Optimization of a car bonnet's material combination based on stiffness requirements and pedestrian safety

By

Kevin ChackoSID: 1102532

Supervisor

Dr.MehrdadAsadi

A dissertation in partial fulfilment for the degree

Of

Bachelor of Engineering Honours

In

Mechanical Engineering

Faculty of Science & Technology

Anglia Ruskin University

Acknowledgements

I would have never been able to finish my dissertation without the right guidance of my supervisor, help from colleagues and support from family and friends.

First and foremost I would like to express my deepest gratitude to Dr.MehrdadAsadi for encouraging me to pursue this topic. I want to convey my sincere courtesy for his excellent guidance and also for sharing his wealth of knowledge in the topic of research. He was always available to make sure I was moving forward in the right direction and have always been unstinting in his support and constructive critique.

I would like to thank my colleagues, Simon Hoffman, Nicholas Caldicott for networking with me throughout project and a special thanks to Bashir Karkarna for encouraging me and pointing me in the right directions to use a variety of research methods efficiently.

Finally I would like to thank my family, particularly my father and mother who have patiently supported me and encouraged me to complete the project with be best of my ability.

DECLARATION BY THE AUTHOR

I hereby declare that the work in this report is my own except for quotations and summaries which have been duly acknowledged by citation references. I have clearly stated the contribution of others to the production of this work as a whole. I have read, understood and complied with the Anglia Ruskin University’s academic regulations regarding the assessment offences, including but not limited to plagiarism.

I have not used material contained in this work in any other submission for an academic award or part of part thereof.

I acknowledge and agree that this work may be retained by Anglia Ruskin University and made available to others for research and study in either an electronic format or paper format or both of these and also may be available for library or inter-library loan. This is on the understanding that no quotation from this work may be made without proper acknowledgement.

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ContentsChapter 1: Introduction..........................................................................................................................1

1.1Project Introduction........................................................................................................................1

1.2 Problem Statement.........................................................................................................................2

1.3 Project Aims and Objectives..........................................................................................................2

1.4 Aim................................................................................................................................................2

1.5 Objectives......................................................................................................................................2

1.6 Description of Research.................................................................................................................3

Chapter 2: Literature Review.................................................................................................................4

2.1 The Literature................................................................................................................................4

2.2 Brief Review of the Literatures.....................................................................................................7

2.3 Importance of Research.................................................................................................................8

2.4 Statistical data associated with VRU fatalities and casualties.......................................................9

2.5 Rising trend in KSI Value: (2013 – 2014)...................................................................................10

2.6 Costs associated with Pedestrian causalities................................................................................10

2.7 Financial figures for a typical severe brain injury case...............................................................10

2.8 Facts and figures considering Child-Car front collision..............................................................11

2.9 Lifelong cost for a child with a serious head injury....................................................................11

2.11 Environmental Benefits from Weight Reduction......................................................................12

Chapter 3: Technical Background........................................................................................................14

3.1 Features and Components of a Standard Car Bonnet..................................................................14

3.2 Assembly Process of the Bonnet Panels and the effect in Stiffness............................................17

3.3 Significant Changes in Bonnet Design........................................................................................18

3.4 Bonnet Design Approach Based on Pedestrian Safety................................................................19

3.5 Active Design Approach..............................................................................................................19

3.6 Passive Design Approach............................................................................................................20

3.7 Importance of Lightweight Structure with Adequate Stiffness...................................................21

3.8 EuroNCAP Requirements............................................................................................................22

3.9 Standardised Static Stiffness Tests and Reference Values..........................................................22

3.10 Lateral Stiffness Test.................................................................................................................23

3.11 Transversal Stiffness Test..........................................................................................................23

3.12 Torsional Stiffness Test.............................................................................................................24

3.13 Importance of the specific stiffness tests...................................................................................24

3.14 Head Impact Performance Criteria (HIC)..................................................................................25

3.15 Material specification................................................................................................................26

Chapter 4: Methodology.......................................................................................................................28

4.1 Static Stiffness Test Methods......................................................................................................28

4.2 Finite Element Packages..............................................................................................................29

4.3 The 3D CAD Model....................................................................................................................31

4.4 ANSYS Workbench Model Setup...............................................................................................32

4.5 Boundary Conditions for Torsion Test........................................................................................33

4.6 Boundary Conditions for Transversal Test..................................................................................34

4.7 Meshing of the Model..................................................................................................................35

4.8 Mesh Quality Checks...................................................................................................................36

4.9 Static Impact Analysis of Iteration 5...........................................................................................38

Chapter 5: Finite Element Analysis.....................................................................................................39

5.1 Original Bonnet (Steel)................................................................................................................39

5.2 Material Combinations................................................................................................................42

5.3 Material Combinations with altered Panel thickness...................................................................51

5.4 Static Impact Analysis of Iteration 5...........................................................................................72

Chapter 6: Conclusion and Recommendations....................................................................................78

6.1 Future Recommendations............................................................................................................78

References..............................................................................................................................................80

Appendix 1.............................................................................................................................................83

Appendix2 - Curriculum Vitae..............................................................................................................84

Appendix 3 - Exit Plan...........................................................................................................................86

Appendix 4- Research Proposal.............................................................................................................89

List of Figures

Figure 1 An example of a Passive design approach (Encocam Ltd, 2015).............................................4Figure 2 The bonnet labelled with the chosen locations (SAS Tech Journal, 2012)..............................5Figure 3Theinner frame designs (SAS Tech Journal, 2012)...................................................................6Figure 4 Inner frame with multi cone design (Structural Hinge and hood concept, 2015).....................6Figure 5 Statistical data on road accidents involving VRU (Department for Transport, 2015)..............8Figure 6 Road accident casualties in Great Britain (Department for Transport, 2015)...........................9Figure 7The rising trend in reported death (Department for Transport, 2015)........................................9Figure 8 The recent rise in road accidents (Department for Transport, 2015)......................................10Figure 9 Proportion of greenhouse gases emitted in 2014 (Department for Transport, 2015)..............12Figure 10 The slight increase in emissions in transport sector (Department for Transport).................12Figure 11 General Bonnet components (Bonnet Components, 2011)...................................................14Figure 12Bonnet Panels (IJIRD, 2014)..................................................................................................15Figure 13 Lightweight Bonnet Hinges (Picture courtesy, Kevin 2016)................................................15Figure 14 Bonnet Latch System (Picture Courtesy, Kevin 2016)........................................................16Figure 15 Additional hood pins (Google Images, 2015).......................................................................16Figure 16 Additional Pins latching a bonnet (Google Images, 2016)...................................................17Figure 17 The concept of Hemming process (Bonding Processes, 2006)............................................17Figure 18 Spot welded region (Google Images, 2016)..........................................................................18Figure 19 Changes in Bonnet Designs (Google Images, 2015).............................................................18Figure 20 Active Bonnet System (EuroNCAP, 2016)..........................................................................20Figure 21 Passive Bonnet Concept (EuroNCAP, 2016)........................................................................20Figure 22 High Risk Impact Zones (Google Images, 2016)..................................................................21Figure 23 Car front safety assessment and criteria (EuroNCAP 2004).................................................22Figure 24 Lateral Stiffness Test (Abaqus Users Conference, 2008).....................................................23Figure 25 Transversal Stiffness Test (Abaqus Users Conference, 2008)..............................................23Figure 26 Torsional Stiffness Test (Abaqus Users Conference, 2016).................................................24Figure 27 FE Head Impact model (LS-Dyna Users conference, 2013).................................................25Figure 28 A typical HIC graph (LS-Dyna Users conference, 2013).....................................................25Figure 29 Mechanical properties of Steel and Aluminium (Safety science, 2016)...............................26Figure 30 Concept behind composite material for increased stiffness (Google images, 2016)............27Figure 31 Global stiffness Tests (LS-Dyna Users Conference, 2014)..................................................28Figure 32 Lateral and Stiffness tests from left to right (AutoSteel, 2014)............................................28Figure 33 Crash test simulation using LS –Dyna (Crash Test Simulation, 2016).................................29Figure 34 Implicit event modelling in ANSYS (Google Images, 2016)..............................................30Figure 35 Bonnet Outer Panel (GrabCAD, 2016).................................................................................31Figure 36 Bonnet Inner frame (GrabCAD, 2016)..................................................................................31Figure 37 Bonded contact region (Kevin, 2016)...................................................................................32Figure 38 Friction contact (Kevin, 2016)..............................................................................................32Figure 39 Left and Right Bonnet Hinge condition with DOF12346 = 0. (Kevin, 2016)..........................33Figure 40 Torsion tests boundary conditions (Kevin, 2016).................................................................33Figure 41 Transversal test boundary conditions with DOF12346 = 0 (Kevin, 2016)...............................34Figure 42 Transversal boundary conditions with DOF3 = 0. (Kevin, 2016)..........................................34Figure 43 Force applied for transversal test (Kevin, 2016)...................................................................34Figure 44 Meshed model – Outer panel (Kevin, 2016).........................................................................35Figure 45 Meshed model – Inner frame (Kevin, 2016).........................................................................35

Figure 46 Element quality (Kevin, 2016).............................................................................................36Figure 47 Element quality statistics (Kevin, 2016)...............................................................................36Figure 48 Perfect and ill conditioned elements (Kevin, 2016)..............................................................37Figure 49 Aspect ratio statistics (Kevin, 2016).....................................................................................37Figure 50 Skewness statistics (Kevin, 2016).........................................................................................37Figure 51Applied Equivalent impact force (Kevin, 2016)....................................................................38Figure 52 Applied equivalent impact force – directly above frame web (Kevin, 2016).......................38Figure 53 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................39Figure 54 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................39Figure 55 Total deformation – Transversal test (Kevin, 2016).............................................................40Figure 56 Total deformation – Torsion test (Kevin, 2016)....................................................................40Figure 57 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................42Figure 58 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................42Figure 59 Total deformation – Transversal test (Kevin, 2016).............................................................43Figure 60 Total deformation – Torsion test (Kevin, 2016)....................................................................43Figure 61 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................45Figure 62 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................45Figure 63 Total deformation – Transversal test (Kevin, 2016).............................................................46Figure 64 Total deformation – Torsion test (Kevin, 2016)....................................................................46Figure 65 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................48Figure 66 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................48Figure 67 Total deformation – Transversal test (Kevin, 2016).............................................................49Figure 68 Total deformation – Torsion test (Kevin, 2016)....................................................................49Figure 69 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................51Figure 70 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................51Figure 71 Total deformation – Transversal test (Kevin, 2016).............................................................52Figure 72 Total deformation – Torsion test (Kevin, 2016)....................................................................52Figure 73 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................54Figure 74 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................54Figure 75 Total deformation – Transversal test (Kevin, 2016).............................................................55Figure 76 Total deformation – Torsion test (Kevin, 2016)....................................................................55Figure 77 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................57Figure 78 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................57Figure 79 Total deformation – Transversal test (Kevin, 2016).............................................................58Figure 80 Total deformation – Torsion test (Kevin, 2016)....................................................................58Figure 81 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................60Figure 82 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................60Figure 83 Total deformation – Transversal test (Kevin, 2016).............................................................61Figure 84 Total deformation – Torsion test (Kevin, 2016)....................................................................61Figure 85 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................63Figure 86 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................63Figure 87 Total deformation – Transversal test (Kevin, 2016).............................................................64Figure 88 Total deformation – Torsion test (Kevin, 2016)....................................................................64Figure 89 Equivalent Von-mises – Transversal test (Kevin, 2016).......................................................66Figure 90 Equivalent Von-mises – Torsion test (Kevin, 2016).............................................................66Figure 91 Total deformation – Transversal test (Kevin, 2016).............................................................67Figure 92 Total deformation – Torsion test (Kevin, 2016)....................................................................67Figure 93 Strain energy – Steel Bonnet (Kevin, 2016)..........................................................................72

Figure 94 Strain energy - Iteration 5 (Kevin, 2016)..............................................................................72Figure 95 Total deformation – Steel Bonnet (Kevin, 2016)..................................................................74Figure 96 Total deformation – Iteration 5 (Kevin, 2016)......................................................................74Figure 97 Equivalent Von-mises – Steel Bonnet (Kevin, 2016)...........................................................76Figure 98 Equivalent Von-mises (Kevin, 2016)....................................................................................76Figure 99 Shock absorbing sandwich panels (SharePoint, 2016)..........................................................79Figure 100 The concept of shock absorber and uniform pattern across the frame (Google Images, 2016)......................................................................................................................................................79Figure 101 Traditional inner frame design (Google Images, 2016).....................................................79

List of Tables

Table 1 Average expense for all casualties (Accident prevention trust, 2014).....................................11Table 2 Average medical costs for a serious injury (Accident prevention trust, 2014)........................11Table 3 Lifelong expense due to serious brain injury (Accident prevention trust, 2014).....................11Table 4 Global Stiffness Test Reference values (LS-Dyna Users conference, 2013)...........................24Table 5 Stiffness comparison with reference values (Kevin, 2016)......................................................41Table 6 Stiffness comparison of Iteration 1 with reference values (Kevin, 2016)................................44Table 7 Stiffness comparison of Iteration 2 with reference values (Kevin, 2016)................................47Table 8 Stiffness comparison of Iteration 3 with reference values (Kevin, 2016)................................50Table 9 Stiffness comparison of Iteration 4 with reference values (Kevin, 2016)................................53Table 10 Stiffness comparison of Iteration 5 with reference values (Kevin, 2016)..............................56Table 11 Stiffness comparison of Iteration 6 with reference values (Kevin, 2016)..............................59Table 12 Stiffness comparison of Iteration 7 with reference values (Kevin, 2016)..............................62Table 13 Stiffness comparison of Iteration 8 with reference values (Kevin, 2016)..............................65Table 14 Stiffness comparison of Iteration 9 with reference values (Kevin, 2016)..............................68

List of Graphs

Graph 1 Stiffness comparison Transverse and Torsion (Kevin, 2016)..................................................41Graph 2 Stiffness comparison – Transverse and Torsion values (Kevin, 2016)...................................44Graph 3 Stiffness comparison – Transverse and Torsion (Kevin, 2016)...............................................47Graph 4 Stiffness comparison – Transverse and Torsion (Kevin).........................................................50Graph 5 Comparison of stiffness – Transverse and Torsion (Kevin, 2016)..........................................53Graph 6 Stiffness comparison –Transverse and Torsion (Kevin, 2016)................................................56Graph 7 Stiffness comparison – Transverse and Torsion (Kevin, 2016)...............................................59Graph 8 Stiffness comparison – Transverse and Torsion (Kevin, 2016)...............................................62Graph 9 Stiffness comparison (Kevin, 2016)........................................................................................65Graph 10 Stiffness comparison – Transverse and Torsion (Kevin, 2016).............................................68Graph 11 Stiffness comparison reference value, Steel bonnet and Iteration 5 (Kevin, 2016)...............70Graph 12 Structural weight comparison (Kevin, 2016).........................................................................70Graph 13 Strain energy comparison (Kevin, 2016)...............................................................................73Graph 14 Deformation comparison between Original Bonnet and Iteration 5......................................75

List of Abbreviations

EuroNCAP–European New Car Assessment Programme

VRU – Vulnerable Road Users

KSI – Killed or Seriously Injured

HIC – Head Impact Criterion

RAPT – Road Accident Prevention Trust

EPAOT - Environmental Protection Agency Office of Transportation and Air Quality

FE – Finite Element

EEVC–European Electric Vehicle Congress

ISO–International Organisation of Standardisation

ECU - Electronic Central Unit

HRIZ - High Risk Impact Zones

CAE – Computer Aided Engineering

IJERA–International Journal of Engineering Research and Applications

ETARD - Educational Technology Research and Development

ABSTRACT

Pedestrian head impacted collision is one of the major causes of severe pedestrian head injury

and fatality. The research study considers multidisciplinary design optimization methods for a

typical car bonnet system based on, pedestrian head protection along with the relevant

stiffness requirements. The static stiffness and an indication of the head form collision

procedures are fully analysed in accordance with the most recent regulations. Optimization

solution indicates that the optimum design achieves better head protection effect under the

premise of meeting the standard stiffness requirements. The design solution provides a total

weight reduction of 48% and increases energy absorption by 13% in comparison to the

original steel bonnet. This research demonstrates the procedures undertaken to identify an apt

replacement material combination which meets the standard stiffness regulations whilst

ensuring pedestrian safety and essentially reducing the financial costs revolving around

pedestrian fatalities.

Key Words: Finite Element, Static Stiffness Tests, Pedestrian safety Bonnet, Material Combinations

Chapter 1: Introduction

1.1Project IntroductionNowadays, commercial automobiles are expected to meet certain safety measures associated with pedestrian safety. Organisations such as EuroNCAP and other automotive safety assessment bodies perform several tests to examine the capability of a vehicle to protect VRU’s (vulnerable road users) during collision. Several safety testing requirements are outlined and meeting these standards is believed to help save the lives of VRU’s. To achieve the required structural performance, car bonnets are designed (according to active or passive safety concept) to absorb maximum deformation before the pedestrian’s head reaches the stiff underlying components of engine and thus reduces the chance for serious head injury or even fatalities. In recent years, excellent results in terms of VRU protection has been achieved through the active and passive design solution, states (European Vehicle Passive Safety Network, 2004). The improvement of the passive and active safety of actual vehicles is usually obtained by introducing new electronic and/or mechanical devices and consequently, increases the overall structural weight. It is evident that weight reduction and safety improvements are two fundamental, but opposite tasks in the design process of a new vehicle. With carmanufacturers investing a lot of money in an effort to reduce overall weight of a car, every opportunity for weight reduction is thoroughly investigated. “Lotus has set up an entire lightweight structures division, BMW is investing millions into carbon fibre and Jaguar shows a keen interest in aluminium” (2016, Autoblog).Virtual testing methodologies represent a very useful instrument in the search for optimal compromises in structural design, allowing engineers to evaluate several options such as the introduction of innovative materials to reduce the overall weight whilst meeting the required safety standards.

Additionally, fuel consumption associated with the increasing overall weight of cars has huge environmental impacts when considering the bigger picture. The increasing numbers of automotive and the overall weight are one of the common sources of pollution, according to (European Federation for Transport and Environment, 2006). Among the different sources of pollution, a great deal of attention is currently focused on the production of carbon dioxide (CO2), a greenhouse gas that is widely viewed as responsible for the climatic change of the planet. CO2 is a primary product of combustion, and, for this reason, its production is directly connected to fuel consumption and, consequently, to vehicle weight (Environmental Protection Agency Office of Transportation and Air Quality, 2014). The largest sources of transportation related greenhouse gas emissions include passenger cars and light-duty trucks. These sources account for over half of the emissions from the sector. Relatively small amounts of methane (CH4) and nitrous oxide (N2O) are emitted during fuel combustion. Therefore, vehicle weight reduction is one of the most important tasks in automotive design.

Typically a bonnet consists of an outer panel and the inner frame; where the inner frame is used for structural strength and the outer panel is used for the homogenous style and aerodynamics purposes. More than 70% of car bonnets are manufactured using mild steel or high strength steel which has an average weight of around 18kg, and the remaining 30% made of aluminium and in some rare cases composite materials. A combination of material may hold the key to reducing the structural weight of a car bonnet whilst ensuring the static stiffness requirements. Although the outer panel is less important as far as stiffness is concerned it has a vital role in pedestrian safety since the first contact surface is with the outer panel of the bonnet. Through this investigative study, a car bonnet will be subjected to static stiffness tests by means of finite element methodology in accordance to the most recent stiffness test regulations. The model will be experimentedwith varied material combinations and panel thickness in an effort to achieve maximum weight reduction whilst ensuring that the new material combination meets the static stiffness requirements regarding VRU protection.

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1.2Problem StatementIn the year ending September 2015, there were 1,780 reported road fatalities, a 3 per cent increase from 1,731 in the previous year. According to the data provided by Department for Transport UK (2015), a total of 23,700 people were killed or seriously injured (KSI casualties) in the year ending September 2015, and more than 60% of this KSI figure accounts for injuries and fatalities involving pedestrian head and vehicle front region. The statistical values show the importance in carefully designing a car bonnet with an apt material combination to absorb maximum kinetic energy and therefore avoid pedestrian fatalities or serious head injuries. Since high impacted head collision often lead to death, head injuries are considered to be the most severe injuries in pedestrian-car accidents. Head and face injuries in car–pedestrian accidents account for 60 per cent of all pedestrian fatal injuries of which 17.3 per cent of head injuries were due to the bonnet.  The fatality statistics emphasises the need to identify a suitable replacement material that offers maximum deformation during collision.A number of research studies have been undertaken to identify a suitable design that can reduce the HIC value. The deformation capability of a car bonnet depends on the global stiffness of the structure. By considering stiffness test methods, a system which provides just the adequate deformation needs to be identified.

Financial figures considering a typical admittance with severe head injury could add up to around £7000 for just three days at an intensive care unit, furthermore to the expenses involved, a total of around £45,000 for a typical rehabilitation process. However, if we consider a case study of a child involved in a serious collision which resulted in permanent damage to the brain, the lifelong expense adds up to around £5million, accumulating from factors such as medical, educational, loss of tax revenue, benefits due to unemployment, states “Road Accident Prevention Trust (2015)”. With an average number of five children involved in an accident within England on a yearly basis, the costs can add up to copious amounts.

The key to reduce the chances of fatality or severe head injury during a collision involving vehicle front region is to ensure adequate room between the bonnet and the stiff underlying components of a car engine, also it is equally important to make sure the material combination used is efficiently working to absorb maximum kinetic energy during the first point of impact. Since aluminium is generally a less stiff material, better deformation seems achievable, in other words aluminium bonnet may provide better energy absorption during a collision. However, due to static stiffness requirements of a car bonnet, the right panel thickness needs to be determined to provide the required Torsional and Transversal stiffness as well.

1.3Project Aims and Objectives

1.4 AimTo determine a suitable material combination for car bonnets which meets, the most recent static stiffness regulations and could potentially improve the energy absorption (in comparison with steel bonnets) during head impacted collision.

1.5 Objectives Reasons for the changes in car bonnet systems over time Statistical data regarding pedestrian accidents and fatalities EuroNCAP safety requirements and Static stiffness test regulations Reference values for the standard tests Standard FE bonnet stiffness testing methods Obtain a complete 3D model of a valid car bonnet for FE analysis To carry out Torsional stiffness analysis To carry out Transversal Stiffness analysis Analyse the mechanical behaviour of a bonnet made of steel, aluminium and a combination

of these materials

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1.6Description of ResearchInitially, a detailed research had been carried out to explore yearly pedestrian fatality rates and to identify the trends in KSI values in recent years. Financial figures associated with severe head injuries are analysed and a case study is used to demonstrate the life time costs for a permanent brain injury resulting from a fatal collision. The required statistical data will be collected from the “Reported road casualties Great Britain: annual report 2014” published by the Department for Transport.

A number of literatures will also be studied through the Anglia Ruskin University’s library website using a range of databases such as the open access journals, technical research archive, proquest dissertations and thesis and common internet search engines. A thorough research will be carried out to explore the most recent findings from similar research studies which will be incorporated to the current project. References used in published papers will be used to gather the most recent regulations and test procedures.

Using a comparison between the stiffness analyses methods used in similar literatures, the most appropriate stiffness analysis will be chosen and the corresponding test procedures and model setup will be researched. Reference values for a typical steel bonnet will also be obtained through relevant research. The reference values and stiffness test procedures are studied from published papers and EuroNCAP safety requirements will be identified from “Pedestrian Testing Protocol” published by EuroNCAP.

Information that needs to be obtained prior to undertaking the project are only collected from published papers, articles and documents provided by reliable organisations. Collecting the data in such a selective manner, the reliability of the information can be assured.

As the investigative study is focusing to optimize the material combination of car bonnets, Aluminium or a combination of aluminium and steel will be used to analyse the difference in stiffness compared to that of the original steel bonnet. Chapter 2 consists of a detailed research to identify the most up-to-date work undertaken and the conclusions derived. The chapter also details pedestrian-car accident statistics and the annual expenses associated with road accidents to further emphasise the importance of this research. Furthermore, the “Technical detail” chapter will be used to explain the functions of all components found in a typical car bonnet. Since the investigative study aims to perform static stiffness tests, of FE static stiffness test regulations will be explored and demonstrated together with EuroNCAP safety requirements as well as the stiffness reference values.

Chapter 4 the “Methodology”, demonstrates the methods that can be used to investigate the structural stiffness of a car bonnet. Furthermore, the particular tests selected to identify a suitable material combination will be outlined and the reasons for selecting those particular tests will also be justified.

To carry out the necessary finite element analysis, a standard 3D model of a car bonnet will be obtained. ANSYS-Static Structural will be used to perform Transversal and Torsion stiffness tests on the material combination with varied panel thickness as well. The results obtained from the FE analysis will be analysed to identify a combination that meets the required stiffness requirements and yet provides a significant structural weight.

Chapter 2: Literature Review

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2.1The LiteratureOver the last few years, increasing numbers of research study has been carried out by professional engineers and experts of the field to come up with design solutions which meet the safety requirements in favour ofVRU’s and also in relation to weight reduction and improved fuel consumption. Relevant research works are discussed in this chapter to identify the key principles and grasp a thorough understanding of the work done on the subject so far.

Dr.MehrdadAsadi, Department of Mechanical Engineering, Anglia Ruskin University (at present) identified an apt design solution by modifying the inner panel structure to achieve homogeneous stiffness across the whole bonnet and the design achieved more uniform energy absorption during head impacts.

Figure 1An example of a Passive designapproach (Encocam Ltd, 2015)

Physical testing was carried out upon FE analysis and the design proved to be a successful solution by achieving HIC values of 395 - 600. Future recommendations was also hinted stating that, excellent results in terms of absorbed energy could be obtained with a honeycomb sandwich panel, which can be placed between the skin and the inner panel of the bonnet (M. Asadi, 2011)

Jason A. Stammen, Roger A. Saul and Brian Khaveevaluated the standardised head impact test procedures by the ISO and EEVC. The work was undertaken by considering laboratory impact tests and Computer Aided Engineering (FE analysis). To confirm the findings of the tests both the physical tests and the results obtained from FE analysis were compared. For laboratory testing purposes, a complete model of the Ford Taurus’ bonnet was considered with three different locations identified as ‘A’, ‘B’ and ‘C’. These specific locations of the bonnet had different hood structure and clearance gap between the stiff underlying components below the bonnet.

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Figure 2The bonnet labelled with the chosen locations (SAS Tech Journal, 2012)

First point ‘A’ was considered as open impact area, where the hood had no reinforcement and had large clearance to the engine. The second point ‘B’ was the alternator impact point which had no reinforcement but less clearance with the alternator and the third point ‘C’ had heavy hood reinforcement with less clearance. The tested results showed higher HIC value at point ‘C’ (had the lowest clearance between the skin and the underlying stiff components) and then followed by points ‘B’ and ‘A’, the FE results correlated well with the physical test results as well. The similarity in results between the physical and FE testing encourages the use finite element methodology in finding solutions to similar engineering problems.

Tsukatada Matsumoto, KoushiKumagai and Hideaki Arimoto, has focused on the shape of the inner structure and has concluded that design modifications can be effective for pedestrian safety because, low HIC value was obtained while modifying the shape of inner structure. The section geometry of the hood inner frame has been optimised to achieve the targeting value (<1000) of HIC, where the height of cross section of the inner panel was 0.76 times smaller than the original one and width of the panel was 1.14 times larger than the original hood inner panel and the thickness of the panel was maintained the same. Finally the test results showed that the optimized shape has improved the probability of achieving the target HIC value by 60% to 99%.

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Figure 3Theinner frame designs (SAS Tech Journal, 2012)

The HIC value is directly proportional to stiffness and inversely proportional to the deformation of the hood. Thus in order to design the hood for pedestrian friendliness the inner panel of the hood which provides reinforcement to the outer hood panel is redesigned focusing on reducing the local stiffness of the hood and thereby increasing the deformation of the hood.

Dr. Grace Mary Thompson, ChristophKerkeling and Joachim Schafer focused on the structural hood concepts for pedestrian protection where they used two different concepts of hood in effort to replace the current bonnet system which was designed to meet the standard load cases. The work progressed with two inner panel designs, one with increased number of ribs and the other with multiple cone-like structures using aluminium for both designs.

Figure 4 Inner frame with multi cone design (Structural Hinge and hood concept, 2015)

The second design didn’t include any cut outs or discontinuity in the structure which meant that a more uniform stiffness was achieved through this particular design. Also necessary alternations could be easily made to achieve the reference stiffness values with this particular design.

Scattina A., Gaviglio I., Belingardi G., Chiandussi G., and Gobetto E, considered the redesign of bonnet aiming for lightweight structure and pedestrian safety. They analysed five different concepts with different materials for the inner and outer hood in which three of them showed promising design solutions. The first concept ‘C1’ was the inner hood with three long ribs which was made of short glass fibre polyamide that has good thermal properties and the outer skin was aluminium which offered a good pedestrian safety. In the second concept ‘C2’ the central portion of the inner panel was removed and the outer panel made of aluminium.

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Although concept ‘C2’ did not produce promising results, the conclusion drawn was that the use of aluminium is the best solution for achieving weight reduction and pedestrian safety.

Masoumi A., Mohammad Hassan Shojaeefard and Amir Najibi, compared and analyzed steel, aluminium and composite bonnet for pedestrian protection. Finite element model head impactor was created and impact simulation was performed on three bonnets with different materials; steel, aluminium and composite material. From the results obtained, it was concluded that use of aluminium bonnet resulted in lower HIC value and high energy absorption when compared to that of steel. In addition, it was 50% lighter than steel bonnet which proved that aluminium is an apt choice to make car bonnets. Whereas composite bonnet resulted in lowest HIC value and highest head displacement. The work concluded by suggesting further study on the subject by considering composite materials.

2.2Brief Review of the LiteraturesConsidering the literatures addressed in the above section, it is demonstrated that a vast amount of study is being dedicated by experts of the field to improve protective measures for the safety of vulnerable road users (VRU)and also to minimise the structural weight of car bonnets.

Dr.MehrdadAsadi’s work on the passive bonnet design approach shows a promising design solution that absorbs maximum kinetic energy before the head comes in contact with the stiff underlying engine components during impact to avoid fatalities. To accomplish such a solution, suitable replacement material needs to be identified for the inner frame which provides uniform global stiffness across the whole bonnet.

Research works undertaken by Dr. Grace Mary Thompson and Mohammed Hassan and many other experts of the field focuses on the redesign of the inner frame with an ambition to reduce the HIC values. The literatures discussed above seems to convey the importance to carry out further experiments and research studies considering different material combinations to achieve the required HIC values, however it is essential to ensure the material combination meet the static stiffness requirements as well.The work carried out by Mohammed Hassan, Department of Mechanical Engineering; University of Tehran reduced the weight of the steel bonnet by 50%, acquired low HIC values and also provided maximum highest head displacement during impact.

Focusing on the work carried out by Mohammed Hassan of Tehran University, it seems possible that the relevant stiffness may be achieved with a softer material (in comparison with steel) by controlling the thickness of the panel used. Through the course of this experimental study, both panels of a typical car bonnet will be experimented with a variety of material combinations and altered panel thickness to reduce the weight of the bonnet significantly whilst meeting the global stiffness requirements.

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2.3 Importance of ResearchPedestrians are extremely vulnerable group of road users, and pedestrian protection is becoming one of the major issues in traffic safety world‐wide. “A high percentage of pedestrians (60%) who roll on the bonnet of a car that is moving at more than 40mph are killed or suffer severe injuries” states M. Asadi Senior Lecturer of Anglia Ruskin University. Figure 5 below shows the comparison of fatality rate and serious injuries in relation to all road users. The data from the chart suggests that Vulnerable Road Users (VRU’s) are highly vulnerable to serious injuries.

The annual road fatalities data published by the department of transport of United Kingdom states that the number of fatalities has reduced from 2538 to 1713 between the years 2008 and 2013 and is continuously reducing by year due to traffic control measures and other forms of traffic protective measures. But the number of pedestrians surviving with serious injuries far exceeds than the number of fatalities and emphasises the seriousness of the problem. An apt design solution is imperative in the near future to reduce the number of fatalities and serious injury significantly from the figures at present.

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Figure 5 Statistical data on road accidents involving VRU (Department for Transport, 2015)

2.4 Statistical data associated with VRU fatalities and casualtiesReport published by the Department for Transport UK shows that the total number of VRU’s involved in serious accidents adds up to 25,000 in the year 2014. KSI values in the recent years raises alarming concerns for the safety of pedestrians.

In United Kingdom, the number of reported deaths (pedestrian-car front region collision) in 2014 increased by 4% in comparison to that of 2013. Figure 6 below shows a graphical representation of the data regarding the fatality trend from reported road accidents 2000 – 2014.

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Figure 6 Road accident casualties in Great Britain (Department for Transport, 2015)

The study carried out by the department of transport identified that “VRU’s accounted for around three quarters of the increase in fatalities between 2013 and 2014”. The number of pedestrian fatalities has increased by 12% from 398 in the year 2013 to 446 in 2014. Serious injury reported due to accidents involving pedestrians and automotive are also on the rise. A total of 1775 people were killed and there were nearly 23,000 seriously injured causalities reported in 2014. The chart below shows the comparison of road accident data between 2014 to those of previous years.

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Figure 7The rising trend in reported death (Department for Transport, 2015)

2.5 Rising trend in KSI Value: (2013 – 2014)

The significant rise in the accident figures between the years 2013 and 2014 seems to be very alarming. Although a great deal of countermeasures and interventions are put in place to reduce road accidents, the values visible from the chart above emphasises that furthermore needs to be done to limit the fatality rates and casualties due to pedestrian – car accidents.

2.6Costs associated with Pedestrian causalities“Families with disabled children usually earn between 15% and 20% less than other families due to loss of income from caring for their child.Expenditure of a typical day at a specialist unit from a serious incident costs the NHS £1,000 a day.” States Road Accident Prevention Trust

Almost all of the seriously injuredpedestrians will require significant amounts of long-term care such as outpatient appointments, surgical procedures, as well as the need of specialised medical equipments. Considering the costs associated with such long-term care, the expenses incurred can add up to staggering figures. As for an example, an article published by the “Road Accident Prevention Trust” states that the lifetime medical costs for one child with a severe traumatic brain injury comes to £268,000.

2.7 Financial figures for a typical severe brain injury caseA severe head injury can cause fatal damages to human brain. Every year in England, at least 5 people are hospitalised for intensive care due to a life threatening brain injury resulting from a collision involving car front region. Unless already at a hospital with PICU (Paediatric Intensive Care Unit) facility, the transportation cost to a tertiary facility costs around £2500 per transfer. The cost for one bed for a day at the PICU could cost just over £2300 and the average stay for a serious brain injury of three days adds up to just under £7000.

Furthermore, a pedestrian who have suffered brain injury are highly likely to be in the need for specialised rehabilitation such as physiotherapy, occupational therapy, speech and language therapy, and clinical psychology. A typical cost for one admission at a neurological rehabilitation unit per day costs around £450, considering a typical stay of around 100 days the final figure on average comes to around £45,000.

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Figure 8The recent rise in road accidents (Department for Transport, 2015)

2.8 Facts and figures considering Child-Car front collisionAs seen from Table 1 and 2above, on average around 2352 children are involved in serious accidentsevery year in UK. Taking the costs involved to consideration, it can be seen from table that the sum adds up to staggering figures.

2.9 Lifelong cost for a child with a serious head injury

Considering the lifelong costs for a child with permanent brain injury, the extra financial cost adds up to some serious figures. With a yearly average of around 6 children getting involved in serious head injury in UK itself, the financial costs incurred multiplies furthermore.

2.11Environmental Benefits from Weight ReductionWhen considering the statistics of greenhouse gas emissions 2014, CO2 makes up around 80% of UK’s total emissions. This is clearly evident from the pie chart shown below. The chart also gives information about the proportion of other greenhouse gases as well and clearly CO 2 is dominating in terms of proportion. In 2014, the UK net emissions of carbon dioxide were estimated to be 422.0 million tonnes (Mt)

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Table 1 Average expense for all casualties (Accident prevention trust, 2014)Table 2 Average medical costs for a serious injury (Accident prevention trust, 2014)

Table 3 Lifelong expense due to serious brain injury (Accident prevention trust, 2014)

Figure 9 Proportion of greenhouse gases emitted in 2014 (Department for Transport, 2015)

Figure 10The slight increase in emissions in transport sector (Department for Transport)

Greenhouse gas emissions from transportation have increased by about 16% since 1990. This historical increase is largely due to increased demand for travel and the limited gains in fuel efficiency across the globe.

Increasing the fuel efficiency of cars is one of the huge problems auto companies invest a lot of money in to be resolved.(Sustainable products, 2016) says that for every kilogram of vehicle weight reduction, there is a potential to reduce carbon dioxide emissions by close to 20 kilograms over the vehicle’s life span. Multiply that by the more than 600 million vehicles globally, and the benefits can add up.

Nowadays car manufacturers have keen interest in reducing the overall weight of the car to achieve better miles per gallon (MPG) value. Perhaps in the near future, as a result to this endeavour the fossil fuels used to run vehicles could be reduced substantially and the environmental benefits can add up. “Today, auto companies are putting a lot of effort into reducing weight. Lotus has set up an entire lightweight structures division, BMW is investing millions into carbon fibre andJaguar shows a keen interest in aluminium, because every ounce you take out of a car improves the vehicle's performance and fuel economy and significant reduction in greenhouse gas emissions when we consider the bigger picture” (Autoblog, 2016). The initiative taken by the major car manufacturers suggests that light weight cars are of high importance in the 21st century.

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Combining the environmental benefits and reduced pedestrian fatalities that can be achieved with the use of light weight – pedestrian friendly bonnet systems, it seems that the need to carry out this research study is inevitable.

Chapter 3: Technical Background

The initial stage of the chapter outlines the components and features of a standard car bonnet and describes the assembly process of the two panels of the bonnet. Design changes in car bonnets are illustrated through relevant images and the reasons for design changes are also outlined. The final stage of the chapter demonstrates the two major pedestrian safety design approaches practiced in the industry. EuroNCAP safety requirements and standardised static stiffness tests are also outlined together with reference values.

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3.1Features and Components of a Standard Car BonnetAs shown in the figure below, a complete bonnet system consists of an inner frame and an outer panel which are attached by a process called hemming (further discussed in the sections below), two hinges are used to fix the bonnet to the car body allowing rotation about a single axis. Then finally a latch attached with the bonnet to ensure the bonnet is firmly secure by the front end.

Figure 11 General Bonnet components (IJERA, 2011)

These four main components of the bonnet are as follows:

Outer panel and the Inner frame

The two main components of a car bonnet are the outer panel and an inner frame. The main purpose of the inner frame is to provide sufficient stiffness to the bonnet and also to hold the shape of the bonnet to a certain extent. For a number of decades car manufacturers have been using steel to produce inner frame and the outer panel because sufficient stiffness can be easily achieved with steel. However, nowadays car makers are keen on reducing the overall structural weight to increase car performance and fuel efficiency. In direct response to this aim, a range of materialsare being considered for the manufacture of car bonnets.

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Figure 12Bonnet Panels (IJERA, 2014)

A standard steel bonnet weighs around 16kg. The outer panel contributes to more than half of this figure (9kg). Taking this to consideration, the outer panel has the highest potential for weight reduction. Since the first point of contact of a pedestrian head during collision is on the outer panel, a softer material should be used to attain increased deformation. Using aluminium for both panels of the bonnet may provide the highest achievable deformation; however, the global stiffness (strength) of this particular combination needs to be evaluated in comparison to the strength of a steel bonnet.

Bonnet Hinges

Figure 13 Lightweight Bonnet Hinges (Picture courtesy, Kevin 2016)

Hinges are used to attach the bonnet to the carwith a single degree of freedom, ensuring the bonnet can be opened when necessary. Material choice for bonnet hinge should also be carefully considered because if the head makes contact with the bonnet directly above the hinge the outcome could mean fatal. Bonnet hinge concepts could be considered to evaluate localised stiffness at these particular regions. However, this work focuses on the global stiffness of a bonnet and therefore hinge concepts is to be omitted.

Latches and Pins

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The latching system is used in all cars to securely fasten the bonnet of a car. As shown in the picture below, the steel latch is bolted on to the bonnet panel. The open close mechanism of the latching system ensures the bonnet stays firmly latched once it is closed and therefore prevents the bonnet from flying off whilst driving. To ensure the latch system doesn’t wear away over time, latches (made of steel) are bolted to the inner surface of the steel bonnet panels.

Figure 14Bonnet Latch System (Picture Courtesy, Kevin 2016)

However, in the rare cases of retrofitting an aftermarket/lightweight bonnet, it may be necessary to use additional hood pins to latch the bonnet safe and secure. Especially with fibre glass/carbon fibre bonnet, a piece of steel is bonded to the panels and over time the bond can become weak therefore it is essential to use additional hood pins to secure the bonnet. Figure 15 shows a standard set of additional hood pins that are used by car drivers.

Figure 15 Additional hood pins (AutoSteel, 2015)

Figure 16 below, shows an aftermarket bonnet being firmly latched with the use of additional hood pins.

Figure 16 Additional Pins latching a bonnet (Motorworks, 2016)

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Most cars do not require additional hood pins but they are the only way to make sure that the bonnet is firmly fastened in the case of aftermarket bonnets. If additional hood pins are not used, then there is a high risk of the bonnet flying off whilst being driven.

3.2Assembly Process of the Bonnet Panels and the effect in Stiffness

Hemming

Hemming is the process routinely carried out in bonnet manufacturing process. Specially prepared versions of standard automotive alloys are typically used for panels which requires flat hemming (bonnets, boot lids and doors).

The outer and inner panels of the bonnet and boot lid are typically attached together using thehemming operation at the edges. The front and upper edges are always hemmed by foldingthe outer panel around the inner panel. Figure 17 illustrates the fundamental concept of hemming process.

During hemming the outer surface of the material is plastically deformed. The metal panels must undergo plastic deformation process to ensure the folded panels stays in the required shape. However, during the process the localised stiffness of the structure increases as a result. Thus the manufacturing process used to bind the two panels further increases risk of head injury, due to increased local stiffness.

Spot Welding in Car Bonnet

Spot welding is a common practise in the assembly process of car bonnet panels, the two panels are usually spot welded at the region where, the rib of the inner frame comes in direct contact with the outer panel. Figure 18 illustrates the spot welded regions in red for a particular bonnet.

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Figure 17 The concept of Hemming process (Bonding Processes, 2006)

Figure 18 Spot welded region (Google Images, 2016)

During the FE analysis, it is important to consider the spot weld connection and this particular connection will be replicated to the FE model using a bonded connection.

3.3 Significant Changes in Bonnet DesignTo satisfy a number of criterias and requirements the general design of car bonnets have changed over the last few decades. Figure 19 below the changes in the design of car bonnets over the last 60 years.

Figure 19 Changes in Bonnet Designs (Google Images, 2015)

The three main reasons for the significant changes in the design of car bonnets seem to be to satisfy standardised pedestrian safety requirements, and also for aerodynamic and styling purposes.As shown in figure 19 the general bonnet design in the 1950’s used to be disadvantageous in terms of aerodynamics due to the blunt front end of the bonnet as well as not very appealing visually either. To compromise this problem, the bonnet design was gradually modified to achieve better aerodynamic results and also to look more stylish in comparison. The common bonnet design used by car manufacturers in the 1970’s looks more efficient in terms of aerodynamics as opposed to the common design in the 50’s. However, towards the beginning of the 21st century demand for more stylish cars increased and in effect the design of car bonnets was also further modified.

Considering the high rates of pedestrian-automotive collisions and fatality rates, research studies and investigations were initiated to design pedestrian friendly bonnets.The European Enhanced Vehicle Safety Committee has developed test procedures to assess the level of pedestrian protection for vehicle fronts.Based on pedestrian kinematics during impact, vehicle hood is the critical area where pedestrian head hits and thus causes head injury. Hood performance demands energy absorption capacity and sufficient clearance space between hood and the stiff underlying engine components.

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Over time, design was optimized for better energy absorption capability during pedestrian head impact thus leading to lower HIC values. Various shape changes, hood inner patterns and even different materials such as aluminium and carbon fibre composites are utilized to improve hood performance (Gupta 2014).Taking the safety requirements to consideration, car bonnets are determined to undergo further design changes. Two major safety design approaches are being practised in the car industry nowadays.

3.4 Bonnet Design Approach Based on Pedestrian SafetyDuring pedestrian involved accidents, the pedestrian’s head collides with the hood and applies a dynamic force on to the hood. Since previous bonnet designs had little distance between the bonnet and the engine directly below, any impact with the bonnet pose high probability for serious head injury. A lot of research has already been undertaken to identify ways to improve the bonnet design in terms of pedestrian safety. To satisfy all mechanical property requirements and standards raised by the regulations, two particular design approaches are in practice nowadays.

3.5 Active Design ApproachActive bonnet system works by a mechanism where the bonnet hinges pop up to lift the bonnet by the rear to provide more clearance space during head impact (Huang and Yang, 2009). The active bonnet system consists of the hinge and an actuator under the bonnet. When a pedestrian collides with the vehicle, a sensor attached to the bumper detects the collision and sends a signal to an electronic central unit (ECU). The ECU determines whether or not a pedestrian accident occurs and the actuator is fired and lifts the bonnet using the firing pressure of the gunpowder in the actuator.

Figure 20Active Design Approach (EuroNCAP, 2016)

Based on preliminary work done on active bonnet system, it was shown that a lifted bonnetcould reduce the HIC significantly. Optimization work was also done and concluded

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that by increasing the lift speed and lift height, HIC could be further improved. However the success of an active bonnet system depends on the ability of sensor system to detect the pedestrian and trigger the bonnet deployment.

3.6Passive Design Approach

Figure 21 Passive Design Approach (EuroNCAP, 2016)

Crash specialist Cellbond, based in Huntingdon, Cambridgeshire, has collaborated with researchers at Anglia Ruskin University’s Engineering Simulation Analysis and Tribology (EAST) group to develop and test a prototype based on passive design. Dr.MehrdadAsadi, the engineer at Cellbondwho directed the project states that “During an impact the pedestrian exerts a dynamic force on the car bonnet, If the kinetic energy of the impact is not absorbed the bonnet will exert equal amount of the force that impacts it, causing severe injury”

The passive bonnet design invloves the development of a bonnet system to absorb as much kinetic energy as possible to ensure the reaction force from the bonnet to the pedestrian head during collision is reduced to an acceptable level and therefore prevent serious head injury to pedestrians during collision.

3.7Importance of Lightweight Structure with Adequate StiffnessThe importance in having a lightweight car hood is to improve fuel consumption of vehicles. Increasing the fuel efficiency of cars is one of the huge problems auto companies invest a lot of money in to be resolved. (Sustainable products, 2015) says that for every kilogram of vehicle weight reduction, there is a potential to reduce carbon dioxide emissions by close to 10 kilograms over the vehicle’s operating life. Multiply that by the more than 600 million vehicles globally, and the benefits can add up. Thus it is evident that, every successful action taken towards weight reduction is beneficial to not only drivers (economically) but also greener for the environment on the long run.

During accidents involving VRU’s and automotive the head makes contact with the bonnet and if there is insufficient clearance between the bonnet and the underlying stiff engine components, then fatality or serious head injury to VRU is certain. Also if the point of impact is directly above the stiff ribs of the inner frame, this also increases the chances for head injury as the structure may not deform enough absorbing the kinetic energy at the local point of impact. Such particular points on a bonnet are called the High Risk Impact Zones. When designing car bonnets, it is important to allow sufficient clearance between the bonnet and the underlying stiff components and also to ensure uniform stiffness across the whole bonnet ensuring maximum kinetic energy absorption.

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Figure 22 High Risk Impact Zones (Google Images, 2016)

On the other hand it is equally important to minimise the local stiffness and to reduce the number of high risk impact zones to minimise damage to pedestrian during collision. Crossing both the upper and lower bounds of stiffness will raise safety concerns for both drivers and pedestrians during collisions.However, considering pedestrian safety, it would be more beneficial to design a bonnet that has even stiffness across the whole bonnet as; during collision if head impacts directly to any of the stiff areas, it could cause serious head injury to pedestrians.

3.8 EuroNCAP and EEVC Requirements

Figure 23 Car front safety assessment and criteria (EuroNCAP 2004)

The European new car assessment programme (EuroNCAP) is a car safety programme based in Brussels (Belgium), founded in 1997 by the Transport Research Laboratory for the UK Department for Transport. The programme assesses new cars within the Europe for safety from a VRU’s point of view. The series of pedestrian safety tests performed analyses the risk of injuries that can be incurred to pedestrians head, legs and pelvis. The tests analyses these safety measures by considering bumpers, bonnet leading edge and the bonnet of each model. This is done by deploying dummy body parts such as legs and head forms at the specified areas. Accident tests are simulated at 40km/h with both adult and child head forms.

Upper and lower leg from tests are also in practise to analyse the safety feature of bumpers used in cars to protect lower body of pedestrians.

Head Impact Criteria (HIC) is used by EuroNCAP to analyse the safety offered car bonnets to pedestrian’s brain during collision. HIC values of more than a 1000 suggest high probability for serious head injury. Therefore during the vehicle testing processes lowest possible HIC values are

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preferred since the lower the HIC lower the probability for serious head injury to pedestrians. HIC criterion is further discussed in the sections below.

Measuring devices included inside the dummy parts record the severity of impact, and the results are used to rate each car with a safety rating system.

3.9Standardised Static Stiffness Testsand Reference ValuesThe most common method of stiffness testing of a bonnet is through the analysis of its structural stiffness. Three particular loading cases are used to perform the individual stiffness tests. Three different loading cases are used to perform the structural stiffness tests. In all test configurations the outer panel will also be fixed as appropriate. The three subjected testes are explained below.

3.10 Lateral Stiffness Test

Figure 24 Lateral Stiffness Test (Abaqus Users Conference, 2008)

The lateral stiffness method is used to analyse the bending stiffness of the side beams of the hood. As evident from the figure above, the hood will be fixed at four positions with the labelled degrees of freedom (The degrees of freedom of the front fixed points are different to the ones at the rear end) because, the bonnet will be fixed with rear hinges which restricts motion in all six directions whereas, support points are used with a more flexible degree of freedom. The load is also applied, however, it is noted that the force applied is not point loading and that; the load is applied on to a number of nodes. The force applied and the deflection values are used to plot a stress strain curve and thus the lateral stiffness can be calculated.

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3.11 Transversal Stiffness Test

Figure 25 Transversal Stiffness Test (Abaqus Users Conference, 2008)

Similarly to that of lateral stiffness test, four fixed points (two similar fixed points with same degrees of freedom) are used in transversal stiffness test as well. However, the magnitude of the load applied and the location of the load applied is different. In this particular test, the bending stiffness of the front portion of the bonnet is investigated. The load is applied as per evident from the figure and the stiffness value is calculated.

3.12 Torsional Stiffness Test

Figure 26 Torsional Stiffness Test (Abaqus Users Conference, 2016)

The Torsional stiffness test offers a great indication of the total stiffness of the entire hood structure. With three fixed points on the panel, a load of 100N is applied and the structural analysis of the body is performed.

Reference values for all three stiffness tests

The obtained stiffness reference values will be used in the Finite Element work associated with this study. The table below shows the reference values for three different stiffness tests.

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F =150 N

Table 4 Global Stiffness Test Reference values (LS-Dyna Users conference, 2013)

3.13Importance of the specific stiffness tests

The stiffness test methods outlined in the above sections are performed usingFinite element methodology. Although physical test methods are available to examine the strength provided by the structure, FEA methodologies are morefavoured option as this eliminates the need to manufacture a modified bonnet and to perform tests on each design. Considering the financial and time aspects, FE test methods are far more financially feasible testing method than physical stiffness tests.

Abiding to the stiffness tests mentioned above is import as the validation of the model, steel bonnet will be constrained to achieve the reference values obtained, and thereafter further optimization process can be considered.

Provided the real world conditions are replicated in the FEA packages being used, several tests can be performed to gather the data we require with high accuracy. Considering the cost and time to perform both physical and CAE testing, it is very clear that the benefit of FEA testing outweighs those of real life physical tests.

3.14Head Impact Performance Criteria (HIC)The head impact performance test is a dynamic testing process to analyse the pedestrian safety feature of the bonnet. In the industry the test is either carried out physically or by finite element methodology using a valid car bonnet model and a verified head form impactor model. Figure 27 shows a typical setup of the test in a relevant FE package.

Figure 27 FE Head Impact model (LS-Dyna Users conference, 2013)

The head injury criterion is used to measure the likelihood for head injury due to pedestrian impact on a moving vehicle. Equation 1 shown below describes the head impact criterion.

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1

Equation 1 Head Impact Criterion (LS-Dyna Users conference, 2013)

The criterion is in the form of definite integrals and therefore the area under the curve represents the HIC value. ‘a’ represents the value of standard acceleration due to gravity and t1 and t2 are the time limits of the definite integrals. The criterion is better explained with the aid of the graph shown below.

Figure 28 A typical HIC graph (LS-Dyna Users conference, 2013)

The Y-axis in the graph represents ‘a’ the standard acceleration due to gravity (9.81m/s2), the ‘x’ axis in the graph is the time measured in milliseconds. The values, t2 and t1 are the final and initial times of the interval in which HIC attains a maximum value. Since the concept of the criterion consists of integration, the area under the curve within the initial and final limits represents the value of HIC.Considering the time intervals between the firing of head form and impact point during the impact test, a HIC graph is produced (similar to that shown in figure 28), by numerical methods, the area under the curve is evaluated and is represented as the HIC value. A HIC value of 1000 typically means that, 18% probability for fatal head injury, 55% probability for serious injury, 90% probability of moderate injury.

3.15Material specification

Steel and Aluminium

As mentioned in the previous sections, particular grades of aluminium and steel are usually preferred for themanufacture of car bonnets. The fundamental mechanical properties of these two materials are given in the table above.

1 a is the acceleration due to gravity = 9.81ms-2

t = time in milliseconds

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Figure 29 Mechanical properties of Steel and Aluminium (Safety science, 2016)

Considering the knowledge grasped from literatures and ongoing research it seems logical to focus this investigative study on aluminium since they seem to provide promising results. Although aluminium is relatively cheaper than steel in general, the benefits offered by aluminium in mechanical properties easily outweigh the cost aspect.

Composite Materials

Materials including Honeycomb structures, glass-reinforced plastic (also known as fibreglass), carbon fiber reinforced plastic, may be considered since the unique stiffness to weight ratio of these structures/materials could potentially provide sufficient stiffness with significantly reduced weight.

Composite materials are an effective solution for many engineering problems nowadays. The biggest advantage with composite materials is that they are extremely light and yet provides respective structural strength. By choosing an appropriate combination of matrix and reinforcement material, a new material can be produced which processes the required mechanical properties of a particular application. Thus by tailoring the needs composite materials may indeed be able to provide a suitable lightweight material which provides just the adequate stiffness to satisfy global stiffness requirements.

Figure 30 Concept behind composite material for increased stiffness (ETARD, 2016)

However, considering the cost aspect of composite materials, although the resulting material is efficient, the raw material required are often more expensive in comparison to aluminium. Purely because of the expensive nature of these materials, composites will not be considered in this work.

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Chapter 4: Methodology

A range of global stiffness test methods and simulation packages are presented in the initial stages of this chapter. The benefits of FE testing over real life stiffness testing methods are outlined. Chosen FE tests and the chosen simulation package will also be discussed. Preparation of the model for simulation analysis including mesh quality checks and model setup is explained as well.

4.1 Static Stiffness Test MethodsNowadays, FE methods prove to be powerful instruments in solving many engineering problems. Since the resource and financial benefits of FE analysis significantly outweighs that of physical stiffness testing, Finite element method is chosen to find a suitable material combination through the relevant stiffness tests.

Often the structural strength and pedestrian safety feature of car bonnets are measured by means of static stiffness tests and dynamic head impact tests respectively. However, since the main focus of the project is to identify a suitable material combination, structural stiffness is subjected to evaluation. To evaluate the structural strength of a car bonnet, standardised stiffness tests can be utilised. Figures below demonstrate a range of structural stiffness tests that are practised in the automotive industry to measure the stiffness of car bonnet.

Global Stiffness Tests

28Figure 31 Global stiffness Tests (LS-Dyna Users Conference, 2014)

Usually a single torsion test and a choice of either the lateral or transversal test are sufficient enough to fully assess the structural strength of a car bonnet. Therefore torsion test 2 from figure 31 and transversal testshown in figure 32 will be used to analyse the difference in strength variation with material combinations. Details of the two tests are further discussed in the sections below.

Furthermore, upon identification of an optimum combination which provides acceptable strength, an indication of the energy absorption capability of the combination will also to be explored. A simplified static code is intended to be performed. By considering the parameters (such as mass and size of an adult head form, velocity at which the head form is fired) used in a head impacted test, an equivalent force is to be determined and applied to the surface of the bonnet. The resulting strain energy will be used to show an indication of the energy absorption capability; however energy absorption results can only be verified by means of dynamic head impact analysis.

Appendix 1 demonstrates more detail.

4.2 Finite Element PackagesANSYS and LS-Dyna are Finite element packages than can be used for simulation analysis. Both packages will be analysed to select the most appropriate package for the simulation work involved in this study.

LS-DYNA

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Figure 32 Lateral and Stiffness tests from left to right (AutoSteel, 2014)

Figure 33 Crash test simulation using LS –Dyna (Crash Test Simulation, 2016)

Automotive industry uses a range of 3D CAD packages and FE analysis purposes. LS-DYNA is one of the most powerful simulation software packages with a particular emphasis in explicit solver. For the same reason, it is a common simulation package used for crash/impact testing purposes. The package also have the ability to model static (implicit events), but is generally considered weaker in comparison to other packages such as ANSYS. However, due to high system specification requirements and license limitations, LS-Dyna is not a suitable choice of FE analysis in this research.

ANSYS Workbench – Structural Steel

In comparison to LS-Dyna, ANSYS is weaker to analyse the behaviour of large rigid bodies undergoing dynamic state. However, this software is a general purpose FE package which offers strong potential for the analytical study of objects experiencing deformation and the coinciding stress distribution. A typical field of application is the study of strength of components.ANSYS Workbench is an adequate choice due to the ease of use and license requirements. Static structural of ANSYS workbench will be used to perform all simulation tests.

Considering the advantages offered by ANSYS in modelling implicit events, the Finite Element work involved in this study is to be carried out with ANSYS Workbench. Due to licensing limitations the ANSYS workbench 16.2 the student version will be used to perform the static stiffness tests.

Total deformation and equivalent von mises readings will be considered for every combination experimented. Von mises stress will be used to ensure the material is capable of withstanding the applied force without experiencing plastic deformation and total deformation will be used to determine the corresponding stiffness of the bonnet.

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Figure 34 Implicit event modelling in ANSYS (ANSYS Simulations, 2016)

4.3 The 3D CAD ModelTo perform the FE stiffness tests, a 3D bonnet model had to be obtained. A complete model which consists of the outer panel and the inner frame has been obtained through a 3D model database. Figures below shows the panels obtained from GrabCAD.

The car bonnet displayed above was modelled using Catia V5R12. The latches and hinges of the bonnet are omitted from the model since the effect of these parameters can be included by means of appropriate boundary conditions. Since redesign of the structure is not an objective of the work, further modifications are not to be considered. The model was designed by means of surface modelling which enables to control panel thickness in ANSYS workbench.

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Figure 36 Bonnet Inner frame (GrabCAD, 2016)

Figure 35 Bonnet Outer Panel (GrabCAD, 2016)

4.4 ANSYS Workbench Model SetupTo carry out the necessary static stiffness tests, the model needs to be set up and constrained so that the ANSYS model replicates the behaviour of a real life bonnet undergoing the same stiffness tests. To ensure the model deflects in the appropriate manner, bonded and frictional contact regions have been used.

Bonded Contact Region

Bonded region has been added to the model to resemble the spot welded regions of a car bonnet. The area where the outer panel comes in direct contact with the inner frame is typically spot welded to fully attach both panels of the bonnet. The bonded connection ensures the panels in the ANSYS model are attached and hence prevents separation between the panels during stiffness analysis.

Frictional Contact Region

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Figure 37 Bonded contact region (Kevin, 2016)

Figure 38 Friction contact (Kevin, 2016)

With the use of frictional connection between the panels, merging of the two panels into each other was prevented. This was a recurring problem without the use of a frictional contact during the initial stages of the simulationprocess. This particular connection wasintroduced with a friction coefficient of 0.2 to ensure both panels are being treated as solid objects.

4.5 Boundary Conditions for Torsion Test

In accordance with the standard torsion test boundary conditions, displacement constraint that permits

rotational movement in the “Y” axis is applied at the locations of the hinges and all other displacements are constrained to 0. The displacement used at the front left region of the bonnet permits displacement in all axes except from the “Z” axis. Finally a force of 100N is applied to the front right region of the bonnet as per described in the torsion test requirements.

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Figure 39 Left and Right Bonnet Hinge condition with DOF12346 = 0. (Kevin, 2016)

Figure 40 Torsion tests boundary conditions (Kevin, 2016)

4.6 Boundary Conditions for Transversal Test

In accordance with the standard transverse test boundary conditions,

displacement constraint that permits rotational movement in the “Y” axis is applied at the locations of the hinges and all other displacements are constrained to 0. The displacement used at both sides of front region of the bonnet permits displacement in all axes except from the “Z” axis. Finally a force of 150N is applied to the front middle region of the bonnet as per described in the transverse test requirements.

4.7 Meshing of the ModelThe model was meshed with an element size of 12mm, the chosen element size proved to have adequate mesh quality through relevant mesh quality checks. Figures below shows the meshed ANSYS model

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Figure 41 Transversal test boundary conditions with DOF12346 = 0 (Kevin, 2016)

Figure 42 Transversal boundary conditions with DOF3 = 0. (Kevin, 2016)

Figure 43 Force applied for transversal test (Kevin, 2016)

Figure 44 Meshed model – Outer panel (Kevin, 2016)

Figure 45 Meshed model – Inner frame (Kevin, 2016)

Mesh quality checks were performed by considering element quality, aspect ratio and skewness.

4.8 Mesh Quality ChecksMesh quality checks such as Element quality, Aspect ratio and Skewness was analysed and the results are shown below.

35

Element Quality

Figure46 Element quality (Kevin, 2016)

Figure 47 Element quality statistics (Kevin, 2016)

Element quality of the mesh shows an average value of 84%. Typically a successful mesh is considered to have most elements with more than 70% element quality. The low standard deviation value of 0.19 also points out that most of the elements are dispersed around the 80% quality region.

Aspect Ratio

Equilateral elements are preferred from a mesh for analysis purposes, because the aspect ratio of equilateral elements is 1. High aspect ratio

36

represents the presence of ill conditioned elements which are non-equilateral elements. The table below shows the aspect ratio statistics for the meshed model.

Figure 48 Perfect and ill conditioned elements (Kevin, 2016)

Figure 49 Aspect ratio statistics (Kevin, 2016)

Skewness

Generally a maximum skewness value of 0-0.75 is considered acceptable. The maximum skewness value of the meshed model is 0.72 and is therefore acceptable to perform analysis.

Figure 50 Skewness statistics (Kevin, 2016)

Considering all three of mesh quality checks, it is evident that meshed model is meeting the standard requirements. With the adequate mesh quality, the model is prepared for stiffness analysis. Initially stiffness analysis of an original steel bonnet will be examined followed by material combinations in an effort to find an efficient replacement material combination.

37

A maximum value of 3.7 for the aspect ratio indicates the presence of ill conditioned elements within the meshed model; however, the mesh quality is still adequate as the maximum value is kept below 4 with 12mm element size.

Having this information, an indication of the combination’s energy absorbing capability was also examined by means of static test and by investigating the corresponding strain energy results.

4.9 Static Impact Analysis Set up - (An indication of energy absorption capability)

Setting up the model

Figure 51Applied Equivalent impact force (Kevin, 2016)

Figure 52 Applied equivalent impact force – directly above frame web (Kevin, 2016)

A nodal force of 3552N (See Appendix 1 for details) was applied at the nodes selected (shown in figures 51 and 52). Strain energy, deformation and stress distribution analysis are to be examined

Chapter 5: Finite Element AnalysisA standard steel bonnet is used to compare the stiffness values between a typical steel bonnet and the obtained stiffness values.

38

5.1 Original Bonnet (Steel): 0.6 mm Steel Outer Panel with 0.55mm Steel Inner Frame.

Stress Distribution

Figure 53 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 54 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total Deformation

39

Figure 55 Total deformation – Transversal test (Kevin, 2016)

Figure 56 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 16mm for the torsion test and 2.7mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

Stiffness Analysis

40

The stiffness values of the Steel bonnet from the analysis are 58Nmm-1 and 6.2Nmm-1 respectively. Comparing these values to the reference stiffness values, it is seen that the Steel bonnet meets the stiffness criteria with a negligible degree of error. A combined total of +/-23% error is considered acceptable according to the source of the reference values and hence the stiffness results achieved are considered to be representative of a steel bonnet.

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Original Bonnet Stiffness(N/mm) 58 6.2

% Error 4% 10%

Table 5 Stiffness comparison with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

60

7

58

6.2

Stiffness comparison between Reference Bonnet and Original Bonnet (Steel)

Reference Value Original Bonnet (Steel)

Stiff

ness

(N/m

m)

Graph 1 Stiffness comparison Transverse and Torsion (Kevin, 2016)

From the graph shown above, it is evident that the results obtained are very close to the reference values. The combined errors in the values obtained add up to 14% (below the limits of acceptance). The results also confirms the validity of the mesh used as the stiffness results obtained with the steel bonnet is as per expected.

5.2 Material CombinationsIteration 1: 0.72mm thick Aluminium Panel with 0.72mm thick Aluminium inner frame

41

Stress Distribution

Figure 57 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 58 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total Deformation

42

Figure 59 Total deformation – Transversal test (Kevin, 2016)

Figure 60 Total deformation – Torsion test (Kevin, 2016)

The stiffness analysis shows a deformation of 21.6mm for the torsion test and 2.7mm for the Transversal test. The associated stiffness values have been calculated and relevant comparisonsare made with the reference values.

43

Stiffness Analysis: Iteration 1

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 1 Stiffness(N/mm) 56.4 4.76

% Error 6% 32%

Table 6 Stiffness comparison of Iteration 1 with reference values (Kevin, 2016)

Stiffness values obtained shows almost negligible error with regards to Transversal test, however, the marginal error in Torsion stiffness means that this particular combination is not acceptable with the given panel thickness. Further investigationon the combination is demonstrated under altered panel thickness in the later part of the analysis.

Transverse Torsion0

10

20

30

40

50

60

60

7

56.4

4.76

Stiffness comparison between Reference bonnet and Iteration 1

Reference Value Iteration 1

Stiff

ness

(N/m

m)

Graph 2 Stiffness comparison – Transverse and Torsion values (Kevin, 2016)

From the graph shown above it can be seen that, the combination does not provide sufficient stiffness to be accepted. Increasing the panel thickness could significantly reduce the deformation value and essentially increase the stiffness of the bonnet.

Iteration 2: 0.72mm thick Aluminium Panel and 0.72mm thick Steel inner frame

Stress Distribution

44

Figure 61 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 62 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total Deformation

45

Figure 63 Total deformation – Transversal test (Kevin, 2016)

Figure 64 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 11mm for the torsion test and 1.4mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

Stiffness Analysis: Iteration 2

46

The transversal stiffness of 108.6Nmm-1 and 9.4Nmm-1 of torsion stiffness shows the material combination offers inadequate deformation.

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 2 Stiffness(N/mm) 108.6 9.4

% Error 81% 35%

Table 7 Stiffness comparison of Iteration 2 with reference values (Kevin, 2016)

Transverse Torsion0

20

40

60

80

100

120

60

7

108.6

9.4

Stiffness comparison between Reference value and Iteration 2

Reference Value Iteration 2

Stiff

ness

(N/m

m)

Graph 3 Stiffness comparison – Transverse and Torsion (Kevin, 2016)

According to the stiffness values obtained from the analysis of this particular combination, it is evident the bonnet is too stiff. The marginal error from both stiffness tests means this particular combination cannot be considered acceptable. Panel thickness can be reduced to increase the deformation which will be considered in the later session.

Iteration 3: 0.72mm thick Steel panel with 0.72mm thick Aluminium inner frame

47

Stress Distribution

Figure 65 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 66 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total Deformation

48

Figure 67 Total deformation – Transversal test (Kevin, 2016)

Figure 68 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 17mm for the torsion test and 2.1mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

Stiffness Analysis: Iteration 3

49

The total percentage error from both tests adds up to 34%, which indicates that iteration 3 cannot be considered acceptable as well with the given panel thickness.

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 3 Stiffness(N/mm) 71 5.92

% Error 19% 15%

Table 8 Stiffness comparison of Iteration 3 with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

70

80

60

7

71

5.92

Stiffness comparison between Reference value and Iteration 3

Reference Value Iteration 3

Stiff

ness

(N/m

m)

Graph 4 Stiffness comparison – Transverse and Torsion (Kevin, 2016)

Comparing the stiffness value of iteration 3 and the reference value, it is seen that the transversal stiffness is higher than that of reference but for torsion test, stiffness is lower than that of the reference value. Any effort in reducing the transversal stiffness will result in a higher percentage error for the torsion stiffness value and vice versa.

Further analysis is performed on Aluminium bonnet and Aluminium panel with Steel frame combination to improve the stiffness results by controlling the panel thickness.

5.3Material Combinations with altered Panel thicknessIteration 4: 1.3 mm thick Aluminium Panel with 0.75mm thick Aluminium inner frame

50

Stress distribution

Figure 69 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 70 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total deformation

51

Figure 71 Total deformation – Transversal test (Kevin, 2016)

Figure 72 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 17.5mm for the torsion test and 2.3mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

52

Stiffness Analysis: Iteration 4

Adjusting the panel thickness seems to have had a massive improvement in the stiffness results with some errors in comparison to the reference values. Further analysis needs to be done to further reduce the error between the result and the reference figures.

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 4Stiffness(N/mm) 65 5.7

% Error 8% 19%

Table 9 Stiffness comparison of Iteration 4 with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

70 60

7

65

5.7

Stiffness comparison between Reference value and Iteration 4

Reference Value Iteration 4

Stiff

ness

(N/m

m)

Graph 5 Comparison of stiffness – Transverse and Torsion (Kevin, 2016)

The overall percentage error has been significantly reduced with iteration 4, however a total of 27% is just over the limit of acceptance and therefore further improvements needs to be done to increase the Torsional stiffness value whilst maintain the current transversal stiffness figure.

Iteration 5: 1.2mm thick Aluminium Outer panel with 0.8mm thick Aluminium inner frame

Stress distribution

53

Figure 73 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 74 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total Deformation

54

Figure 75 Total deformation – Transversal test (Kevin, 2016)

Figure 76 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 17mm for the torsion test and 2.6mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

55

Stiffness Analysis: Iteration 5

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 5Stiffness(N/mm) 56 6

% Error 6% 14%

Table 10 Stiffness comparison of Iteration 5 with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

60

7

56

6

Stiffness comparison between Reference value and Iteration 5

Reference Value Iteration 5

Stiff

ness

(N/m

m)

Graph 6 Stiffness comparison –Transverse and Torsion (Kevin, 2016)

With an increased inner frame thickness, the percentage error has been reduced significantly. The percentage error found between the reference value and iteration 5 can be considered negligible since the total percentage error adds up to just 20%, and therefore it seems that iteration 5 meets the standards stiffness test requirements. The combination also shows improvements in weight to stiffness ratio, as this iteration (Aluminium bonnet) weighs 7.6Kg.In comparison to the Original Steel Bonnet, a total weight reduction of 48% can be achieved with iteration 5.

Iteration 6:0.8mm thick Aluminium panel with 0.6mm thick Steel inner frame

Stress deformation

56

Figure 77 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 78 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total deformation

57

Figure 79 Total deformation – Transversal test (Kevin, 2016)

Figure 80 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 15.5mm for the torsion test and 1.8mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

Stiffness Analysis: Iteration 6

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Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 6Stiffness(N/mm) 82.9 6.4

% Error 38% 8%

Table 11 Stiffness comparison of Iteration 6 with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

70

80

90

60

7

82.9

6.4

Stiffness comparison between Reference Bonnet and Iteration 6

Reference Value Iteration 6

Stiff

ness

(N/m

m)

Graph 7 Stiffness comparison – Transverse and Torsion (Kevin, 2016)

Although an acceptable Torsional stiffness value has been achieved, the transversal stiffness of iteration 6 seems to be a lot higher than the required value. Since the overall percentage error is higher than the accepted value, this particular iteration does not meet the stiffness requirements. Reduction in panel thickness is to be considered to analyse the effects it can have on stiffness values.

Iteration 7: 0.7mm thick Aluminium panel and 0.6mm thick Steel inner frame

59

Stress distribution

Figure 81 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 82 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total deformation

60

Figure 83 Total deformation – Transversal test (Kevin, 2016)

Figure 84 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 16.1mm for the torsion test and 1.9mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

Stiffness Analysis: Iteration 7

61

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 7 Stiffness(N/mm) 83.3 6.25

% Error 39% 11%

Table 12 Stiffness comparison of Iteration 7 with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

70

80

90

60

7

83.3

6.25

Stiffness comparison between Reference Bonnet and Iteration 7

Reference Value Iteration 7

Stiff

ness

(N/m

m)

Graph 8 Stiffness comparison – Transverse and Torsion (Kevin, 2016)

Having reduced the panel thickness of iteration 6, the stiffness does not seem to have a significant difference. Thickness of the inner frame can be further reduced to examine the difference in stiffness of the bonnet.

Iteration 8: 0.6mm thick Aluminium Panel with 0.55mm thick Steel inner frame

62

Stress distribution

Figure 85 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 86 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total deformation

63

Figure 87 Total deformation – Transversal test (Kevin, 2016)

Figure 88 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 17.7mm for the torsion test and 2.04mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

Stiffness Analysis: Iteration 8

64

Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 8Stiffness(N/mm) 73.5 5.9

% Error 23% 16%

Table 13 Stiffness comparison of Iteration 8 with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

70

80

60

7

73.5

5.9

Stiffness comparison between Reference value and Iteration 8

Reference Value Iteration 8

Stiff

ness

(N/m

m)

Graph 9 Stiffness comparison (Kevin, 2016)

The transversal stiffness of the iteration 7 has been significantly reduced with reduction in panel thickness and inner frame thickness. However, the total percentage error adds up to 39% when compared to the reference values. Therefore, further thickness reduction needs to be considered to investigate the stiffness fluctuation.

Iteration 9: 0.6mm thick Aluminium panel with 0.5mm thick Steel inner frame

65

Stress distribution

Figure 89 Equivalent Von-mises – Transversal test (Kevin, 2016)

Figure 90 Equivalent Von-mises – Torsion test (Kevin, 2016)

Total deformation

66

Figure 91 Total deformation – Transversal test (Kevin, 2016)

Figure 92 Total deformation – Torsion test (Kevin, 2016)

The results from the stiffness analysis show a deformation of 20.4mm for the torsion test and 2.25mm for the Transversal test. The associated stiffness values have been calculated and comparison is made with the relevant reference values.

Stiffness Analysis: Iteration 9

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Stiffness Test Transversal TorsionReference Stiffness Value (N/mm) 60 7

Iteration 9 Stiffness(N/mm) 67 5

% Error11% 29%

Table 14 Stiffness comparison of Iteration 9 with reference values (Kevin, 2016)

Transverse Torsion0

10

20

30

40

50

60

70 60

7

67

5

Stiffness comparison between Reference value and Iteration 9

Reference Value Iteration 9

Stiff

ness

(N/m

m)

Graph 10 Stiffness comparison – Transverse and Torsion (Kevin, 2016)

Further reduction in inner frame thickness has reduced the transversal stiffness considerably and the percentage error has been significantly reduced as well. However, the Torsional stiffness has also reduced to give a rise of 29% error for torsion stiffness itself and therefore the combination proves to be difficult to achieve the acceptable stiffness values with this particular design of inner frame.

Having performed the relevant stiffness tests, stiffness comparisons has been made for both Transverse and Torsion tests. Figures below show the global stiffness offered by each iterations.

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Transverse results

Referen

ce

Steel

Bonnet

Iterat

ion 1

Iterat

ion 2

Iterat

ion 3

Iterat

ion 4

Iterat

ion 5

Iterat

ion 6

Iterat

ion 7

Iterat

ion 8

Iterat

ion 9

0

20

40

60

80

100

120

60 58 56.4

108.6

71 6556

82.9 83.373.5

67

Transverse Stiffness Comparison

Stiff

ness

(N/m

m)

Graph 11 Transverse Stiffness Comparison

Torsion results

Referen

ce

Steel

Bonnet

Iterat

ion 1

Iterat

ion 2

Iterat

ion 3

Iterat

ion 4

Iterat

ion 5

Iterat

ion 6

Iterat

ion 7

Iterat

ion 8

Iterat

ion 9

0123456789

10

76.2

4.76

9.4

5.92 5.7 6 6.4 6.25 5.95

Torsion Stiffness Comparison

Stiff

ness

(N/m

m)

Graph 12 Torsion Stiffness Comparison

The data in the above graphs shows that the best outcome is obtained with iteration 5 (1.2mm Aluminium panel with 0.8mm Steel inner frame).

A direct Comparison between Reference value, Steel bonnet and Iteration 5

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A direct comparison of the stiffness values between reference values, steel bonnet and iteration 5 is shown in the figure below.

Reference Value Original Bonnet (Steel) Iteration 50

10

20

30

40

50

60

7060 58 56

7 6.2 6

Stiffness Comparison

TransversalTorsion

Stiff

ness

(N/m

m)

Graph 13 Stiffness comparison between reference value, Steel bonnet and Iteration 5 (Kevin, 2016)

From the graph it is seen that, the aluminium bonnet provides similar global stiffness as the steel bonnet provides. Structural weight reduction has also been achieved and the results are illustrated in the graph 14 shown below.

Structural weight comparison between Steel bonnet and Iteration 5

Excellent weight reduction has also been achieved with the aluminium design. Graph 14 shows the results.

Original Bonnet (Steel) Iteration 50

2

4

6

8

10

12

14

16 14.8

7.6

Structural weight comparison

Weight (Kg)

Wei

ght (

kg)

Graph 14 Structural weight comparison (Kevin, 2016)

A total of 48% weight reduction was also achieved with Iteration 5 (aluminium bonnet). As evident from the above bar charts, almost the same stiffness provided by steel bonnet can be obtained with aluminium with a significant weight reduction.

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Having this information, an indication of the combination’s energy absorbing capability was also examined by means of static test and by examining the corresponding strain energy results.

5.4 Static Impact Analysis of Iteration 5-(An indication of energy absorption capability)

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The equivalent impact force was used to analyse the strain energy and stiffness between steel bonnet and iteration 5, the results are shown below.

Comparison of strain energy

Figure 93 Strain energy – Steel Bonnet (Kevin, 2016)

Figure 94 Strain energy - Iteration 5 (Kevin, 2016)

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Under the force applied strain energy stored in the steel bonnet, is around 33mJ whereas the aluminium bonnet stores almost 40mJ (21% higher than steel) of strain energy.

Strain energy comparison

Original Bonnet (Steel) Iteration 50

5

10

15

20

25

30

35

40

45

Comparison of strain energy

Strain energy (J)

Stra

in e

nerg

y (m

J)

Graph 15 Strain energy comparison (Kevin, 2016)

Although strain energy doesn’t give a direct equivalent for energy absorbed, it is indicating the ability of aluminium bonnet to absorb more energy than a steel bonnet which is essential during head impacted collisions to decrease the possibility for serious head injury.

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Comparison of deformation

Figures below shows the deformations offered by the steel bonnet and iteration 5

Figure 95 Total deformation – Steel Bonnet (Kevin, 2016)

Figure 96 Total deformation – Iteration 5 (Kevin, 2016)

As expected, the aluminium bonnet (iteration 5) offers more deformation than steel bonnet. The steel bonnet deforms by 8.9mm whereas the aluminium bonnet deforms by almost 11mm.

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Deformation comparison

Original Bonnet (Steel) Iteration 50

2

4

6

8

10

12

8

11

Deformation comparison between Original Bonnet and Itera-tion 5

Deformation (mm)

Def

orm

atio

n (m

m)

Graph 16 Deformation comparison between Original Bonnet and Iteration 5

From the graph shown above, it is evident that the optimum iteration offers around 24% more deformation in comparison. The increased deformation is important as the more the bonnet deforms during head impact, more kinetic energy is to be absorbed and therefore reduces the chance for serious head injury.

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Comparison of Stress distribution

Figures below shows the equivalent von mises comparisons

Figure 97 Equivalent Von-mises – Steel Bonnet (Kevin, 2016)

Figure 98 Equivalent Von-mises (Kevin, 2016)

From the analysis results, 277Mpa of equivalent stress is achieved for the steel bonnet whereas 225Mpa of equivalent stress is obtained by the optimum iteration (aluminium bonnet).

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Taking the strain energy and deformation comparisons to consideration, the aluminium bonnet provides sufficient global stiffness with the specified panel thickness. This material combination seems to deform better than the steel bonnet which is reflected through values of strain energy obtained by the bonnets under the same loading conditions. Although the static impact analysis performed does not give a standard representation of the energy absorbed, it promises potential for a significantly reduced HIC value if dynamic head impact test is to be performed. Hence the aluminium bonnet seems to be an efficient replacement for steel bonnet.

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Chapter 6Conclusion and Recommendations

The static stiffness analyses were performed on the obtained bonnet model in accordance to the most recent stiffness test regulations. In addition, an equivalent impact force was calculated by considering the parameters used in an adult head impact test. Working with the limitations of ANSYS workbench, a static study was undertaken instead of a standardised dynamic test. Stiffness results obtained with the original steel bonnet were compared with the relevant reference values and the initial FE analysis was considered successful since the total % error in results were within the acceptable limits.

A range of combinations were trialled to identify a suitable combination offering just the adequate structural strength. Due to cost aspect of composite materials, only aluminium and steel were considered for the analysis. By controlling the panel thickness of the panels, it seems from the results that aluminium bonnet is capable of providing similar structural strength as offered by steel bonnets. The optimum material combination (Iteration 5) provided a transversal stiffness of 56Nmm -1 and a Torsional stiffness of 6Nmm-1, comparing to reference values of 60Nmm-1and 7Nmm-1 respectively, the total % error adds up to 20% which is within the acceptable limits.

Excellent structural weight reduction were also achieved through the optimum combination (1.2mm Outer panel with 0.8mm Inner frame), proves to be 48% lighter than the original steel bonnet. Comparing the structural weight of the Steel bonnet (15kg) and the Iteration 5 (7.5kg), the benefits can add up by completely replacing steel car bonnets with aluminium bonnets.

According to the strain energy results, the aluminium bonnet seems to perform better than the steel bonnet as well. With the same magnitude of force applied the aluminium bonnet absorbed 21% more energy than that of the steel bonnet. Although this particular result is not sufficient enough to verify better HIC values, it shows an indication that the aluminium bonnet can deform better than the steel bonnet absorbing more kinetic energy during head impacts.

6.1 Future Recommendations

Honeycomb structure with shock absorbing sandwich panel - Design

Since the stiffness requirements have been obtained with a lighter combination, the focus now needs to be directed towards achieving a desired HIC value. Shock absorbing ability of the bonnet is crucial in this regard. A thin shock absorbing panel which offers the necessary deformation could significantly reduce the kinetic energy of a head during impact. Further design modifications are necessary to explore the effect of a shock absorbing sandwich panel placed in between the outer panel and the inner frame. Material selection and associated bonding processes will need to investigated, if the concept proves to be plausible.

Further weight reductions can be obtained, if a suitable lightweight structure can be used as the reinforcements. Since honeycombpanels provide excellent stiffness, it may be considered ideal for inner frames. A bonnet system which consists of honeycomb panel as the inner frame with shock absorbing panels sandwiched between the honeycomb and the outer panel could possibly increase energy (kinetic) absorption more effectively during head impact. The concept described is illustrated in the figure shown below.

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Figure 99Concept of Honeycomb structure in car bonnets (Google Images, 2016)

With the use of appropriate adhesives, the shock absorbing panels may be bonded to the outer panel and the honeycomb structure. However, a detailed experimental study will be required to identify a suitable shock absorbing material. Relevant stiffness tests will also need to be performed to evaluate the stiffness capability of honeycomb structures.

Design modification to eliminate High Risk Impact Zones

A design approach to eliminate the HRIZ regions on the bonnet could reduce the chance for serious head injury significantly. With a design modification of the inner frame to match the characteristics of shock absorbing panel,increased energy absorption may be obtained. With this particular design approach, ribs and discontinuities are eliminated (as seen in traditional inner frame).

The advantage with this uniform pattern design is that by controlling the panel thickness, the overall strength of the bonnet structure could be made weaker or stronger at preference. It is suspected that with this design modification approach, just the adequate stiffness may be achieved with a lightweight structure. Furthermore, due to the absence of HRIZ regions in this design, the localised stiffness could be reduced significantly with substantial benefits for head impact. Taking the shock absorbing concept to consideration, a standard inner frame could be redesigned with the aid of advanced modelling tools such as Catia V5. The concept could be integrated to the aluminium bonnet combination. Finite element methodologies could be used to perform the standardised head impact tests to investigate the effects in HIC values.

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Figure 100 Traditional inner frame design (Google Images, 2016)

Figure 101 The concept of uniform pattern across the frame (Google Images, 2016)

References

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Andrew, C (2011) Noval car bonnet and pedestrian fatality reduction, Available at:http://www.theengineer.co.uk/novel-car-bonnet-could-reduce-pedestrian-fatalities/(Accessed: 15-02-2016).

Blanco, S (2011) how does weight affect the efficiency of a vehicle, Available at:http://www.autoblog.com/2009/10/29/greenlings-how-does-weight-affect-a-vehicles-efficiency/ (Accessed: 19-02-2016).

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Dominic, S (2010). Comparison of Steel and Aluminum Hood with same Design in View of Pedestrian Head Impact. Germany: FKA. p9

Dr. Grace, T (2009) Structural Hood and Hinge Concept for Pedestrian Protection,Availableat: http://www-nrd.nhtsa.dot.gov/Pdf/ESV/esv19/05-0304-W.pdf (Accessed: 15-02-2016).

Gupta, V., 2014.Anglia Ruskin university library. [online] Available at: <http://search.proquest.com/pqdtglobal/docview/1526408334/fulltextPDF/223E2B4085084114PQ/1?accountid=8318> [Accessed 1 Nov. 2015].

Hamacher, M (2008). Simulation of Vehicle hood in Aluminium and Steel . Germany: Abaqus Users Conference. p5&6

Hassan, M (2011). Comparison of steel, aluminum and composite bonnet in terms of pedestrian head impact. Iran: ELSEVIER. p49

Huang, S., and Yang, J., 1136. Optimization of a reversible hood for protecting a pedestrian’s head during car collisions. Accident Analysis & Prevention, [online] 42(4), pp.1136–1143.

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Jason, S. (2012). Design of Hood Stiffener of a Sedan Car for Pedestrian Safety. SAS Tech Journal. 11 (2), p72.

Jones. P (2011) 'Soft' car bonnet that folds inwards on impact could save thousands of lives Read more: http://www.dailymail.co.uk/sciencetech/article-1356847/Soft-car-bonnet-folds-inwards-impact-save-thousands-lives.html#ixzz3zbXDI1xW Follow us: @MailOnline on Twitter | DailyMail on Facebook', Mail online, 14th February, p. 1.

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Appendix 1

Equivalent force of a typical head form impact

Mass of an adult Head = 4.8kg

Velocity at the head form is fired = 40km/h or 11.1 ms-1

Typical time taken for the head form to make contact = 0.015s

Force (N) = Mass (kg) x Acceleration (ms-2)

Due to constant acceleration, acceleration can be found by using the fundamental equation,

a = V−Ut

2

Therefore,

a = (11.1 – 0)/0.015

a = 740ms-2

Thus the equivalent force of impact can be determined by,

Force = 4.8(N) x 740(ms-2)

Force = 3552N

2 a = Acceleration (ms-2) v = final velocity (ms-1) u = initial velocity (ms-1) t = time (s)

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Appendix2 - Curriculum Vitae

Kevin Chacko3 Greenway, Bishop’s Stortford, Hertfordshire, CM23 5LX

01279 491698, 07824479747kevin12rick@hotmail.co.uk

PROFILE A highly ambitious Mechanical engineering student, who is keen to learn further about Design/Finite Element engineering discipline through relevant industrial experience, I currently seek a challenging position which will enable me to widen my expertise as a professional engineer, providing me with opportunities to broaden my knowledge, work experience and professional growth.

KEY ACHIEVEMENTS Sports captain for secondary school inter-house competitions at Birchwood high, encouraging

students to participate in sport events The Course Representative for my (BEng) Mechanical Engineering Course, making decisions to

make campus life and university experience better for students Contributed to good customer service, developing confidence to interact with people and acquired

good communication skills At several occasions, I have achieved the student of the month award and many other prizes from

secondary school and college

EMPLOYMENT EXPERIENCE Wilkinson Stores in Bishop’s Stortford, Hertfordshire – Customer Sales Assistant Beard & Fitch Gear Manufacturers, Harlow, Essex – Work Experience Pitney Bowes (Franking machine manufacturers), Harlow, Essex – Work Experience HadhamEngineering, Bishop’s Stortford, Hertfordshire – Trainee Draughtsman [part time]

TITLE HELD, NAME OF THE COMPANY DATES OF EMPLOYMENT Cashier (Wilkinson) 16-03-2011 to 12-10-2013 Work experience (Beard & Fitch) 18-07-2012 to 22-07-2012 Work experience (Pitney Bowes) 22-10-2012 to 26-10-2012 Trainee fabricator (Hadham Engineering) 01-07-2013 to 22-12-2015 Draughtsman 01-01-2016 to Present

EDUCATION Birchwood High School, Bishop’s Stortford

11 GCSE’s including Mathematics, Science and English2 A Levels (Chemistry and Biology)

Harlow College, HarlowBTEC Extended National Diploma in Manufacturing Engineering

Anglia Ruskin University, ChelmsfordStudying 3rd Year BEng (Hons) Mechanical Engineering

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Relevant Modules and Results

Introduction to Engineering Materials 78% AManufacturing Processes 70% AIT, Communication and Research Skills 75% AApplied Software 62% BMechatronics 82% AMathematics for Engineers 1 93% AStatistics and Process Quality Assurance 84% AMathematics for Engineers 2 95% AEngineering Principles 95% AGroup Design Project 88% AMaterials and Processes 84% AComputer Aided Solid Modelling 85% AApplied Mechanics 90% AComputer Aided Engineering (FE Module) 77% AProject Management 81% AStress and Dynamics 86% A

CORE SKILLS Good communication skills Planning and prioritising work Creative thinking Problem solving skills Time management Self confidence Able to work efficiently within a team and as an individual IT skills: Microsoft Office products , AutoCAD, SolidWorks, Autodesk Inventor, ANSYS,

Autodesk Advance Steel

INTERESTSTaking up leadership positions is something that I am always keen on. My fascination to such roles have evolved since taking up several positions such as sports captain and Course representative during my time at secondary school and college. One of my hobbies include, finding out how machines work specially motors. Blending electrical and mechanical knowledge to design such appliances is something that I love to do. Using creative thinking and innovative ideas to solve real life problems is something that intrigues me. I thoroughly enjoy sketching objects in both 2D and 3D styles. Taking part in group sports such as cricket, during my spare time is also something that I enjoy.

REFERENCES

Mr. Raymond BegahSenior Lecturer (Manufacturing Engineering)Harlow CollegeVelizy EveHarlow, Essex01279868000

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Appendix 3 - Exit Plan

Module Skills developed Skills gap / reflection Proposed self-development with completion date

MOD002565

Introduction to Engineering

Materials

Concept of alloying in metals

Equilibrium phase diagrams

Effect of grain size and growth in mechanical properties of metals

Effects of carbon content in steel

Application of cooling curves

Concept of proof stress and poisons ratio

Calculations associated with phase diagrams

Further reading and practise after finishing

exams in May

MOD002306

Mathematics for Engineers 2

Introduction to matrices

Lagrange multipliers

Laplace transformations

Eigen values and Eigen vectors

Differential equations

Statistics

I would like to be able to solve further

complex engineering problems using

numerical methods

Private lessons and further independent learning prior

to joining postgraduate course in January

MOD002634 Behaviour of Engineering materials under stress

Concept of stress transformations and tensors

Fatigue and Creep failures on materials

Stress concentration due

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Materials and Processes

to discontinuity

Corrosion and degradation of materials

Application of adhesives in bonding materials

Analysis of material failure

Application of modified Goodmans diagram

Basic forging calculations

Effects of heat treatment in materials

Von-mises criterion

Lack of confidence in performing lab tests without supervision

Attend short courses to improve lab test skills before commencing

postgraduate study in January

MOD002668

Stress and Dynamics

Mechanical vibrations (Damped and Undamped)

Use of second order differential equations to solve engineering problems

Ability to apply fundamental principles to unfamiliar problems

Further reading to grasp thorough understanding of the principles, to be done

by the end of May

MOD002684

Thermofluids

First and second law of thermodynamics

Introduction to Bernoulli’s equation

Properties of liquid, vapour and gas

Chemical reactions in combustion

Introduction of fluid mechanics

Conservation of energy in thermodynamics

Saturated vapour and dry air

Engine cycles

Ability to perform volumetric analysis

with combustion

Further practise on calculations and reading on from external sources

within the 1st week of May

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MOD002610

Computer Aided Engineering

Finite Element using ANSYS workbench (Study on Implicit events)

Component design and stress analysis

Introduction to the use of Inventor CAM to generate G codes for CNC machining

Ability to model and solve Explicit events

Attending private lessons in India to learn LS-Dyna and Computational Fluid Dynamics during summer

break

MOD002387

Research Methods and Individual

Project

Research skills

EuroNCAP safety requirements

Static stiffness tests for a standard car bonnet

Pedestrian safety and car front design approach

Head Impact Criterion

Finite Element study on multiple part using ANSYS Workbench

Lack of knowledge in modelling Head Impact Test in an appropriate

Software

3D Surface modelling

Attend private tutorials to learn LS-Dyna, Catia and

SolidWorks during the summer break

MOD002666

Project Management for Technologists

Project lifecycle

Principles in Building teams

Conflict management strategies

Risk management strategies

Lack of experience in Project management roles in engineering

discipline

Explore for work experience opportunities

upon graduation

Appendix 4- Research Proposal

Research Introduction

Nowadays, commercial automobiles are expected to meet certain safety measures associated with pedestrian safety. Organisations such as EuroNCAP and other automotive safety assessment bodies perform several tests to examine the capability of a vehicle to protect VRU’s (vulnerable road users) during collision. Several safety testing requirements are outlined and meeting these standards is believed to help save the lives of VRU’s. To achieve the required structural performance, car bonnets

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are designed (according to active or passive safety concept) to absorb maximum deformation before the pedestrian’s head reaches the stiff underlying components of engine and thus reduces the chance for serious head injury or even fatalities. In recent years, excellent results in terms of VRU protection has been achieved through the active and passive design solution, states (European Vehicle Passive Safety Network, 2004). The improvement of the passive and active safety of actual vehicles is usually obtained by introducing new electronic and/or mechanical devices and consequently, increases the overall structural weight.

In the year ending September 2015, there were 1,780 reported road fatalities, a 3 per cent increase from 1,731 in the previous year. According to the data provided by Department for Transport UK (2015), a total of 23,700 people were killed or seriously injured (KSI casualties) in the year ending September 2015, and more than 60% of this KSI figure accounts for injuries and fatalities involving pedestrian head and vehicle front region. The statistical values show the importance in carefully designing a car bonnet with an apt material combination to absorb maximum kinetic energy and therefore avoid pedestrian fatalities or serious head injuries. Since high impacted head collision often lead to death, head injuries are considered to be the most severe injuries in pedestrian-car accidents. Head and face injuries in car–pedestrian accidents account for 60 per cent of all pedestrian fatal injuries of which 17.3 per cent of head injuries were due to the bonnet.  The fatality statistics emphasises the need to identify a suitable replacement material that offers maximum deformation during collision.A number of research studies have been undertaken to identify a suitable design that can reduce the HIC value. The deformation capability of a car bonnet depends on the global stiffness of the structure. By considering stiffness test methods, a system which provides just the adequate deformation needs to be identified.

Through this investigative study, a car bonnet will be subjected to static stiffness tests by means of finite element methodology in accordance to the most recent stiffness test regulations. The model will be experimentedwith varied material combinations and panel thickness in an effort to achieve maximum weight reduction whilst ensuring that the new material combination meets the static stiffness requirements regarding VRU protection.

Aim

To determine a suitable material combination for car bonnets which meets, the most recent static stiffness regulations and could potentially improve the energy absorption (in comparison with steel bonnets) during head impacted collision.

Objectives

Reasons for the changes in car bonnet systems over time Statistical data regarding pedestrian accidents and fatalities EuroNCAP safety requirements and Static stiffness test regulations Reference values for the standard tests Standard FE bonnet stiffness testing methods Obtain a complete 3D model of a valid car bonnet for FE analysis To carry out Torsional stiffness analysis To carry out Transversal Stiffness analysis Analyse the mechanical behaviour of a bonnet made of steel, aluminium and a combination

of these materials

Methodology

A detailed research to identify and understand the materials used and the manufacturing/assembly methods of the bonnet will be the initial stage of this research study. The methods used in industry to measure the stiffness and weight of bonnet will also be studied and embodied in the later stages of this

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research work. A fully defined 3D model of a commercial car bonnet will be designed using Autodesk Inventor 2015, this model will be analysed on ANSYS workbench to measure the stiffness, with predetermined boundary conditions and appropriate loading cases. Using the ANSYS workbench software, FEA analysis will be carried out by assigning a wide range of materials to the reinforcement of the bonnet and the corresponding performance will be examined. During these analyses, I will be looking for a lightweight material that can provide the same stiffness as the reinforcement materials used at present. Upon successful identification of such material this research can be considered a success.

The main areas of this methodology rely solely on 3D modelling and simulation software. The reason for choosing this particular plan of action is to ensure that, as a student I am exposed to the ways in which similar problems are solved in the engineering industry nowadays. Another huge advantage is that, there is no need to fund this research as the testing of the solution is carried out by the simulation software rather than testing a real modified bonnet at a lab. The only cost that can incur is the prototyping of the solution and the mechanical tests that needs to be done to confirm the results produced by Finite element analysis which is beyond the scope of this research study.

Due to the number of stages involved in this project, a well planned project schedule is essential therefore, Gantt project was used to schedule the stages of work which can be seen under the project timeline below.

Project Timeline

Fig: 1 Gantt chart showing the project timeline of this project (Kevin, 2015)

Expected Outcome

With the successful completion of this research study, a suitable lightweight material which provides the required stiffness will be identified. The optimised material combination could potentially replace standard steel bonnets. With a significantly lighter reinforcement, the performance and the fuel economy of commercial cars may be improved significantly. The optimised design which offers higher deformation will have just the adequate stiffness to satisfy the stiffness regulations.

Conclusion

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Increasing the fuel efficiency of cars is one of the huge problems auto companies invest a lot of money in to be resolved. (Sustainable products, 2016) says that for every kilogram of vehicle weight reduction, there is a potential to reduce carbon dioxide emissions by close to 10 kilograms over the vehicle’s operating life. Multiply that by the more than 600 million vehicles globally, and the benefits can add up. Combining the economical and environmental concerns regarding this problem, it is critical to find an apt solution quickly in the near future. With clearlyplanned out research study, I hope to find a solution to the problem which I intent to tackle through this research.

With the optimised design, the bonnet could absorb more kinetic energy and thus reduce chances for head injury to pedestrian during collisions. The pedestrian – car fatality rates as well as the yearly KSI (Killed or Seriously Injured) value could be reduced significantly and the expenses revolving around pedestrian accidents could also be reduced with the identification of an efficient energy absorbing bonnet system.

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