thermal Spray Research

(www.sunysb.edu/ctsr) an interdisciplinary industry-university partnership in the field of

thermal spray materials processing and surface engineering. CTSR was created in 1996

through the National Science Foundation’s Materials Research Science and Engineering

Centers program. He received his B.Tech from IIT-BHU and Ph.D. from Stony Brook in

1989. He established Industrial Consortium for Thermal Spray Technology comprising of

35 leading companies aimed at knowledge transfer from fundamental research to

applications. Dr. Sampath has 220 journal publications to his credit, 15 patents and winner

of several best paper awards


41


Hydrogen embrittlement in steels: why does it occur?

Vikram Deshpande

Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK.

One of the recurring anomalies in the hydrogen induced fracture of high strength steels is the apparent

disconnect between the toughness and tensile strength. For example, the toughness of a high strength steel

is typically reduced from approximately 100 MPam to about 20 MPam in the presence of hydrogen while

concurrently the strength reduces from 2 GPa to about 400 MPa. Traditional fracture mechanics then suggests

that quasi-brittle fracture under uniaxial tension occurred by the growth of a pre-existing flaw of size ≈1600

μm. There is no evidence of the presence of such large pre-existing flaws in high quality steels. This raises the

question as to what is the hydrogen-mediated fracture process that reduces the strength of such steels?

Here we propose, supported by detailed atomistic and continuum calculations, that unlike macroscopic

toughness, hydrogen-mediated tensile failure is a result of a fast-fracture mechanism. Specifically, we show

that failure originates from the fast propagation of cleavage cracks that initiate from cavities that form around

inclusions such as carbide particles. The failure process occurs in two stages. In stage-A, hydrides rapidly

form around the roots of stressed notches on the cavity surfaces with hydrogen fed from the hydrogen gas

within the cavity. These hydrides promote cleavage fracture with the cracks propagating at >100 ms-1 until

the hydrogen gas in the cavity is exhausted. Predictions of this hydrogen-assisted crack growth mechanism

are supported by atomistic calculations of binding energies, mobility barriers and molecular dynamics

calculations of the fracture process. Typically, cracks grow by less than 1 μm via this hydrogen-assisted

mechanism and thus insufficient to cause macroscopic fracture of the specimen. However, this stage is then

followed by a stage-B process where these fast propagating cracks can continue to grow, now in the absence

of hydrogen supply, given an appropriate level of remote tensile stress. This is surprising because the fracture

energy is now that of Fe in the absence of H and cleavage fracture requires opening tractions on the order of

15 GPa to be generated. Thus, fracture is usually precluded due to plasticity around the crack-tip. Here we

show via macroscopic continuum crack growth calculations in a rate dependent elastic-plastic solid with

fracture modelled using a cohesive zone that cleavage is possible if the crack propagates fast enough. This

is because strain-rates at the tips of fast propagating cracks are sufficiently high for the drag on the motion

of dislocations resulting from phonon scattering to limit plasticity. This combined atomistic/continuum model

is used to explain a host of well-established experimental observations including (but not limited to): (i)

insensitivity of the strength to the concentration of trapped hydrogen; (ii) the extensive microcracking in

addition to the final cleavage fracture event and (iii) the higher susceptibility of high strength steels to

hydrogen embrittlement.

Prof. Vikram Deshpande joined the faculty of Engineering at the University of Cambridge as a lecturer in October 2001 and was promoted to a professorship in Materials Engineering in 2010. He has written in excess of 270 journal articles in experimental and theoretical mechanics solid mechanics with an h-index of 71. He serves on the editorial boards of a number of journals in mechanics and biomechanics including Journal of the Mechanics and Physics of Solids, Modelling and Simulation in Materials Science and Engineering and the Proceedings of the Royal Society, London. He has awarded the Philip Leverhulme Prize, the William Hopkins medal, the 2020 Rodney Hill Prize in Solid Mechanics and has been elected Fellow of the Royal Society, London


42


Probabilistic design and uncertainty quantification for structural integrity Dr. Sankar Narayanan

Technical Expert,

Siemens Technology, Bangalore, India.

[email protected]

For the structural design of rotating machineries, the conventional deterministic approaches engage

assumed minimum or maximum values of material-properties, operating variables like temperature,

stress etc., and hence oftentimes are conservative in nature. Probabilistic approaches on the other

hand account for uncertainties in the aforementioned random variables, by statistically harnessing

the available data and via appropriate statistical formulations based on the physics of the failure

mechanisms involved. As a result, a risk level associated with a certain failure mode or a

combination of several modes, can be quantified. These statistical formulations facilitate the

integration of risks for an entire component or an engineering system, which helps transcend from

a local deterministic approach to a robust integrative risk quantification. Probabilistic design

enables a reliable risk quantification in engineering design, allowing for appropriate service

decisions, including recertifications and life-time extensions. It allows for a reliable flexible operation

of energy components critical for the energy transition including intermittent renewable energies. In

my talk, I will give an overview of probabilistic design for structural integrity, the underlying

technologies, and computational schemes for implementation on actual components.

Dr. Sankar Narayanan is a Technical Expert at Siemens Technology, Bangalore,

India and specializes in technology development in the field of probabilistic

design and analytics. His academic background and expertise are in

computational mechanics, multiscale material modelling and statistical

modelling. He received his PhD in Mechanical-Engineering from Georgia

Institute of Technology, USA, in 2014. .


43


Structural Integrity Aspects of Gas Turbine Parts Shri BVA Patnaik

Technology Director, Gas Turbine Research Establishment, Bangalore

Structural integrity of a Gas Turbine is the ability of structure/system to perform its intended function without failure under all operating conditions for a specified life. Achieving very high specific workout put as a means of producing large power with minimum possible size of Gas turbine aero engine was the target of aero thermodynamic engineers for a long time. This required development of high pressure ratio compressors and development of Turbines which can withstand Turbine Entry Temperatures of the order of 1900K.The evolution of Titanium alloys as a replacement to steels and development of high temperature super alloys have brought tremendous advantage of designing the aerodynamic flow paths required besides meeting long life requirements. The critical parts undergo various failure modes like High Cycle Fatigue (uniaxial and multiaxial) due to phenomenon like resonance, aeroelastic interactions, Low Cycle Fatigue and thermal fatigue due to start stop and transient operations. The combination of extreme mechanical and high temperatures experienced by these components often result in significant amounts of plasticity and cyclic time dependent plasticity which makes the structural analysis and life prediction a challenging job. This requires exhaustive material characterisation and structural simulation techniques.

Subsequent to the design and life prediction it is equally important to assess the residual life due to operational usage in order to ensure safe and economic exploitation. The life of critical components of the engine is declared based on the flight envelope consisting of various mission cycles and the corresponding operating environment of the component & failure modes.

The Low cycle fatigue life is declared in terms of number of 0-Max-0 cycles. This fatigue life can always be correlated to equivalent damage cycles with respect to actual mission profile by summing up the damages due to minor sub cycles and the major cycle of the mission profile. The life of the cold parts is dictated by Low Cycle Fatigue behavior with respect to mission cycle whereas the components for which the operating temperatures are high (hot parts) the life is dictated by combination of Creep & thermal fatigue.

In order to ensure that the components in service have not exhausted the equivalent declared safe life, it is essential to assess the damages incurred in these components during engine operation. The cyclic exchange rate for the mission profiles in terms of hours are generally defined by apportioning speed excursion ranges in to predominant speed ranges. However more accurate damage consumptions are to be evaluated so that life potential of the critical components is exploited very effectively. Diagnostics, Prognostics play vital role in ensuring integrity and economic life exploitation (Including life extension) of the Gas Turbine parts.

Shri BVA Patnaik is M.Tech. in Aerospace Engg from IIT Khargpur and presently

working as Technology Director at, Gas Turbine Research Establishment, Bangalore

. His area of specialization is Structural analysis ,Life prediction and Life monitoring,

Material Charactertisation of Gas turbine critical parts.


44


Modeling Progressive Damage and Failure of Fiber Reinforced Laminates

Anthony M. Waas

University of Michigan, Ann Arbor, MI, 48109

High-strength and high-stiffness carbon fiber-reinforced polymer composite laminates (CFRP)

arEbeing increasingly used for primary load bearing structures in many industries. The most

common material system used is based on thermoset resins (matrix material), which come in the

form of convenient prepreg tapes allowing high flexibility and productivity using advanced

automated manufacturing technologies. Engineers must provide mechanics based models for the

deformation response and failure of these materials and structures. The mechanisms responsible

for progressive damage accumulation and failure are (intralaminar) matrix cracks, which can lead to

delamination initiation and spreading resulting in ultimate failure. Interlaminar fracture in CFRP,

referred to as delamination, is defined as an out-of-plane discontinuity between two adjacent plies

of a laminate.

Delamination behavior has been studied by many researchers and now can be characterized in a

standardized manner. Fracture properties of Mode I, Mode II, and mixed-mode (between Mode I and

Mode II) delamination can be obtained from ASTM standard tests in conjunction with finite element

analysis (FEA). In a CFRP structural component, the intralaminar and interlaminar modes of failure

can interact and therefore, developing a computational model to accurately replicate the

failure mechanisms and their interaction has been challenging. In this presentation, a series of

experimental results that delineate the different mechanisms of failure will be presented. Based on

these results, a validated model will be presented, resulting in a progressive damage and failure

modeling framework that can be used for assessing the structural integrity and damage tolerance

of CFRP structures.


45

TS01

Structural Integrity of Additive Manufactured

Components

Organizer

D. Srinivasan, Pratt & Whitney

11th Dec 7-10 pm


46

Invited Speakers

Large Part Additive Manufacturing using Direct Metal Deposition (DMD®)

Dr. Bhaskar Dutta

President DM3D Technology

[email protected]

As additive manufacturing (AM) is emerging as a main stream manufacturing technology,

demand for large part manufacturing is getting stronger. Direct Metal Deposition (DMD) is

a DED technology based on laser and powder metal application using a closed-loop-

feedback control system. This presentation will give an overview of the DMD technology

highlighting its capability to scale up to large size parts. Challenges, such as high throughput

and associated distortion control to build large parts weighing more than 1000 lbs will be

discussed along with potential solutions. Finally, DMD’s capability of large part

manufacturing will be demonstrated through case studies from component manufacturing

for rocket engines.

Bhaskar Dutta is president and chief operating officer of DM3D Technology, United States, an

additive manufacturing company. Dr. Dutta has almost 30 years of experience in the field of

metallurgy and metal processing including 16 years in the AM industry. He has been directly

involved in AM research and technology development as well as commercial product

development using AM. Dr. Dutta has several patents, multiple technical publications and

presentations in the field of AM, and authored several books and book chapters on AM.


47

Accelerating Additive Manufacturing parts certification

Dr Sergey Mironets Collins Aerospace, Poland

[email protected]

Certification of parts produced by Additive Manufacturing techniques is one of the most

critical challenges that enables transition to production especially in the aerospace market.

Often, the cost for quality control and part certification is more expensive than printing a

part. The certification process may include in-situ monitoring, on the plate testing and final

inspection. The importance of developing a robust on the plate techniques for 3D print

certification will be discussed.

Sergey Mironets has 10 years of Additive Manufacturing experience and over 30

years of combined experience in fields of Powder Metallurgy and Composites, Heat

Treatment and Fusion Welding. As an Advanced Technology Leader at Pratt &

Whitney Additive Manufacturing Group Sergey played a significant role in the

development of various Additive Manufacturing prototypes for NGPF jet engines. At

Collins Aerospace Sergey has been active developing Additive Manufacturing

Strategy, selecting components for manufacturing cost reduction utilizing Powder

Bed Fusion and Direct Energy Deposition technologies. Sergey has over 35 patents

either awarded or in the application process. Sergey is an active member of ASTM

F42.05, ISO/TC 261, SAE AMS AM and America Makes ANSI Additive Manufacturing

committees contributing to development of standards for various Additive

Manufacturing materials and processes. Sergey is actively involved in collaborating

with RTRC on Additive Manufacturing modeling efforts. He serves as Additive

Manufacturing advisor to University of Connecticut Graduate Student Projects.

Sergey received a Mechanical Engineering degree from National Transport University

(Kiev, USSR), completed Powder Metallurgy and Composite Materials PhD course

work from Institute for Problems of Material Science (Kiev, USSR) and received MBA

from Rensselaer Polytechnic Institute.


48

TS02

Applications of Data Science

Organizer

A. Alankar, IIT Bombay

18th Dec 4-6 pm


49

Invited Speakers

A Deep Learning Approach for Development of Virtual Sensors to Compute

Responses for Structures Under Dynamic Loading Conditions

Dr. Giri R Gunnu

Suprabhash Sahu, and G. R. Gunnua

Tardid Technologies Pvt. Ltd. Bangalore, India.

[email protected]

Measurement of dynamic responses plays an important role in structural health monitoring, damage

detection and other fields of research. With current technology, the number of sensors is often

limited and the locations may also be inaccessible for instrumentation. To obtain the desired

responses using limited physical measurements, virtual sensing techniques have developed rapidly

in the last decades. Recently, considerable attention has been focused on Artificial Intelligence (AI)

which has been proven to be a powerful response modeling tool and approximator. An approach

based on virtual sensor techniques based on the Convolutional Neural Network (CNN) to estimate

the dynamic responses of a structure given measurements at some locations, where real sensors

are placed is implemented in this work. As proof of concept, a beam simply-supported at both ends

was modelled for training, testing and subsequent validation. Loading Condition: A random load

populated by Gaussian white noise was applied at one/multiple points on the beam. A script on

MATLAB was written implementing the dynamic time-history response of the beam using the

Newmark-Beta Method. A virtual sensor network was developed based on the data created. A

functional Convolutional Neural Network was used with varying number of convolutional layers,

hidden layers and fully connected layers based on the implementation. The model takes the

geometric and material properties of the beam as an input and also allows flexibility to change the

loading conditions, allowing us to use random loads, sinusoidal loads and other loads based on

mathematical functions. Moreover, point of application of loads can be changed to one/multiple

points. The CNN was exhaustively inclusive of all intrinsic beam parameters, loading conditions and

support types. Based on all these specified parameters, the CNN give an accurate time-history

response of the acceleration, velocity and displacement for the beam, effectively capturing the

underlying physics, while simultaneously decreasing the computation time by a factor of a thousand.


50

Statistical Learning for Infrastructure Vulnerability Assessment under

Natural Hazards

Jayadipta Ghosh Assistant Professor

Indian Institute of Technology Bombay

[email protected]

Infrastructure systems, such as highway bridges constitute the socio-economic backbone

of any nation that aids the safe transport of pedestrians and traffic. Adequate functioning

of these key elements of the transportation network are particularly relevant in the aftermath

of natural hazards, such as earthquakes, to ensure post relief and recovery operations.

Consequently, the vulnerability assessment of highway bridge structures in the wake of

natural hazards becomes imperative for highway authorities and disaster mitigation

agencies.

The assessment of structural integrity under extreme events, however, must be

conducted while acknowledging uncertainties from a multitude of sources, such as hazard

characteristics, structural parameters, and often the environmental effects on bridge

component deterioration. This talk will focus on the application of modern statistical

learning algorithms for seismic fragility assessment of highway bridges. Of relevance will

be the prediction of seismic response of critical bridge components for lateral load

resistance and the mutual interdependence of component behaviour that dictates bridge

system-level behavior. Parallels will be drawn with traditionally adopted naïve Monte Carlo

simulations to highlight the efficiency in vulnerability assessment with significant

reductions in computer runtime.

Dr. Jayadipta Ghosh is an Assistant Professor in the Department of Civil

Engineering at IIT Bombay. He obtained his Ph.D. degree from Rice University, TX,

USA following which he worked in portfolio-level seismic loss assessment in AIR

Worldwide in Boston. He joined IIT Bombay in 2014 where his primary research

focuses on efficient methods for vulnerability estimation of civil engineering

systems. Several of his research articles have been selected as the ‘Editor’s Choice’

papers in the American Society of Civil Engineers.



51

Machine Learning Applications in Contact Problems

Sachin Singh Gautam Assistant Professor

Department of Mechanical Engineering, IIT Guwahati, 781039

[email protected]

Machine learning has recently attracted a lot of attention in various fields. The field of computational

mechanics has also found application of machine learning in areas such as constitutive modelling,

fracture mechanics, fatigue failure etc. Computational contact mechanics is one such field where

the machine learning algorithms are been applied. Artificial neural network (ANN) is one of such

highly accurate machine learning methods that has been used in various engineering problems to

analyse discrete nonlinear data and find complex interrelations therein. After forming sophisticated

interrelation with non-linear data, ANN is widely used to predict the system output set corresponding

to single or multiple input set. Backpropagation neural network (BPNN) is a kind of multi-layer

artificial neural networks (MLANNs) where sensitivity of weights is back-propagated from output to

input layer via one or more hidden layers. In the present talk, the BPNN is applied to two contact

problems – gecko adhesion and fretting damage. First, the Bayesian regularization (BR) based

BPNN model is employed to predict some aspects of the gecko spatula peeling such as the variation

of the maximum normal and tangential pull-off forces and the resultant force angle at detachment

with the peeling angle. The input data is taken from finite element peeling results. The neural network

is trained with 75% of the FE dataset while the remaining 25% is used to predict the peeling

behaviour. The training performance is evaluated for every change in the number of hidden layer

neurons to determine the optimal network structure. The relative error is calculated to draw a clear

comparison between predicted and FE results. It is observed that BR-BPNN models have significant

potential to estimate the peeling behaviour. In the second problem, BPNN models are considered to

predict Ruiz parameters (F1) for the nominal and optimized liner geometries in diesel engines.

Overall, good correlation is observed in terms of the predicted F1 results using 2D FEA, full factorial

DOE, BR-BPNN and 3D FEA.

Dr. Sachin Singh Gautam is currently an Assistant Professor in the Department of

Mechanical Engineering, Indian Institute of Technology Guwahati. His research

interest is in computational mechanics specifically isogeometric analysis, contact

problems, GPU computing. Recently, he has started to explore machine learning

applications in contact problems. He has published 23 journal papers, 12 books

chapters, and made more than 50 conference presentations. He has supervised 3

PhDs, 17 master students and many bachelor students. Currently he is supervising 7

PhD students and 4 master students. Dr. Gautam is currently involved in development

of contact and isogeometric modules for FEAST® software being developed by VSSC,

ISRO.


52

Contributed Speakers

Detection of Fretting Fatigue Using Machine Learning Algorithms

Khizr Mohammad Khan, IIT Guwahati

Khizr Muhammad Khan, Sachin Singh Gautam

Department of Mechanical Engineering, Indian Institute of Technology Guwahati

[email protected]

Abstract

Fretting is very common in machines that experience relative movement among mechanical

components resulting in wear, corrosion, and fatigue especially in parts experiencing

vibrations such as in aircraft, turbine/blades etc. The main purpose of the paper is to

develop a classification model that can predict fretting fatigue by using different machine

learning algorithms. To make any machine learning model the first most important aspect

is to collect the data as much as possible by experiments or by some other means. Recently,

there has been some attempt to predict the life of the specimen by using artificial neural

networks. The main objective of this work is to develop a classification model to determine

whether the specimen will pass or fail, using the experimental dataset available in the

literature and transforming the data to make it suitable for classification. In the experiments,

the specimen which crosses a million cycles is considered to safe and said to be run-out

and the specimen which does not cross a million cycles is considered to be a failure. The

data points which show a million cycles greater than 107 are categorized as 1 (runouts) and

the data points which are showing a million cycles less than 107 are categorized as 0

(failed). The classification model is trained by splitting the whole dataset into 80% training

data and 20% test data. The dataset is imbalanced as there are more number of data points

showing failure than the data points showing the run-out. To balance the dataset Synthetic

Minority Oversampling Technique (SMOTE) is used. The result is validated using the

performance metrics like precision, recall, and F1 score. Results show that classification

models are working well on test data

Keywords: Fretting Fatigue, Machine Learning Algorithms, SMOTE, F1 score.


53

Debond detection in metallic stiffened plate by estimating mahalanobis

distance

Abhijeet Kumar, IIT Bombay

Abhijeet Kumar1, Anirban Guha1, Sauvik Banerjee2

1 Department of mechanical engineering, Indian Institute of Technology Bombay, Mumbai,

400076, India 2 Department of civil engineering, Indian Institute of Technology Bombay, Mumbai, 400076,

India

[email protected]

Abstract

In this study, the feasibility of statistical technique Mahalanobis square distance (MSD) with

combination vibration-based approach is examined to debond detection and quantification

in metallic stiffened plate structure. The numerical simulated and experimental model

displacement data is used as damage sensitive feature vector. For debond identification,

the undamaged feature vector set as baseline data, the MSD, a covariance weighted

distance is calculated on any future data to discriminate the damaged or undamaged state

structure. The sensitivity of technique is first examined to set the threshold with numerical

simulated data there after the experimental data is processed to validate the technique. It

is observed that, MSD estimation-based damage detection technique has quite significant

capacity for debond detection and quantification with numerical as well as experimental

data.

Keywords: Structural health monitoring, Debond Detection, Mahalanobis distance,

Vibration-based


54

TS03

Creep and High Temperature Failure

Organizers

S. Gollapudi, IIT Bubhaneswar

R. Kottada, IIT Madras

11th Dec 5-10 pm

20th Dec 4-6.30 pm


55

Invited Speakers

Creep and high temperature deformation behaviour of Al0.2 CoCrFeNiMo0.5

high entropy alloy

Rajesh Korla, IIT Hyderabad Rajesh Korla, Yasam Palguna

Indian Institute of Technology, Hyderabad [email protected]

Continuous decrease of fossil fuels along with rapid increase in carbon foot print pushing towards increasing the efficiency of thermally operated systems such as thermal power plants. One way of increasing the efficiency is to increase the operating temperature which can be possible only with the development of new structural materials with enhanced high temperature strength, creep resistance and oxidation resistance. In this direction, studies in last decade showed that high entropy alloys (HEAs) exhibiting better properties compared to conventional steels and super alloys. One of the interesting observations with high entropy alloys, as observed recently, is that many of these high entropy alloys retaining their high strength even at temperatures above 700oC . Further, some of these alloys exhibit good corrosion resistance which make these alloys a suitable candidate as high temperature material especially for the present generation advance ultra-super critical thermal power plants.

Present work investigated the high temperature strength and creep behavior of Al0.2CoCrFeNiMo0.5 high entropy alloy. Alloy was prepared through vacuum induction route followed by thermo-mechanical process and further, precipitation hardening and the structural stability at high temperature was studied using Iso-thermal annealing experiments. High temperature tensile experiments were performed on the peak aged samples at different temperatures along with the post deformed microstructural studies. Preliminary results on the creep behavior will be discussed.

Dr. Rajesh Korla is an Assistant Professor in the department of Materials Science and

Metallurgical Engineering at Indian Institute of Technology, Hyderabad. He obtained his M.E.

and Ph.D. Degree from IISc Bangalore. He worked as Post-Doctoral fellow at Oxford

University. His research interest is in mechanical behaviour of materials and creep


56

Physics based versus empirical models for creep

Ramkumar Oruganti Principal scientist

GE Research

[email protected]

While there is a constant effort to deepen understanding of high temperature mechanical behavior and create better physics-based models, the industry prefers to use methods that are simple and time tested. In most cases at the practical level there is an unshakeable reliance on hard data. Where behavior has to be extrapolated beyond the range of available data, the tendency is to use empirical methods and equations. This talk will cite examples of these scenarios and outline reasons for why this situation persists. We will also try to provide directions on how this gap might be addressed.

Obtained Ph.D in materials science from University of Michigan, Ann Arbor in 2002. Working with GE Research since then. Areas of focus include high temperature mechanical behaviour, constitutive modelling, superalloys, steels, novel non-destructive methods for microstructure



57

Multiscale modelling and prediction of high temperature mechanical

response – are we there yet?

S. Karthikeyan

Associate Professor

Materials Engineering, Indian Institute of Science, Bangalore

[email protected]

The past several decades has seen an exponential growth in the application of

computational tools to a variety of engineering disciplines, including materials engineering.

While there has been reasonable success in usage of these modelling tools towards alloy

design and processing, prediction of mechanical response remains a challenge. These

efforts have remained largely academic and limited to idealised situations. In my talk, I will

review the state-of-the-art on various computational approaches to predicting high

temperature strength and failure of engineering alloys. I will present specific results from

our multiscale modelling efforts combining first principles calculations with FEM and

dislocation dynamics to predict the high temperature behaviour of Ni- and Co-base

superalloys. I will discuss some novel computationally inexpensive yet accurate models that

we have developed that enables high throughput prediction of properties relevant to high

temperature strength, not just in model systems but in multicomponent engineering alloys

and at operating temperatures. I will close the talk by highlighting the current challenges in

the applicability of these tools to engineering problems.

Prof. S. Karthikeyan’s interests are in mechanical response of metals and intermetallics

under extreme conditions of strain rate and temperature. The experimental activities in

his group include creep testing, high strain rate testing and electron microscopy, while

the computational activities include atomistic simulations, electronic structure

calculations, phase field methods and FEM.


58

New Insights into Creep in the So-Called Harper-Dorn Creep Regime

Praveen Kumar Praveen Kumar, Shobhit P Singh,Michael E Kassner

Associate Professor

Department of Materials Engineering, Indian Institute of Science, Bangalore 560012 (India)

[email protected]

Creep response of pure materials at very low stresses (<10-5 G, where G is the temperature

compensated shear modulus of the material) and very high temperatures (>0.9 Tm, where

Tm the melting temperature of the material) is not fully understood. After the classic work

of Harper and Dorn, in 1957, on high purity Al in this “stress-temperature” regime, this creep

test regime is often called the Harper-Dorn regime. Although the creep response is

conventionally characterized by dominance of dislocation-climb, a creep stress exponent, n,

of 1 and a stress independent dislocation density, several studies did not observe a

transition to n = 1 in the Harper-Dorn regime. This study aims to provide some insights into

creep behaviour in this regime that may help resolve the debate. Here, creep responses of

pure LiF and Al single crystals were examined. After long term (~ one year) annealing at

high temperatures (>0.9Tm), a frustration dislocation density was observed in these crystals.

This frustration density restricts any further coarsening of the dislocation network. Hence,

a stress independent dislocation density might be observed in the Harper-Dorn regime.

However, crystals initially grown with dislocation density lower than this frustration limit can

show a stress dependence at such low stresses, and then n can be close to 3 in the Harper-

Dorn creep regime. Overall, n can be in between 1 and 3, depending on the initial dislocation

density. A model, which is based on the higher dependence of dislocation climb velocity on

the applied stress, is developed to explain the effect of dislocation density variation on the

stress exponent observed in the Harper-Dorn as well as “five”-power law regime. A

consensus is now building that Harper-Dorn creep is most likely a special case of “five”-

power law.

Praveen Kumar received his Bachelor of Technology degree in Mechanical

Engineering from Indian Institute of Technology, Kanpur, in 2003. Subsequently, he

received M.S. and Ph.D. degrees in Mechanical Engineering from University of

Southern California, Los Angeles in 2005 and 2007, respectively. He is currently an

Associate Professor with the Department of Materials Engineering, Indian Institute

of Science, Bangalore. His main research interests are mechanical behaviour of

materials, with particular emphasis on studying effects of electric current,

temperature and sample length scale, and constructive usage of electromigration,

both in solid and liquid metals.



59

Transition from dislocation to diffusion dominant plastic flow in nanolayered

thin films

Dr. Rejin Raghavan, IISc Bengalore

R. Raghavana, J.M. Wheelerb, T.P. Harzerc, V. Chawlad, S. Djaziric, B. Philippic, C.

Kirchlechnere, J. Wehrsf, J. Michlerf, G. Dehmc aDepartment of Materials Engineering, Indian Institute of Science, Bangalore

bLaboratory for Nanometallurgy, Department of Materials Science, ETH Zürich cStructure and Nano-/Micromechanics of Materials, Max-Planck-Institut für

Eisenforschung GmbH, Max-Planck-Strasse 1, 40237 Düsseldorf, Germany dInstitute Instrumentation Centre, Indian Institute of Technology Roorkee

eInstitute of Applied Materials, Karlsruhe Institute of Technology fEmpa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for

Mechanics of Materials and Nanostructures, Feuerwerkerstrasse

Email address: rejinr@ gmail.com

This presentation highlights the transition from dislocation to diffusion dominant plastic flow

observed during the deformation of mutually immiscible, nanolayered systems at moderately

elevated temperatures. Three different systems of nanolayered thin films consisting of varying sub-

100 nm thick Cu layers sandwiched between TiN, W, and Cr layers were studied. Diffusion barriers

such as W or TiN prevent Cu diffusion into the Si during synthesis and service. On the other hand,

do supersaturated Cu-Cr alloys supersede nanolayered Cu-Cr films of the same average

composition irrespective of the layer thickness?

The mechanical response of 2 μm (Cu-Cr system) & 4-5 μm (Cu-W & Cu-TiN) nanolayered

films up to 400 oC was studied by compressing focused ion beam machined micropillars in situ SEM

using an Alemnis® indenter modified for high temperature testing. Shearing and tearing by

separation of the columnar Cr, W & TiN layers across the layers was observed up to ~100 oC. But,

lateral flow or plastic flow perpendicular to the load direction of Cu was observed at ~0.35

homologous temperature in all three systems. The confined layer slip model captures the trend of

the yield strength as a function of Cu layer thickness at 25 oC well. At elevated temperatures, the

applicability of existing stress-assisted diffusion plasticity models is considered.

Dr. Rejin Raghavan is working on the high temperature mechanical behavior of NiAl with

Pt and Pd additions as a Research Associate under the supervision of Prof. Vikram

Jayaram in the Materials Engineering department at IISc (Bangalore, India). He had joined

MPIE after working as a Scientist/Post-doc at Empa, Swiss Federal Laboratories for

Materials Science and Technology (Thun, Switzerland) in the department of Dr. Johann

Michler (Laboratory for Mechanics of Materials and Nanostructures) for five years. He is

the recipient of the Prof. K. P. Abraham medal Best thesis award for his PhD thesis on

“Effect of free volume on the fracture and fatigue of amorphous alloys”.


60

Impression creep and its application to magnesium alloys and magnesium

composites

Dr. Ashok Kumar Mondal, Assistant Professor,

Department of Metallurgical Engineering, Indian Institute of Technology (BHU) Varanasi,

Varanasi - 221005, India.


Impression creep test is a special type of indentation creep test. It uses a cylindrical indenter

to impress the specimen surface, and the depth of penetration is recorded as a function of

time. The technique is useful for studying the creep behaviour of many materials. The

impression creep test has been employed successfully to investigate the creep behaviour

of several magnesium alloys like AE42, MRI230D, AZ91, AZ91+Ca, AZ91+Sb, AZ91+Bi,

AZ91+Ca+Sb, AZ91+Ca+Bi, and AZ91+Bi+Sr alloys as well as several magnesium alloys-

based composites and nanocomposites. The values of stress exponent (n) and activation

energy of creep (Q) have been calculated using the impression creep tests to determine the

dominant creep mechanisms operating in these magnesium alloys, composites and

nanocomposites. The creep behaviour of some of these materials has also been evaluated

using the conventional tensile and compression creep tests for comparison. The results

obtained using the impression creep test are in good agreement with that produced by the

conventional creep tests. In this talk, a brief introduction on impression creep will be

provided. In addition, the results obtained on some magnesium alloys, composites and

nanocomposites using impression creep tests and their comparison with the results

produced by conventional creep tests will be discussed.

Dr. Ashok Kumar Mondal obtained his B.E. from the Department of Metallurgical

Engineering, Bengal Engineering College Shibpur (Presently IIEST) in 2001. He

completed his M.E. in 2003, and Ph.D. in 2009 from the Department of Materials

Engineering, Indian Institute of Science, Bangalore. He served the Metallurgical Quality

Control, Bharat Forge Limited, Pune from August 2009 to July 2011. He then worked

as the Associate Professor at the Department of Metallurgical and Materials

Engineering, National Institute of Technology Rourkela from August 2011 to May 2018.

Dr. Mondal is presently working as the Assistant Professor at the Department of

Metallurgical Engineering, Indian Institute of Technology (BHU) Varanasi.


61


Compositionally graded nanosize precipitates at grain boundaries of

directionally solidified GTD444

Richa Gupta, IIT Bombay

Richa Gupta*, M.J.N.V. Prasad and Prita Pant

Department of Metallurgical Engineering and Material Science, IIT Bombay

*Email- [email protected]

Abstract

Minor addition of boron as a grain boundary strengthener improves the creep rupture

properties of the Ni-based superalloys. However, the existence of boron in the

multicomponent system remains questionable. The role of boron in altering the grain

boundary chemistry has been investigated in directionally solidified GTD444. DS GTD444 is

a grade of General Electric (GE) suitable for later stage gas turbine buckets. The samples

from the airfoil were characterised extensively by time of flight-secondary ion mass

spectrometry (ToF-SIMS), transmission electron microscopy (TEM) in conjunction with

energy dispersive X-ray spectroscopy (EDS). The investigation suggests that most of the

boron presents at the γ-γ' interface lies along the grain boundary in the form of nanosize (~

80-90 nm) precipitates. These particles are further confirmed as (Cr, W, and Mo) borides.

Presence of borides suppresses the agglomeration of mostly reported M23C6 carbides at

the grain boundaries of GTD444. An elemental partitioning within the borides is also

observed which suggests that they are at their initial stage of forming. Such type of

compositionally graded nanosize precipitates is not reported in superalloy systems so far.

Keywords: Grain boundary borides, Nanosize precipitates, Time of flight- secondary ion

mass spectrometry (ToF-SIMS), Transmission electron microscopy (TEM), Energy

dispersive X-ray spectroscopy (EDS).


62

Residual stress analysis in large water quenched stainless steels

S. Hossain, Military Technological College, Oman

S. Hossain1,*, A.M. Shirahatti2

1. Department of Aeronautical Engineering, Military Technological College, Al Matar Street,

PO Box 262, PC 111, Muscat, Sultanate of Oman

2. Jain College of Engineering, Visvesvaraya Technological University, India

*Corresponding author email: [email protected]

Abstract

Age related degradation mechanisms in nuclear plants are crucially dependent on the

magnitude and distribution of weld residual stress. Earlier studies focussing on

measurements of residual stresses in thick section welded components revealed there is

sufficient driving force for the creation of creep damage, in particular during high

temperature operation. Detail of how the presence of residual stress influences creep

degradation need to be investigated. The main aim of the research programme is to assess

how stresses act as a driving force for creating creep damage. To numerically predict creep

damage using finite element analysis (FEA), it is required to accurately model the stress

distribution and validate the stresses experimentally. Quenching is a practical means of

introducing residual stress field in laboratory specimens in a controlled manner.

Residual stresses measured deep into metal parts using neutron diffraction (ND) technique

with the application of a novel ENGIN-X stress instrument are presented. A time-of-flight

method developed at ISIS facility at Rutherford Appleton Laboratory was used to measure

residual stress distributions in type 316H stainless steel specimens of large size. The

specimens included two cylindrical bars of diameter 60mm, length 160mm and a cylinder

of diameter 60mm, length 60mm. Residual stresses were introduced into the specimens by

rapid spray water quenching. This study was part of a research motivated by a need to

model and understand creep in ageing power plant. An extensive finite element analysis

was carried out to predict the residual stress following water quenching. Overall, an

excellent correlation existed between the measured and FEA simulations for both residual

strains and stresses.

Keywords: quenching, residual stress, finite element analysis, neutron diffraction


63

TS04

Fracture and Fatigue in Materials and Structures

Organizers

V. Chintapenta IIT Hyderabad

D. Mahajan, IIT Ropar

12th Dec 4-9 pm

20th Dec 4-9 pm


64

Invited Speakers

Relation between strain localization and micro-void coalescence in ductile

fracture

Shyam Keralavarma

Associate Professor

Department of Aerospace Engineering, IIT Madras

[email protected]

The ductility of structural metals is often limited by strain localization phenomena, such as

necking and shear banding. A criterion for the onset strain localization, viewed as an

instability in the incremental constitutive response of the material, was developed by Rice

and co-workers (1975, 1976). However, application of Rice's theory to ductile metals

obeying classical porous plasticity models leads to predictions of unrealistically large

strains to failure compared to experiments. In this study, we show that this discrepancy can

be addressed by accounting for alternative "inhomogeneous" modes of yielding at the meso-

scale of the voids. At sufficiently large porosities, localized yielding of the ligaments

between neighbouring voids leads to void coalescence and crack initiation/propagation. It

is shown that Rice's instability criterion combined with a recently developed model for void

coalescence can yield realistic predictions for the strain to failure in ductile materials as a

function of the loading path. The predictions of the new model are compared with numerical

estimates of the strain to failure, obtained using finite element cell model simulations of

void growth under proportional loading paths, and good quantitative agreement is

demonstrated. The advantages of the new model via-a-vis existing ductile fracture criteria

in the literature are discussed.

Shyam Keralavarma obtained his Ph.D. from the department of Aerospace Engineering

at Texas A&M University, USA, in 2011. After a short stint as a post-doc at Brown

University, USA, and EPFL, Switzerland, he joined the faculty of the Aerospace

Engineering department at IIT Madras in 2013. His research interests are in the broad

area of mechanics of materials, with emphasis on problems in the micromechanics of

plastic deformation and fracture.


65

Snap-buckling and failure analysis of CFRP laminate with embedded circular

delamination subjected to four-point bending load

Dr Gangadharan

Lala Bahadur Andraju, Gangadharan Raju*, M Ramji

Department of Mechanical and Aerospace Engineering, Indian Institute of Technology

Hyderabad, India

Snap-buckling of delaminated carbon fiber reinforced polymer (CFRP) composite laminate

under pure bending load may lead to critical failure, which needs to be understood for

damage tolerant design. In this work, a multi-angle CFRP composite beam specimen with

embedded circular delamination is studied under four-point bending. Experimental

techniques like digital image correlation (DIC) and acoustic emission (AE) are used to

evaluate the strain at which the snap-buckling of sub-laminate happens and the subsequent

delamination propagation in the beam specimen. Detailed fractography studies are carried

out on the post-failed specimens to get insights on the various damage modes.

Subsequently, a three-dimensional finite element model is developed in the Abaqus

software to model the beam specimen with delamination for simulating the snap-buckling

of the sub-laminate and the associated damage modes in the laminate. The cohesive zone

model technique is used to model the delamination failure, and a continuum damage model

employing user material (UMAT) subroutine is implemented to model the fiber, matrix, and

fiber-matrix shear failures in the laminate. The sub-laminate buckling strain and damage

evolution results predicted by the numerical is compared with experimental observations.

The developed numerical models can aid in the design of damage tolerant composite

structures under bending loads.


66

Adhesion Durability of Interfaces in Photovoltaic Module

Naresh V Datla Associate Professor

Mechanical Engineering, IIT Delhi

[email protected]

The photovoltaic (PV) module is a multi-layered structure that is expected to work under

prolonged outdoor exposure with consistent power output. The loss of integrity at the

interfaces of the module due to service loads and environments adversely affects the

module efficiency. An understanding on how water diffuses within the module and how it

affects the fracture toughness will help us to assess and prevent the long-term degradation.

This talk shall show by both experiments and simulations on how fracture toughness of

encapsulant-glass adhesion changes with service life. Methods developed to corelate

fracture with water exposure and characterize water diffusion will be presented. These

methods will be used to predict spatial and temporal loss of adhesion in PV module.

Naresh V. Datla is an Associate Professor in the Department of Mechanical Engineering

at IIT Delhi. He received his B.Tech. from NITW in 2002, M.E. from IISc in 2004 and Ph.D.

from Univ. of Toronto, Canada, in 2011. He worked as a postdoctoral fellow at Temple

University, Philadelphia, and as a scientist at ISRO Bangalore. His research concerns

deformation and failure of materials using both experimental and numerical techniques.

His current research activities include work on tissue biomechanics, composite joints,

nanocomposites, and photovoltaic modules.



67


Multiaxial Fatigue Behavior of Near Alpha Titanium Alloy for Aeroengine

Applications

Adya Charan Arohi, IIT Kharagpur

Adya Charan Arohi1, Vikas Kumar2, N. Narasaiah3

1Department of Metallurgical and Materials Engineering, Indian Institute of Technology,

Kharagpur, India

2Defence Metallurgical Research Laboratory, Hyderabad, India

3Department of Metallurgical and Materials Engineering, National Institute of Technology,

Warangal, India

Email of corresponding author: [email protected]

Abstract

Titanium alloys are considered as an attractive material for the aerospace applications

owing to their unique characteristics such as high specific strength, good ductility and better

corrosion resistance. IMI 834 alloy is a near α Ti -alloy which is used in the compressor discs

and blades of turbine engines. These components rotate at very high RPM and often

experience the combined effect of axial and centrifugal stress. Most of the times, the failure

of these components occurs due to the cyclic loading during its normal operation. Hence,

the aim of the present study is to evaluate the tensile and multiaxial fatigue behavior of IMI

834 alloy at room temperature. Tensile tests are performed at a strain rate of 6.67 x 10-4 s-

1. Fully reversed pure axial, pure torsion, and combined axial torsion fatigue experiments are

conducted on the tubular specimen in in-phase loading condition at a frequency of 0.3 Hz.

Hysteresis loops are determined for all the fatigue tests at half of the fatigue life. Cyclic

stress response curves are generated and noted that the alloy tends to show neither cyclic

hardening nor cyclic softening during the pure axial fatigue. On the other hand, it shows

cyclic softening for the case of pure torsion and combined axial torsion fatigue.

Subsequently, fatigue life is correlated to Von Mises equivalent stress and strain under

various loading combinations. The alloy exhibits lowest fatigue life under pure axial and

highest life under pure torsion fatigue. It is noteworthy to observe that the effect of torsion

is more dominant under the combined axial torsion fatigue. Fractography is also carried out

to understand the fracture micro mechanism with respect to loading conditions.

Keywords: IMI 834, multiaxial fatigue, tubular


68

Use of Compression-bending Fracture Geometry to Study the Effects of

Stoichiometry on Fracture Toughness of NiAl

Devi Lal, IISc Bengaluru

Devi Lal a, Ananya Tripathi a, Abhijit Ghosh a, b, Ravi Bathe C, Praveen Kumar a and Vikram

Jayaram a

a. Department of Materials Engineering, Indian institute of Science, Bengaluru 560012

b. Department of Metallurgy Engineering and Materials Science, Indian Institute of

Technology Indore

c. Centre for Laser Processing of Materials, International Advanced Research Centre for

Powder Metallurgy and New Materials (ARCI), Hyderabad

E-mail: [email protected]

The study of fracture in hard materials requires a stable test geometry that eliminates the

need for fabricating a large number of samples. Compression-bending fracture is an old

technique in which compressive loads on a pre-cracked sample induce bending moments

that lead to mode I conditions at the crack tip1 2. Since this geometry shows stable crack

growth, it is useful for studying crack propagation and associated processes, such as crack

bridging and microstructural and compositional inhomogeneity induced variation of fracture

toughness and R-curve behaviour. In addition, due to the relative ease of sample fabrication,

handling as well as of performing tests, this geometry has recently been re-discovered for

studying the fracture behaviour of hard coatings 3. In the present work, we apply this

technique to the study of toughness in -nickel aluminides which constitute the principal

component of bond coats used to protect superalloys from oxidation. We have further

developed some mechanistic details of this geometry to understand the effect of friction

between pillars and loading punch and geometry dimension on stress distribution and

fracture behaviour using finite element (FE) analysis. We have prepared compression

fracture samples from two compositions of NiAl alloys: Ni-50Al, Ni-40Al. Herein, 20 mm

diameter disks of NiAl of desired composition were arc melted and homogenized for 100 h.

Post homogenisation, composition, grain size and grain orientation were analysed. Fracture

samples were prepared from the cast alloy using electro-discharge machining, followed by

femtosecond laser ablation to create a sharp notch in the range of dimensions in which

fatigue pre-cracking or focused ion beam machining are difficult to implement. Fracture

toughness and hardness were measured at room temperature.

Key words: Compression bending fracture Geometry, FEM, NiAl, Fracture toughness


69

Multiaxial cyclic test response of low C-Mn steel under proportional/ non-

proportional conditions and constitutive material equations aspects

Punit Arora, BARC

Punit Arora*, Suneel K. Gupta, M.K. Samal and J. Chattopadhyay

Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai 400 085, India

*Email of corresponding author: [email protected]

Tel.: +91 22 2559 7139; Fax: +91 22 2550 5151

The piping and vessel components in Nuclear Power Plants (NPP) are generally subjected

to multiaxial state of cyclic stresses/ strains owing to their complex geometries/ loading

conditions. Depending on variation of stress (or strain) components, multiaxial loading can

be categorized as ‘Proportional’ with fixed principal stress axes and ‘Non-Proportional (NP)’

with varying principal stress axes. In general, the damage caused under these two loading

categories is significantly different. Non-proportional cyclic condition results in higher

hardening in material as compared to corresponding proportional case resulting is

reduction of fatigue life. Most of the commercial Finite Element (FE) softwares are not

equipped with advanced material models which are capable of simulating higher hardening

under NP loading. This is due to the reason that these models are mainly based on

associative flow rules and Armstrong-Frederick family of kinematic hardening rules.

In this view, recently a large number of multiaxial tests have been performed on primary

piping material (low C-Mn steel) of Indian Pressurized Heavy Water Reactor (IPHWR) under

uniaxial, proportional and non-proportional multiaxial conditions to determine cyclic

response of material. The material follows Masing idealization with a linear shift along

elastic line under uniaxial and proportional conditions. The uniaxial and proportional

responses are attributed to be modelled by combined kinematic and isotropic hardening

rules with von-Mises yield function and associative flow rule of Prandtl-Reuss. However,

tests hysteresis loops under NP loading conditions have brought out that material does not

follow associative flow equations for von-Mises yield equation. Material once subjected to

90° out-of-phase axial-torsion conditions, does not bring back stress state in elastic regime

even after several un-loadings of axial/ shear strain cycles.

This study mainly highlights some of the key test observations in connections with material

constitutive equations, generally used to model cyclic stress-strain behaviour.



70

Effect of notch configurations on geometric factor solutions of an SENW

fracture test geometry.

Hrushikesh Sahasrabuddhe, IIT Bombay

Hrushikesh Sahasrabuddhe*, Abu Zubair, Tejas Chaudhari, Nagamani Jaya Balila

Department of Metallurgical Engineering and Materials Science,

Indian Institute of Technology Bombay, Mumbai 400076, India

[email protected]

Abstract

Materials in fiber or wire form are used at several length scales, sometimes bunched into

cables and at other times reinforced into composites. Knowledge of fracture toughness of

these wires is critical in life prediction. The influence of wire aspect ratio on the Mode I

geometric factor solutions of a straight fronted notch in a wire specimen was recently

established [1]. The present study extends the contem-porary physical understanding to the

modelling of asymmetric notches vis. a vis. convex, concave,chevron, and angled chevron,

as well assymmetric notches vis. a vis. circumferential and double-edged. Multi-parametric

mode I geometric factor solutions as a function of relative crack depth, wire aspect ratio

and location on the crack front have been computed using extended finite element method

(XFEM). Dependence of geometric factor on wire aspect ratio is explained in terms of the

change in stress state ahead of an asymmetric notch and the boundary conditions that

result out of the axial con-straints of a tension test. Additionally, the double-edged-notched

wires are shown to provide the re-quired geometric stability for controlled crack growth in

brittle materials, enabling the measurement of R-curves and cyclic crack growth.

Experimental validation of the geometric factor solutions is obtained through mode I notch

toughness measurements on a brittle linear elastic polymeric material - Poly (me-thyl

methacrylate).

Keywords: Finite Element Analysis, Mode I geometric factor, notch configurations, stable

crack growth


71

Effect of pre-strain on fatigue life of DP600 steel in presence of stress

concentrators

Puja Ghosal, IIT Patna

Puja Ghosala, Surajit Kumar Paula, Bimal Dasa, Manaswini Chinarab, K.S. Arorab

a Mechanical Engineering Department, Indian Institute of Technology Patna, Bihar, Patna -

801106, India

b R&D, Tata Steel Limited, Jamshedpur, India

[email protected], [email protected]

Abstract

This study investigates the influence of pre-strain on high cycle fatigue behavior of DP600

steel for a center hole notch specimen. Uniaxial monotonic pre-strain of 12.5% is imposed

along the rolling (RD) and transverse (TD) direction of DP600 steel blank. The center hole

notch specimen is fabricated from the pre-strained blank along parallel and transverse to

the initial pre-strain direction. Monotonic and fatigue performances are assessed for as-

received, parallel, and orthogonal pre-strain conditions. An increase in yield and tensile

strength are noticed after pre-straining. The presence of stress concentration at the notch

tip results in the lower plastically deformed zone for pre-strained specimens relative to as

received specimens. Pre-strain results in negligible influence on the notch fatigue limit.

Advancement of stress-concentration with pre-straining nullified the increased yield stress

and fatigue limit for the notched specimen.




72

Static and Dynamic Fracture Toughness Properties of HSLA Steel for Naval

Application

Jeetesh Kumar, NIT Warangal

Jeetesh Kumar*,@, Adya Charan Arohi* ,Jalaj Kumar#, G. Brahma Raju* and Vikas Kumar#

* NIT, Warangal; # DMRL, Hyderabad

@ Corresponding author


Abstract

In the present investigation, static and dynamic fracture toughness properties of HSLA

steel have been evaluated. Standard fracture mechanics CT (compact tension) type

specimens for static fracture toughness, CVN (Charpy V-notch) specimens for dynamic

fracture toughness have been extracted from the industrial plate in LT and TL directions.

Elasto-plastic fracture toughness tests (JIC) have been performed using single specimen

unloading compliance technique. For the dynamic elasto-plastic fracture toughness (JID)

tests, CVN samples have been fatigue precracked to different crack lengths levels.

These samples are further tested under impact loads in an instrumented impact

machine. Crack initiation energies have been deduced from dynamic load-deflection

curves. Subsequently, JID have been evaluated using these energies. No significant

difference is observed in the dynamic fracture toughness properties w.r.t. orientations.

However, the dynamic fracture toughness values are lower than static fracture

toughness. This may be due to higher strength of materials under dynamic conditions

which is known to lower the fracture toughness values. Further, SEM based

fractographic analysis have been performed on all the tested samples to identify various

fracture micromechanisms.

Keywords: JIC; JID; HSLA steel



73

Effect of deformation and aging on hardening behaviour of Maraging Steel

250

Kevin Jacob, IIT Bombay

Kevin Jacob a, Saurabh Dixit b, Anton Hohenwarter c, B. Nagamani Jaya a

a Department of Metallurgical Engineering and Materials Science, Indian Institute of

Technology Bombay,Mumbai, Maharashtra, India - 400076

b Mishra Dhatu Nigam Ltd. (MIDHANI), Hyderabad, Telangana, India - 500058

c Department of Materials Science, Chair of Materials Physics, Montanuniversität Leoben,

Jahnstraße 12, 8700 Leoben, Austria

[email protected]

Abstract

Plastic flow of materials is dependent on the ability of dislocations to move along specific

crystallographic planes under the application of an external stress. Hindrances encountered

to this flow will result in a higher stress required to facilitate this movement, leading to the

overall hardening of the material. The activation of the different slip planes along which the

dislocations move are governed by Schmids law. In certain situations however dislocations

prefer to move along a single plane in a condition called as planar slip, the occurrence of

which leads to an overall softening of the material. Maraging steels are one such class of

materials where in their as-solutionised condition, majority of slip is planar. Upon ageing,

they acquire a diverse microstructure with the presence of lath boundaries, precipitates and

reverted austenite each of which has a different effect on the overall hardening behaviour

of the material. In the current study the extent of different strengthening or softening

mechanisms is quantified as a function of applied deformation strain through High Pressure

Torsion (HPT) and ageing parameters. The stages of hardening and their mechanisms are

identified for both the as-received and HPT processed maraging steels. HPT processing

leads to an increase in strength by nearly 70% along with a change in the morphology and

distribution of the precipitates. On the flip side, the structural integrity of these steels suffers

from poor ductility. The precipitate morphology, distribution and spacing has been

characterised using Atom Probe Tomography (APT). The effect of the change in

morphology of the precipitates has been studied through finite element modelling to

understand the distribution of stresses around the differently shaped precipitates that act

as stress concentrators for early onset of fracture.



74

Remaining Life of Fastener Joints under Bearing and Bypass Fatigue

Loading

I Syed, Jain University

I Syed, B. Dattaguru and A.R. Upadhya

School of Aerospace Engineering, Jain (Deemed-to-be University)

Bengaluru

[email protected]

Abstract

Fastener joints are widely used in aircrafts to connect different parts in primary and secondary

structures. These create a non-permanent joint, unlike the case of welded or adhesive bonds and

also allow easy assembly and dismantling. However even though fastener joints provide easy

access to inspect, they cause stress concentrations and are susceptible to damages such as cracks

under overload and/or fatigue. Such cracks could grow to the critical sizes under aircraft flight loads

during service life. It becomes necessary that such a fastener joint is analysed suitably to ensure

safety. In normal joints the life of the joints is estimated using the S-N curve whereas critical joints

are designed based on the damage tolerance approach. This paper presents both approaches for a

few typical joints under bearing and bypass loading.

In this paper, the fatigue life of lap joints between rectangular plates with one to three bolts in series

is estimated numerically. Marginal clearance is used in the bolts to represent a practical

configuration. The current analysis is for metallic plates, but the approach is also applicable to

composite plates. A 2-dimensional non-linear contact stress finite element model (FEM) is used to

study the stresses and strains around the bolt holes in the upper plate of the joint. The FE model is

validated with the results in the literature on similar configurations. The variation in stress

concentration is studied with varying bearing to bypass load ratios. The reduction in strength of joint

due to the presence of cracks is also investigated. For damage tolerance analysis, initiation of

cracks is assumed to be at the stress concentration points. In the initial studies, constant amplitude

(CA) fatigue loading is applied and these cracks are grown till failure. The life, in terms of such CA

cycles, is presented in this paper. The Modified Virtual Crack Closure Integral (MVCCI) technique is

used to compute the strain energy release rate in mode – I of the crack. Crack growth life is

computed using the Paris law with Elber correction. Finally, the fatigue analysis loading is carried

out using variable amplitude FALSTAFF standard flight load spectra for typical fighter aircraft. Rain

flow cycle counting is used to extract the damage causing cycles. Results are presented in a way

that remaining life can be estimated at any stage of operational loading. This type of prognostic

approach helps in scheduling maintenance operations. The study presented in this paper is a prelude

to the development of a computational model as a part of a digital twin for structural joints.

Keywords: Lap joint . Fatigue life . Crack . Prognosis


75

Viscoplastic Constitutive Parameters for Inconel alloy-625 at 843K

S.C.S.P. Kumar Krovvidi, IGCAR S.C.S.P. Kumar Krovvidi1*, Sunil Goyal2, J. Veerababu1, A. Nagesha1, A.K. Bhaduri1

1Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, India. 2Nuclear Fuel Complex, Kota Project, Rawatbhata- 323305, India

* [email protected]

Abstract

Inconel alloy-625 is one of the candidate materials for high temperature bellows in sodium-

cooled fast reactor (SFR) systems. Typical temperature in SFR systems is around 843K at

which failure modes such as creep and creep-fatigue interaction are significant.

Viscoplastic analysis gives the combined strains due to fatigue including stress relaxation

during hold time. This paper presents the estimation and validation of the parameters of

Inconel alloy-625 for Chaboche and Rousselier viscoplastic constitutive model at 843K. A

set of low cycle fatigue and creep-fatigue interaction tests were carried out. The parameters

defining the isotropic and kinematic hardening of the material were estimated from the LCF

tests. The viscous parameters were estimated from the stress relaxation data obtained

from the CFI tests. Validation of the parameters of the viscoplastic constitutive parameters

was carried out by successfully predicting the hysteresis loops and the stress relaxation

behaviour exhibited by the alloy.

Keywords: Inconel alloy-625; SFR systems; visco-plastic; isotropic hardening; kinematic

hardening; finite element analysis.



76

Mechanical behavior of PEM membrane under uniaxial tension

Kartheek Pilla, IIT Bombay

Kartheek Pilla, Aakash Tanwar, Krishna N Jonnalagadda

Department of Mechanical Engineering, Indian Institute of Technology Bombay

[email protected]

Abstract

Polymer electrolyte membrane (PEM) based fuel cells have numerous advantages

over conventional power generation sources owing to their low operating noise, higher

efficiency compared to diesel or gas engines, and negligible pollution. These positive

factors have contributed to the demand of PEM based fuel cells. PEM membrane is a crucial

component of a fuel cell, whose reliability limits the life of the fuel cell. In this work, the

fracture toughness of the PEM membranes under tensile loading at room temperature was

investigated. Nafion-212 was the PEM polymer chosen for this work. Under operating

conditions, Nafion is highly ductile. In this work, the methods available to compute fracture

toughness of ductile polymers in thin film form were reviewed. Depending on the

constitutive behaviour of the polymer under tensile loading, suitable methods for fracture

toughness measurement were also suggested. Fracture toughness was calculated through

in-situ experiments on the thin films of Nafion-212. The essential work of fracture method

was employed, and its applicability as a measure of fracture toughness was verified. Digital

image correlation technique was employed for the validation of EWF as well as computation

of J-integral. The equivalence between EWF and J-Integral calculation methods was also

established. The effect of notch preparation had significant effect on the essential work of

fracture value due to the varying crack tip root radius.

Keywords: Polymer Electrolyte Membrane (PEM); Essential work of fracture (EWF); Fracture

of thin films; Digital image correlation.



77

Investigation into hydrogen induced blister cracking and mechanical failure

in pipeline steels

Vishal Singh, IIT Ropar

Vishal Singh*, Dhiraj K. Mahajan

Ropar Mechanics of Materials Laboratory, Department of Mechanical Engineering, Indian

Institute of Technology Ropar, Rupnagar, Punjab, 140001, India

*[email protected]

Abstract

This work aims to investigate the role of hydrogen-induced blisters on tensile and fatigue

damage of pipeline steels (X65 and X80). The electrochemical method of hydrogen charging

is employed to simulate hydrogen-induced blister formation. Similar hydrogen charging

conditions result in different sizes, shapes, and number of blisters in both types of steels.

DIC analysis coupled with in-situ tensile/fatigue investigations confirmed the blisters as

potential stress concentration sites. Synergistic action of hydro-gen and stress

concentration around these blister type notches intensify the overall mechanical damage of

material under hydrogen atmosphere. Morphology and relative positioning of blisters is

confirmed to affect overall tensile and fatigue behavior significantly.

Keywords: Hydrogen embrittlement, blisters, pipeline steels, fatigue damage


78

Analysis of a turbofan engine bearing failure

Swati Biswas, DRDO

Swati Biswas, Jivan Kumar, Satish Kumar VN

Materials Group, Gas Turbine Research Establishment

Defence Research & Development Organization, Bengaluru, India

Structural integrity of the rotor support systems of the turbofan engines in aircraft

propulsion system application is of utmost importance as they constrain the relative motion

between the rotating elements at a speed close to 50,000rpm. Premature failure of a ball

bearing was encountered during ground testing of a turbofan engine leading to seizure of

shaft rotation.

Dis-assembly of the engine components revealed severe distress in one of the bearings.

The bearing cage was fractured, a portion was melted and few balls were stuck to the outer

race with the cage material. The inner race, all the rolling elements (balls) and outer race

were found to be covered by a golden layer which was subsequently found to be the cage

material. The fractured surface of the bearing cage was examined visually, macroscopcially

using stereo-binocular microscope and microscopically under scanning electron

microscope. Lower magnification view of the fractured surface reveled crack front

emanating from the ball pocket surface of the cage. Higher magnification observation

revealed striations on the fractured surface indicating fatigue failure of the cage. The

fractured surface was found to be oxidized. Other cage pieces collected from the failure

location showed solidified structure indicating melting and re-solidification of the cage

material.

Examination revealed that failure of the cage in the ball bearing of the engine was

associated sequentially with cage failure, seizure of cage and ball motion, cage melting,

flow and subsequent solidification, and inner race shift with respect to the outer race

towards the front face. Failure of the cage appeared to be the first event in this case. The

fatigue failure of the cage resulted in restricted cage movement, impeding the ball

movements which in turn resulted in huge frictional heat thereby melting the cage material.

The melt re-solidified later when the temperature cooled down.

Key words: ball bearing, inner race, outer race, rolling elements, fatigue

1Corresponding author, e-mail: [email protected]


79

Evaluation Of Cyclic Properties Of 50Ni-24Cr-20Co-0.6Mo-1Al-1.6Ti-2Nb

Alloy At Advanced Ultra Supercritical Steam Temperature

Ashmita Patra Banerjee, Midhani

Ashmita Patra Banerjee, Rajasekhar Kondabolu

Research & Development, Mishra Dhatu Nigam Ltd

[email protected]

Abstract

50Ni-24Cr-20Co-0.6Mo-1Al-1.6Ti-2Nb alloy is a candidate material for superheater tubes

and turbine rotors operating at 750°C in proposed A-USC power plant. Present study aims

to estimate cyclic strength and creep fatigue interaction behavior at operating steam

temperature. Strain controlled LCF tests are carried out within the strain range of 0.2%-1%

at RT and 750°C to evaluate effect of temperature on endurance limit. Substantial hardening

at all temperatures, which becomes more evident with increasing strain amplitude, is

attributed to the cumulative effects of dislocation tangle formation with their mutual

interaction and to the immobilization of dislocation by fine γ' precipitates. Deformation

mechanisms influencing the endurance limit as a function of strain rate are identified. Hold

times upto 500s are introduced at 750°C to evaluate creep fatigue interaction behaviour,

one of the primary damage mode in this case. Effect of direct aging on cyclic properties also

comes under the scope of present study.

Keywords: Ultra supercritical, Low cycle fatigue, Alloy 740


80

TS05

Fracture Mechanics at Multiple Length Scales

Organizer

N. J. Balila, IIT Bombay

13th Dec 4-6 pm, 7-10.30 pm


81

Invited Speakers

Load Interaction in Fatigue Crack Growth – Cracking a Lasting Controversy

R. Sunder

ITW-India (P) Ltd

100th years of Griffith’s Theory and fifty years of regimented application of

Linear Elastic Fracture Mechanics into engineering practice have seen notable

improvements to residual life of safety critical structures. Residual life

estimates rely on the ability to estimate the duration of service usage

associated with the growth to critical proportions of a fatigue crack that may

have been too small to detect at the previous inspection.

A striking anomaly in research on fatigue crack growth has been its focus on

constant amplitude loading even if there is hardly any case of engineering

application that is essentially constant amplitude by nature. As a

consequence, even after more than fifty years of awareness of load interaction

effects that cause significant variation in crack growth rate from what one

may expect under constant amplitude loading, controversy continues to

persist about what exactly causes such variation. One school of thought

attributes load interaction and stress ratio effects to the phenomenon of crack

closure in the wake of the crack tip. Another school of thought attributes these

effects to the response of the material ahead of the fatigue crack tip.

This talk describes an essentially local research effort that appears, finally, to

resolve contradictions between the two contradictory schools of thought by

coming up with irrefutable empirical evidence backed up by simple and

transparent analytical modeling that together explain how the two load

interaction mechanisms actually operate in concert. The results of the

ongoing study open new avenues for path breaking research to improve the

quality of residual fatigue life estimates in engineering application, including

development of a new testing practice, emerging opportunities in additive

manufactured components and design of fatigue critical components.

Dr. R Sunder obtained his M.Tech. and Ph.D. from Kiev Institute of Civil

Aviation. He is currently research director at Instron Centre of Excellence,

Bangalore. He founded Bangalore Integrated System Solutions (P) Ltd (BISS)

in 1992, a developer and manufacturer of mechanical test systems. BISS now

operates as an amalgamated Division of Instron, a world-leader in mechanical

test systems. He is a fellow of Indian Academy of Sciences . He is President

at Indian Structural Integrity Society


82

Role of Photoelasticity in Advancing Fracture Mechanics Education and

Research

K. Ramesh Professor

IIT Madras

[email protected]

Photoelasticity has had a significant influence in the development of fracture mechanics

ever since the experimental work on running crack by Post and Wells, and the fringe

interpretation by Irwin. The importance of higher-order terms in crack-tip stress field

equation has been beautifully illustrated by Sanford and his co-workers. With developments

in digital computers and progresses made in image processing, use of statistical methods

for data processing, digital acquisition of fringe data has been perfected over the decades

to evaluate stress field parameters reliably. This has enabled solving complex problems

involving multi-axial loading with interacting cracks in mechanical and thermal loadings as

well as in the presence of residual stresses. Hybrid photoelastic-FE analysis has helped in

improving boundary conditions for numerical analysis. Crack-growth prediction is also

influenced by higher-order terms as revealed by photoelasticity. The talk would trace these

developments and also highlight the educational and processing tools available for

researchers.

K. Ramesh is currently the K Mahesh Chair Professor at the Department of Applied

Mechanics, IIT Madras and formerly a Professor at the Department of Mechanical

Engineering, IIT Kanpur. He has authored 175 technical papers, two books, two e-

books and three book chapters and four video courses in NPTEL. He is a Fellow of the

Indian National Academy of Engineering and has received the Zandman award from

Society for Experimental Mechanics, Distinguished alumnus award from NIT Trichy.

He has developed several educational software and processing software that are

copyrighted. Member of the Editorial boards of Strain and Optics and Lasers in

Engineering


83

Hydrogen Behaviour in Rail Steel during Steel Manufacture

Dr G Balachandran Vice-President (R&D)

JSW Steel, Vijayanagar

[email protected]

The damage associated with hydrogen in steel may be divided into environmentally assisted

damage and those which are due to other reasons. In the former category, the damages

include Hydrogen embrittlement, stress corrosion cracking and corrosion fatigue. The latter

category of damage is associated with the hydrogen that dissolves in the steel during

manufacture that ends up in severe damage during service. The hydrogen dissolved in the

steel during manufacture manifests as hydrogen flaking of the steel, that leads to what is

popularly called as shatter cracks or Tache Ovales in Rail steels. There can be other

damages in this category, which are blow hole or pin hole formation, fish-eye formation and

longitudinal cracking. Rail steels are very sensitive to hydrogen pick up during the

manufacture and it has potential to generate damage in service, in spite of passing through

all the initial inspection stages. The Hydrogen flaking event has not yet been successfully

timed. Hence, every precaution is taken to prevent the hydrogen pick up during the

manufacture of the steel. Every 1 ppm H, if it freely evolves in a solid steel, it has potential

to generate 9% by volume void. The present study deals with two rail steel grades VAR89S

(typically, 0.70%C–0.3%Si–1.1%Mn–0.015%S) and VAR101 (typically, 0.80%C–0.42%Si–

1.01%Mn–0.65%Cr–0.005%S) manufactured at JSW Steel Ltd for application in Euro Rail in

Italy. The hydrogen distribution in the steel varies from surface towards the core associated

with the phase transformation. This also explains the reason why hydrogen flaking takes

place towards the mid-section of a wrought steel product. In the present study, the hydrogen

levels were tracked in 15 heats produced right from the melting stage to rail making stage.

In one heat, where a higher level of hydrogen content was identified, the steel was hot rolled

and a series of anti-flaking heat treatments was carried out to reduce the hydrogen levels.

The removal of hydrogen by anti-flaking heat treatment was explained using a Fick’s Law

based model. The presentation deals with the damages caused by hydrogen in steel during

steel making and the measures needed to mitigate the same during manufacture.

Dr G Balachandran has done his M Tech from IIT Kanpur and PhD from IIT Bombay. He

has served as a scientist for over 20 years with DMRL, Hyderabad. He served later nearly

2 years with Ashok Leyland, Chennai. Subsequently, he served for more than 6.5 years at

Kalyani Carpenter Special Steels Ltd., Pune. He was a visiting faculty with IIT, Madras close

to a year. During the past more than 3 years, he is with JSW Steel Ltd. and has served in

the Salem unit and presently working in the Vijayanagar unit.


84

Structural Integrity of ship hull structures

K. Sridhar Scientist, Naval Materials Research Laboratory (NMRL),

Defence Research Development Organisation (DRDO), Ambernath

email : [email protected], [email protected]

Metals are widely used for the fabrication of various marine engineering components and

therefore their protection in aggressive seawater environments is of prime concern to marine

designers, engineers and constructors. Generally the choice of materials and the protection

methods depend on life cycle cost, regular maintenance required during the life of the component,

criticality of the component etc. Other factors of importance include strength, expected functional

performance, availability of materials and capital cost. Hull structures and its appendages of naval

ships are constructed by joining numerous assemblies/sub-assemblies / sub-systems made of

HSLA steel, primarily by various welding processes. This being the most critical structural member,

its structural integrity is of prime importance due to varying type of loads experienced by it due to

operating machinery inside as well as due to impacting sea waves from outside.

During service, the ship’s hull structure is subjected to external loading by impacting sea wave

from outside, whose amplitude and frequency depends on the sea state. The hull is also subjected

to fatigue loads due to operating machinery inside the ship. Thus the steel, its weldments & heat

affected zone (HAZ) are subjected to a complex spectrum of loading in an aggressive chloride

environment, which are both dynamic and static. This leads to initiation of crack at highly stressed

critical regions either from externally formed pits on the hull surface and from intrinsic defects in

the material such as porosities / blowholes /inclusions.

In this talk, the conjoint effect of fatigue loading and aggressive seawater environment effect on

the corrosion fatigue crack growth rates (CFCGR) are presented for two different types of

shipbuilding steels are presented. The mechanism of corrosion fatigue process, the various

parameters affecting the crack growth rates and the effect of environment and the loading frequency

on the fracture morphology will be delivered. The methodology adopted for fatigue life estimation

of hull structures based on the analytical approach and the experimental determined parameters will

be dealt with. Further the futuristic in-situ fatigue life prediction of ship hull structures estimation

based on sensors and AI/ML will be highlighted.

Dr.K.Sridhar has done his Ph.D. in Corrosion Science and Engg, from I.I.T, Bombay. His field of

interest includes Surface Engineering using HVOF and laser processing for marine corrosion

resistant coatings, Localized corrosion, Cathodic protection, Stress corrosion cracking, Corrosion

fatigue and Failure Investigation. He has done his postdoctoral fellowship from Boston University,

USA on PVD coatings and published 40 papers (national & international) including 3 chapters in

ASM handbooks & 2 in books and granted 4 patents. He is a reviewer for 6 international journals

published by Elsevier and Taylor & Francis, USA.




85

Elastic-plastic fracture mechanics at micrometer scale: Requirement,

Challenges and possible solutions

Prof. Ashish Kumar Saxena

Assistant Professor

School of Mechanical Engineering, Vellore Institute of Technology Vellore

[email protected]

In the current era of miniaturization, it necessary to understand the materials behaviour and

reliability at application length scale. For brittle materials the linear elastic fracture

mechanics is well established, but for semi-brittle materials linear elastic fracture

mechanics cannot be used to determine the fracture toughness of micro length scaled

material volume due to relatively large plastic zone size compare to sample size. In these

case the elasto-plastic fracture mechanics (EPFM) using J-integral method have to be used

to determine the fracture behaviour. There are still many challenges exist even application

of EPFM at micrometer length scale. In the talk, these challenges as well as possible

solution for reliable estimation of fracture toughness of elastic-plastic materials will be

presented.

Dr. Ashish Kumar Saxena, is currently working as Assistant Professor in School of

Mechanical Engineering, VIT Vellore. Before joining current position, he worked on elasto-

plastic fracture mechanics in Mac-Planck Institute for Eisenforschung Germany as Mac-

Planck Post-Doctoral Research Fellow. He also works briefly in Materials Modelling lab

of GE Global Research Centre. His research interest are micromechnics of materials,

microstructure property correlation and materials processing.


86


FRACTURE EVALUATION OF A HIGH-PRESSURE GAS BOTTLE BY J-

INTEGRAL BASED FAILURE ASSESSMENT DIAGRAM USING ANSYS

K. Anjali Raj, MBCET

K. Anjali Raj1, A. K. Asraff2,Viswanath V.2, Vivek S.2 and Aneena Babu1

1 Mar Baselios College of Engineering and Technology,

2 Mechanical Design & Analysis Entity, LPSC/ISRO

[email protected]

Abstract

Metallic pressure vessels are used in launch vehicles in the form of propellant tanks, high pressure

gas bottles, water tanks etc. Different metals like Titanium alloys, Aluminium alloys, steels etc. are

used for the fabrication of these pressure vessels. These structures may contain cracks or crack

like defects, either inherently present in the base material or introduced during fabrication processes

such as welding. These crack-like defects have the potential to propagate rapidly under tensile

stresses during pressure testing or during service condition loadings leading to its catastrophic

failure. It is required to study the effect of these crack-like defects in pressure vessels through the

application of linear elastic as well as elastic-plastic fracture mechanics principles. The Failure

Assessment Diagram (FAD) concept is used to evaluate whether a crack may cause structural

failure. The FAD technique accounts for both brittle and ductile failure modes of the cracked

structure using two ratios: Load ratio (Lr) and Brittle fracture ratio (Kr). In this work, the variation of

fracture parameters such as stress intensity factors and J integral values along the crack front in a

high-pressure gas bottle containing part through crack used in an ISRO developed satellite launch

vehicle has been studied using ANSYS/Workbench (Version 18.1) general purpose finite element

analysis code. The objective of this paper is to ensure the structural integrity of the above gas bottle

using J integral based FAD. Both elastic and elasto- plastic fracture analysis of the gas bottle has

been done, the latter being done using multilinear kinematic hardening plasticity model. The ultimate

pressure carrying capacity of the structure in the presence of a specific crack has been calculated

directly from the FAD. The mode of failure of the structure, whether brittle or ductile, is also predicted

from the above diagram.

Keywords: Failure Assessment Diagram; Stress Intensity Factor; J integral; part through crack.


87

Clamped Beam Bending for Mixed Mode and Interface Fracture Toughness

Measurements

Ashwini Kumar Mishra, IIT Bombay

Ashwini Kumar Mishra*, Neha Kumari, Balila Nagamani Jaya

Department of Metallurgical Engineering and Materials Science,

Indian Institute of Technology Bombay, Mumbai, 400076, India

*[email protected]

Abstract

Clamped beam geometry is successfully used for evaluation of mode-I fracture toughness on micro

and bulk scale[1][2]. The present study explores a combination of mode I and mode-II fracture

toughness by changing the position of the loading point with respect to notch, and of angular

notches with respect to the bending axis. Mode-II stress intensity factor is computed as a function

of different position of loading point and relative crack length using the finite element method. Using

this information, mixed mode fracture trajectory is predicted, which is relevant for evaluation of

fracture behavior of multilayered and composite structures. Systematic study of interface fracture

energy in bi-material composite structures is also performed using finite element method and a

compliance based solution is proposed, which is applicable for various extents of elastic mismatch.

This will broaden the scope of the clamped beam as a generalized fracture toughness testing

technique for brittle systems.

Keywords: Mixed mode loading, interface fracture energy, finite element method, clamped beam

bending


88

Deformation of Polycrystalline Copper during Mode-I Loading

Ashutosh Rajput, IIT Patna

Ashutosh Rajput, Surajit Kumar Paul*

Department of Mechanical Engineering, Indian Institute of Technology Patna, Bihar, Patna -

801106, India

[email protected],* [email protected], [email protected]

Abstract

Molecular Dynamics simulation is carried out to analyses the effect of crack in arranged

polycrystalline copper under mode-I loading. The orientation of centre grain is [100] [010]

[001], and surrounding grains are oriented randomly and kept 200,400, and 600 with respect

to the centre grain. Higher stress concentration has been observed at the crack tip, and

nucleation of dislocation is noticed at the triple point junction. The centre grain produces a

continuous generation of dislocations, which gives rise to a slow and stable transgranular

failure of polycrystalline copper during subsequent mode-I loading.



89

Implementation of phase-field model for fracture in functionally graded

brittle materials for various material property gradations

Aravind R, IIT Madras

Aravind R a,b, Ratna Kumar Annabattula a, Jayakumar K b

a Department of Mechanical Engineering, Indian Institute of Technology, Madras

b Vikram Sarabhai Space Centre, Thiruvananthapuram

Abstract

Modelling fracture failure using conventional techniques based on discrete modelling is very

complex as it requires continuous tracking of discontinuities in the displacement field.

Phase field model based on variational frame work replaces sharp crack surfaces by a

damage variable which is diffused onto the crack surface. The crack diffusion is controlled

using a regularization parameter. The phase field approach offers the advantage of

modelling crack where multiple crack nucleation, crack branching and crack coalescence

can be captured without prior knowledge of the crack path. In this investigation, phase field

model is applied to simulate crack growth characteristics in Functionally Graded Materials

(FGMs) for various material property gradations for standard reference cases. Functional

gradation of material property can be controlled from point to point by varying volume

fractions in a controlled manufacturing processes. For determining effective properties,

several models like Voigt Scheme, Mori-Tanaka Scheme, Sigmoid Scheme, Exponential

Scheme etc are employed. The phase field model for brittle fracture is implemented in a

commercial finite element software using user defined UEL and UMAT subroutines.

Numerical simulations show that the crack growth significantly varies for FGMs under

various material gradation laws.

Keywords: Phase Field Method (PFM), Crack Propagation, Functionally Graded Materials

(FGM).


90

On the role of secondary voids in the mechanics of plane strain ductile

fracture – A numerical study

A. K. Dwivedi

A. K. Dwivedi, I.A. Khan, J. Chattopadhyay

Reactor safety division, BARC, (HBNI)

[email protected]

Abstract

Ductile fracture in metals occurs due to the nucleation, growth and coalescence of

microscopic voids, resulting in the formation of a macroscopic crack. These voids often

originate at different length scales as a result of cracking of larger size inclusions or

decohesion at second phase particles.

In several structural alloys like carbon-manganese steels, secondary voids play a vital role

in the growth and coalescence of the primary voids. The existing literature on ductile

fracture suggests that for a given initial void volume fraction, the spatial distribution of the

secondary voids in the intervoid ligament between the primary voids has a significant

influence on the fracture ductility. A systematic study analyzing the effect of orientation,

clustering and the shape of secondary voids, however, has yet not been performed. In the

present study, cell model based finite element analyses are performed to understand the

role of secondary voids on the growth and coalescence of the primary voids at mesoscale.

Both the primary and secondary voids are modelled explicitly and an elastic-plastic

response is assumed for the matrix. A double periodic array of primary voids subjected to

different magnitudes of applied stress tri-axiality is analyzed assuming plane-strain

condition. The numerical results obtained from explicit modelling of primary and secondary

voids are compared with the case where a homogenized response of the latter is simulated

using the Gurson model. The initial void volume fraction is the same in the two cases. Our

numerical studies reveal that the orientation of secondary voids relative to primary voids

may change the mode of coalescence from internal necking to void-sheeting and vice-versa.

Clustering of secondary voids, for the same initial void volume fraction, leads to onset of

primary void coalescence at lower magnitudes of nominal strain. It is observed that the

shape of the secondary voids also influences the fracture ductility of the material.

Keywords: Ductile fracture, Porous plasticity, Secondary voids, Flow localization.



91

Nonlocal diffused approach to model delamination in composites

D. Pranavi

D. Pranavi*, A. Rajagopal

Department of Civil Engineering, IIT Hyderabad, 502285.

[email protected]

Abstract

Delamination is a critical failure mode in composites as its constituents get separated due

to the weakening of the interface between the layers of such composites. Manufacturing

defects, sites of stress concentrations, free edge effects are causes for delamination. Upon

loading of such composites the delamination can grow and also mitigate between layers,

finally leading to the structural failure. In order to assess structural integrity, the material

parameters especially of the interface that governs the delamination growth should be

determined. In the present work, a nonlocal diffused approach, is proposed to model the

delamination. Nonlocal approaches helps in understanding the complex mechanisms of

delamination growth and mitigation and operates at a material length scale. The

performance of the proposed formulation is illustrated through representative numerical

examples.

Keywords: Delamination, Composite, Nonlocal approach, Interface.


92

TS06

Fracture and Fatigue of Structural Adhesives

Organizer

N. Datla, IIT Delhi

18th Dec 7-8 pm, 9-10 pm


93

Invited Speakers

Fatigue behaviour of polymer nanocomposites

CM Manjunatha Chief Scientist and Head

Structural Integrity Division, CSIR-National Aerospace Laboratories

Bangalore 560017, India

[email protected]

In this presentation, improved fatigue properties of polymer nanocomposites

containing various types of nano fillers such as carbon nano tubes, graphene, silica

nano particles etc., is reviewed. It has been observed that over 10-100 times

improvements in fatigue life could be obtained in polymer composites by addition of

nano fillers. In particular, the constant amplitude fatigue behavior of a glass fiber

reinforced silica nano particle modified epoxy composite is described in detail. Further,

it is shown that significant spectrum fatigue life enhancement could also be obtained

in GFRP nanocomposites. The underlying mechanisms for such fatigue life

improvements in nanocomposites are discussed. Also, fatigue life prediction

methodology under spectrum loads is discussed with examples. With such

enormously improved fatigue resistance, nanocomposites could well be developed as

fatigue immune structural materials in the near future.

Dr. CM Manjunatha obtained his B.E. (NITK) in 1988, M.E. (IISc.), in 1991 and Ph.D.

(Cambridge Univ., UK) in 1995. He was a post-doctoral fellow at Imperial College,

London, UK in 2008. He is a recipient of Gold medal for first rank in B.E. (1988),

Cambridge-Nehru Scholarship (1991), ORS award from CVCP London (1991-1994) and

UKIERI research fellowship (2008), NAL outstanding award for project execution-2013

and NAL best innovation award- 2017. He has over 150 publications to his credit in

international journals, conferences and seminars. He is founder secretary of InSIS and

member of many professional societies


94

Adhesively bonded joint in scarf jointed composite structures

M. Ramji Professor and Head

Department of Mechanical and Aerospace Engineering

[email protected]

In this talk focus is on the mechanical behaviour of both single and double tapered scarf

adhesively bonded joint of Carbon fibre reinforced polymer (CFRP) adherend subjected to

tensile loading. The layup sequence of the CFRP adherend having unidirectional (UD) [0°]16

and quasi [+45/−45/0/90]2S are considered. The adhesive used here is Araldite 2015 supplied

by Huntsman which is a two-part epoxy system of intermediate toughness grade. Here, 2D

digital image correlation (DIC) technique is used for capturing the whole field longitudinal,

peel and shear strain distribution over the adhesive bond line of the CFRP specimen. In

addition, 2-D finite element analysis (FEA) of scarf joint model is carried out for validating

the DIC results. In the finite element model, cohesive zone elements are used for the

modelling of both adhesive layer and inter/intra laminar interface of the composite laminate.

To verify the proposed numerical model, joint's initial stiffness, failure load and

corresponding displacement obtained from FEA are compared with the experimental load

– displacement results.

He obtained his Ph.D. Degree from Applied Mechanics Department, IIT Madras in the area

of digital photoelasticity and graduated in Dec 2007. After his PhD, he worked as Engineer

in General Electric, JFWTC, Bangalore in the area of stress analysis of GenX engine till

March 2009. Currently, he is Professor and Head, Mechanical Engineering Department at

IIT Hyderabad. His areas of interest are material characterization, experimental solid

mechanics, composite structures, and fracture mechanics.


95


Fracture R-curve and Cohesive Law of Aged CFRP Composite Adhesive

Joints

Mohd. Tauheed, IIT Delhi

Mohd. Tauheed*, N.V. Datla

Department of Mechanical Engineering, Indian Institute of Technology Delhi, Hauz Khas,

New Delhi, 110016, India

*Corresponding author: Mohd. Tauheed ([email protected])

Abstract

R-curve behaviour of brittle epoxy adhesive was studied using CFRP/epoxy adhesive joints.

Moreover, we studied the variation in cohesive law between crack initiation and steady state

part of the R-curve. Double cantilever beam (DCB) specimens were made of composite

adhesive joints to determine the mode I fracture toughness. The adherends are made of

CFRP laminates and adhesives used are AV138/ HV998 (brittle adhesive). The mode I

tractions-separation relations were extracted with the help of digital image correlation (DIC)

of the crack tip images. AV138 showed independence of G on crack length with initiation

and steady-state fracture toughness. The fracture R-curves of a brittle adhesive that was

aged under the ageing environment of 40 °C and 82 % relative humidity. The adhesive layer

was then dried before fracture testing in order to measure the effects of irreversible

degradation (i.e., without the reversible, plasticization effect of absorbed free water). The

cohesive parameters were used in the FE modelling using ABAQUS to predict the joint

strength numerically.

Keywords: ageing, cohesive law, R-curve, CFRP joint


96

Mode-I fracture behavior of carbon nanofiber reinforced epoxy adhesive

joints

Amit Chanda, IIT Delhi

Amit Chanda, Sujeet Kumar Sinha, Naresh Varma Datla*

Department of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi-

110016


Abstract

Adhesives are increasingly used in joining structural components owing to its high specific strength,

ability to join intricate shapes and capability of better stress transfer capability. Epoxy adhesives are

the commonly used structural adhesives, which are used to bond components in aerospace,

automotive and marine industries. Though epoxy has good mechanical properties, chemical stability

and adhesive properties, it has very low fracture toughness and impact resistance. Fracture

toughness of epoxy can be increased by fillers, specially carbon-based nanofillers. In this study,

epoxy was modified using carbon nanofiber (CNF) and the effect of CNF was checked on mode I

fracture toughness (GIC) of epoxy.

Carbon nanofibers were dispersed into epoxy using ultrasonication method. P2-etched aluminum

adherends were bonded using pure and CNF modified epoxy to fabricate double cantilever beam

(DCB) specimens. Fracture tests were conducted with these DCB specimens to assess and evaluate

the mode-I fracture behavior. Modified beam theory was used for fracture toughness calculation.

Presence of CNF was observed to increase the GIC value significantly. Improvement ~ 300 % were

found when 0.5 wt% CNF was added. Fractured surfaces were studied under SEM to understand the

toughening mechanisms. Cohesive zone model with bilinear traction separation law was used in this

study to predict load displacement behavior of pure epoxy and CNF/epoxy joints. Obtained results

from finite element analysis were found to be in good agreements with experimental results.

Keywords: Carbon nanofiber/epoxy, DCB joint, fracture toughness, cohesive zone modeling


97

A MACRO-MECHANICAL STUDY OF THE EFFECT OF CIRCULAR

DELAMINATION ON FATIGUE LIFE CYCLE OF A COMPOSITE STRUCTURE

Jnanakshi Snigdha B, Sagar University

Shubha Javagal1, Shashidhar Naik H.G.2, Jnanakshi Snigdha B. 1*, Premkumar B.2

1Dept. of Mechanical Engineering, Dayananda Sagar University, Bangalore, Karnataka, India

2Compressors Global Department, QuEST Global Pvt. Ltd., Bangalore, Karnataka, India.

Composite materials are radically replacing metals in various structural applications due to

their high performance and adaptability. Composites have better load bearing capacities

and resistance to failure compared to metal structures. In order to quantify this, the damage

tolerance mechanisms of composites are studied extensively. One of the methods of failure

in composites is fatigue. The structural composites are subjected to various types of fatigue

loads, i.e., static and variable amplitude failure loads during service.

Although composites are believed to have better fatigue resistance compared to

conventional materials, it is necessary to study the effect of internal damages in the

structure on the fatigue life cycle. Delamination being one of the major types of damage in

polymer composites, can cause catastrophic failures. It causes stress concentration in load

bearing laminates and a local instability leading to a further growth of delamination which

results in a comprehensive failure of the laminate. This paper aims to study the fatigue life

cycle of a Carbon Fibre Reinforced Polymer (CFRP) specimen with a circular delamination.

A square plate specimen is assumed to contain a circular delamination due to barely visible

impact damage at the centre. A quasi-isotropic arrangement of Carbon fibre polymers is

considered and modelled. The material properties of the carbon fibre are taken from existing

literature. A commercially available Finite element software is used to carry out the analysis.

A low cycle fatigue load is applied on the specimen and analysis is carried out to generate

a suitable S-N curve for the considered case. The S-N curve further acts as an input to study

the onset of delamination in the specimen. The number of cycles required for the specimen

to fail under fatigue is be determined and the corresponding Strain Energy Release Rate will

be computed using Virtual Crack Closure Technique (VCCT). This study is further carried for

various delamination sizes and thru thickness locations of the delamination.

Keywords: Fatigue, CFRP, Virtual Crack Closure Technique, Strain Energy Release Rate.


98

Field-Induced Poynting Effect in Magneto-Active Polymers in Simple Shear

Krishnendu Haldar Department of Aerospace Engineering, Indian Institute of Technology Bombay, Mumbai

400076, India [email protected]

Magneto-Active Polymers (MAPs) are polymer-based composites with micro-magnetic particles em bedded in an elastomeric matrix material. The presence of magnetic particles provides strong tunability properties to the stiffness and damping of the polymeric composite under the magnetic field. It is a common observation that during simple shear deformation, conventional elastomers exhibit positive Poynting effect, i.e., the shearing planes tend to expand, and compressive stress is required to maintain a shear deformation. However, certain polymers exhibit a negative or reverse Poynting effect. In many biomedical applications, e.g., artificial muscles or magnetic gels, such a reverse Poynting effect for coiling, torsional, or shear deformation, is of fundamental interest. We solve a coupled simple shear problem with a specific constitutive equation and found that the magnetic field shows a significant influence on the Poynting effect and its sign.

Keywords: Magneto-active polymers, field-induced shear deformation, Poynting effect


99

T07+TS26

Integrity of Concrete Structures Against Blast and

Ballistic Loading and Construction materials, and

concrete and steel structures

Organizer: P. Nanthagopalan, IIT Bombay

18th Dec 6-8 pm


100

Invited Speakers

High strain rate behavior of concrete

Dr. Manmohan Dass Goel

Assistant Prof., Department of Applied Mechanics, Visvesvaraya National Institute of

Technology (VNIT), Nagpur, India.

Although, effect of strain rates on materials behaviour is not a new area but with the

advancement in technology and innovations in experimental techniques are leading to

understand the effect of strain rates on deformation behaviour of materials in different

ways. This is an area, particularly in India, research is gaining momentum in recent time in

different engineering disciplines. A structural design engineer deals with different types of

materials to be used in buildings and structures and thus understanding their behaviour

under extreme loading condition such as blast, impact and earthquake becomes utmost

important. Hence, it is necessary to characterize these materials at high rate of loadings to

design and use these materials efficiently. In this talk, focus will be on concrete material

and its behaviour under high strain rates. It is well acknowledged that concrete behaves

differently under dynamic loading conditions than static loading. Further, enhancement in

the compressive strength of the concrete material is observed due to the increased strain

rates under dynamic loading conditions. This strength enhancement can be determined by

experiments using Split Hopkinson Pressure Bar (SPHB) device. The discussion on SHPB

and its working will also be presented.

Dr. Manmohan Dass Goel completed his bachelor of engineering from Yeshwantrao

Chavan College of Engineering at Wanadongri, Nagpur under the then Nagpur

University in 2000. He was awarded three gold medals by Nagpur University for

academic excellence. He pursued master of technology (M. Tech.) in offshore

engineering from Indian Institute of Technology (IIT) Bombay, Mumbai till 2003. He

completed his Ph. D. from Department of Civil Engineering, Indian Institute of

Technology (IIT) Delhi and University of Federal Armed Forces, Munich. Awards:

Surendranath Mukherjee Memorial Medal, Innovative Student Project Award 2013,

CSIR Young Scientist Awards-2014, IGS-HEICO Biennial Award- 2017, Young Engineer

Award.Currently he is serving as Assistant Professor, Department of Applied

Mechanics, Visvesvaraya National Institute of Technology (VNIT),


101


Dynamic performance of RC slabs under combined blast and impact loading

Akshaya Gomathi

Akshaya Gomathi K1, A Rajagopal2

Department of Civil Engineering, Indian Institute of Technology Hyderabad

[email protected]

The development of numerical tools for efficiently modelling the Reinforced Concrete (RC)

structures subjected to high velocity blast and impact has been one of the major recent

study in military and research, with the increased terrorist attacks. Even with advanced

development of finite element tools for modelling and analyzing of the complicated

structural behavior, it is difficult to understand the structural and material behavior of RC

structural components under dynamic loading. There are various literatures available for

understanding the complex behav ior of structure under blast or impact loading separately.

The analysis shows that under dy namic loading the RC structures show very complex

behavior. The concrete is exposed to rap idly changing stress state and material shows

strain rate sensitivity. The damage mechanism and deformation is different under dynamic

loading condition, failure in tension with increase in dynamic tensile strength, crushing of

concrete caused by compaction of material, flow stress and ductility increases with higher

strain rate. Failure is concrete is caused by the formation of micro cracks and it develops to

form fracture process zone. In this paper the failure mechanics and the dynamic response

of RC slab subjected to combined blast and impact dynamic loading is studied by

numerically implementing in explicit software LS-DYNA. The validation is done separately

for RC slabs subjected to impact and blast loading. Then the response of RC slabs is

analyzed by varying the sequence of application of loads. Blast fol lowed by impact loading

and impact followed by blast loading. The time lag between the load initiation. It is seen that

the RC slabs subjected to impact loading followed by blast, shows more severe damage and

spallation because of the flexural and shear failure caused by impact load before the

subsequent blast load application. The numerical analyzes is carried out using in-built

models in LS-DYNA and the performances are compared. Performance based on crack

development and propagation, maximum displacement, acceleration-time and

displacement time responses were plotted and investigated. The parametric study is carried

out by analyzing the mechanical and damage response by var ying the slab depth,

reinforcement ratio by giving single and double reinforcement, velocity and the distance of

impact and blast loading. It is seen that the better performance can be ob tained for the slab

with increased thickness and doubly reinforced.

Keywords: Failure mechanisms, Dynamic response, Blast loading, Impact loading


102

TS09

Material Behaviour Characterization using Miniature

Specimens

Organizer: Z. Alam, DMRL

18th Dec 4.30-8 pm


103

Invited Speakers

Length Scale Effects on Power Law Creep of Materials: Cases of Uniform

and Graded Stress Fields

Praveen Kumar

Praveen Kumar (Other authors: Vikram Jayaram, Syed Idrees Afzal Jalali)

Associate Professor


[email protected]

revealed once the smallest dimension of the specimen decreases below a threshold value. In this

talk, the effect of sample dimensions on power law creep, which is controlled by dislocation climb, will be discussed, in context of uniaxial testing and cantilever bending. Experimental observations

suggest the existence of a surface affected region (SAR), wherein the dislocation substructures are significantly coarser than those formed in the interior. The origin of SAR lies in the classic

phenomena of dislocations escaping the sample through the surface, and its expanse is determined

by the applied stress, with its maximum value limited by the grain size. As the fraction of SAR in the

sample increases with a decrease in the sample size, the steady-state strain rates tend to increase and the “apparent” creep stress exponent registers a decrease, thereby clearly showing a sample

size effect on the observed creep behaviour of material. These variations, which are clearly observed in uniaxial loading, can be rationalized using the iso-strain composite model with SAR and interior

as two constituents. In bending, the strengthening effect of geometrically necessary dislocations associated with strain gradients, which increases with a decrease in the sample dimensions, gets

coupled with the “softening” effect of SAR, thereby producing a plethora of interesting cases, ranging from strengthened to “uniaxial-like” softened responses; these can be mapped using digital image

correlation. From induction, one may envision a cross-section in the cantilever wherein the strain

gradient and SAR effects perfectly balance each other. This extraordinary condition allows obtaining bulk creep response from miniaturized cantilever samples. Accordingly, this also enables accurate

assessment of the residual life of an in-service component using small volume specimens, which

can be scooped out from the component without disrupting its usual functioning.

Praveen Kumar received his Bachelor of Technology degree in Mechanical

Engineering from Indian Institute of Technology, Kanpur, in 2003. Subsequently, he

received M.S. and Ph.D. degrees in Mechanical Engineering from University of

Southern California, Los Angeles in 2005 and 2007, respectively. He is currently an

Associate Professor with the Department of Materials Engineering, Indian Institute of

Science, Bangalore. His main research interests are mechanical behaviour of

materials, with particular emphasis on studying effects of electric current,

temperature and sample length scale, and constructive usage of electromigration,

both in solid and liquid metals.



104

Mechanical properties of multi-phase complex concentrated alloys

Koteswararao V. Rajulapati*

School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad

500046, India.

*E-mail: [email protected], [email protected]

In a quest to develop new materials with enhanced properties, a novel class of material

systems called as “high-entropy alloys (HEAs)/ complex concentrated alloys (CCAs)” have

emerged recently, challenging the conventional alloy making principles. This concept gives

a “near-infinite” compositional space for exploration which was untouched till now.

Therefore it is also expected that unprecedented properties would be exhibited by these

materials. Our efforts at University of Hyderabad, India include development of various

classes of these materials by adding different alloying elements in equiatomic/ non-

equiatomic proportions and understanding the resultant mechanical properties vis-à-vis

structural/microstructural features. Ball milling coupled with spark plasma sintering (SPS)

as well as vacuum arc melting have been used to fabricate various multi-phase HEA

systems. Ball milling has resulted in either single/dual phase structures whereas multi-

phase structures have been realized while heating the samples as part of

sintering/homogenization. These multi-phase structures have resulted in interesting

mechanical properties w.r.t. hardness, strain rate sensitivity, activation volume, fracture

toughness etc. Development of some of our HEA systems was inspired by conventional

superalloys such as IN 718/ IN 617/Haynes 188. Detailed characterization has been done

using X-ray diffraction and electron microscopy. Mechanical properties were evaluated by

microindentation and high throughput nanoindentation at room temperature. This talk

would address the relationship between microstructural features and the corresponding

indentation based mechanical properties of different HEA systems investigated. It was

broadly observed that a multi-phase structure is desirable to have a balanced mechanical

properties in various alloy systems.

Dr. Koteswararao V. Rajulapati had his academic training in Metallurgical and

Materials Engineering and obtained his PhD, M. Tech. and B. Tech. degrees from

North Carolina State University, Raleigh, USA (2006), IIT-Kharagpur, India (2002) and

JNTU-Hyderabad, India (2000) respectively. He did his postdoctoral work in the

University of Michigan, Ann Arbor (2007) and the University of Southern California

(2008), Los Angeles, USA. He has been with the School of Engineering Sciences and

Technology, University of Hyderabad from 2009 onwards and is currently a Professor

here. His research interests include nanomechanics, high-entropy materials, friction

stir welding/processing, additive manufacturing, advanced high strength

steels/superalloys etc.

about:blank



105

In-Operando Nanomechanical Testing and its applications

S.A. Syed Asif

Industron Nanotechnology

[email protected]

Understanding the mechanical response and properties of materials at multiple length, time

scales, and the test conditions are becoming very important to optimize the performance

and develop materials with unique properties. Materials science community has been

coming out with new materials with outstanding properties and for applications at normal

and extreme conditions. For the underlying research effort, recent instrumentation for

structure property correlation has played a critical role. In recent two decades, depth

sensing nanoindentation emerged as not only a tool to measure hardness and modulus of

materials but other important properties such as viscoelasticity , creep resistance, fracture

resistance etc.. at depths as shallow as a few nanometers and temperatures as high as

1000oC. The measurement techniques that were believed not possible a decade ago are

becoming possible now with much superior resolutions and accuracies. Besides

indentation, today’s nano- and micromechanical methods include compression, tension

bending, fracture, fatigue and creep tests. This talk will demonstrate this capability of

structure property correlation from results on the in-operando nanomechanical testing of

various engineering materials. The results will be reported and the physical insight regarding

the deformation mechanisms will be discussed. The main focus will be on the

instrumentation techniques to improve the research efforts, and develop fundamental

understanding of deformation mechanisms of materials

Key Words: In-Operando, Nanoindentation, Hardness, Creep


106


Length Scale Effects on Power Law Creep of Materials: Cases of Uniform

and Graded Stress Fields

Syed Idrees Afzal Jalali

Syed Idrees Afzal Jalali, Vikram Jayaram and Praveen Kumar



Mechanical properties of materials are sensitive to specimen dimensions, which are readily

revealed once the smallest dimension of the specimen decreases below a threshold value.

In this talk, the effect of sample dimensions on power law creep, which is controlled by

dislocation climb, will be discussed, in context of uniaxial testing and cantilever bending.

Experimental observations suggest the existence of a surface affected region (SAR),

wherein the dislocation substructures are significantly coarser than those formed in the

interior. The origin of SAR lies in the classic phenomena of dislocations escaping the

sample through the surface, and its expanse is determined by the applied stress, with its

maximum value limited by the grain size. As the fraction of SAR in the sample increases

with a decrease in the sample size, the steady-state strain rates tend to increase and the

“apparent” creep stress exponent registers a decrease, thereby clearly showing a sample

size effect on the observed creep behavior of material. These variations, which are clearly

observed in uniaxial loading, can be rationalized using the iso-strain composite model with

SAR and interior as two constituents. In bending, the strengthening effect of geometrically

necessary dislocations associated with strain gradients, which increases with a decrease in

the sample dimensions, gets coupled with the “softening” effect of SAR, thereby

producing a plethora of interesting cases, ranging from strengthened to “uniaxial-like”

softened responses; these can be mapped using digital image correlation. From induction,

one may envision a cross-section in the cantilever wherein the strain gradient and SAR

effects perfectly balance each other. This extraordinary condition allows obtaining bulk

creep response from miniaturized cantilever samples. Accordingly, this also enables

accurate assessment of the residual life of an in-service component using small volume

specimens, which can be scooped out from the component without disrupting its usual

functioning.



107

In-Situ Mechanical Behavior of Multi-layered Steel at Mesoscale

Mahavir Singh

Mahavir Singh, Krishna N Jonnalagadda

Department of Mechanical Engineering, Indian Institute of Technology Bombay

[email protected]

Abstract

The layered mixture of dissimilar materials to achieve the multi-functional properties has

widen-up their application in the fields of transportation, energy, infrastructure etc. The

structural steel industry has also seen advancement by various structural changes and

mixing of different phases; the layered structure is being one the most popularly used. In

this study, the multi-layer steel sheet fabricated by cold pressing of alternate layers of

martensitic (high strength) and austenitic (high ductility) nature was analysed to understand

its in-depth mechanical behaviour. The samples were cut by using wire EDM, polished and

etched to see the grain boundary structure and interfaces of the two phases. Subsequently,

they were fabricated again to obtain dog-bone tensile geometry. The uniaxial tensile loading

at the quasi-static rate was applied along the longitudinal direction to generate the iso-strain

loading for individual layers. High-resolution images were captured and processed by digital

image correlation (DIC) technique to obtain the full-field behaviour at mesoscale. The

heterogeneity in the intralayer region and across the interfaces was investigated to correlate

the same with the structural positioning and microstructure. The microstructure was

analyzed using scanning electron microscopy. The results obtained showed potential in

further growth by controlling the microstructure and variation in the thickness of individual

layers to obtain a tailored behaviour between high ductility and high strength.

Keywords: Multi-layered Steel, Digital Image Correlation, High Resolution.


108

Finite Element Modelling of Deformation and Fracture Behaviour of Barium

Titanate Thin Films

Nidhin George Mathews

Nidhin George Mathews*, N Venkataramani, Nagamani Jaya Balila

Department of Metallurgical and Materials Engineering,

Indian Institute of Technology Bombay, Mumbai-400076, India

*[email protected]

Abstract

Barium Titanate (BTO) is a widely accepted lead-free piezoelectric ceramic used at micron

length scales and in thin film forms in applications. It is important to estimate mechanical

response of a material in the length scale of its real application as the mechanical properties

are different from their bulk values due to size effects. Here we study the mechanical

behaviour BTO thin film systems using different micromechanical experiments and finite

element modelling (FEM). Damage tolerance of the film-substrate is not dependent on the

applied loads alone but also on other parameters such as film thickness, residual stresses,

grain sizes, nature and number of interfaces. Nanoindentation is a high throughput

technique for measuring the deformation and fracture response of thin films. It has not been

exploited fully due to the complex stress-state that results underneath an indenter tip.

Stress-strain response of thin films estimated from nanoindentation experiments are

therefore compared to uniaxial microscale experiments on single crystals for

benchmarking. FEM models are used to eliminate substrate effects to obtain actual

response from the film. Microcantilever fracture measurements revealed that thin film

showed a 60% lower KIC than bulk due to the weak inter-columnar boundaries. Changing the

interlayer material and/or substrate type varies the residual stresses in the film and this will

in turn control their fracture resistance. These effects of residual stresses, film thickness,

and material anisotropy on the fracture toughness are estimated from different FEM

models. Fracture toughness from microcantilever experiments are compared with

indentation fracture toughness value to determine the effect of different stress states. An

insight to improve the damage tolerance of thin film systems is therefore obtained from the

combination of nanoindentation based experiments and FEM modelling.


109

Extracting uniaxial flow stress-strain behavior of metals from cantilever

under bending using Digital Image Correlation

Priya Goel

Priya Goel, Praveen Kumar, Vikram Jayaram

Department of Materials Engineering, Indian Institute of Science Bengaluru

[email protected]

Abstract

The accuracy and reliability of material parameters obtained through small scale testing of

the next generation of materials is a challenge as testing is limited by difficulty in sample

preparation, its mounting and alignment. In a cantilever, the measurement of strain gradient

using digital image correlation (DIC) generates a large volume of data from a single

specimen. The use of a single specimen in bending improves accuracy and reliability as

scatter is reduced. Bending also simulates the behavior of structures in applications more

closely than uniaxial testing. Therefore, in addition to ease of gripping and alignment,

bending also allows optimization of material volume in applications as well as in testing by

knowing the overall distribution of stress and strain in the sample. However, the non-linear

stress-strain law in plasticity leads to redistribution of stress across the cantilever to

maintain section planarity. The stress redistribution is transient and evolves as a function

of elastic to plastic strain ratio before it saturates at large plastic strain. The extraction of

flow parameters using a cantilever relies upon the estimation of stress during the

deformation. In the present work, the methodology to extract flow parameters from a

cantilever under deflection rate-controlled tests using DIC is explored. The studies on Al

show that yield strength and strain hardening exponent can be estimated within an error of

10%. The accuracy and limitations of the proposed methods in terms of extent of hardening

and DIC resolution are discussed using a model which numerically calculates stress

evolution during deformation.

Keywords: Bending, Flow parameters, Digital image correlation, modelling


110

TS10

Material Behaviour Characterization Under High

Strain Rate Loading

Organizers: E. P. Korimilli – IIT Indore

K. N. Jonnalagadda – IIT Bombay

G. Tiwari – NIT Nagpur

Dec 11th 5.00 pm to 6 pm

Dec 11th7 pm to 10 pm

12th Dec Time: 6 pm to 10 pm


111

Invited Speakers

Metal Foams and Their Behaviour at High Strain Rates

Manmohan Dass Goel

Assistant Prof. Department of Applied Mechanics, Visvesvaraya National Institute of

Technology (VNIT), Nagpur, India


Metal foams are a new class of materials and can be tailored for their mechanical properties

with particular focus on their end applications. In comparison with dense materials, metallic

foams have very low densities, higher energy absorbing capability, higher specific stiffness,

and improved acoustic damping and mechanical properties. These metallic foams are

smart option for various applications, wherein they are used as sandwich cores in structural

application, packaging along with blast-resistant structures/components. The talk will

discuss about foam in general and metal foam in particular.

Further, deformation of metal foams under high rate of loading is a complex phenomenon

due to the effects of various parameters involved therein. In this talk, primary focus will be

dynamic behaviour on aluminium metal foams at high rate of loading. The talk will focus on

experimental investigation of metal foams using split Hopkinson pressure bar (SHPB).

Dr. Manmohan Dass Goel completed his bachelor of engineering from Yeshwantrao

Chavan College of Engineering at Wanadongri, Nagpur under the then Nagpur

University in 2000. He was awarded three gold medals by Nagpur University for

academic excellence. He pursued master of technology (M. Tech.) in offshore

engineering from Indian Institute of Technology (IIT) Bombay, Mumbai till 2003. He

completed his Ph. D. from Department of Civil Engineering, Indian Institute of

Technology (IIT) Delhi and University of Federal Armed Forces, Munich. Awards :

Surendranath Mukherjee Memorial Medal, Innovative Student Project Award 2013,

CSIR Young Scientist Awards-2014, IGS-HEICO Biennial Award- 2017, Young Engineer

Award. Currently he is serving as Assistant Professor, Department of Applied

Mechanics, Visvesvaraya National Institute of Technology (VNIT),




112

Resistance of Masonry Walls under Repeated Impact Loading

Dr. K. Senthil

Assistant Professor

Department of Civil Engineering, NIT Jalandhar

[email protected]; [email protected]

Masonry can be designated as the urban curtains due to their extensive usage in residential

and industrial structures. Further, the outer periphery walls of almost 80% structures are

made up of brick units stick together with mortar. These walls are at times subjected to

accidental impact loads such as large mass of hard objects traveling with low velocities.

Therefore, present study is focused to estimate the multi hit impact response of clay brick

masonry wall under low velocity and large mass loading. The experiment as well as

simulations were performed in order to predict the behvaiour of masonry walls under multi

hit impact. The experiments were performed on pendulum impact testing frame capacity

of 250 kN and the response history was measured using dynamic load cell and high

frequency data logger system. The response of 110 mm thick clay brick masonry wall was

studied against 60 kg mass with hemisphere nose shape. The specimens were tested under

repeated loading of same magnitude and direction until failure. In addition to that, the

influence of aspect ratio of the wall and boundary conditions of the walls were studied. The

numerical simulations were performed using ABAQUS finite element technique and the

results thus predicted were compared with the experimental results. The damage behavior

of masonry wall was incorporated through Drucker-Prager and traction- separation law has

been implemented to model the hardening behaviour and brick-mortar joint interface of clay

bricks respectively.

Dr. Senthil has been actively involved in research since 2010 and he has published

31 refereed International Journal [11 SCI, 13 Scopus and 7 Peer Review Journal]

and 40 refereed international Conferences. He have two International

Collaborative project and first one Sponsored by the Royal Society UK in

collaboration with University of Bath UK – NIT Jalandhar and Second one

sponsored DST-RFBR in collaboration with the Saint Petersberg State University

Russia - IIT Roorkee India – NIT Jalandhar. He has received Seven National as

well as International awards for his academic and research excellence including

Best Teacher Award at NIT Jalandhar for the year 2018- 19. He has organized one

national Conference sponsored by TEQIP, STTP Sponsored by DST-SERB, five

national level workshop’s sponsored by TEQIP and few seminars. He is member

of 10 Civil Engineering Society including ASCE, Indian Concrete Institute and

Indian Geotechnical Society


113

Technical talk and Demonstration of Physical simulation in high strain rate

therm-mechanical processes using the Gleeble platform

Dr. Fulvio Siciliano

Metallurgist and Senior Application Consultant, Dynamic Systems Inc., USA

Gleeble systems are powerful tools for high temperature forming, processing and dynamic

mechanical behavior studies that enable world-class researchers to solve real-world challenges. Its unique ability to accurately and easily reproduce the thermal-mechanical history permits simulation

of large scale industrial processes such as rolling, forging, heat treating, welding, casting and others.

This presentation shows a compilation of Gleeble applications in high strain rate metallurgical processes including non-contact measuring techniques such as DIC, Laser Ultrasonics and

Pyrometers.

Dr. Fulvio Siciliano has close to 30 years of international experience in the areas of hot rolling, microstructural evolution, mathematical modeling and steel development for transmission pipelines and other applications. He visits India since 2003 and has accumulated extensive experience with Indian Steel Companies, Universities and R&D Institutes. Fulvio has a Ph.D. degree in Physical Metallurgy of Hot Rolling from McGill University (Canada / 1999) directly supervised by Prof. John J. Jonas; Master in Engineering and Metallurgical Engineer Degrees from University of São Paulo, Brazil. He is also a Professor of Metallurgy, Materials Science and International Relations.


114

Complex plastic flows and the machining of metal polycrystals

Narayan K. Sundaram

Associate Professor of Civil Engineering

Indian Institute of Science

[email protected]

The simulation of machining of soft metals in the critically important 100 micron-few mm

length-scale is challenging, requiring one to capture the complex flow physics induced by

the high ductility and polycrystalline aggregate nature of these metals. This talk will provide

an introduction to the phenomenology and engineering importance of these flows, and a

recently developed remeshing and mesh-to-mesh transfer-based FE approach that can

successfully simulate the cutting of polycrystalline aggregates. I will discuss the design of

these simulations including plasticity models, microstructural models, ductile failure, and

meshing / remeshing strategies; the trade-offs required, and outstanding problems that

remain to be addressed.

I am an Associate Professor of Civil Engineering at IISc, Bangalore. My group (the

Interfacial Solid Mechanics Group) explores a range of problems in contact

mechanics, adhesion, indentation, and large strain plasticity in metals processing with

a focus on polycrystalline aggregates. Our goal is often a first-in-class simulation in

these areas. I have a BTech Metallurgical (IIT Roorkee); and an MS in Materials and a

PhD in Aerospace Engineering both from Purdue University. I joined IISc after

postdoctoral work at the Center for Manufacturing Processes and Tribology, Purdue.



115


The effect of sabot mass and the interfacial friction between the sabot and

striker on the incident signals of a split-Hopkinson bar

D. Kumar

D. Kumar, S. N. Khaderi

Department of Mechanical and Aerospace Engineering, Indian Institute of Technology

Hyderabad


Abstract

The split Hopkinson pressure bar (SHPB) setup is used to characterize the dynamic

mechanical response of material. It consists of a coaxially aligned striker, incident (input),

and transmission (output) bar. Usually, same gas gun barrel is used for different diameters

of the striker. Sabots (plastic, brass) are fitted on the striker to keep striker radially aligned

in the barrel. From literature, it has been established that the sabot mass increases the

magnitude and time duration of the input pulse. These findings are studied through the

hypothesis of equivalent density of striker. The drawback of this hypothesis is that it cannot

explain the variation in the input signal pulse due to change in fabrication or the installation

method of striker (like the sabot length, sabot-striker frictional interfacial conditions, and

sabot location).

In present work, the influence of sabot on the amplitude and shape of input pulse was

experimentally studied. An integral striker with sabot projection was used for experiments.

We observe that the magnitude of strain at the beginning and the end of the incident pulse

is larger than that of the plateau. This enhancement is larger when the length of the integral

sabot is larger. These features of the incident signals have not been reported. It was inferred

that the way strikers are fabricated/fitted on to the striker also determines the nature of the

incident signal. The axisymmetric and 1D finite element simulations were performed for

validation of the input signal. The effect of fabrication/assembling method of sabot on

striker, effect of sabot length, and sabot- striker interface conditions on the input pulse has

been simulated. An analytical solution by 1D wave propagation complements the

experimental observation. Moreover, the integral striker and sabot mounted striker has been

compared.

Keywords: shpb, high strain rate characterization.



116

Evolution of deformation modes, microstructure, texture during high strain

rate deformation of Zircaloy-4

G. Bharat Reddy

[G. Bharat Reddy], [Rajeev Kapoor], [Apu Sarkar]

[Mechanical Metallurgy Division], [Bhabha Atomic Research Centre, Mumbai]

[[email protected]]

Specimens of recrystallized Zircaloy-4 were deformed at room temperature at a strain rate

of ~1000 s-1 using a split Hopkinson pressure bar. The compressive deformations were

carried out in different specimen orientations to study the effect of loading direction (for a

given texture of the material) on the selection of deformation modes, microstructure and

subsequent flow behaviour. The microstructure and texture evolution was studied by

deforming the specimens to intermediate strains. Electron backscatter diffraction was

used to characterize the microstructure and texture of deformed specimens. The applied

strain was found to be accommodated by both slip and twin modes. A crystal plasticity

model was used to determine the evolution of deformation modes in terms of their relative

activities by simulating the observed flow behaviour and texture evolution.

Keywords: Zirconium, split-Hopkinson pressure bar, EBSD, crystal plasticity


117

Through-Thickness High Strain-Rate Compressive Response of Glass/Epoxy

Laminated Composites Embedded with Randomly Oriented Discontinuous

Carbon Fibers

Shubham

Shubham*1, Chandra Sekher Yerramalli2, Rajesh Kumar Prusty1, Bankim Chandra Ray1

1FRP Composites Laboratory, Department of Metallurgical and Materials Engineering,

National Institute of Technology, Rourkela, India-769008

2 Department of Aerospace Engineering, Indian Institute of Technology Bombay, Mumbai,

400076, India

[*[email protected]]

The fiber-reinforced polymer (FRP) composites, due to its outstanding mechanical

properties over metallic materials has gained a lot of attention in the last few decades. Many

structures made up of FRP composites are subjected to high strain rate (HSR) loading

conditions. This study presents the HSR compressive behavior of woven E-glass fiber

reinforced epoxy embedded with randomly oriented discontinuous carbon fibers (RODCF).

A compressive split Hopkinson pressure bar (SHPB) apparatus was used for testing the

samples along the through-thickness direction. Cylindrical samples were used for SHPB

testing having a length to diameter ratio (L/D) of 0.75. All the samples were tested at a

constant propelling cylinder pressure of 30 PSI and the strain rate range of 1819-2135/s.

The amount of RODCF dispersion in the sample tested was 0.25% and 0.5% by weight of

epoxy. It was observed that the mean compressive strength of the glass/epoxy (GE) sample

increases up by 10 % and 12.7% with the RODCF addition of 0.25% and 0.5% by weight of

epoxy, respectively. The peak force obtained from the strain gage mounted on the incident

bar was found to be higher as compared to the peak force received from the strain gage

mounted on the transmitter bar, which was explained by the phenomenon of stress wave

attenuation. An increase in the mean ultimate strain was also observed for the samples

containing RODCF. Dynamic plots of true stress–true strain, strain rate versus time, true

strain versus time, true stress versus time, as well as forces versus time were obtained for

each type of sample and discussed.

Keywords: fiber-reinforced polymer, high strain rate, compressive split Hopkinson pressure

bar, glass/epoxy


118

Evaluation of J-integral of pre-cracked steel specimen using Split

Hopkinson Pressure Bar Setup

Sonal Chibire

Sonal Chibire1, Nitesh P. Yelve1, and Vivek M. Chavan2

1Department of Mechanical Engineering, Fr. C. Rodrigues Institute of Technology, Vashi,

Navi Mumbai, India

2Bhabha Atomic Research Center, Trombay, Mumbai, India

The mechanical properties of the material respond distinctively at quasi-static as well as

high strain rate conditions. The Split-Hopkinson Pressure Bar (SHPB) is established for high

strain rate testing in the range of 102 to 104 s-1 of strain rates and used to carry out dynamic

three-point bend (TPB) test for measuring J-integral. The mechanical properties of the pre-

cracked steel specimen and the methodology of calculation of J-integral are presented.

Prior to this, stress intensity factor is evaluated experimentally and analysed using Finite

Element Method (FEM). The relevant ASTM fracture toughness test standards considered

in this paper are E399 for KIC testing, E1820 for J-integral. The J- integral obtained

experimentally are compared with the values obtained by using Finite Element Method

(FEM).

Keywords: Fracture mechanics, Split Hopkinson Pressure Bar, J-integral, Fracture

toughness.


119

High strain rate deformation behavior of dual phase high entropy alloy

Al0.65CoCrFe2Ni

Samrat Tamuly

Samrat Tamulya, Saurabh Dixitb, V. Parmeswaranc, Prasenjit Khanikara

a Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Assam

781039, India

b Mishra Dhatu Nigam Limited, Hyderabad , Telangana 500058,India

c Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Uttar

Pradesh 208016, India

A novel high entropy alloy Al0.65CoCrFe2Ni is designed, and fabricated at industrial scale

through induction arc melting at a solidification rate of ~10 K/s. The XRD analysis confirms

the presence of both FCC and BCC phases in the alloy sample. The presence of both phases

improves the balance of strength and ductility of the material. Split Hopkinson pressure bar

test is carried out under compressive loading over a range of high strain rates of the order

of 103 s-1. The effect of dynamic deformation on the microstructure of the alloy is

investigated using orientation image microscopy. The work hardening behavior of the alloy

is studied, and the strain rate sensitivity is evaluated. The predictability of high strain rate

behavior of the high entropy alloy is also examined using Johnson-Cook (J-C) modeling.


120

Modified Cowper-Symonds model for predicting the stress-strain behaviour

of SA516 Gr. 70 carbon steel

S Sharma

S Sharma1, M K Samal2,3, V M Chavan4

1HomiBhabha National Institute, Mumbai 400 084, India

2Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai - 400 085, India

3Division of Engineering Sciences, Homi Bhabha National Institute, Mumbai 400 084, India

4Refueling Technology Division, Bhabha Atomic Research Centre, Mumbai - 400 085, India

[email protected]

Abstract. The flow behaviour of SA516 Gr.70 carbon steel under dynamic loading condition

was studied experimentally using the split-Hopkinson pressure bar (SHPB). These tests

were performed at room temperature at strain rates ranging from 450/s to 3500/s. Quasi-

static tensile tests were performed for comparison with high strain rate test results. The

strain rate sensitivity at these dynamic rates was found to be positive. The experimental

data was fit to the Cowper Symonds (CS) model. As the CS model did not fit the high strain

rate data satisfactorily, the Cowper Symonds model was modified. This modified Cowper

Symonds model gave the best fit to the experimental data.



121

Strain path effects on martensitic transformation in medium Mn steels.

Poornachandra

Poornachandra1, Saurabh Kundu2 and Prita Pant1

1Department of Metallurgical Engineering and Materials Science, IIT Bombay, Mumbai,

India.

2Research and Development division, TATA steel, Jamshedpur, India.


Most of the industrial metals forming processes are characterized by a complex strain path.

To make effective use of medium Mn steels in automotive parts, the formability analysis

along with the proper understanding of deformation mechanisms and their effect on

delayed fracture phenomenon at different strain and strain paths are important areas to be

investigated. In the present work, we carried out formability analysis of Fe-5Mn-0.2C-0.73Si-

0.34Al medium Mn steels at different strain paths. We observed that the samples failed at

low effective strain in case of plane strain conditions as compared to uniaxial and biaxial

loading conditions. We observed more martensitic transformation during deformation (TRIP

effect) in case of plane strain loading condition as compared to uniaxial and biaxial loading

conditions. Favored texture development to austenite to martensite transformation could

be the reason behind more martensitic transformation in plane strain loading condition.

Key words: Strain path, martensitic transformation, texture.


122

Enhancing dynamic fracture behaviour of laminated composite by short

fiber reinforcement

Manoj. K. Singh

Manoj. K. Singh1, R. Kitey2

1Ph.D Student, 2Associate Professor, Department of Aerospace Engineering, IIT Kanpur-

208016, India


Abstract: Continuous fiber reinforced laminated composites are mostly preferred in

engineering applications where in-plane strength and modulus are key requirements.

Although the composites’ in-plane mechanical and failure behavior can be tailored to meet

the end user requirements, their weaker out-of-plane characteristics often remain a cause

of concern. Failure in such materials initiate either at fiber/matrix interfaces or from matrix

rich regions within the laminae or at the interlaminar regions. Stiffening matrix rich zones

by using reinforcements is one of the methods which can be employed to reduce the

probability of failure. In this investigation short fiber reinforced matrix is used to enhance

the failure characteristics of laminated composites under impact loading conditions. Plain

weave bidirectional Glass Fiber Reinforced Polymer (GFRP) composites are fabricated by

employing hand layup technique. Laminae are prepared by coating fiber clothes with

chopped fiber (of 6 mm length and 16 m diameter) reinforced epoxy systems. Fillers are

embedded into the epoxy at 4% volume fraction. Sixteen plies are stacked together and

cured in a vacuum assisted hot press. Test specimens are prepared by following ASTM

D7136M standards and the experiments are conducted at 5 J and 20 J impact energies by

employing INSTRON CEAST 9340 drop weight impactor. The fracture energy is calculated

from the force history recorded by an instrumented tup with hemispherical end. The visible

damage areas at the front and back surfaces and the depth of the dent are measured to

assess the degree of damage in the laminates. Failure mechanisms are identified through

optical micrographs of the damaged area and by imaging the cross section of the laminates

under scanning electron microscope (SEM) at the failure sites. Experimental data show that

the chopped fiber reinforcements increase the resistance to deformation as well the energy

required to induce fracture in the laminates. Energy dissipation during fracture is observed

to decrease for reinforced case. Optical micrographs show that the visible damage area and

the indentation depth increase with increasing impact energy. SEM images reveal

transverse matrix cracking at lower impact energy in both unreinforced and reinforced

laminate cases with a few interlaminar failure in the prior. On the contrary when the

laminates are subjected to higher impact energy, significant matrix cracking along with the

delamination at several interfaces is observed. Keywords: GFRP; Impact energy; chopped

fiber reinforcement; damage mechanisms; energy dissipation


123

TS12 + TS16

Multiscale Modeling of Plasticity, Creep, Fracture,

and Fatigue and Role in Material and Structural

Integrity

Organizers:

A. Alankar, IIT Bombay

P. Chakraborty, IIT Kanpur

13th Dec 4-6 pm

19th Dec 5-9 pm

20th Dec 4-7.30 pm


124

Invited Speakers

Hydrogen assisted crack initiation in metals: Insights using novel

experimental analysis and multiphysics simulations

Prof. Dhiraj Mahajan

Associate Professor

Ropar Mechanics of Materials Laboratory, Department of Mechanical Engineering, Indian

Institute of Technology Ropar

[email protected]

Hydrogen is associated with the embrittlement phenomenon in metals that causes

substantial damage to the infrastructure due to reduction in the ductility, fracture strength

and fatigue life of metallic components. Thus, understanding hydrogen-assisted crack

initiation in metals is of prime importance. In this work, hydrogen-assisted crack initiation is

studied on the surface of uncharged and hydrogen charged specimens of pure nickel during

in-situ tensile experiments under SEM. A novel experimental analysis combines high-

resolution digital image correlation (HR-DIC) and EBSD measurement to provide

microstructural stress maps, through strain and stiffness tensor extracted at each point in

the region of interest (RoI). Maximum Schmid factor as well as elastic modulus maps in the

loading direction, hydrostatic stress, von Mises stress and triaxiality factor maps are

correlated with the crack initiation sites in the hydrogen charged specimens. This novel

analysis highlighted two independent factors responsible for hydrogen enhanced

decohesion (HEDE) based intergranular failure observed at the random grain boundaries of

hydrogen charged specimens, (i) strain localization due to hydrogen enhanced localized

plasticity (HELP) mechanism of hydrogen embrittlement, and (ii) hydrostatic stress-based

hydrogen diffusion to the crack initiation sites. These insights are then used to design a

fracture indicator parameter (FIP) which is implemented within the coupled framework of

dislocation density-based crystal plasticity model and slip rate dependent hydrogen

transport model showing high degree of correlation in the crack initiation sites observed

during experiments and simulations using similar microstructure of RoI. The work highlights

the role of metallic microstructure on hydrogen-assisted crack initiation and thus will help

design metallic microstructures that are resistant to hydrogen embrittlement.

Dr. Dhiraj K. Mahajan is an Associate Professor in the Department of Mechanical Engineering, IIT Ropar,

Punjab, India. At IIT Ropar, he is coordinating a research laboratory naming “Ropar Mechanics of Materials

Laboratory” that is focused on mechanics of materials and advanced manufacturing. His immediate focus is

on the manufacturing of critical biomedical devices (like bioresorbable polymeric stents) and hydrogen energy

technology development (including the development of high-pressure hydrogen storage Type IV tanks, proton

exchange membrane fuel cells) towards zero-emission future for the country. He has recently filed two patents

and has more than INR 40 million worth of sponsored and consultancy projects running in his lab. He has (co)-

authored more than 18 refereed journal publications (h-index: 8, total citations > 222) and 10 refereed

conference publications. He is also the winner of several awards from the Hydrogen Association of India.


125

Life Management of Aeroengine Components: A Damage Mechanics Approach

Dr. Jalaj Kumar

Defence Metallurgical Research Laboratory (DMRL), DRDO, Hyderabad-500058

Contact: [email protected]

Current life management of turbine engine fracture critical components is based on design limits, which requires replacement of all components at pre-determined flight intervals as specified by manufacturers irrespective of actual usage. This approach is based on nominal fleet-wide usage and ignores the actual capability of each component. These fatigue design limits are derived from extensive testing and statistical assessment of data assuming uniform material microstructure in all specimens and components, resulting in very conservative replacement intervals and high sustainment costs. There is a growing need to improve the current life managements practice and significantly reduce the sustainment costs of legacy and future systems. Next generation life management can be achieved by integrating life prediction that incorporates variations in microstructure with material state awareness based on nondestructive material and damage characterization techniques. Characterizing each component’s microstructure at critical locations will enable prediction of remaining life for each component based on actual usage. This analysis based performance assessment, when coupled with nondestructive damage characterization will facilitate replacement of components only as needed, thus increasing readiness and decreasing sustainment costs significantly.

As a result of the in-house research efforts as well as interaction with other academic institutes/ research agencies, a multi-disciplinary expertise in the area of Damage Mechanics has been established in DMRL. This includes finite element analysis (FEA) based simulation expertise and damage assessments using NDT technologies. In the present talk, the expertise / technology thus developed in the area of damage mechanics would be discussed with few case studies related to life managements of aeroengine components.


126

Spall Characterization via Laser Spallation: A New Optical Technique

Prof. R. Kitey, IIT Kanpur

Associate Professor


[email protected]

The strength of materials under extreme dynamic loading conditions is assessed from their

spall characteristics. The spall strength is often evaluated by employing flyer plate impact,

or sometimes by using laser-induced stress waves, in combination with velocity

interferometer system for any reflector (VISAR). Although the VISAR can record the velocity

of extremely fast-moving surfaces, it requires a complex optical setup and a specialized

data reduction technique. In this presentation, a newly developed approach for determining

the spall strength of polymers is discussed. The epoxy layers with different thicknesses are

deposited onto glass substrate. Laser spallation method is extended to instigate spall in the

(thick) epoxy films, while in situ interferometric measurements are directly performed on

their aluminium coated top surface. Laser-induced stress waves transmit across the

substrate/film interface and induce subsurface failure in the epoxy at sufficiently high

incident laser energy. The interferometric data reveal the development of two (temporally)

well-separated stress waves: an ablation-induced high-amplitude short-duration

longitudinal pulse, which is referred to as the primary wave, and a secondary wave, which

travels at a comparatively slower speed. The complex constructive interaction of the two

waves develops a high-magnitude tensile stress region in the epoxy layer. The spall strength

is quantified by superimposing the two stress wave histories associated with the critical

energy fluence. The spall depths predicted from spatiotemporal wave travel analyses are in

excellent agreement with the experimental observations.

Dr Rajesh Kitey is Associate Professor in the Department of Aerospace Engineering, Indian Institute of

Technology Kanpur (IITK) India. He received his doctorate from Auburn University, Auburn AL USA. He was

Postdoctoral Research Associate at the University of Illinois at Urbana-Champaign. Prior to joining IITK, he has

worked at Penn State, Dubois PA USA, as Assistant Professor. His area of specialization is Fracture Mechanics

and Experimental Stress Analysis. His research interests involve quasi-static and dynamic fracture in

heterogeneous materials, mechanics of thin films, novel material development and testing, and optical

methods and measurements. Dr Kitey has 50+ articles in international journals and conference proceedings.


127

A Novel Cohesive Constitutive Law for Simulating Fatigue Delamination in

Composites

Prof. S. Mukhopadhyay, IIT Kanpur

Assistant Professor

Indian Institute of Technology Kanpur

[email protected]

Fibre reinforced composites are gradually replacing metals for manufacturing load-bearing

primary structures in aircraft and automobile industries due to the many structural and

functional advantages that they provide. However, failure behaviour of composites is

inherently more complex than metals. In particular, failure under fatigue loading is more

concerning to designers. Under high-cycle fatigue, small ply delaminations can initiate and

grow in a stable manner at a load amplitude that can remain much below than the static

failure load, and yet, can bring in unexpected failure, curtailing its designated operational

lifetime significantly.

In this work, the development of a novel cohesive constitutive law to simulate fatigue

delamination in composites will be discussed. This is implemented in a 3D cohesive finite

element framework using a user-defined interface in a commercial solver. A set of novel

physically based onset and propagation criterion is used that is shown to provide very

accurate predictions for delamination onset and growth in large composite structures.

Dr Supratik Mukhopadhyay obtained his B.E in Production Engineering from Jadavpur University, Kolkata in

2009 and an M.Tech in Manufacturing Science and Engineering from IIT Kharagpur in 2011. Subsequently, he

went to the UK on a Dorothy Hodgkin Postgraduate Scholarship to pursue a PhD in Aerospace Engineering in

the University of Bristol on a Rolls-Royce sponsored project. His research was on experimental and

computational investigation of failure from manufacturing induced defects in composite laminates used for

aircraft engine applications. As part of that, he developed several novel predictive tools for damage analysis

of composite structures subjected to static and cyclic loads. After finishing his PhD in 2016, he joined the

Rolls-Royce University Technology Centre at the Bristol Composites Institute, University of Bristol, as a Post-

Doctoral Research Associate where he continued to work for nearly two years on several projects involving

efficient design of composite structures guided by high-fidelity computational simulations. Since late 2018, Dr

Mukhopadhyay is based in IIT Kanpur, as an Assistant Professor in the Department of Mechanical Engineering.

His present research interests include simplified modelling methods for large scale structural simulation of

composites, virtual structural health monitoring and damage prognosis, fatigue failure, multiscale modelling

techniques, machining of composites.


128

Thermal stability of nanocrystalline materials: Alloy and Microstructural

design and Implications for creep

Prof. Srikant Gollapudi

Assistant Professor

Indian Institute of Technology Bhubaneswar

[email protected]

The focus of the presentation will be on understanding the thermal stability of

nanocrystalline materials and how grain growth tendencies of nanocrystalline materials has

prevented systematic investigations on creep deformation of these materials. Work in the

last decade has demonstrated that in addition to Zener drag approach, the grain size of

nanocrystalline materials can also be stabilized through solute additions, wherein the solute

element chosen is one that has a tendency to segregate at the grain boundary of the parent

element. This in turn can reduce the grain boundary energy of the parent element and can

introduce higher thermal stability to the nanostructure. A thermally stable nanostructure

would allow the determination of the stress exponent, activation energy and grain size

exponent, key creep parameters which will reveal the mechanism of creep operating in these

materials. The alloy and microstructural design approaches to making thermally stable

nanocrystalline materials will be discussed in this context.

Dr. Srikant Gollapudi obtained his Bachelors in Metallurgical Engineering from NIT Rourkela, Masters in

Metallurgy from Indian Institute of Science, Bangalore and PhD in Materials Science and Engineering from NC

State University. He pursued his post doctoral research at Massachusetts Institute of Technology and gained

industrial experience from his stints at Defence Metallurgical Research Laboratory, Hyderabad and Saint

Gobain Research India, Chennai. His research interests are in the area of Nanocrystalline materials, Corrosion

and Creep of a variety of materials. He has more than 25 publications in national and international peer

reviewed journals and 6 patent applications to his name.


129

Post-Critical Instability in Nonlocal Strain Gradient Arches

Prof. S. Mishra

Associate Professor

Department of Civil Engineering,


[email protected]

The buckling and post-critical behavior of classical arch is an important benchmark problem in nonlinear mechanics. This study investigate the same for nano-arch subjected to external

pressure using nonlocal (NL) and Strain Gradient (SG) theory, assuming the arch to be

shallow and is restrained in its out-of-plane. The governing equations are derived as a sixth

order nonlinear integro-differential equation, in contrast to the fourth order for classical

arch. The equation is then solved numerically using Differential Quadrature (DQ) with a set

of boundary conditions. An arc-length continuation is employed for the solution of the

resulting system of equations. The equilibrium paths are obtained for the possible instability

modes; e.g. symmetric/anti-symmetric bifurcations, snap through and limit point instability.

Each mode is triggered at certain range of the slenderness ratio for the arch and are

significantly influenced by the NL and SG interactions, which not only cause quantitative

changes but may also lead to qualitative changes (cessation, shift and conversion of

modes). The pre-buckling nonlinearity is significant and cannot be linearized meaningfully.

Sudib K. Mishra is an Associate Professor in the Department of civil engineering at the IIT Kanpur. He

completed his bachelor's in Civil Engineering from Bengal Engineering College (Now IIEST), Shibpur in 2003,

followed by his masters from IIT Bombay in 2005 and doctoral studies from the University of Arizona, Tucson.

Thereafter, he served as a post-doctoral associate in the Mechanical and Aerospace Engineering Department

in the University of California, Irvine. Prof. Mishra has varying research interests from Vibration and structural

dynamics, Vibration based structural health monitoring to instability in structures and Solid Mechanics. He

has authored around forty journal publications across various international journals of repute. He also

presented his work in various National and International conferences and delivered a number of invited

presentation on various topics. Prof. Mishra was awarded the Young engineer award in the year of 2016 by

the Indian national Academy of Engineering, the Young Engineer Award in the year of 2013 by the Institute of

Engineers and the Young Faculty Research Fellowship by IIT Kanpur in the year of 2020.


130

A Diffused Interface Crystal Plasticity Model to Investigate the Effect of

Corrosion Pit Geometries on Microscale Deformation

Prof. Pritam Chakraborty, IIT Kanpur

Assistant Professor


[email protected]

Pitting corrosion significantly reduces the fatigue life of Aluminium alloys, which are widely

used in aircraft industry. This results in loss of useful life, and increases maintenance

schedules of aircrafts. Thus, development of mechanistic models incorporating the

influence of pits on fatigue life reduction can aid life extension and optimal planning for

maintenance. Experimental studies reveal that pits interact with the microstructure and

have a significant effect on crack nucleation. The extent of this influence depends on the pit

geometry and surrounding microstructure. To understand this interaction, a diffused

interface crystal plasticity finite element method model has been developed in this work.

The framework helps in ensuring a structured mesh while discretizing polycrystalline

representative volume elements; incorporating interface behaviour as constitutive models,

and natural coupling with phase-field or electron-microscopic image based microstructures.

The method has been applied on microstructures containing a narrow deep pit and a

subsurface pit with similar geometric parameters to compare their influence on localization.

The comparisons show that the interaction of the pit geometry with the surrounding

microstructure can have a strong influence on microcrack nucleation.

Dr. Pritam Chakraborty has done in Ph.D. from The Ohio State University and worked as a Scientist at Idaho

National Lab., US, before joining his current position. His interests are in solid mechanics, multi-scale modeling,

fatigue, fracture, plasticity and large scale computing.


131


Effect of strain localisation on constitutive model for porous metal plasticity

under combined shear and tensile loading

Suranjit Kumar, BARC

Suranjit Kumar1,2∗, M. K. Samal1,2, P. K. Singh2, J. Chattopadhyay1,2

1Homi Bhabha National Institute, Mumbai 400 094, India


[[email protected]]

Abstract

The micro-mechanism of ductile fracture involves processes of void nucleation, growth, and

coalescence. The evolution of void with loading in porous metals affects their stress

carrying capability. Most of the existing material constitutive models for the porous ductile

solids were derived through limit-analysis of hollow representative volume element (RVE)

under influence of homogeneous boundary strain rate. First, widely accepted material model

was presented by Gurson (1977). This model captures the spherical growth of voids only

and disregarded void shape effects. Gologanu et al. (1993, 1994, 1997) account for the

effects of void shape on the derivation of yield function considering the axisymmetric

ellipsoidal void geometry. Madou and Leblond (say, M&L) (2012) extend the Gologanu work

for more general ellipsoidal void geometry. All these constitutive models are developed for

a randomly distributed void in infinite space. It does not account for the effect of the

interaction of voids. The ductile failure under the low-stress triaxiality occurs by a void

sheeting mechanism, where voids rotate and form a shear band. It contains a localized

strain in a very thin band. The onset of strain localisation may also contribute to the yielding

of a particular representative volume.

In view of the above, the numerical determination of the yield surfaces of an RVE having an

elliptical cylindrical void has been carried out under the combined shear and tensile loading

to capture the effect of strain localisation on yielding behaviour. Performance of the M&L

constitutive material model was also checked against the numerical results. It has been

found that strain localisation takes place in a narrow band under the shear dominated

loading which leads to early yielding of RVE. This effect decreases with an increase in the

contribution of tensile load. It has also been found that the ML model doesn’t reproduce the

yield surface accurately under low-stress triaxiality loading, however, it works well for

relatively higher stress triaxiality.

Keywords: Ductile material, Shear loading, Void fraction, Stress triaxiality


132

CDM Model for Creep life prediction of Alloy 625M nickel base superalloy

for high temperature power plant applications

Somnath Nandi, BHEL

*Somnath Nandi and Kulvir Singh

Metallurgy Department, Corporate R&D Division, BHEL, Hyderabad 500093, India

*Email: [email protected] FAX: 0091-40-23776320

Creep life prediction of critical components in thermal power plants has become an

important metallurgical area to study over the last few years. Prediction of Creep strain

trajectories and rupture strains is of generic importance for ensuring stable operation of

existing power plants and for developing current procedures to extend design lifetimes

safely. It is very important to understand how various degradation mechanisms affect the

creep strength of the components and to incorporate these in constitutive laws to ensure

effective extrapolation. Nowadays, with the advancements in new technologies heat

resistant steels are being replaced by nickel base superalloys which can withstand high

temperature and pressure. Alloy 625M is one of the probable alloy to be used in steam

turbine. Traditional parametric methods for estimating the long-term creep rupture lifetimes

of alloys from short term data are employed. Larson Miller parameter methods and

Robinson’s Rule are generally employed for prediction but these methods never incorporate

the microstructural degradation of the alloys at high temperatures. In the present paper,

preliminary idea of the creep curve using constitutive laws, Continuum Damage Mechanics

(CDM) model based on microstructure/ property relationships and relevant aspects of

microstructure are discussed to have a realistic prediction of the creep life of the Alloy 625M

for power plant applications.

Keywords: Creep, CDM Model, Alloy 625M, Creep life predictions, Creep Curves.


133

Phase field modeling of crack propagation in crystalline microstructures

under hydrogen atmosphere

Vishal SIngh

Vishal Singh*, Rakesh Kumar, Dhiraj K. Mahajan Ropar

Mechanics of Materials Laboratory, Department of Mechanical Engineering,Indian Institute

of Technology Ropar, Rupnagar, Punjab, 140001, India

*[email protected]

Insight to the damage behavior of metallic materials is of great significance to understand

the overall mechanical performance even in not so favorable environmental conditions.

Present work intent to simulate the hydrogen-induced damage in crystalline metallic

materials. Crystal plasticity coupled with phase-field for fracture and hydrogen transport

model is used to simulate crack propagation under the hydrogen atmosphere. The proposed

model istested on simple geometry with face-centered cubic single crystal and image-based

multi-grain RVE. Crystallographic orientation and hydrogen content are shown to affect the

test results in terms of failure pattern and corresponding global and local response.

Keywords: Phase field modelling, crystal plasticity, hydrogen embrittlement, damage


134

Coupled Thermomechanical Analysis of SMA Structures

Animesh Kundu

Chenna Sai Krishna Chaithanya, Animesh Kundu, Atanu Banerjee

Department of Mechanical Engineering, Indian Institute of Technology, Guwahati


Abstract

Of late, Shape Memory Alloys (SMA) are found in wide variety of applications in the field of

aerospace, robotics, biomedical, etc., due to their well-known behaviors called, Shape

Memory Effect and Super-elasticity. To simulate the behavior of these alloys several

constitutive models are proposed over the past four decades. In one of them, the phase

evolution was derived based on fundamental laws of thermodynamics and maximization of

dissipation potential. This approach has been reported to be more suitable for the analyses

of structural problems in 2D and 3D, under practical thermomechanical loading conditions.

In literature, temperature is considered as an input variable, whereas, in practice, it evolves

as a state variable, depending on applied thermal and mechanical loads and material

properties. The martensitic transformation processes exhibit endothermic and exothermic

effects, significantly affecting temperature and the response. Hence, a fully coupled

thermomechanical finite element-based analysis tool is required simulate the behavior of

these materials.

The objective is to develop a coupled thermomechanical analysis tool to predict the

response of SMA structures under practical thermomechanical loading conditions in

ABAQUS. The constitutive model proposed by Qidwai and Lagoudas (2000) is implemented

in UMAT, a user material subroutine of ABAQUS, to analyze the response of SMA actuators,

beams etc., considering the effect of material level coupling terms, i.e., the latent heat of

transformation and thermoelastic heating effects. The results emphasize a significant

difference in the transient response of SMA structures while thermal coupling terms are

considered; illustrating the importance of the coupled analysis of these materials. Finally,

the response of a SMA biomedical staple, used for idiopathic scoliosis treatment of

vertebral body, is simulated using the developed FE tool, considering the practical

thermomechanical loading conditions.

Keywords: Shape Memory Alloy, Coupled Thermomechanical Analysis, Material Non-

linearity, Latent heat.


135

Phenomenological Constitutive Modeling of Magnetic Shape Memory Alloys

Avinash Kumar, IIT Bombay

Avinash Kumar, Krishnendu Haldar

Department of Aerospace Engineering, Indian Institute of Technology Bombay, [email protected], [email protected]

Abstract

Increasing demand for a lighter and more durable material with sensing and actuation functionality, Magnetic Shape Memory Alloys (MSMA) are one of the promising members, among many other smart materials. This study investigates the magneto-thermal-mechanical (MTM) the behavior of MSMA through a 3D phenomenological constitutive modeling in a thermodynamically consistent way. A specific Helmholtz free energy function is postulated after identifying the external and internal state variables. The evolution equations of the internal state variables are defined by proposing a transformation function. The model parameters are calibrated through different MTM loading conditions. Selective loading conditions demonstrate the magnetic field coupling with the actuation strain.

Keywords: Magnetic shape memory alloy (MSMA), magneto-thermal-mechanical (MTM), magnetic field induced strain.


136

Dynamic creep response of MWCNT-COOH filled PP nanocomposites

Vivek Khare

Vivek Khare* , Sudhir Kamle#

*Ph.D. Scholar, #Professor


Corresponding author: [email protected]

Polypropylene (PP) is a widely used thermoplastic polymer in aerospace applications due

to, its strength, low cost, low weight, ease of formability and fatigue resistant properties. It’s

semi crystalline state provides both strength and flexibility. Nano fillers such as multi walled

Carbon nanotubes (MWCNT) significantly enhance mechanical properties of PP

nanocomposites. However, at higher MWCNT concentrations, MWCNTs are self-assembled

in form of agglomeration due to high van-der-waal attraction which hinders matrix to fiber

stress transfer efficiency. Present investigation elucidates the effect of functionalized

carbon nanotubes (MWCNT-COOH) and temperature on dynamic creep and recovery strain

in nanocomposites through experiments and nonlinear viscoelastic modeling. The strain

response is studied to address stress dependent nonlinear parameters that characterize

nonlinearity. Solution casting method is used for development of thin nanocomposite films

using PP in pellet form and –COOH functionalized multi walled carbon nanotubes with

varying MWCNT concentrations. Temperature controlled dynamic creep and recovery

experiments were performed at constant 10 MPa creep stress in dynamic mechanical

analyzer (DMA). Prior to creep measurements, the dynamic properties of nanocomposites

were obtained from a temperature ramp test at constant frequency of 1 Hz for storage

modulus, loss modulus and loss factor. Experiments reveals that temperature activated

deformation is controlled by incorporating MWCNTs up to 1% fraction. High temperature

and stress loading pertain to the development of recoverable viscoelastic strain and

unrecoverable viscoplastic strains. Schapery nonlinear viscoelastic model coupled with

Zapas-Crissmann viscoplastic model is incorporated to characterize the creep response,

stress induced nonlinearity in material and viscoplastic strain predicted in experiments. The

model prediction agrees with experimental findings.


137

A meso-mechanical simulation of the effects of Stress Concentration

around a counter sunk hole in a Hybrid Fibre Metal Laminate

Chandrashekhar Telkar

Shashidhar Naik H.G.1, Shubha Javagal 2, Prem Kumar B.1 , Chandrashekhar Telkar2*

1Compressors Global Department, QuEST Global Pvt. Ltd., Bangalore, Karnataka, India.

2Dept. of Mechanical Engineering, Dayananda Sagar University, Bangalore, Karnataka,

India

Fibre metal laminates (FML) are one of the novel engineering materials developed for

applications in the Aerospace industry. They are composed of several layers of very thin

metal (often aluminium), along with layers of uni-directional Glass Fibre pre-pregs, bonded

to each other with the use of matrix such as epoxy-resin system. The major advantage of

this material is that it can be tailored to fit the stress condition by varying the orientation of

the Glass Fibre layers. They possess all the expedient characteristics of both the materials

and have several advantages like better damage tolerance, corrosion resistance, fire

resistance, low specific weight and improved impact resistance.

Usage of FMLs in structural components of aircrafts has various challenges. One such

challenge is joining FML plates to the airframe. The most widely used method of joining

various structural components is riveting. This method of joining introduces stress

concentration due to rivet holes, varied load paths, added secondary loads etc. Accurate

prediction of these local stresses will lead to better prediction of fatigue life as well as the

joint strength of the structures.

In the current paper, stresses around a centrally located countersunk hole is investigated in

a plate specimen. The major aim of this work is to determine the Stresses around the hole

for a commercially available GLARE configuration. Various lengths of the countersunk hole

in the specimen are considered and the effect of the hole is studied without altering the

countersunk angle. The GLARE plate is modelled using ABAQUS Standard platform to

appropriately simulate the stress concentration developed in each layer for a particular load.

The detailed layer wise behavioral study is presented by plotting the stress and force values

obtained across time and displacements. Furthermore, a parametric study is carried out to

formulate a holistic understanding of the effect of tensile load in a plate with a countersunk

hole.

Keywords: Fibre metal laminates, Counter sunk holes, GLARE, Stress Concentration


138

Homogenisation of Transformed β Colony of a Titanium Alloy using CPFEM

S. Mustafa Kazim

S. Mustafa Kazim1*, Kartik Prasad2, Pritam Chakraborty1*

1Department of Aerospace Engineering, Indian Institute of Technology Kanpur, India 2Defence Metallurgical Research Laboratory, DRDO, Hyderabad, India


Abstract

The microstructure of Timetal 834 (Titanium alloy) consists of primary α grains and

transformed β colonies. The colonies contain consecutive lamellae of alpha (HCP) and beta

(BCC) phases. Depending on the Burger’s Orientation Relation (BOR) the common slip

systems between the two phases govern the transmission or hindrance of the mobile

dislocations across the phase boundaries. These interactions dictate the elasto-plastic,

fracture and fatigue response of the alloy and needs consideration in the Crys tal Plasticity

Finite Element Method (CPFEM) models of the alloy. Though crucial, it is computation ally

not viable to include both the lath structure and the primary-alpha grains in the CPFEM Repre

sentative Volume Element (RVE) owing to the disparate length-scales of these

microstructural features. Thus, homogenised models of the lath structure have been

proposed in the literature to incorporate their effect in RVE simulations. In one class of

model a virtual homogenised crystal with both the BCC and HCP slip systems has been

proposed. The other class of model considers both the phases separately at a material point

with the assumption that they experience the same deformation gradient but has sepa rate

evolution of state. The stress at the material point is obtained from a mixture rule. In this

work, a RVE of the lath structure (alternate alpha and beta lamella) has been developed and

simulated using CPFEM. The size effect due to dislocation pileup at the lath interfaces has

been captured using the Hall Petch relation. Strain controlled Periodic Boundary Condition

has been applied to the RVE to capture the homogenized stress-strain behaviour of the

lamellae microstructure. The results from the RVE anal yses have been compared with the

homogenized models to identify their adequacy for Timetal 834.

Keywords: Homogenization; Crystal Plasticity Finite Element Method; Titanium alloys; RVE

analysis


139

An atomistic study of activation parameters for plasticity evolution from a

pristine and damaged grain boundary in Ni

Sagar Chandra

S. Chandra1, M. K. Samal2,3, V. M. Chavan4

1Homi Bhabha National Institute, Mumbai 400 084, India


3Division of Engineering Sciences, Homi Bhabha National Institute, Mumbai 400 084, India

4Refueling Technology Division, Bhabha Atomic Research Centre, Mumbai - 400 085, India

[email protected]

Abstract

Grain boundaries are important microstructural features in polycrystalline materials that

impact their deformation and failure behavior at the macroscopic scale. Thus, we perform

atomistic simulations at the nanoscale along with nudged elastic band calculations to

quantify activation parameters for dislocation nucleation from a grain boundary. Since ∑3

grain boundaries are most common in polycrystalline metals and alloys of face-cantered

cubic structure, we choose ∑3 twin boundary in bicrystal Ni as a model system for this

purpose. We also introduce a pre-existing defect (a void) at the grain boundary and contrast

the activation parameters for partial dislocation nucleation from pristine as well as

damaged grain boundary in the material. We find that the activation energy as well as kinetic

parameters for dislocation nucleation are different for pristine and damaged grain

boundary. This highlights a change in the underlying kinetics of deformation process when

a damaged grain boundary is present in the material. Consequently, this approach can be

generalized to determine kinetic parameters for other thermally activated grain boundary

dominated deformation or failure processes in metallic crystals like grain boundary sliding

at higher temperature, intergranular crack growth etc. It can, therefore, provide direct

numerical inputs to the flow rules of phenomenological crystal plasticity based finite

element models that explicitly take into account the grain boundary effects on plasticity and

damage behavior of the material at the continuum scale.

Keywords: Molecular dynamics, plasticity, grain boundary, damage.


140

Effect of tungsten addition on shock loading behavior in Ta-W system: A

molecular dynamics study

Kedharnath A

A. Kedharnatha,b, Rajeev Kapoora,b, Apu Sarkara,b

aMechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai 400085, India bDivision of

Engineering Sciences, Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India

Tantalum-tungsten (Ta-W) alloys are used for applications in various fields such as defense,

nuclear, electronics, furnace, and medical due to their enhanced corrosion resistance, high

temperature strength, and biocompatibility properties. Ta-W alloys are proposed alloys for

high temperature reactors and are already been used in containing molten plutonium and in

ballistic missile parts. They also have potential space applications as a coating on base

materials and intricate parts to withstand micrometeroids and debris. However, the effect

of tungsten addition on mechanical behavior during shock loading and dynamic high-

pressure conditions in Ta-W alloys is not explored atomistically. In this article, the effect of

tungsten addition to tantalum on spall strength is studied using molecular dynamics

technique. The single crystal configurations with piston lying on different planes are

modeled. The atoms within piston region are frozen and do not deform. The configurations

with various tungsten contents (0, 5, and 10 atomic percent tungsten) is added as solvent

and equilibrated. The piston velocity is fixed and initial temperature is 0 K. The piston is

displaced till 1 nm and stopped which produces a square shock wave. The configurations

are allowed to evolve dynamically using microcanonical ensemble. The elastic and plastic

wave is analyzed at different time period for various crystallographic orientations of the

single crystal with various tungsten contents. The spall strength increases as tungsten

content is increased. The spallation event is visualized and analyzed using stress-time

response.

Keywords: Molecular dynamics, Tantalum-tungsten, Shock loading, Spall strength


141

TS13

Non-destructive Testing and Evaluation for Structural

Integrity Assessment

Organizer: K. Jonnalagada, IIT Bombay

12th Dec 5.30-6 pm, 9-10 pm


142


Optimal Location of Single Sensor for Structural Health Monitoring of a

Steel Truss using Acoustic Emission Technique: An Experimental

Investigation

Sheersha Karmakar

Sheersha Karmakar, Dr. Pijush Topdar, Dr. Aloke Kumar Dutta

Department of Civil Engineering

National Instittute of Technology, Durgapur, Durgapur, India.

[email protected]

Continuous monitoring of any engineering structure involves use of sensors. However, from

the economic and computational viewpoint, only a limited number of sensors can be used.

Hence finding out the optimal location of sensors is very important. In light of this, the

current study makes an effort to achieve the mentioned work. Structural Health Monitoring

refers to the continuous monitoring and maintenance of the strategic engineering

structures. The research primarily focuses on steel bridge structures owing to the Acoustic

Emission (AE) Testing. The study involves placing of one R15D sensor on the different

nodes of the laboratory scale model of the steel bridge and executing Pencil Lead Break

(PLB) at other nodes. Based on statistical analysis of the obtained waveform components,

a series of nodular positions were inferred which implicated the optimal position for the

sensor on the steel bridge to track the best quality waveforms in decreasing order. This

study also showed that the acoustic waveforms follow a pattern religiously when travelling

across similar sections. More research work and study can help detect the exact location

of the crack in real time for better structural health monitoring and also to prevent the

catastrophe of engineering structure failure.


143

Influence of elastic follow-up and residual stress on structural integrity

assessment of an engineering component

Anilkumar Shirahatti

Anilkumar Shirahatti1 , Y. Wang2

1 Jain College of Engineering, Visvesvaraya Technological University, Belagavi, India

2United Kingdom Atomic Energy Authority, Culham Science Centre, Abingdon, United

Kingdom

Email of corresponding author : [email protected]

Abstract

One of the many challenges in the behavior of structures is to understand if the presence of

residual stress plays an important role in contributing to the failure of a structure. The

presence of residual stresses in safety-critical engineering components can lead to an

increased tendency for degradation and premature failure, thereby compromising structural

integrity and necessitating costly servicing overheads. Residual stresses are generally

induced during the manufacturing of engineering components, and the magnitude of the

residual stresses can be comparable to the yield strength of the material, for instance in

welds, and the effect of the residual stresses can be either beneficial or detrimental for the

static and fatigue strength of the component. Residual stresses arise because of

incompatibility of strains and therefore are usually treated as secondary stresses. However,

when residual stresses are seen as sufficiently long range and do not balance across a

cracked section, these stresses are classed as primary. In practice, the boundary conditions

on a structure can be any combination of primary and secondary stresses and

understanding their interaction is difficult. Whether the residual stresses contribute to the

primary stresses depends on two things: how plastic deformation or crack growth

accommodates the original misfit and how the structure responds or elastic follow-up (EFU)

when changes in relative stiffness occur as a consequence of plastic deformation or crack

growth. In this paper, the concept of EFU as per R5 structural integrity assessment

standards is discussed. Further, the experimental results obtained from long term creep

tests (316H SS) performed on low and high EFU test rigs is presented. It is concluded from

the test results that EFU will affect the rate of residual stress distribution in the components

& will intern influences the creep crack initiation time.

Keywords: Residual stress, elastic follow-up, 316H stainless steel, Crack


144

TS14

Nuclear Reactor Safety, Radiation and other Extreme

Conditions

Organizer: A. Alankar, IIT Bombay

12th Dec 4-8 pm


145


Modelling of hardening and loss in ductility due to neutron irradiation in

Zircaloy-4

Nevil Martin Jose

Nevil Martin Josea, M K Samala, P. V. Durgaprasada, A. Alankarb, B. K. Duttac

aReactor Safety Division, Bhabha Atomic Research Centre,Trombay, Mumbai-400085

bIIT-Bombay, Powai, Mumbai-400076

cHomi Bhabha National Institute, Anushaktinagar, Mumbai-400094

Corresponding author email: [email protected]

Abstract

Zircalloy-4 is a material used to make the cladding of nuclear fuels. The fuel cladding

is subjected to neutron irradiation during its service inside the nuclear reactor, which leads

to degradation of its mechanical properties. In this work, the irradiation hardening and

softening of the polycrystal Zircalloy-4 material subjected to various doses of neutron

irradiation is simulated using crystal plasticity finite element model. The crystal plasticity

model is based on dislocation density and defect (produced during irradiation) density

based kinetics of plastic deformation in crystals. Increase in yield stress due to irradiation

is modelled via interaction of dislocations and irradiation defects. The defect density

evolution accounts for the loss in ductility occurring to the irradiated material due to the

formation of defect free channels with plastic straining. The model parameters are obtained

by fitting the model against experimental data reported in the literature. The calibrated

model is then used to predict the irradiation hardening behaviour of Zr-4 subjected to

different levels of irradiation dose.

Keywords: Zircaloy-4, Irradiation, Crystal Plasticity


146

Design of shock absorber for radioactive coolant tube transportation cask

and impact analysis of cask with shock absorber

J.V. Mane

J.V. Mane1, Ravindra Pal2, Lokendra Kumar1,V.M. Chavan1

1Refuelling Technology Division, Bhabha Atomic Research Centre, Mumbai, INDIA - 400085

2 Remote Tooling Systems, Nuclear Power Corporation of India Ltd., Mumbai, INDIA – 400094.

[email protected]

Abstract

Radioactive coolant tube transportation cask has been designed for in-house storing of full

length pressure tube of 220 MWe IPHWR. It is 8200 kg, Lead shielded, cylindrical cask of OD

435mm and length of 5735mm. It is required to transport full length pressure tube from

reactor site for post-irradiation examination and will require Type B(M) cask qualification.

The existing configuration of cask is not Type approved and will not qualify regulatory

accident condition tests. In order to meet compliance to the regulatory requirements such

as 9m drop on unyielding target and 800°C thermal test, an external shock absorber along

with thermal shield should be designed and used. Therefore a suitable shock absorber is

conceptualized and designed without modifications in the cask which will meets the

regulatory requirements of accident condition drop. Thermal shield in the form of

sandwiched ceramic board is mounted inside shock absorber cage which will meet in

qualifying requirement under thermal tests. Through number of FE simulations,

configuration of shock absorber is finalized. The performance of cask with shock absorber

is evaluated in all possible most damaging orientations under 9m drop on rigid target. It is

observed that cask components meet the structural integrity requirements. Also delicate

thermal shield is protected without any damage. Thermal analysis of cask with thermal

shield for regulatory accident condition is also carried out. Two different thermal

environments of equivalent to average flame temperature of 800°C and fully engulfing pool

fire condition are considered. It is found in CFD analysis that temperature of outer Lead

surface reaches upto 139°C under sever condition and there is sufficient margin for Lead

melting. The detailed shock absorber design along with thermal shield and compliance to

regulatory requirement using FE and CFD simulations are presented in the paper.

Keywords: cask, impact, shock absorber, FE and CFD simulations


147

Design, impact and thermo-mechanical analysis of radioactive surveillance

specimen transportation cask

J.V. Mane

J.V. Mane, S. Sharma, H. Ali, V.M. chavan

Refuelling Technology Division, Bhabha Atomic Research Centre, Mumbai, INDIA - 400085

[email protected]

Abstract

Transportation of radioactive material through public domain is carried in Type qualified

casks. One of the important issues in designing of cask is shielding material. The widely

available and used shielding material is Lead due to its ease of manufacturing and better

radiation shielding property. However Lead is having low melting point and upon melting, it

expands. Melting and subsequent solidification will generate void in shielding which will

lead to direct streaming of radiation. Also it is difficult to meet structural integrity

requirement under molten Lead conditions. Therefore surveillance specimen transportation

cask without Lead is conceptualized, designed as Type B(M) package and its compliance

to regulatory requirement is demonstrated using FE simulations. Considering availability of

material and its form, present cask is designed as welded plates structure to form a cylinder

with removable and bolted end closure on both sides. Steel plates are used effectively both

for shielding as well as structural material. Type B(M) cask should demonstrate compliance

to regulatory 9m drop test on rigid target in most damaging orientations and 800°C thermal

tests. As welded steel plate cask will act as monolithic solid piece, shock absorber is needed

to meet the structural integrity criteria under regulatory 9m drop on rigid target. Therefore

shock absorber is conceptualized and designed in such way that it will reduce number of

worst orientation drops. FE simulations under 9m drop on unyielding target are carried out

with shock absorber and finalized cask configuration so as to meet the structural integrity

requirement. Coupled transient thermo-mechanical FE simulation of cask has been carried

out to evaluate performance and assess structural integrity of cask design under regulatory

thermal test. The detailed cask design with shock absorber and demonstration of

compliance to regulatory requirement using FE simulations are presented in the paper.

Keywords: cask, impact, shock absorber, FE simulation


148

Structural Integrity Assessment of Calandria End-Shield Assembly for In-

Vessel Corium retention under Severe Accident Condition

V.Chaudhry

V.Chaudhry*, Nirmal Kumar, Varun Mishra, D. Faisal, R.K.Chaudhary, S.M.Ingole

Nuclear Power corporation of India limited, Mumbai-400094, India

*Corresponding author email: [email protected]

Abstract

Safety demonstration of nuclear power plant for Beyond Design Basis Accident (BDBA)

conditions, called as design extension conditions, has become an important requirement in

Indian Pressurized Heavy Water Reactors (IPHWRs). The BDBA condition resulting in severe

core damage has been postulated due to loss of coolant accident along with failure of

emergency core cooling system and loss of moderator circulation. Under such condition,

the reactor core geometry progressively degrades and results in core collapse. Calandria

End-Shield assembly of standardised IPHWRs acts as an important barrier in limiting the

accident progression. Structural integrity assessment of calandria end-shield assembly has

been carried out for in-vessel retention of collapsed core/corium due to a postulated BDBA

scenario by maintaining the calandria vault cooling water level surrounding the calandria

vessel as a heat sink, as per the Severe Accident Management Guidelines (SAMG) provision.

Coupled thermo-mechanical analysis of the assembly has been carried out to simulate the

accident scenario with SAMG provision. The thermal analysis accounts for the variation of

decay heat, melt solidification, and also corium latent heat. The analysis gives spatial

distribution of temperature at various locations of the assembly in time domain. Using this

temperature distribution, structural analysis of the assembly has been carried out

accounting for temperature dependent material properties. Sensitivity analysis has also

been carried out to account for the uncertainties associated with input parameters,

specifically, heat transfer coefficient. The failure modes provided in IAEA TECDOC-1549 viz.,

failure due to creep, failure due to molten metal, and failure of drain lines have been

analyzed. Based on analytical evaluation, structural integrity of calandria end shield

assembly for in-vessel corium retention for IPHWRs has been demonstrated.

Keywords: safety, structural integrity, in-vessel retention, thermo-mechanical analysis



149

Numerical modeling of clad tube ballooning phenomenon under transients

conditions

Ashwini Kumar Yadav

Motilal Nehru National Institute of Technology Allahabad, Uttar-Pradesh 211002, India

[email protected]

Abstract. The high temperature deformation of clad tube plays a vital role in design of

emergency core cooling system (ECCS). Accordingly several investigations regarding effect

of internal pressure, heating rate and temperature on ballooning deformation of Zircaloy-4

cladding has been widely carried out in the past. The recent experiments conducted at

Halden-IFA-650 [1] with high burn-up fuel seeking attention of research community. In

addition to that, the revised ECCS acceptance criterion is compelling precise prediction of

fuel rod behavior by the safety analysis codes. In this context, a one-dimensional code is

developed to simulate the thermo-mechanical behavior of Zircaloy-4 cladding under

transient conditions. The radial deformation of the clad tube in α-phase was predicted by

time integration of plastic equation of state [2] and steady state creep equation [3]. The

predicted results were compared with the experimental results conducted by in the past [4].

Due to time-independent behavior, the plastic model was not able to predict the rupture

precisely. The gradual increment in hoop stress with ballooning until burst by the creep

model led to better prediction of the hoop-strain, burst time, and burst temperature.

Keywords: Loss of coolant accident, Clad tube ballooning, LOCA, Nuclear Fuel.


150

TS15+TS23

Reliability of coatings-Keshri+TS23-Thin Film

Deformation and Failure

Organizer: K. Jonnalagadda, IIT Bombay

18th Dec 4-8 pm, 9-10 pm


151

Invited Speakers

Fe-based Amorphous Metallic Coatings –A Cost Effective Way to Design and Synthesis

for Tribological Application

Kaushal Kishore1, Pavan Bijalwan2, Abhishek Pathak2, Kuntal Sarkar2, Mohd Shaberoz

Uddin3, Amit Bikram Sengupta3, P K Tripathy4, Atanu Banerjee2*

1Scientific Services, Tata Steel; 2Research & Development, Tata Steel; 3Iron Making Area

Mechanical Maintenance, Tata Steel; 4Product Technology Group, Tata Steel

*Corresponding Author (Email: [email protected])

Abstract:

Corrosion and wear are the two most important challenges in tribology that limit the service

lives of engineering components. The current work is aimed to design and synthesis of

amorphous metallic coating (metallic glass) from blast furnace pig iron which can

potentially replace costly metal grades used for these tribological applications. Good glass

forming ability of the blast furnace hot metal (with inherent impurities) as determined by

thermodynamic calculation has been experimentally validated by making its glassyribbons

by melt spinning in air. Subsequently, the pig iron ingots were converted to metallic powder

using water atomization technology. These predominantly amorphous powders were used

as feed stock to synthesize metallic glass coating using thermal spray technology. The

effect of powder feed rates, plasma energy etc. during thermal spray process on the

microstructure, corrosion and wear behaviour of the coating was studied in detail at

laboratory using x-ray diffraction, scanning electron microscopy, potentiodynamic

polarization tests, electrochemical impedance spectroscopy, sliding wear and dry sand

abrasion tests. The optimised coating showed an amorphous structure with porosity less

than 2 %, corrosion resistance comparable to that of austenitic stainless steel, hardness

value greater than 800 HV and specific wear rates lower than conventional wear resistance

steel grades. Subsequently, successful field trials were taken on corrosion and wear prone

components used in iron ore fine conveyor circuitat sinter plant area of Tata Steel.

Keywords:Pig iron, thermal spray, metallic glass coating, corrosion, wear

Acknowledgement:

Authors sincerely acknowledge the contribution from the collaborative partners – Prof. Kallol

Mondal, IIT Kanpur; Prof. Anup K. Keshri, IIT Patna and Dr. Ashis K. Panda, NML Jamshedpur;

M/s Padmashree Ent., Hyderabad; M/s MEC Pvt. Ltd., Jodhpur


152

Plasma Spraying of Yttria Stabilized Zirconia Based Thermal Barrier

Coating

Kantesh Balani

AriharanS1, Pratyasha Mohapatra2, Alok Bhadauria3, Ashutosh Tiwari4,S.T. Aruna5, Anup

Keshri6, KanteshBalani3,*

1Department of Metallurgical and Materials Engineering, IIT-Madras, Chennai-600036

2Department of Materials Science & Engineering, Iowa State University of Science and

Technology, Ames, IA 50011, USA.

3Department of Materials Science and Engineering, IIT Kanpur, Kanpur-208016

4Department of Applied Sciences and Humanities, Rajkiya Engineering College Banda-

210201

5Surface Engineering Division,CSIR-National Aerospace Laboratories, Bangalore -560 017

6Metallurgical and Materials Engineering, IIT Patna, Bihta, Patna-801106.

* Corresponding author e-mail id: [email protected]

Thermal barrier coatings (TBC) provide thermal insulation due its low thermal

conductivity (1.8-2.2W/mK) and comparable thermal expansion coefficient (~7x10-6K-1)

compared to that of nickel-based turbine blades. It may be pointed out that the coating

failure occurs owing to the poor fracture toughnessof coatings and development of residual

stresses during coating deposition and also during service. Herein, Al2O3is deposited as TBC

material on Inconel 718 alloy with incorporation of 20 wt.% of 0, 3 and 8 mol.%Y2O3doped

zirconia(YSZ). Further, 4vol.%multiwall-carbon nanotubes (CNTs)are reinforced to enhance

the fracture toughness ofplasma sprayedcoatings. Complimentary spark plasma sintering

technique is also utilized to produce bulk YSZ-CNT composites. Phase retention has been

analyzed using x-ray diffraction, transmission electron microscopy and Raman

spectroscopy. The retentionof ~26% transformable tetragonal ZrO2phase is believed to play

a major role in imparting enhanced fracture toughness (by 28%, from ~4.3MPa.m1/2 to

~5.4MPa.m1/2), whereas, CNTs have shown to provide synergistic toughening (from ~5.2to

~5.9MPa.m1/2).The orientation of CNTs may also provide anisotropic thermal conduction

(lower transverse conductivity) to suit the needs of application as coatings of turbine

blades. Thus, synergistic toughening can render enhanced damage resistance and provide

prolonged life to thermal barrier coatings.

Keywords: Thermal barrier coating, plasma sprayed coatings, spark plasma sintering, yttria

stabilized zirconia (YSZ), Al2O3, carbon nanotubes (CNTs).


153

Wetting Phenomena in Plasma Sprayed Rare Earth Oxide Coating

Anup Kumar Keshri

O.S. Asiq Rahman, Biswajyoti Mukherjee, Anup Kumar Keshri

Plasma spray Coating Laboratory, Metallurgical and Materials Engineering

Indian Institute of Technology Patna

We have fabricated the novel parahydrophobic cerium oxide (CeO2) coating using a

industrially viable plasma spray technique, which has prospective applications in

microfluidic chips, no loss microdroplet transportation and chemical microreactors. Our

coating displays significantly high water contact angle (∼159.02˚) along with high contact

angle hysteresis (CAH≥90˚), very much similar to a ‘Rose petal’. This is supported by by the

fact that the coating displayed remarkable adhesion even with large inverted water droplets

of 70 μL, which is significantly higher than the reported values of 18 μL for polymer and 20

μL for drop casted CeO2 nanotubes. A systematic characterization results have been

displayed to clarify the ongoing confusion regarding the hydrophobicity of CeO2 coatings

often reported in literature. Meanwhile, our parahydrophobic coating also showed

remarkable thermal and mechanical stability even at a significantly high temperature of 200

°C for 14 h and with 50 g abrasive paper.

Anup Kumar Keshri is currently an Assistant Professor in Dept. of Metallurgical and

Materials Engineering at Indian Institute of Technology (IIT), Patna, India since

October 2013. Before joining IIT Patna, Dr. Keshri worked with Centre for

Nanotechnology Group, Bharat Heavy Electricals Limited (BHEL), Corporate R&D,

Hyderabad between April 2012-September 2013. He worked as an Associate

Professor in School of Mechanical and Building Sciences at Vellore Institute of

Technology (VIT), Vellore, India since April 2011. Anup Kumar Keshri, received his

Ph.D. degree in Materials Science and Engineering from Florida International

University (FIU), Miami, USA in July, 2010 and worked as Postdoctoral fellow in FIU

until March 2011. He has a B.E. degree in Metallurgical Engineering from Bihar Institute of Technology (BIT),

Sindri, India in 2002 and a M.S. degree in Metallurgical and Materials Engineering from Indian Institute of

Technology (IIT), Madras, India in 2004. He worked as Asst. Manager in Ispat Industries Limited, Mumbai

(2004–2006). During his Ph.D., he has worked on Process Map Development of Plasma Spraying, Splat

Formation, Liquid Precursor Plasma Spray and High Temperature Tribology. He has published 73 papers in

peer reviewed journals, delivered 30 talks in international conferences and 14 invited talks in academics and

industries. He is a recipient of many awards and honors such as, Research stay grant by Humboldt Foundation,

Dissertation Year Fellowship (2009–2010) from FIU, Arthur E. Focke leadership award by ASM Foundation

delegate of “President’s Council of Student Advisors (PCSA)” formed by The American Ceramic Society

(ACerS). Dr. Keshri also serves as reviewers for several journals in the area of coatings and thermal spray. His

h-index of 26 (total citations close to ~2000) strongly endorses his research productivity.


154

Delamination and cracking in Ni-HVOF coating

Deepesh Yadav

Deepesh Yadav1, Sanjay Sampath, Balila Nagamani Jaya1

1Department of Metallurgical Engineering and Materials Science, IIT Bombay, Mumbai,

Maharashtra, India

Abstract

Thermal spray coatings are widely used to enhance the surface properties of materials like wear resistance, hardness, corrosion resistance, and thermal insulation. The substrate is

the primary load-bearing material but since the coating is intimately attached to the

substrate, load transfer can take place from substrate to coating when substrate is loaded

in tension. Load transfer from substrate to coating leads to cracking and delamination in

coatings. This study investigates the adhesive and cohesive strength of Ni coating,

manufactured by a high-velocity oxy-fuel technique, on a steel substrate, under tensile

loading. To understand the load transfer mechanism shear lag tests on coatings of different

thicknesses have been done and numerical simulations have also been carried out. Tensile

properties obtained from testing of free-standing coatings are input into the simulations.

Delamination or cracking in coatings starts from edges or terminated surfaces. Decrease

in coating thickness from 2 mm to 0.1 mm improves the resistance for delamination but

cracking cannot be avoided. This establishes a methodology to determine interface

dominated properties in such coatings.

Keywords:- Delamination, Cracking, Shear lag, Load transfer mechanism and FEA


155

Phase transformations on aging of air plasma sprayed commercial purity

and high purity 7YSZ thermal barrier coatings

Vikram Hastak

Vikram Hastak1, Sanjay Sampath2and A. S. Gandhi1

1Department of Metallurgical Engineering and Materials Science, Indian Institute of

Technology Bombay, 400076, India

2Center for Thermal Spray Research, Stony Brook University, Stony Brook, NY, USA


ABSTRACT

Air plasma sprayed (APS) 7 wt% Y2O3 stabilized ZrO2 (7YSZ) thermal barrier coatings (TBCs)

are widely used in gas turbine engine components for increasing thermal stability. However,

thermal exposure induced phase changes in yttria-stabilized zirconia (YSZ) are still a subject

of concern as it might lead to TBC failure. The present work is mainly focused on examining

the evolution of multiple phases on aging of 7YSZ APS-TBCs. The topcoats were first

removed from the substrate through acid etching. Both, commercial purity 7YSZ (CP7YSZ)

and high purity 7YSZ (HP7YSZ) free-standing coatings were heat treated at 1200˚C, 1250˚C

and 1300˚C for various aging periods (from 0.5 to 512 h). Characterization by X-ray

diffraction reveals that the initial non-transformable t’ phase gradually transformed into

yttria-lean tetragonal (t) and yttria-rich cubic (c) phases in both CP7YSZ and HP7YSZ free-

standing coatings. However, cubic phase precipitation started sooner in CP7YSZ as

compared to HP7YSZ. Some amount of t’ phase was also retained even after aging for

considerably higher

aging periods. The variation in tetragonality (of t and t’) and phase fractions (t, t’ and c)

with increasing thermal exposure were investigated and further correlated with changes in

Raman spectra.

Keywords: Yttria Stabilized Zirconia, APS-TBCs, CP7YSZ, HP7YSZ, Phase transformations


156

Hot Corrosion Kinetics of Alumina plus 8% Yttria-Stabilized Zirconia Applied

on Cast Iron Substrate”

Abhinav

Assistant Professor, Department of Mechanical Engineering, Alliance University,

Bangalore.

.Email id: [email protected]

Abstract:

The hot corrosion test was conducted as per ASTM G111-97 standards on the plasma

coated specimens. Three cast iron specimens of size 30 mm x 30 mm were prepared and

act as a substrate. A mixture of pure alumina and 8% yttria-stabilized zirconia in 50:50

proportion was used as a topcoat. The topcoat thickness was varied in 100,200 & 300 μm.

Blended mixture of vanadium pentoxide (V2O5) plus 45 wt.% of sodium sulphate (Na2SO4)

powders were prepared and used as a corrosive medium. The test was conducted at 850±2

°C in a muffle furnace. Results obtained from the SEM & EDX analysis found that that

microcracks and micropores facilitated the corrosive elements diffuse into the bond coat.

It has been understood that as the thickness increases, the rate of diffusion of corrosive

elements decreases. A detailed discussion is made on the mechanism of corrosion and on

corrosion prevention of functionally graded composite coatings.

Keywords: Hot corrosion, Al2O3+ ZrO2ꞏ8Y2O3, Muffle furnace.


157


The study of adhesion and viscoelasticity on hardness and elastic modulus measurement in different cross-linked SU-8 thermoset

polymer

Prakash Sarkar, IIT Bombay

Prakash Sarkar1, Prita Pant1and Hemant Nanavati2

1Department of Metallurgical Engineering and Materials Science,

2Department of Chemical Engineering,

Indian Institute of Technology Bombay, Mumbai- 400076, India


Abstract

SU-8 is a cross-linked thermoset amorphous polymer, which is involved to design ultra-thick and high aspect ratio micro-electrical mechanical system (MEMs) components. We are interested to measure elastic modulus (Er) and hardness (H) of different extent of cross-linked SU-8 samples. To study this, we have fabricated samples by following standard photolithography process where the duration of post-exposure baking and hard baking are varied to achieve different extent of cross-linking. The amount of cross-linking is estimated by Fourier-transform infrared spectroscopy (FTIR). Nanoindentation is carried out to measure Er and H values at constant 0.01 strain rate (1/s) by applying 800 μN maximum load. By following conventional method, we have obtained high Er and H values for less (~ 82 %) cross-linked samples and less values for high (~ 95 %) cross-linked samples. The main reasons for these inverse values of Er and H are adhesion between the tip surface and contact sample surface, the influence of viscoelastic behavior and wrong measurement of contact area (Ac). After minimization of adhesion effect and viscoelasticity, we have considered Ac as residual indent impression projected area, which is obtained from scanning probe microscopy (SPM). Thereafter, obtained values of Er is 4.61 ± 0.13 GPa and 5.02 ± 0.18 GPa, and H is 256.97 ± 1.42 MPa and 285.48 ± 1.17 MPa for less and high cross-linked samples respectively.

Keywords: SU-8; Lithography process; FTIR; Nanoindentation; SPM


158

Synthesis and comparative characterization of electroless Ni-P, Ni-P-nano Al2O3 and duplex Ni-P/ Ni-P-nanoAl2O3 coatings on aerospace graded Al2024

alloy

Rajsekhar Chakrabarti, Techno India University

Rajsekhar Chakrabarti, Souvik Brahma Hota, Pradipta Basu Mandal

Department of Mechanical Engineering, Techno India University

[email protected]

Abstract

The essence of electroless coatings is realized by the scientists since last decade which makes them a vital player in material coating industry. Incorporation of a second phase micro or nano element into the Ni-P matrix widens the area of applications for these types of coatings. Researchers are showing their interest to develop more innovative electroless coatings where they are deploying different types of second phase material to enhance their physical, mechanical and chemical properties. Duplex coatings have shown promising capabilities by providing excess hardness, wear and corrosion resistance which can be attributed to the resultant effect of two consecutive layers of coating. In our research, three different types of electroless nickel phosphorous (EN) coatings were applied on the aerospace graded Al2O24 alloy substrate. The first type was plain Ni-P coating, the second one was a composite coating where nano alumina incorporated into the electroless Ni-P matrix and the third coating was a duplex coating with the inner layer having Ni-P and the outer layer consisting of a Ni-P layer incorporated with nano alumina particles. Characterization of the deposits by Scanning electron microscopy (SEM) along with energy dispersive X-ray spectroscopy (EDS) confirms the production of flawless, adherent coatings onto the substrate. Maintaining the surface roughness at acceptable level, a great increase in nano hardness was observed that was further enhanced by incorporation of nano Al2O3 particles and inclusion of one additional external layer in duplex coating. Excellent wear resistance also evaluated by the Nano-scratch test and cost effective Ferroxyl test supports the evidentiary fact of producing non porous electroless duplex coating which provides an excellent corrosion resistance to the inner Al2024 alloy. This study further provides a scope for analysis of heat treated electroless duplex coating onto various substrates especially used in Aerospace and defence industries.

Keywords: Duplex coatings, Nano-scratch test, Ferroxyl test, Aerospace and defence industries.


159

TS17

Reliability Aspects in Medical Devices and Implants

+

TS25

Biomechanics

Organizer:

A. M. Kuthe, NIT Nagpur

20th Dec 6-8 pm

20th Dec 9-10 pm


160

Invited Speakers

Class III medical devices development - challenges and opportunities for

India

Dr. A.M.Kuthe, VNIT A. M. Kuthe

Professor Mechanical engineering Department Visvesvaraya National Institute of Technology (VNIT) Nagpur

Email: [email protected] The Class III medical devices are more critical as the devices are either implanted in the patient body or their function directly affect the metabolism of the patient body and hence, they are classified under high risk category. Unfortunately, in India, most of the class III devices are imported and Indian manufacturer are not willing to enter in the market of class III medical devices as quality plays important role which needs high technical know-how. This has boomeranged in developing confidence of medical fraternity on the imported class III devices and the import bill for such devices are increasing every year. Despite having premier educational & research institutes in India, the scenario in the design and manufacturing of class III medical devices is poor. This is mainly because of lack of team effort in R & D activity on national level. There is a tremendous opportunity to develop in house class III medical devices like metallic implant. The confidence of the medical fraternity can be built if the human resources from premier educational and research institutes play role in design and manufacturing of the Class III medical devices. The perfect coordination of premier institutes and research-oriented company will bring down drastically the import bill of such devices. The customised medical class III devices developed at VNIT and implanted in the patient body and tissue engineering research can prove as important steppingstone. .

Prof. Kuthe earned his PhD in 2001. His research work is focussed in the area of rapidprototyping(RP). The capabilities of RP equipment were extensively exploited by him to make custom build metallic implant that were implanted in human bodies by surgeons in several complicated medical cases including some cases of cancer. His contribution to international and national journals, demonstrates his deep study as well as authority on the subject. Creation of well-equipped CAD-CAM centre at VNIT speaks volumes of his passion for raising the bar of academic standard.


161

The Challenges of Additive Manufacturing in Medical Devices

Gaffar Gailani

Professor, New York City College of Technology of the City University of New York [email protected]

In the last few years, the market of Additive Manufacturing (AM) of medical devices has been growing very fast. Financial forecasts estimate that this market will reach $10.8 billion by 2021. AM is playing a big role because it offers shorter supply chains, shorter lead time, optimised design, and precise customisation. However there are still some challenges needs to be addressed. These challenges include price of machines, sustainability of materials, reliability, high-volume production, lack of standards and many others.

Gaffar Gailani is a professor in the Mechanical Engineering Technology Dept at New York City College of Technology and the founder and director of the Centre of Medical Devices and Additive Manufacturing. He received his Master and PhD degrees from the City College of New York. His research areas include poroelasticity, design and manufacturing of medical devices and bone biomechanics.


162


An in-depth look into mechanical testing of biomechanics & orthopedics

Jochen Niederberger, Industry Manager for Biomechanics &

Orthopedics, Dental and Biomaterial

ZwickRoell in ULM, Germany

The medical devices industry in India consists of large multinationals as well as small and

medium enterprises (SMEs) growing at an unprecedented scale with estimated current

market size of $11 bn.

The Government of India has taken several steps to ensure the growth of medical devices

manufacturing in India. Few amendments like implementation of the new Medical

Device Regulation will make tests of each medical device legally mandatory. This evolved

needs to assure quality standards and perform testing of the medical devices.

We would be focusing on the mechanical testing of spinal, hip, knee,

osteosynthesis implants, medical bone screws and other biomedical devices which

needs testing to assure the quality of the devices abiding the stringent medical devices

regulation. We will also highlight the requirements of different global standards (like ISO

and ASTM) and the importance of their existence in the testing world.


163

Non-invasive, anesthesia free Glaucoma screening device for early

detection and monitoring of glaucoma: A fully automated approach

Neha Lande

Neha Lande*1, Mahesh Mawale2, Abhaykumar Kuthe3, Nitesh Raul, Ashwini Lande

Production department, Okoicaresolutions private limited, Nagpur1

Mechanical engineering department, Kavikulguru Institute of Technology and Science Ramtek, Nagpur2

Mechanical engineering department, Visveswaraya National Institute of Technology, Nagpur3

[[email protected]]

Glaucoma is a progressive optic neuropathy caused by high intraocular pressure (IOP)

results in permanent vision loss within a few years. About 120 Lakhs Indians are affected

by Glaucoma with 10% of them permanently losing their vision. This can be prevented by

suitable care and treatment, if the condition is diagnosed early enough. Currently available

devices are invasive need anesthesia drops for taking IOP also not enough for large scale

screening. Considering all these aspects we have developed a novel glaucoma screening

device overcoming all mentioned problems which will greatly reduce the skill level, time and

cost involved in glaucoma screening. This device is robust, portable, non-invasive which is

placed over the eyelid and takes only few seconds to detect the level of IOP. We have used

a novel approached combining two different principles applanation and fixed indentation.

The goal to screen large number of patients especially from rural areas where glaucoma

awareness is poor. Such patients can be referred to ophthalmologists for confirmation and

further treatment. 50 patients were screened with new device they have found the new

device is more comfortable than conventional devices. The project has been granted by

BIRAC start-up grant for product development.

Keywords: Intraocular pressure, applanation, indentation, vision, robust


164

Integration of nanotechnology and 3D printing technology for organ printing

Arun Bharali

In today’s world the applications of Biomedical Nanotechnology is growing day by day.

Integrating this technology with the current 3D printing techniques and their applications

towards bone, cartilage and Osteochondral regeneration leads to vast scope in this field. In

this paper, with the help of a computer software a solution to repair, restore or replace

skeletal elements and associated tissues that are affected by acute injury, chronic

degeneration or cancer related defects is discussed with an overview to future research in

the related areas.


165

Coupling of Mechanical Deformation and Electrophysiology of Brain Neuron

Cell

Rahul Jangid

Rahul Jangid and Krishnendu Haldar

Aerospace Engineering Indian Institute of Technology, Bombay

[email protected]] [[email protected]

Traumatic Brain Injury (TBI) due to a vicious head impact in motor or space vehicle accidents, falls, and sports injuries, causes severe tissue damage. The impact forces make the brain tissue distorted, twisted, and injured. The stress inhomogeneity, due to the impact, creates highly nonuniform strains and damages the axons in the white matter. For more than half a century, electrophysiology of brain neurons was considered pure electrical phenomena. However, recent experimental studies show that mechanical deformation plays a vital role in the electrophysiology of brain neurons. In this work, we model the coupling of mechanical deformation with the Hodgkin-Huxley (H-H) model of electrophysiology of neurons. The sensitivity of pressure on the neuron cell due to the generated electrical field and mechanical stretching is demonstrated.

Keywords: Traumatic Brain Injury, Electrophysiology, Hodgkin-Huxley (H-H) Model.


166

TS20-Structural Integrity of Weldments and Welded

Structures

Organizer: A. Shrivastava, IIT Bombay

11th Dec 4:30-6 pm


167

Invited Speakers

Cracks and Failures in Space Transportation Systems

Dr. SGK Manikandan, IPRC ISRO Deputy General Manager

ISRO Propulsion Complex, ISRO, Mahendragiri [email protected]

Space systems need defect free components for the intended performance. Space systems are experiencing different loading conditions such as pressure, temperature and other external loads. Same system will behave in a different manner for every condition. Even a micro defect can lead to a catastrophic failure of the mission. All the space systems are qualified at ground prior to flight. This talk addresses the failures encountered in both flight and ground systems and root cause findings through metallographic analysis.

Graduated in mechanical engineering (1997) and joined in ISRO (1998). Completed PhD in Metallurgical and Materials engineering from IIT Madras.

RESEARCH INTERESTS :Metal Joining; Friction stir welding / processing/ surfacing; Electron beam welding; Metallurgical and Mechanical property evaluation of welds; Solidification in superalloy systems Process development for Thermal barrier and wear resistance coating for aerospace components. Development of metamaterials, super strong materials for temperatures exceeding 2000°C, High entropy alloy wear and thermal resistance coatings, thermally assisted friction stir welding of superalloys, Superalloy filler metal with inoculants, Self reacting friction stir welding and Self healing thermal barrier coatings. Publications in international journals (15), books(2) and international conferences (9)


168

Material Joining – Aero Engine Perspective

Dr. Vijay Petley, GTRE ISRO Scientist

Gas Turbine Research Establishment (GTRE), DRDO [email protected]

Aero engines have led to the development of advanced materials and processes over the last few decades. Materials with high temperature capability, high specific strength are developed for usage under harsh environments of aero engines. The advancement of processes to develop these materials is the necessity and natural outcome due to the rigorous quality requirement of these materials used for critical application. Further, the fabrication processes are inevitable during part realization and assembly of components. Of the many special processes, metal joining is one of the crucial processes that need to be employed on these advanced materials. Superalloys are the materials used in the hot zone of the aero engine. The combustor and turbine casings, nozzle guide vanes, rotor shafts, turbine blades, core burner ring are few of the components where metal joining is required to be performed. These components operate under the harshest environment of engine and so are the material joints on these components. While both fusion and solid state welding have seen application in aero engines, high temperature high vacuum brazing is a technology in itself for joining of hard-to-access locations of cast superalloys. The characterization of these weld joints and its qualification is utmost important for functional assessment of these parts. Mechanical evaluation and metallurgical characterization of these joints are complimentary techniques to understand the structural integrity of such joints. Additive manufacturing process itself is a micro-arc welding of powder particles with a highly precise mechanism to control the heat input and path travel. Laser cladding, surface crack repair by brazing, IPTIG welding are few of the material joining technologies towards repair and reclamation of aero engine parts. Conventional usage of composites for aero engines requires metal-composite interfaces that are realized by riveting, active brazing, etc. With advancement of material technologies meant for specific product development like BLING has multitude of process specific technologies of which diffusion bonding, linear friction welding are few of the material joining technologies. Even for sensor application like lead wire routing, micro welding techniques are developed for the specific type of sensor material and design. The present talk illustrates and provides a brief about the work performed on material joining for aero engine application and the challenges required to be met with advancement of technologies. With emerging material technologies on several fronts like superalloys, composites, sensors, the advances in material joining technologies has to go hand-in-hand for part and assembly realization. The field of material joining is very expansive and there is a necessity for the collaborative work amongst researches, academicians and institutes to propel these technologies for aero engine application.

Dr. Vijay Petley did his graduation in year 2001 from Department of Metallurgical Engineering & Materials Science of Visvesvaraya Regional College of Engineering, presently, VNIT Nagpur. He joined GTRE DRDO in year 2001. He pursued his doctoral work at Indian Institute of Science. Presently, he works as Scientist at Materials Group of GTRE and is responsible to address the metal joining related issues on the various programs at GTRE.


169


Finite element simulation of residual stresses in friction stirs welding of

AA2219 plates

Krishnajith Jayamani Krishnajith Jayamani, K. Abhishekaran, Vasudevan R. , H. M. Umer & A. K. Asraff

Mechanical Design and Analysis Entity, Indian Space Research Organization (ISRO), India,], [Institute]

[[email protected]]

Friction Stir Welding (FSW) is a solid state welding process in which the temperatures never

exceed the melting point of the work-piece material. The process is widely used in

aerospace industry for welding of aluminium alloys and aluminium-lithium alloys used in the

fabrication of propellant tanks. Knowledge of the residual stresses developed due do the

welding process is an important parameter used in the design of propellant tanks.

The present work details the finite element simulation of friction stir welding of two flat

plates made of AA2219 material, a material used for fabrication of the propellant tanks used

in the launch vehicles of ISRO. The simulation is performed using a non-linear, fully coupled

thermal-structural finite element analysis using ANSYS (Version 18.1) code. The

computational model involves two work-plates and the FSW tool modelled using three

dimensional solid elements and the effect of the fixtures supporting the work-piece is

brought in using appropriate structural and thermal boundary conditions. The constitutive

models used for the analysis are capable of simulating the frictional heat generation and

the associated temperature-dependent mechanical response of the material. The entire

sequence of operations involved in the welding process from initial plunge of the tool to the

final removal of clamps after cooling is simulated.

It is seen that the predicted temperatures on the work-piece falls with 70% to 90% of the

melting temperature of this particular alloy. The predicted residual stress pattern shows a

characteristic M-shaped distribution along the width of the work-piece which agrees fairly

well with results reported in literature.

Keywords: Friction Stir Welding, Residual stress, Finite element simulation


170

TS21

TS21-Structural integrity of Gas Turbine Engine

Materials

Organizer: A. Patra, IIT Bombay

13th Dec 4-5.30 pm

20th Dec 4-6 pm


171

Invited Speakers

Deformation in thermal barrier coating (TBC) ensemble

Md. Zafir Alam, DMRL

(Other authors: Chandrakant Parlikar, Rajdeep Sarkar and Dipak Das) Scientist & Head

High Temperature Coatings Group [email protected]

The Ni-base superalloy components operating in the hot sections of advanced gas turbine engines are applied with thermal barrier coatings (TBCs). The TBC is a multi-layered ensemble providing thermal insulation, oxidation resistance and enhanced high temperature durability to the components. The advanced TBC system contains: (i) an outer layer of columnar textured 8 wt.% yttria stabilized zirconia (YSZ) which is 150 µm in thickness and provides thermal insulation, (ii) an intermediate layer of thermally grown oxide (TGO) which comprises polycrystalline alumina and is 2-6 µm in thickness, (iii) a subsequent inner layer of diffusion Pt-aluminide (PtAl) bond coat which is about 100 µm thick, exhibits randomly oriented B2-NiAl phase with graded stoichiometry and provides oxidation resistance, and (iv) the directionally solidified (DS)/single crystal (SX) Ni-superalloy substrate containing the γ-Ni/γ´-Ni3Al phases which bears the mechanical loads. Therefore, the constituents transition from ceramic (YSZ, TGO) to brittle intermetallic (PtAl bond coat) and metallic (superalloy) across the TBC coated superalloy. Considering the inherently different slip characteristics in metallic, intermetallic and ceramic systems, scientific understanding of the deformation behavior within the multi-layered and multi-phase TBC ensemble is crucial. The present study evaluates the micro-mechanisms of tensile deformation at various temperatures until 1000°C for a directionally solidified (DS) CM247 LC superalloy applied with TBC. The representative properties of the TBC constituents, i.e. that of freestanding diffusion PtAl bond coat, TGO and EB-PVD columnar YSZ coating are ascertained using micro-tensile testing and nano-indentation techniques. The large B2-NiAl grains (size > 10 µm) oriented for high Schmid factor with respect to the neighboring grains in the PtAl bond coat experience high shear stress on {100}<001>, {110}<001> slip systems and exhibit profuse dislocation activity at room temperature, which is otherwise unusual for the brittle NiAl intermetallic. The outward propagation of cracks from the bond coat along the PtAl/TGO/YSZ interface causes delamination of the YSZ coating layer, whereas the inward propagation of cracks causes lowering of strain tolerance in the superalloy and tensile failure is marked by negligible post-necking strain for temperatures below 800°C. At higher temperatures, the ductile deformation in the PtAl bond coat, aided by its low strength and concomitant dynamic recrystallization, causes shear displacements of the YSZ/TGO/PtAl interface and buckling delamination of the YSZ coating.

Dr. Zafir Alam works as a Scientist in Defence Metallurgical Research Laboratory (DMRL), Hyderabad, India and leads the High Temperature Coatings Group. He obtained Ph.D. from The Department of Materials Engineering, Indian Institute of Science (IISc), Bangalore and purused post-doctoral research at Johns Hopkins University, USA. His research interests are in the processing and micro-mechanical characterization of coatings for advanced high temperature applications. He is recepient of ACTA Student Award-2013, IISc Best-PhD Thesis Award-2013, IIM-Young Metallurgist Award-2011, and DRDO Young Scientist Award-2010. He has about 50 publications in peer-reviewed journals.


172

Dheepa Srinivasan, Pratt & Whitney

Chief Engineer Pratt & Whitney R&D Center

[email protected]

Materials and Manufacturing technologies have enabled Gas Turbine engine advancements and played a critical role in various aspects of the engine performance metrics of, thrust, efficiency, firing temperature and weight, since the last 7-8 decades. The temperature capability at the turbine inlet temperature (is higher than the melting point of the metal), the compressor by pass ratio, compressor outlet temperature, have all more than doubled in the last several decades,and owe their advancements to materials capability enhancements,which has gone up by leaps and bounds with each new successive product generation. Today, all these have been possible because of the availability of high temperature alloys and coatings, for rotating turbo machinery. A glimpse of the materials capability from flange to flange will be shared. Directionally solidified and single crystal blades, light weight carbon fiber composite blades and hybrid metallic airfoils, hollow Ti and γ-TiAl blades, Ceramic matrix composites and low K thermal barrier coatings (TBC’s) have all played an everlasting role in the development of new material architectures and enabled propulsion innovation. Several 1000’s of parts receive coatings to address erosion, corrosion, abradable, fretting, oxidation, hot corrosion and thermal protection coatings that optimize the application performance.The talk will address the evolution of Nickel based superalloys in the gas turbine development, and share a couple of examples of the time and effort involved in development of high temperature capability alloys and coatings. Future engine capabilities require lightweight structures and higher temperature capability with greater durability. While evolutionary progress will help, new high temperature materials and manufacturing systems are needed with improved development speed and cost to enable new system architectures.

Dr. Dheepa Srinivasan is the Chief Engineer, at Pratt and Whitney, R&D Center, Bangalore. She is leading research activities at academic and industrial research sites in India for Pratt and Whitney. Dheepa has more than 20 years of total work experience in the area of gas turbine materials and manufacturing technologies.


173


Tensile properties and statistical analysis of freestanding YSZ thin films

with circular holes

Supriya Patibanda, IIT Bombay

Supriya Patibanda1, Ralph Abrahams2 and Krishna N Jonnalagadda3

1Department of Mechanical Engineering, IITB-Monash Research Academy, 2Department of Mechanical and Aerospace Engineering, Monash University,

3Department of Mechanical Engineering, Indian Institute of Technology Bombay.


Abstract

Yttria stabilized zirconia (YSZ) is used as a top coat in the thermal barrier coating system on

superalloy components of aircraft engines, for its low thermal conductivity and superior thermal

insulation properties. To avoid the premature failure due to excessive operating temperatures,

turbine blades and some engine components are provided with holes for cooling purpose. As TBCs

are coated on to these blades, it is important to understand the effect of these holes on the fracture

behaviour of TBC. Therefore, in this study, the effect of stress concentrations on the tensile

properties of free standing YSZ thin films of ~300 μm was studied using samples with inherent

circular hole of Ø1 mm at the centre of the tensile sample, devoid of any machining. The effect of

the presence of a circular hole on the tensile strength was studied and compared to that of

continuous YSZ films using a custom built uniaxial microtensile setup in conjunction with digital

image correlation. A drop in fracture strength from 16±4 MPa in continuous samples to ~11±3 MPa

in samples with a circular hole was observed. The cracks initiated at the circumference of the hole

and perpendicular to the loading direction. To address the basic problem of data scatter in fracture

strength in these materials, designers have proposed a probabilistic approach in ceramic materials

based on Weibull’s weakest link theory. Hence, Weibull statistical analysis was performed on tensile

strength of continuous and hole containing samples. It was observed that the three-parameter

method is more accurate for YSZ films than two-parameter analysis. The properties reported in this

current study could contribute to the design database for modelling the mechanical behaviour of

YSZ.

Keywords: Freestanding YSZ films; tensile properties; digital image correlation; Weibull analysis,

stress concentration



174

Numerical slosh studies of multiple ring baffles in a semi-cryogenic fuel

tank

Aleena Seban, Mar Baselios College of Engineering and Technology

Aleena Seban1, Kodati Srinivas2,M. Satyakumar3, Sarath Chandran Nair S.4

1 Graduate student, Mar Baselios College of Engineering and Technology, Thiruvananthapuram-695015,

[email protected] 2 Head, Structural Dynamics Division, Mechanical Design & Analysis Entity, LPSC/ISRO, Valiamala, Thiru

vananthapuram, 695547

3 Head, Department of Civil Engineering, Mar Baselios College of Engineering and Technology, Thiruvanan

thapuram-695015

4 Engineer, Structural Dynamics Division, Mechanical Design & Analysis Entity, LPSC/ISRO, Valiamala, Thir

uvananthapuram, 695547

Abstract

One of the heavy lift launch vehicles being developed by ISRO uses semi-cryogenic stage.

Semi cryogenic stage uses Isrosene as a fuel and liquid oxygen (LOX) as the oxidizer. These

propellants will be supplied at a specific flow rates to the rocket engine to develop the

required thrust. Sloshing is an important phenomenon to be considered for

liquid/cryogenic/semi-cryo genic stages in order to design control system for the launch

vehicle. For modelling slosh for control system studies, mathematical parameters such as

slosh frequency, slosh mass and its location are required to be evaluated. In addition to

these parameters, damping also play a major role in containing the vehicle response due to

slosh. In the present study the parameters required for mathematical modelling of slosh for

control stability analysis are evaluated using two different FE codes. The requirement of

damping and duration envisaged from control sta bility analysis is met by designing multiple

ring baffles using semi-empirical relations. In ad dition to the above, the achievable damping

values for the designed baffle and its effect on slosh parameters are also studied.

Keywords: Semi-Cryogenic Stage; Sloshing; Slosh Frequency; Slosh Mass.


175

TS22-Damage and Failure modeling in Composite

Materials

Organizer: C. Yerramalli, IIT Bombay

19th Dec 6-10 pm


176

Invited Speakers

Process optimization in manufactring of composite structures

Amit Salvi, TRDDC, TCS

Fiber reinforced Polymer matrix composites are increasingly used in large Aerospace and Wind Energy Blades. These structures pose unique challenges due to their size, life under fatigue loads and long term reliability. The durability of these structures depend on the damage accumulated over its operational life which in turn depend on the residual stresses developed in the manufacturing stage itself. Thermoset epoxy resin used in the structures acquire their mechanical as well as physical and chemical properties during its cure in which cross-linking of polymers take place. In presence of reinforcing fibers, the elastic as well as inealstic properties of the in-situ resin differs from virgin resin and create lot process induced residual stresses. In this study, a time dependent, multiscale analysis framework is developed to compute process dependent residual stresses in large structures. A n optimisation framework is also developed to control desired quality of these components to reduce the distortion and residual stresses to increase the reliability of these structures.


177

TBD


Laminate and Sub-laminate Buckling on Delamination Mechanics in Hybrid

Composites

Savitha N Nambisan and B. Dattaguru School of Aerospace Engineering, Jain (deemed to be University)

Bengaluru Laminated composites have become preferred material system in a variety of industrial applications and particularly in Aerospace Engineering. Laminates made of single fibre type and resin are extensively used in aerospace primary structural components with weight saving and in these cases further benefits can be achieved by fibre hybridization. It is the purpose of this paper to demonstrate that combining layers of lamina of different fibres is a promising strategy to enhance tolerance to delamination type of defects in laminates. Also by combining two or more fibre types, the hybrid composites offer a better balance in mechanical properties than non-hybrid composites.For instance, replacing carbon fibres in the middle of a laminate by cheaper glass fibres can significantly reduce the cost,while the flexural properties remain almost unaffected. A 24-layer all carbon layer composite of (+45/-45/0/90)3s lay-up is considered for analysis. The laminate dimensions are 92 X 74 mm with 3mm thickness is analyzed with and without hybridization. This laminate was considered earlier in literature [1] for delamination tolerance analysis. Low velocity impact could result in delamination/s in top or bottom few layers. Parametric study of delamination and its tolerance depending on its size, shape and depth are analyzed.This composite will be converted into a hybrid composite demonstrating the benefits of hybridization. Both the top and bottom 4 layers are replaced by (+45/-45/0/90) layup glass fiber composite laminates maintaining symmetry about the centerline. 3-dimensional finite element analysis is conducted using PATRAN for modeling and NASTRAN software package for structural analysis. Static displacements such as delamination opening and Strain Energy Release Rates (SERR) are compared for all carbon and hybridized composites. The shape of delamination considered is primarily of circular shape. Finite element analysis is conducted using 20-node brick elements and layered composite elements used with 2 or 4 layers in elements. The laminate (in x-y plane) is subjected to compression strain along the edges in x-direction and all edges are simply supported in z-direction. The delamination opening is measured and the SERR are estimated along the delamination front by using Modified Virtual Crack Closure Integral (MVCCI)technique [2]. There is a primary aspect to be considered in the analysis.Buckling of the entire panel and the sub-laminate affects delamination and its growth. So the entire panel and also the delaminated sub-laminate are checked for buckling failure. It is observed that the delamination growth is accentuated as sub-laminate bubbles before buckling failure. On the other hand buckling failure will make the delamination to close. At much higher load levels the total laminate failure could occur and the laminate ceases to take any further load. The buckling failure loads are evaluated with various parameters of the laminate. The hybridization leads to much earlier delamination closure and zero strain energy release rates. Delamination tolerance is much better in hybridized composite due to less stiffness layers at the top and bottom of the layup. This is shown for one typical case. The paper demonstrates these results with variation of some of the geometric parameters.


178

Al/GFRP interface strength under quasi-static and dynamic loading

conditions

Madhusudhanan U, Sooriyan S, R Kitey aStudent, Department of Aerospace engineering, IIT Kanpur, India

b Reseracher, TCS Research (TRDDC), Pune, India cAssociate Professor, Department of Aerospace engineering, IIT Kanpur, India


With continual increase of composites in aerospace applications, metal/composite bonded joints have become quite common because several aircraft components cannot be riveted, bolted or welded due to their miniature sizes and/or complex shapes. Apparently, the reliability of such components highly depends upon their interfacial properties. Often pull tests are suggested to evaluate the interface strength of bonded joints. Unless the effect of stress concentration is taken into account, reliable interface strength data cannot be obtained from the experiments. In this investigation the interface strength between Al 6063-T6 alloy and glass fiber reinforced polymer (GFRP) composite is evaluated under quasi-static and extreme dynamic loading conditions. A modified axisymmetric butt joint sample is designed to negate the effect of stress concentration.

Al/GFRP bonded joint specimens to conduct pull tests are prepared by co-bonding.

Laser spallation technique is adopted to measure the interface strength of Al/GFRP

bonded joint at a strain rate of ~ 107/s. Failure initiation is identified through optical

microscopy and interface strength is evaluated by employing experimental/numerical

approach. The dynamic adhesion strength of Al/GFRP joints is measured to be 330.8

MPa.


179

A FEA based study on the behaviour of multiple-micro bolted hybrid CFRP

joint under tensile loading

Isha Paliwal and Ramji M. Engineering Optics Lab, Department of Mechanical and Aerospace Engineering,

IIT Hyderabad, India

*Email: [email protected]

Abstract

The extensive use of composite materials in aircraft primary structures led to the increasing

interest of many researchers to improve the joint efficiency of existing joints techniques as

well as develop new joining techniques for composite material. The conventional joints use

in composite structures are bolted, bonded, and hybrid (bonded/bolted) joint. The hybrid

joint exhibits the advantages of both adhesively bonded and bolted. Hence, have the

potential to be employed in primary aircraft structures joint requirement.

To understand, the mode of failure of hybrid joint and the effect of various parameters on

joint strength, many studies have carried out in the previous two decades. From the

literature, we can conclude that the percentage load sharing through the bolt has a

significant effect on hybrid joint strength. In this study, multiple micro bolts are used instead

of a single bolt to fasten the hybrid joint. Multiple micro holes laminate takes a higher

ultimate tensile load than the single hole laminate while keeping the area of cutout constant.

The use of micro bolts also leads to reducing the weight of the joint assembly.

To investigate the effect of multiple-micro bolts in the hybrid joint scenario, a finite element

analysis (FEA) has been performed using a three-dimensional finite element model. A 3-D

progressive damage model is used to assess the damage evolution and prediction of the

ultimate strength of the hybrid composite joint under in-plane tensile loading. The results

show that joint strength is higher for the multiple-micro bolted hybrid model than the single

bolt hybrid model. The percentage of load transfer through-bolt is increased significantly

due to multiple bolts.

Keywords: Hybrid joint; FEA; Micro-bolt; Progressive damage.


180

Hot-wet environmental effects on in-plane shear strength of IMA/M21E

aircraft grade CFRP composites

Kishora Shetty* Kishora Shettya, Shylaja Sriharia,b, C M Manjunathaa,b, Suhasini Gururajac

aAcademy of Scientific and Innovative Research (AcSIR), Ghaziabad - 201002, India bCSIR-National Aerospace Laboratoires, Bangalore - 560017, India

cIndian Institute of Science, Bangalore - 560017, India

[email protected]

Abstract

Application of Carbon Fibre Reinforced Plastic (CFRP) composites in aerospace structures

are increasing due to their high specific strength and stiffness. During their service, aircraft

composite structures are usually exposed to a variety of environmental conditions including

hot – wet or hygrothermal, ultraviolet (UV) radiation, chemical environments, biological

conditions etc. These conditions make the composite structures to deteriorate mainly by

making changes to polymer matrix and to matrix/ reinforcement interface. Effect of hot –

wet environments by moisture absorption on properties of CFRP structures is a valuable

factor to designers and application engineers in assessing the structural integrity of the

parts. In this present study, UD-CFRP composite laminates were manufactured from

HexPly® M21E/34%/UD/194/IMA prepreg by standard autoclave process. In-plane shear

strength (IPS) being the matrix dominated property of the CFRP, it is important to evaluate

the effect of moisture absorption in this. In-plane shear (IPS) strength test specimens were

obtained from theses laminates. Specimens were subjected to three hot – wet

environmental conditions: 45 oC/85% RH (relative humidity), 75 oC/85% RH and 55 oC/100%

RH until achieving complete moisture absorption saturation. IPS tests were carried out as

per ASTM test standard ASTM D3518 specifications using a 25 KN servo-hydraulic test

machine. The in-plane shear strength properties were determined for both conditioned and

un-conditioned (control) laminate specimens. Corresponding hot-wet conditions were

maintained during the IPS tests. Tests results show that moisture absorption rate increases

gradually and attains saturation at about 1.2 wt. % under these three conditions. IPS

strength reduced by about 8% due to presence of moisture. Tensile strengths were also

measured while carrying out IPS tests. This paper describes the details of hot – wet

conditioning, moisture absorption and IPS test results.

Keywords: Structures, Composite, Hot-wet, IPS


181

Performance driven fan case design for durability evaluation in a blade

impact event

Ashutosh Bhat, Lavya Sharma and Sandeep Sharma

Ashutosh Bhata, Lavya Sharmab , Sandeep Sharmac

a,b Research Associate, Aerosphere Technologies, Chandigarh, India c Technical Head,

Aerosphere Technologies, Chandigarh, India

Abstract: The objective of present work focuses on identifying containment capability of a hybrid fan case which uses an impact absorbing (periodic) corrugated lattice structure core (LSC), sandwiched between the inner ring and outer shell having distinct impact resistance followed by perforation, buckling and crushing as a result of excellent strength to stiffness ratio at low relative density. Three different configurations comprising of general (a), twill (b) and triaxial (c) patterns are built for this study and by varying cell parameters such as inclination angle (θ), thickness and face width similar relative densities are derived for numerical investigation. In order to maintain structural integrity during blade penetration at first contact, estimation of maximum allowable thickness for inner ring is critical and best suitable value of 0.9 mm was found deterministically by sub-scale impact tests. Further, to determine design reliability; contact force history, energy locus, triaxial stresses, plastic strain and large deformations that occurs during blade-case interaction in cases a, b and c are studied for effective comparison using finite element solver LS-DYNA. Results reveal that number of unit cells have relevant effect on containment capability within the same spatial envelop. For one-third number of relative cells in 2-d (x-y) plane, significant local buckling causes sudden collapse of corrugated cells circumferentially which is undesirable as it loses interferential strength to counter (shear). However, marginally higher energy is absorbed for case (c) when compared to cases (a, b) and additionally crushing response is also delayed resulting is lesser plastic strain during damage. Effect of multi-blade interaction on blade breakage at is not a part of current study. Lastly, it is concluded that to exploit maximum energy absorbing capacity of a corrugated lattice structure, factors such as topology, cell parameters and unit repetition must be carefully identified.

KEYWORDS: Fan Blade out, Containment, Corrugated lattice core, Hybrid casing


182

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