8th ANNUAL CONFERENCE OF THE

CDT IN ADVANCED COMPOSITES FOR INNOVATION AND SCIENCE

POSTER BOOKLET

Tuesday 16th April 2019 University of Bristol, Queen’s Building, University Walk,

Bristol, BS8 1TR, UK

8th ANNUAL CONFERENCE OF THE

CDT IN ADVANCED COMPOSITES FOR INNOVATION AND SCIENCE

POSTER BOOKLET

Tuesday 16th April 2019 University of Bristol, Queen’s Building, University Walk,

Bristol, BS8 1TR, UK

Front cover photo credits: Robin Hartley (top), Dominic Palubski (far left), Samuel Scott (top left), Lourens Blok (centre), Hernaldo Mendoza Nava (top right), Francescogiuseppe Morabito (far right), DBT Team Curiosity (bottom left), Chiara Petrillo (bottom), Jonthan Stacey (bottom right).

Materials

High velocity impact on hemispherical UHMWPE compositesBehjat Ansari, Luiz Kawashita, Stephen Hallett, Ulrich Heisserer **DSM Materials Science Center, Geleen, The Netherlands.

Modelling the interface

Dyneema® is an ultrahigh molecular weight polyethylene (UHMWPE), gel-spun to form fibres embedded within athermoplastic matrix to form pre-impregnated composites. Previous studies on the failure mechanisms of thesecomposites under impact have exclusively focused on flat plates. Certain armour applications however, require the useof hemispherical geometries. Spherical geometries feature curvature and in-plane shearing of plies, each affectingthe performance of the laminate in its own way. The project is aimed at developing the tools required to effectivelypredict the behaviour of curved and sheared plates of Dyneema® under ballistic impact, and enhancing the ballisticperformance of the material to reduce induced trauma in body armour applications.

AcknowledgementsMany thanks to the Engineering and Physical Sciences Research Council for their support through the EPSRC Centre for Doctoral Training in AdvancedComposites for Innovation and Science at the Bristol Composites Institute (ACCIS), and to DSM Dyneema for their continued support and funding for this research.

Clockwise from left: The two approaches to CZM; its implementation; numerical residual velocitypredictions with Lambert-Jonas curve fits for surface-based and element-based CZM models.

Parametric studiesa) b)

c) d)

Clockwise from top left: Modelling parameters investigated; modelling curvature with a) Deep-drawnpanel of Dyneema® modified from Dangora et al. (2016), b) flat plate mesh, c) curved plate mesh witha 15 inch radius, d) curved plate mesh with a 5 inch radius; Mode-mixity, the ratio of Mode II to totalstrain energy release rate, across the middle interface of a laminate under 250 ms-1 impact.

In-plane dimensions

Total thickness

Sub-laminate thickness

Single curvature

Investigating effects on ballistic impact performance

of material

Manufacture and testing of sheared platesCohesive elements

Homogenised sub-laminate elements

Zero thickness achieved bytranslation of top node setto coincide with bottom set.

Nodes shared by sub-laminate and cohesive elements

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absorbed through Mode I and Mode II

fracture→ Investigate effect

of interface parameters on impact

performance

Surface-basedValidated by Hazzard

et al. (2018)Output mixed-mode energy absorption

90° Reference plate

80 ° Sheared plate

From left to right: Cross-sections of specimens with varying fibre angles, tested at a strike velocity of755 ms-1. The different stages of the process developed for manufacturing sheared plates.

Ballistic impact testing, a) a top-down view of the test apparatus (not to scale), with the arrowdepicting the idealised direction of projectile motion, b) the testing facility at DSM Dyneema, c) asheared plate held loosely in position with four grips in the corners directly before impact, d) bulgingof the back face of a sheared plate following penetration by the FSP upon impact.

Clockwise from left: thickness evolution of Dyneema® HB26 with increasing shear angle. Opticalmicroscope images of cross-sections from an un-sheared specimen, a sheared specimen that wasnot pressed, and a sample that was sheared and pressed under heat.

t = 0.02 ms t = 0.12 ms t = 0.20 ms

→ The degree of curvature corresponds to thelocation of impact on a hemispherical surface.

Mode-mixity in the middleinterface at 250 m/s

Use of Nonwoven interleaves to increase damage tolerance in compositesEileen Claire Atieno, Prof. Ian Hamerton, Dr. Thomas PozegicOver the last decade, demand for high performance materials in the aerospace and automotive industries has led to an increase in the application of laminated composite materials, specifically carbon fibre reinforced polymers (CFRPs).

The main obstacle that limits widespread use of CFRPs is their low interlaminar fracture toughness (IFT) making them highly susceptible to interlaminar separation or delamination as a result of crack propagation when subjected to mode I and mode II load cases as well as out-of-plane, low velocity impacts; leading to formation of local stress concentrations and reduction in residual compressive strength and stiffness.

This work aims at understanding the effect of graphene nanofillers inside electrospun Nylon 66 nonwoven veils on the mode I and mode II IFTs, measured using DCB and ENF tests.

Mode I Fracture Toughness: Results Interleaf Areal weight (gsm) Maximum Force (N) GIC,ini (J/m2) GIC,prop(J/m2)Control 4.5 56.2 ± 4.9 313.9 ± 18.2 235.5 ± 6.3

PA-6,6/ 5 wt.% G 4.5 (+5 wt.% G) 54.5 ± 4.1 282.1 ± 38.5 (-10%)

236.4 ± 19.8 (+0.38%)

PA-6,6/s. G 1 15.72 34.5 ± 1.3 181.5 ± 28.0 (-42%)

129.5 ± 1.2 (45%)

Interleaf Areal weight (gsm) Maximum Force (N) GIIC,ini (J/m2)Control 4.5 510.0±15.2 2354.0 ± 88.4

PA-6,6/ 5 wt.% G 4.5 (+5 wt.% G) 570.0 ± 14.4 2694.8 ± 316.2 (+14.7%)

PA-6,6/s. G 1 15.72 566.2 ± 53.1 3258.5 ± 74.6 (+38.4%)

Mode II Fracture Toughness: Results

Conclusions:1.) In mode I, GI decreased with an increase in areal weight.2.) In mode II, GIIC,ini increased with increase in areal weight and wt.% of the nanoreinforcements inside the PA-6,6 veils.3.) Optical microscopy images of a single cross-section of the DCB samples indicated that crack propagation avoided the interleaved reinforcements.

Acknowledgements: The author would like to thank Dr. Simon G. King, University of Surrey as well as Revolution Fibres, NZ for supply of materials.

References[1] Such M. et al., J. Multifunct. Compos, 2014[2] Yu H. et al., Composites Part A, 2014.

"A pathway to low-cost, high-strength composites parts"

HiPerDiF Filament, a High Performance Discontinuous Fibre Reinforced 3D Printing Filament

Research aim Develop a fibre reinforced 3D printing filament with fibres above the critical fibre length, such that the full strength of the fibres is obtained, without the need for cumbersome and restrictive fibre cutting and initial laydown procedures within the additive manufacturing process.

Filament forming

Thermoplastic preforms

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Aligned discontinuous fibre reinforced thermoplastic tapes were prepared with a Vf of 12% using film impregnation and a custom built double belt press applying a pressure of 1 bar. Their tensile performance was assessed and compared to the benchmark continuous fibre filament (MF-CF).

Figure 4. Tensile properties of preforms for a Vf of 12%

Figure 3. Cross section of PLA specimen

Flow analysis

The flat preform tape (Figure 3) has to be shaped into an uniform circular filament without fibre breakage. A custom heated channel is manufactured and the highly aligned fibres in the thermoplastic matrix are pushed through a converging duct. Because the fibres are highly aligned through the HiPerDiF method, blocking issues are prevented. The flow behavior and fibre alignment of the preforms are studied.

Figure 1. Trade-off in processing and performance for composites [1]

Figure 5. Filament forming process reshaping the preform into a filament

(a) (b)

(a) schematic and (b) results for filament forming

Multi-physics analysis is required to model the the flow of the short fibre polymer composite as the rheological and thermal properties are strongly coupled. Different simulation techniques are employed, from quick numerical methods to high fidelity particle based methods, to capture and validate the flow behavior of the aligned discontinuous fibre thermoplastics.

The results show that the fibres reach their full strength and can compete with existing continuous fibre printing solutions.

HiPerDiF fibre alignment method

Short fibres above the critical fibre length (3mm) are aligned using theHiPerDiF method into a continuous tape of aligned discontinuous fibres [2].

Figure 2. HiPerDiF fibre alignment method schematic

Vacuum

Moving mesh conveyor belt

Figure 6. Smoothed Particle Hydrodynamics for flow analysis:

L.G. Blok, M.L. Longana, B.K.S. Woods

CANs: from reversible reactions to functional composites

Callum Branfoot, Hartmut Fischer, Tim Coope, Duncan Wass, Paul Pringle and Ian Bond

Covalent adaptable networks (CANs) are polymers that exploit dynamic crosslinks to reversibly transitionbetween thermoset and thermoplastic materials. Upon stimulus the crosslinks break, affording thesurrounding polymer very high levels of chain mobility. This mobility allows stress relaxation and plasticitywhich can be used in reshaping, repairing and recycling. The implementation of CANs in fibre-reinforcedpolymer composites (FRPs) presents an opportunity to address some of their limitations: low toughness,difficult repair and limited recyclability. In this project we synthesise novel crosslinkers, prepare new CAN-epoxies, characterise these materials and then investigate their applications with FRP composites.

Self-healing Recycling

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Diels-Alder Epoxyresin rheology

Diels-Alder crosslinkedEpoxy powders

Damage Decrosslink CompressMild delamination repair

Immerse in DCM, as the polymer swells into a gel this internal pressure pushes thethe plies apart. The gel is then cast, dried and milled for re-use (not shown).

Supported by

Active thermal management via embedded vascular networksJim Cole, Ian Bond, Andrew Lawrie

Fibre-reinforced polymer composites are limited in high temperature applications by the matrix glass transition temperature, Tg. Above Tg the matrix transitions from a glassy to a rubbery state. Mechanical strength and fibre-matrix interfacial properties are reduced.

A solution to this issue is active thermal management, which can regulate matrix temperatures and retain laminate performance. This can be achieved by circulating coolant fluid through a network of internal vessels, or vascules. Heat energy is removed via conduction and convection and rejected elsewhere in the system.

Carbon/epoxy specimens of Hexcel IM7/8552 (Tg = 200°C) with straight vascules were manufactured by embedding PTFE-coated wire into the layup (Fig. 1). These wires were then extracted manually after cure. A compressed air supply was attached to the vascule inlets through hypodermic needles.

To test the thermo-mechanical benefits of the concept, bespoke thermal testing apparatus was developed. This comprised a four-point bend fixture, deflection potentiometer, thermal chamber, heat source, temperature sensors and a cooling air supply (Fig. 2). Test temperatures ranged from ambient to 170°C.

Force and deflection data was measured for pristine and vascular specimens at various temperatures and coolant flow rates. From this flexural modulus and strength were determined.

Flexural modulus was largely insensitive to temperature and coolant flow rate. The vascules had a stiffening effect due to displacement of 0° fibres from the neutral axis (Fig. 5).

While pristine specimens at 170°C failed by delamination, intra-laminar cracking in cooled specimens was dominant. This more closely resembled damage observed at 23°C (Fig. 3).

Non-vascular specimens suffered a 25% loss of in flexural strength at 170°C. In vascular specimens with maximum coolant flow, this reduction was limited to just 6% (Fig. 4). These findings prove the concept has validity in providing extended high temperature performance for polymer-matrix composites.

Fig. 2: Bespoke test chamber

Fig. 5: Micrograph of a typical vascule cross-section. The trapping of 0 fibres above and below the vascule is visible. This slightly increased the flexural rigidity of the specimen. It also caused fibre waviness throughout the thickness.

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Fig. 4: Ultimate flexural strength at various test conditions, normalised by the 23°C pristine average value (red crosses are individual specimen strengths, blue bars are averages)

Fig. 1: Embedding PTFE-coated wires into layup

Fig. 3: Optical micrographs of failure zones; a) pristine (23°C), b) & c) pristine (170°C), d) vascular (23°C), e), & f) vascular (170°C, 1.00 bar). Intra- and inter-laminar cracks, splitting,

buckling and shear cracking are all visible.

Mechanical performance, residual stress and microstructural analysis of multiple ceramic matrix composite systemsJoachim-Paul Forna-Kreutzer, Dong Liu, Martin Kuball, Fabrizio Scarpa

Ceramic matrix composites (CMCs) offer great potential towards the development of novel materials withimproved strength-to-weight ratios and high temperature performance retention. The present study was aimedtowards the room temperature investigation of the link between the microstructure, residual stresses andsubsequent damage mechanism in oxide CMCs.

Four types of CMCs were tested: (i) Woven NextelTM 312 / SiOC (312/SiOC); (ii) Woven NextelTM 720 / Al2O3(720/A); (iii) Woven NextelTM 720 / Aluminosilicate (720/AS); (iv) Unidirectional Al2O3 / Al2O3 (A/A).

These were all tested in a four-point bending configuration with in situ observation using digital image correlation(DIC). The flexural strength and the force-displacement curves are shown in Fig. 1. Micro-Raman spectroscopywas used to measure the local residual stresses in the CMCs (Fig. 2). In addition, synchrotron X-ray computedmicro-tomography (µ-XCT) was adopted to obtain information about their 3D microstructure (Fig. 3).

Materials & Methods

Results & Discussion

• Three-point bending tests at ambientand elevated temperatures (900-1100°C) with in situ synchrotron X-raytomographic imaging followed bydigital volume correlation to derive the3D strain distribution in CMCs as afunction of the applied load.

• Larger compressive values (i.e. largernegative peak shift values) wereobserved in the fibre-dominatedareas.

• In the 720/A and 720/AS systems,tomography scans revealed evidenceof tow splitting which almostinvariably resulted in the formation ofmacropores.

• These macropores are believed to actas the main nucleation andpropagation sites for cracks, causingthe extensive delamination observedvia DIC.

Future work

Fig.1: Representative Force vs. Crosshead displacement curves.

Fig.2: R1 peak shift mapping of Cr3+

impurity ubiquitous in alumina containing compounds (720/AS).

Fig. 3: 3D representation of the microstructure in 720/A sample reconstructed from µ-XCT projections. The zoomed in image shows the three-way split of a

longitudinal tow.

2. Bleed resistor (R2) Optimisation

Optical switching of artificial muscles using Functional Composite materials

Calum Gillespie, Dr Andrew Conn, Professor Johnathan Rossiter, Professor Fabrizio Scarpa, Dr Asier MarzoSoft artificial muscles (SAMs) are an emerging subset of smart materials that exhibit highpercentage strains very similar to biological systems. This allows for novel designs ofactuators with multiple degrees of freedom. This project aims to design a photo-responsiveSAM system by implementation of novel nano-composite materials. The focus of this projectis to achieve high resolution response and high-speed switching using local photonicstimulation, allowing for this technology to be implemented across a number of fieldsincluding morphing skins in wing designs as well as haptic displays and visual technologies.

1. Manufacture

3. High Voltage Testing

Dielectric Elastomer Actuators (DEAs) have been manufactured using a typical

methodology.

Hydrogenated Amorphous silicon deposited on glass slides using plasma enhanced chemical vapour deposition. 30 minutes

deposition time achieves a 840 nm layer and was connected to the DEA with spluttered gold electrodes.

A-Si on a glass substrate was

tested using a high voltage ramp from 200v to 2kV. It was found that at 2kV a

Dark current of 25.1MΩ and a

Bright current of 82.6 M Ω.

A-Si on a glass substrate tested in

series with a Dielectric actuator muscle. Shining light on the a-Si

was found to generate a 2.2

micron deflection in the weighted disc actuator.

Light on Light onLight off Light offLight off

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Residual Stress Analysis in Composite InterleavesRobin Hartley, James Kratz, Ivana Partridge and Ian Hamerton

Particle Interleaf Toughening

Future work

• Resin characterisation Cure kinetics Coefficient of thermal

expansion Cure shrinkage Thermal properties

• Model validation CT DIC experiment to

determine the strain field development around a particle during processing

• Fracture testing and fractography Fracture testing of interleaved

composites reinforced with different particle materials

Comparison of crack paths and toughness

CT experiment for validating the numerical model.Red spheres represent the interleaf particle. Greyspheres represent X-ray dense trackablenanoparticles.

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Cure kinetics of 8552 resin going through a standard two stagecure cycle

Incorporating 20 – 30 µm particles into resin rich regions between composite laminate plies has been shown toimprove the interlaminar fracture toughness of composite materials. Some theorise that the particles act as spacers,allowing the full fracture toughness of the matrix resin to be realised by reducing the likely hood of the interlaminarcracks travelling along the interleaf/fibre bed interface. Recent numerical studies have shown that during crackpropagation, crack tips are attracted towards particles, keeping cracks within the interleaf and hence realising thelaminate toughness. This is indicative that the particles are acting as stress concentrators and the interaction betweenthe crack tip and particle stress fields draws the crack towards the particle.

Matrix selectionCannot be too brittle as plastic deformation required for toughening tobe possible. Two thermoplastic toughened formulations with differentepoxy constituent ratios tested in compression for plastic yielding:

ISSUES:• Video gauge loses track of points prior to sample yielding• Samples tend to fail under shear due to specimen buckling as shown in Figure 2

Figure 1

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Composition B

Force v TimeForce v Strain 1Force v Strain 2

t = 60 s: Linear elastic.t = 120 s: Significant plastic deformation (barrelling).t = 300 s: Drop in load corresponds to lateral slip of samplest = 375 s: Premature failure of samples

**Re-test with samples with 1:1 aspect ratio to prevent ‘buckling’.

Figure 2

Durability of composite materials in deployable space structures

Yanjun Hea, Agnieszka Suligab, Alex Brinkmeyerb, Mark Schenka, Ian Hamertona

a Bristol Composites Institute (ACCIS), Department of Aerospace Engineering, University of Bristol, Bristol, BS8 1TR, UKb Oxford Space Systems, Zephyr Building, Harwell Space Cluster, Harwell, OX11 0RL, UK

In low Earth orbit (LEO), atomic oxygen (AO) is a key limitation to service longevity of composite materials. In thiswork, the AO resistance is examined for three different space-resistant composite materials. The selected materialsunderwent exposure in a ground-based facility which simulated the AO environment of space. The degradation ofthe performance of the materials was determined by measuring selected properties before and after variousexposure. The results presented in this work can act as a benchmark for the development of new compositesystems or protection technologies which can provide an extended service life for flexible deployable structures inLEO.

Key Results

FTIR data (a) and Principle component analysis of FTIRspectra :loading plot of PC1, PC2 and PC3(b), cumulativeeigenvalue of each component (c) score plot of PC1 vs.PC2. (d) score plot of PC1 vs. PC3(e).

(a)

FTIR results

Surface morphology before (a) and after (b) exposure

Conclusions• Surface resin on the laminate has suffered significant degradation after exposure.

• The materials were gradually eroded with the increase of exposure.

• PCA results indicated that alkyl moieties are the weak points of the structures.

• The results can act as an benchmark for the development of new resin system.

Supported by

Chemical structures of epoxy resin : (a) TGDDM, (b)epoxidised novolak and (c) DGEBA resin initiated by (d)N’-(3,4-dichlorophenyl)-N,N-dimethylurea).

(b)(a)

PC1PC1

(a)

(b)

(c) (d) (e)

Toughening composite laminates using electrospun interleavesKonstantina Kanari, Michael Wisnom, Steve Eichhorn

Composite laminates are an environmentally friendly approach to reduce fuel consumption in the aerospace andautomotive industry by lightweighting the materials used. Composite laminates are materials that consist of pliesof polymeric matrix with fibre reinforcements. The stacking of plies makes composite laminates susceptible todelamination and low fracture toughness. In this study polystyrene is used for the production of electrospunnanofibrous mats. The mats will be incorporated as interleaves between the plies to improve the toughness oflaminated composites. Cellulose nanocrystals are to be embedded in the fibres for the enhancement of the fibres’mechanical properties through a mechanism called crazing.

Enhancement mechanismThe incorporation of nanofibrous interleaves in betweenlayers improves the fracture toughness of the laminatecomposite by:• Nanofibre bridging• Crack path modification

Why electrospinning?• Fibres with high aspect ratio and forced molecular

orientation• Nano- and micro- dimensions• Possible aligned fibres

Crazing in fibres• Toughening mechanism in polymers through

localised plastic deformation• Enhancement of local strain to failure

Preliminary results• Bead-free fibres have been produced• Wrinkles on surfaces due to fast solvent evaporation• FTIR confirms no solvent on fibres• Visible necking on the fibres after tensile testing

Future work• Study on the structural and mechanical properties of

fibres with and without cellulose nanocrystals• Identification of the effect of the polystyrene

interleaves on the properties of composite laminatesReferences

[1] Daelemans, L. et al. ACS Appl. Mater. Interfaces 8, 11806–11818 (2016)[2] J. Polym. Sci. Part B Polym. Phys. 53, 1171–1212 (2015)

[3] A. Asran et al./ J. Appl. Pol. Science 125, 1663-1673 (2012)

(left) Polystyrene bead-free fibres– (right) Necking of the fibres after tensile testing

The different toughening mechanisms of the epoxy [1]

Basic electrospinning process [2]

Schematic representation of crazing development (3)

Understanding leading-edge protection erosion performance using nano-

silicates for modificationImad Ouachan1, Martin Kuball2, Dong Liu2, Kirsten Dyer3, Carwyn Ward1, Ian Hamerton1,

Bristol Composites Institute1, Physics Laboratory (University of Bristol)2, Offshore Renewable Energy Catapult3

• Offshore wind turbine blades are expected to remain in operation withminimal maintenance for a service life of 25 years.

• For the European offshore wind industry, degradation caused by rainerosion is a significant cost [1],[2] ;

• Reduction of aerodynamic performance (€56m - €75m annually).

• Maintenance and downtime (€56m annually).

• Understanding of failure mechanisms for rain erosion is limited,particularly the viscoelastic properties and high strain rates (106 - 109

Hz) of raindrop impacts [3].

• The effect of glycidyl functionalised polyhedral oligomeric silsesquioxane(POSS) into a commercial polyurethane (PU) coating system wasstudied using nanoindentation, dynamic mechanical thermalanalysis (DMTA), and rain erosion testing.

• Manufacture and coating of both unmodified and POSS modified LEP samples (Fig. 1).

• Characterisation of material properties using nanoindentation and DMTA.

• Comparison of material properties of both LEP systems to rain erosion performance.

• Unidirectional E-Glass and E-Glass biaxial +/-45 (Saertex) were usedwith the low temperature cure epoxy resin system (Hexion Epikote MGSRIMR135) and hardeners (Epikure MGS RIMH 134 and 137).

• Selected nanoindentation test results are displayed below (Fig. 3).

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Figure 3 – Left: Modulus (𝐸𝐸) and hardness (𝐻𝐻) were determined using Oliver-Pharr analysis. Right: Short term recovery, a measure of elastic recovery, was also correlated to loading rate.

• Selected DMTA test results are displayed below (Fig. 4).

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Figure 4 – Left: DMTA was used to determine glass transition temperature 𝑇𝑇𝑔𝑔 values were from tan 𝛿𝛿 maxima and onsets calculated from the storage moduli. Right: DMTA frequency sweeps were also utilised to investigate variation of strain rates for each of the coating components.

• Example rain erosion test specimens is displayed below (Fig. 5).

Figure 5 – Failed rain erosion specimen examples tested at the Energy Technology Centre rain erosion rig at 1200 RPM (equivalent to 128.81 m/s). Left: Unmodified LEP coating at 35 minutes.

Right: POSS modified LEP (10 wt. %) coating at 35 minutes.

• Nanoindentation obtained previously unreported mechanical properties for thiscommercial PU based coating system (hardness, modulus, and short-termrecovery) and highlighted a correlation between loading rate and a reduction ofshort-term recovery.

• DMTA results show modification of the LEP increases dampening at lowertemperature ranges introducing an additional mechanism of storing energy.Additionally, sweep data show an increase in elasticity at higher frequencies.

• Initial rain erosion data showed importance of surface quality of samples.Refinement of POSS incorporation is required as shown by both the rain erosiontest results and short-term recovery data.

1. Wiser R et al. Forecasting Wind Energy Costs and Cost Drivers: The Views of the World’s Leading Experts. 2016.2. Herring R. Integration of Thermoplastic/Metallic Erosion Shields into Wind Turbine Blades to Combat Leading Edge Erosion. In: Fraunhofer Offshore Wind R&D 2018. Bremerhaven, Germany, 2018.3. Dyer K. Developing Tools to Improve Leading Edge Erosion Coatings. In: Wind Blade Materials Development Forum. Hamburg, Germany: TBM, 2018.4. Cortés E, Sánchez F, O’Carroll A, Madramany B, Hardiman M, Young TM. On the Material Characterisation of Wind Turbine Blade Coatings: The Effect of Interphase Coating-Laminate Adhesion on Rain

Erosion Performance. Mater (Basel, Switzerland) 2017; 10: 1146–1168.

Figure 1 - Cross section of test coupon. Left: SEM of sample cross section. Right: Graphic representation of cross section with approximate thicknesses.

This work was supported by the Engineering and Physical Sciences Research Council through the EPSRC Centre for Doctoral Training at the Advance Composites Centre for Innovation and Science (ACCIS,Grant number EP/L016028/1), and The Future Composites Manufacturing Hub (Grant number EP/P006701/1). This project was also funded by the Wind Blades Research Hub (WBRH), a joint collaborationbetween the University of Bristol and ORE Catapult.

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Objectives

Conclusions

References

Acknowledgements

Methods

Introduction Results

• The Leading edge protection (LEP) coating was modified by the additionof 10 wt. % POSS (Hybrid Plastics) (Fig. 2). This POSS variant is ahybrid molecule with an inorganic silsesquioxane at the core and organicglycidyl groups attached at the corners of the cage.

bristol.ac.uk/composites

Nanodiamond composites; comparing detonation and high-pressure/high-temperature nanodiamonds within epoxy matricesN. Fox1, D. R. Palubiski2, F. Scarpa2.1School of Chemistry, University of Bristol, Cantocks Close, Bristol, United Kingdom2Bristol Composites Institute (ACCIS), University of Bristol, University Walk, Bristol, United Kingdom

Figure 2. Comparison of composite UTS to nanodiamond loading percentage.

Future Work• Further mechanical testing and physical testing,

including three point bends, thermal conductance, and viscosity of uncured resin.

• Incorporation of CVD diamond from new pulsed-DC reactor.

• Analysis of surface chemistry of nanodiamond to enhance integration.

• Attempt manufacture of samples with high grade aerospace resin RTM-6.

Current workSamples of nanodiamond (Figure 1), with load percentages of 0.5, 1, and 3 %, were incorporated into Prime-20 LV epoxy resin and slow hardener, shear mixed for 5 minutes and cured for 48 hours at room temperature. They were then tested in tension according to ASTM D638-14.Data (Figure 2) showed a difference between the samples tested. While 0.5% loading produced almost identical UTS for both types of diamonds, higher load percentages showcased a variation in UTS. To rule out issues with aggregation, TEM/SEM images (Figure 3) were taken and work towards improving mixing is being conducted.

Figure 3. TEM images of 3% loaded HPHT in Prime-20 resin showing aggregation of the nanodiamond.

Figure 1. TEM images comparing detonation (a) and HPHT (b) nanodiamond from Ray Techniques LTD. and Element 6 respectively.

b.

(a) (b)

5 11 17 23 29 35 41 47 53 59

Inte

nsity

(a.u

)

2Ѳ (degrees)

Adsorption/ Desorption Moisture sensitive

Solution: Surface Functionalisation with Polymers

Why Metal-Organic Frameworks (MOFs)?

Functional Nanocomposites for Sustainable Energy Storage

Chiara Petrillo, Dr. Adam Perriman, Prof. Ian Hamerton, Dr. Valeska Ting

A key limitation to global dependence on renewable energy is the lack of efficient storage methods of excess energy. Whilst conversionof renewable energy to hydrogen promises a clean fuel viable for storage, the requirement of highly pressurised tanks hinders theresulting energetic efficiency. Owing to their extremely high surface areas and permanent porosities, metal-organic frameworks (MOFs)represent a promising solution for the storage, separation, and catalysis of a catalogue of molecular species. The present study soughtto tackle the three key barriers to the implementation of MOFs: limited processability, uncontrollable desorption, and moisture sensitivity.

1 µm

1 µm

Progress: (2) Improved Moisture StabilityProgress: (1) Proof of Polymer Integration

Inorganic LinkerTerephthalic acid

Metal NodeZinc(II) oxide

Unit CellSecondary building unit

MOFIRMOF-1

High surface area Permanent porosity Tailorable

Nanocrystalline MOFProcessability limited

Molecule adsorption

Degradation

Reactive amine

Amine functionalized MOF IRMOF-3

MOF/ Polymer Composite IRMOF-3/ PLA

1000200030004000

Inte

nsity

/ %

Wavelength/ cm-1

Sodium Methoxide

Reflux, 80 oC

24 hrs

PolyesterPoly (lactic acid) - PLA

T < Tg GATE CLOSED

T > Tg GATE OPEN

Resin compatible Controllable gating Water blocking

IRMOF-3 clusters

IRMOF-3/ PLA clusters

Powder X-Ray DiffractionFT Infrared SpectroscopyAmide formation observed

Temperature Controlled Gating

SEM

Method developed for functionalisation of IRMOF-3 with PLAWell-integrated smooth surface of MOF composite observedProof-of-concept achieved for improved water stability

IRMOF-3 SimulatedIRMOF-3

IRMOF-3/ PLA composite

IRMOF-3 @ 180 mins in air

IRMOF-3/ PLA @ 180 mins in air

Why Not MOFs?

Development of nano-MOF composites to enhance compatibilityThermal behaviour analyses for gating proof-of-conceptElectrostatic coupling of polymer to influence phase-change behaviour

• Retained crystallinity of composite MOF: blocking of water by polymer

• Loss of crystalline structure in parent MOF indicated by broad peaks

Conclusions Future Work

IRMOF-3

IRMOF-3/ PLA composite

[1] S. Bonakala et al., Effect of Pillar Modules and Their Stoichiometry in 3D Porous Frameworks of Zn(II) with [Fe(CN)6]3–: High CO2/N2 and CO2/CH4 Selectivity, Inorganic Chemistry, 52 (2013) 11385-11397[2] Yao, S. Qiu et al., Selective adsorption of carbon dioxide by carbonized porous aromatic framework (PAF), Energy & Environmental Science, 5 (2012) 8370-8376

5 10 15 20 25 30 35 40 45 50 55 60

Interfacial properties• Superior interlaminar shear strength (ILSS) of

anhydride cured epoxy resin system• Microbond testing used to determine interfacial

shear strength (IFSS)• Next test phase to assess IFSS on carbon fibre

for optimal sizings for the resin system.

Development of resin and curing process for wind turbine blade application

Bethany. K. Russell, Carwyn Ward, Shinji Takeda and Ian Hamerton beth.russell@bristol.ac.uk

Resin characterisationA novel anhydride resin was extensively characterised in order to understand the cure kineticsand the thermo-mechanical properties of the cured resin. The effect of the anhydride curing agentwas studied and comparison of key properties to an industry benchmark was undertaken.

Vascular curingExploring a novel curing method which utilises a secondary internal heating system during thecure of a thick composite part. This aims to reduce thermal gradients through the thicknesswhich lead to the development of residual stresses that often result in the formation of defectssuch as warpage and delamination.

• Initial trials shown the reduction in exotherm and more gradual reaction kinetics is facilitatedby the introduction of a vascule at the centre of a oven cured 25 mm thick small GFRPpanel.

• Future work- Evaluation of model and optimisation of vascule placement in larger panelswith more complex geometry. Can cure cycle be optimised, higher temperatures/ shortercure cycles for wind turbine blades?

Epoxy resin ILSS (MPa) IFSS (MPa)Anhydride-cured 66 36

Industry benchmark 55 -

Microvise~20 μ

Glass fibre-17 μm diameter

droplets

Lab-scale setup for vascular curing

VasculeNo vascule

VasculeNo vascule

ConclusionThe work conducted allows for the development of a resin system and process that offer higherquality wind turbine blade production. The aim in next few months is to make a small bladedemonstrator which exhibits the main outcomes from this work.

Surface modification of UHMWPE fibres with Ar-O2 plasma treatment

Usman Sikander, Ian Hamerton, Michael Wisnom, Mark Hazzard*

Understanding changes in Surface Roughness - HS-AFM

Ultrahigh Molecular Weight Polyethylene (UHMWPE) fibres show a wide range of excellent properties such as low weight, high specific strength, lowdensity, excellent corrosion, chemical & abrasion resistance. However, these fibres do not bond well to most of the matrices leading to a lowInterfacial Shear Strength (IFSS). Consequently, the composites employing UHMWPE fibres have a low Interlaminar Shear Strength (ILSS). Thisbehaviour is due to a non-polar, non-interactive nature of the fibre’s surface, thus limiting them to a fewer applications. This project is aimed to studyfeasibility of improvement in IFSS between UHMWPE fibres and Epoxy resin via plasma treatment, which is known to induce oxygen-bearingfunctionalities onto the surface of the fibre. During the treatment, fibres were subjected to an Ar-O2 (1:5) plasma at a high power, short exposure timeand a consistent process pressure of 7 x 10-4 mbar.

• Microdroplets of Prime20 LV dispensed on UHMWPE fibres• Contact angle decreased & average embedded length of the

droplet increased after plasma treatment• Contact angle depends on microdroplet diameter

• Increase in surface roughness, formation of surface cracks & fibredegradation observed after plasma treatment

Contact Angle Post-treatment SEM

• Survey scans identified C1s, O1s, Ca2p, S2p & Si2p peaks• Deconvolution of C1s & O1s high resolution peaks indicate presence

of Oxygen functionality

A 66% increase in oxygen functionality after plasma treatment

• No significant changes in main peaks after plasma treatment• Addition of O2 bearing peaks after plasma treatment

Proof of chemical modification - FTIR-ATR Quantification of oxygen functionality - XPS

• Increase in statistical parameters of roughness i.e. Sv, Sp, Sz, Sq, Sa & surface area of fibre after plasma treatment• Large St. Dev. in data due to high surface roughness & attraction between tip & fibre

Conclusions:• Decrease in contact angle, increase in embedded length, formation of cracks and

increase in surface area after plasma treatment – higher expected wettability• Fibre degradation at higher wattage during plasma treatment• Increased oxygen functionality on fibre surface after plasma treatment• Use of yarn instead of single fibres for obtaining stronger XPS & FTIR signals

Acknowledgements:• ACCIS labs, Chemistry &

Interface Analysis Laboratory (University of Bristol)

• Surface Analysis Laboratory (University of Surrey)

*DSM Materials Science Centre, Geleen, The Netherlands

Supported by

Suppressing delamination through vertically aligned carbon nanotubesRobert Worboys, Ian Hamerton, Stephen Hallett, Rob Backhouse and Luiz Kawashita

Vertically aligned carbon nanotubes (VACNTs) are investigated as an interlayer reinforcementtechnique. This nano-technology have been selected based on its upscaling capabilities to industrial rates using current manufacturing technologies. This alternative to Z-pinning and stitching offers negligible interference to the laminate architecture, thereby minimising in-plane elastic property losses and mass gains. Discrete interlayer strengthening aims to increase laminate fracture toughness and impact resistance, while also offering the ability to control the initial delamination location.

VACNTs Manufacture

Vertically aligned carbon nanotubes embedded in the

interlaminar region.

VACNTs

Available as a film of nanotubes within a user selected epoxy or raw.

Nanotubes engage with carbon fibres to enhance interlaminar properties.

[1]

Ply-drop Strength Enhancement

Reinforced Ply DropsDelamination

Approximate 5% increase in tensile strength through

delamination suppression.

Initial Failure

Good agreement on failure load and location between experiments and cohesive element numerical model.

Notch Strength Enhancement• Every ply interface of quasi-

isotropic laminate reinforced with VACNTs.

• CT X-ray and optical video cameras used to investigates mechanisms of failure.

Fracture Toughness Enhancement

• VACNTs induce predominately intralaminar failure and 10 –20% enhancement in toughness properties relative to an unreinforced laminate.

• Nanotube length and density investigated in Mode I and Mode II conditions.

Nanotubes integrated at every ply interface

Intralaminar fracture

Ply termination reinforced with VACNTs of differing lengths.

NanotubeBridging

Low Density VACNTs

High Density VACNTs

Structures

Granular jamming as a variables stiffness mechanism for morphing aerostructures

David Brigido, Stephen Burrow, Benjamin Woods.

One of the most persistent challenges hindering the development of effective morphing aerostructures is the needto have material/structural solutions which provide a viable compromise to the directly competing design drivers oflow actuation energy requirements and high resistance to deformation under external loading. This work isproposing an entirely new solution. Granular jamming is a physical mechanism present in particulate materials thatallows the material to undergo a fast, repeatable state change, from a liquid-like state to a solid-like state and viceversa under the action of a controllable external pressure field, which locks the particles together. If the externalpressure field is continuously variable, then granular jamming is also able to create proportional changes instiffness, thereby creating a material with variable stiffness. The aim of this work is to develop a novel concept ofmorphing wing structure using granular jamming, with the objective to adjust stiffness and control shape fordifferent flight conditions.

A novel method for designing blended laminate composite structuresNoémie Fedon, Alberto Pirrera, Paul M. Weaver, Terence Macquart

To reduce the weight of aerospace structures, composite laminate shells are divided into panels with differentthicknesses and stacking sequences. However, ply drops have a detrimental influence on the strength ofstructures. Moreover, stacking sequence mismatches at the panel’s boundaries increase the manufacturingcomplexity. The challenge is to design manufacturable multi-panel structures that satisfy global continuity andstrength requirements, with panel layouts adapted to local loadings. Due to the large number of discrete designvariables, no optimisation technique can currently be used to retrieve a globally optimal design in a reasonablecomputational time.

Principles of the novel blending technique

Design of the benchmark 18-panel horseshoe structure under panel buckling constraints

Blending methodology

• Greater-than-or-equal rule: the plies of a panelmust continue in adjacent thicker panels

• Random generation of a few ply drop layoutssatisfying blending constraints to be tested foreach group of plies

Subdivision of the optimisation problem

• Stacking sequences are divided into groups ofplies for which the fibre orientations are retrievedsuccessively and iteratively

Novel deterministic optimiser to designthe fibre orientation of the groups ofplies

• Inspired from branch and bound

• Specific objective and bound functionsfor stacking sequence design

• Controlled level exploration of thesearch tree, hence controlled executiontimes

Panel 1 Panel 2 Panel 3 Panel 4

Group 1

Group 2

Group 3

Results

• Weight of the horseshoe structure similar to the weights reported in the literature

• Design obtained in less tan an hour(improvement possible with parallelprogramming)

• Many laminate design guidelines can be considered: symmetry, balance, contiguity, disorientation, 10% rule, ply drop spacing and stacking.

• Uniform distribution of the ply drops through the thickness

Initial thickness distribution from individual panel optimisations

Multi-panel structure optimisation

Addition of a ply to the most critical panel if the buckling constraints are

not all satisfied

Nx = -700Ny = -400

Nx = -375Ny = -360

Nx = -1100Ny = -600

Nx = -900Ny = -400

Nx = -375Ny = -525

Nx = -400Ny = -320

Nx = -270Ny = -325

Nx = -305Ny = -360

Nx = -300Ny = -610

Nx = -330Ny = -330

Nx = -320Ny = -180

Nx = -190Ny = -205

Nx = -300Ny = -410

Nx = -815Ny = -1000

Nx = -250Ny = -200

Nx = -290Ny = -195

Nx = -210Ny = -100

Nx = -600Ny = -480

18 in. 20 in.

24 in

.

12 in.

Load intensities in lbf/in (x 1751.1 for N/m)

[0, 90, -45, ?, …, ?]

0° -45°45° 90°

0°

0° 45° 90°

-45°

45° 90°

0° 45° 90° -45°

-45°

Strain reversal in actuated origamiSteven Grey, Fabrizio Scarpa, Mark Schenk

Finite element model investigates the effect of facet and fold elastic stiffness

Reduced order model allows independent tuning facet in-plane and bending stiffness

Understanding the decay of actuation in origami is essential for designingdeployable or morphing structures based on the folding of materials. Bending ofthe material between folds causes a strain-reversal in locally actuated Miura-oristructures. Physically this is a deformation of the opposite sense to the actuation.

Strain-reversal: A deformation of the opposite sense to an actuation

Physical behaviour is a combination of in-plane and bending deformations of facets

Strain-reversal due to facet bending (kB)Spring-back due to facet stretching (kS)

Locally squeezing Miura-ori tubes causes strain-reversal and spring-back

Local actuation: ‘squeezing’ one unit cell

Elastic decay: reducing effect of actuation

A Miura-ori origami tube is studied. Bending of the facets causes decay of actuation

kB is the facet bending stiffness kS is the in-plane material stiffness

Spring-back: Structure is undeformed at a distance far from the actuation

Supported by

The influence of complex through-thickness stress states on in-plane fibre tensile strength of CFRP Kilian Gruebler, Stephen R. Hallett, Michael R. Wisnom

1

3

2

Support materialCFRP

σ33 + τ13 due to simple stamp andfibre curvature

Stamp

Stamp

F11F11

F 33

F 331

3

2

Support materialCFRP F11F11

F 33

σ33 + τ13 due to special stamp geometry

Stamp

Stamp

F 33

This PhD project will investigate the influence and interaction of combinations of through-thickness (primarily compression)and shear stresses on the in-plane tensile strength of fibre reinforced composites. A bespoke test method is beingdeveloped to study the material behaviour and based on this a numerical model will be developed and validated. Asuccessfully developed model and test method will give the opportunity to improve the design and the reliability ofcomposite components. Such a model and test method can be applied to applications where composites are subject tocomplex 3D stress states and the results will give a better understanding on the strength of composites.

State of the art:K.W. Gan, S.R. Hallett, M.R. WisnomBespoke test methods were developed for testing material properties in the presence of through-thickness stress. It was shown that:• Fibre direction tensile strength decreases significantly

with increasing through-thickness compressive stresses,which can be expressed as:

This work did not however account for the effect of through-thickness shear on fibretensile strength. A case that has been observed in industrial applications.

Bespoke test methods:For longitudinal tensile loading under combined through-thickness compressive and shear stress (σ11

+ + σ33- + τ13 stress state)

• Bi-axial 4-point bending test with use of stress concentrations

• Bi-axial test with inserted fibre curvature in test specimen

Expected results:

3D fibre failure envelope expressible as:

Definition of β will be project outcome

τ13σ11

τ31

σ33

σ11

σ33

τ13

τ311

32

𝝈𝝈𝟏𝟏𝟏𝟏𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓∗ = 𝝈𝝈𝟏𝟏𝟏𝟏𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊

∗ − 𝜶𝜶 ∗ 𝝈𝝈𝟑𝟑𝟑𝟑− − 𝜷𝜷 ∗ 𝝉𝝉𝟏𝟏𝟑𝟑

𝝈𝝈𝟏𝟏𝟏𝟏𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓∗ = 𝝈𝝈𝟏𝟏𝟏𝟏𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊

∗ − 𝜶𝜶 ∗ 𝝈𝝈𝟑𝟑𝟑𝟑−

Investigated stress state Possible fibre failure envelope for IM7/8552, in case 𝜶𝜶=1 and 𝜷𝜷=1

Strain will be measured with digital image correlation technique. Failure stress state will be predicted by numerical models.

Supported by

5 × 10 elements10 × 20 elements20 × 30 elements

3D stress analyses

Stiffnessanalyses 𝜎𝜎33

𝜎𝜎12𝜎𝜎23

3D-FEM

Variable-kinematics shell model: Application to delamination analysisAewis Hii, Luiz Kawashita, Alberto Pirrera

Our overarching objective is the efficient numerical analyses of complex composite shells. A nonlinear variable-kinematicscontinuum shell model was developed based on the Unified Formulation. Essentially, the formulation hierarchically generatefamilies of models with varying orders of in-plane and thickness kinematics. This presents a flexible tool to investigate thekinematic requirements for specific problems, where models with good tradeoffs between accuracy and computational costs,are identified to gain computational efficiencies. For delamination analyses, we developed the framework for a variable-ordercohesive segment method, where elements are adaptively split without inducing spurious dynamic oscillations. The higher-ordervariants host complex crack front geometry per element, and allow for stable crack propagation using large mesh size.

3. Parametric study for analysis-specific model kinematics

Damaged state

Elastic

Twisted composite shell with variable thickness

1. Variable-kinematics shell model

• Different model classes are generated with the variable-kinematics framework.• Classes suitable for specific analyses can be identified. • Accurate 3D stress analyses with the higher-order variants.

2. Hierarchical model classes

4. Variable-order cohesive segment method

In-plane order (n)

Thro

ugh-

thic

knes

s or

der (

m)

Model order N,M

…

…

…

…

• Initiation: unique shifts in cohesive laws to remove spurious oscillations.• Propagation: node-independent softening, i.e. curved crack front in an element.

In-plane displacement fieldThrough-thickness displacement field. . .

. . .

5. Adaptive delamination modelPadding elementsImprove local stress state.

Regular elementsEquivalent stiffness for the local laminates.

Transition elementsKinematics blending.

DelaminationElements are split ‘on-the-fly’; interface elements are not pre-defined at the crack planes.

2 × M th order

M th order

2M th order M th order

𝐮𝐮𝑝𝑝 = 𝐮𝐮𝑡𝑡

𝜕𝜕𝐮𝐮𝑝𝑝𝜕𝜕𝐱𝐱 ≠ 𝜕𝜕𝐮𝐮𝑡𝑡

𝜕𝜕𝐱𝐱

Blended kinematics

6. Parametric study of kinematic requirements in CZM

Generalised principle of virtual work

Independently defined/refined in-plane and thickness kinematics.

The tally numbers indicate the polynomial order of:

• The level of oscillation during crack propagation is measured by the signal-to-noise ratio (SNR).

• The mesh size requirements in using cohesive zone model are relaxed for higher-order models..

1.0 mm1.5 mm

0.5 mm

DCB with cohesive zone length of 1mm

1st order in-plane, 2nd

order thickness

2nd order in-plane, 2nd

order thickness

3rd order in-plane, 2nd

order thickness

AutomationDesign and build of a three degree-of-freedom WrapToR winding machine has demonstrated the automatability of the manufacturing process. Thismachine has proved a valuable tool for researching the truss concept as it allows fastand repeatable production of test samples.

Experimental verificationThree-point bending tests have been conductedproviding experimental data to verify the computationalmodel. A variety of measurement techniques havebeen used to gatherdeflection and straindata, including: videogauge, DIC, straingauges and lasersensors.

Process developmentMoving beyond the simple prismatic truss towards morecomplex geometries, such as curved and non-prismatictrusses would expand the possibilities for thetechnology. The ability to produce tapered trusses, ideal

for applications such as aircraft wings andwind turbine blades, has been

demonstrated using the windingmachine.

WrapToR composite truss structuresChristopher Hunt, Prof Michael Wisnom, Dr Benjamin Woods

Manufacturing Analysis

Wrapped Tow Reinforced (WrapToR) trusses combine theimpressive properties of composite materials and thestructurally advantageous geometry of trusses resulting inhighly efficient structural members.

The trusses are produced using a novel winding process thatis automatable, repeatable and uses low-cost fibre feedstock.

In an experimental comparison to conventional UD carbon fibretubes, the truss configuration offered 9 % lower mass, a 130 %increase in load carrying capability, and a 570 % increase inflexural rigidity.

UpscalingFor widespread industrial application, the concept will need to be proved advantageous at larger scales. Current work is developing a multi-spooling device that allows the production of trusseswith larger shear members that are formed from multiple tows.

Model developmentUsing matrix structural analysis techniques a model has been developed within MatLab. Work so far has been

focused on predicting deflections andmember strains. Future work will

apply failure criterionto the model for

strength predictions.

Key findingsThe analysis work hasdemonstrated the abilityto capture the underlyingmechanical performanceof the truss structures. Ithas also highlighted theimportance of modellingthe behaviour at thejoints between shear andchord members onoverall stiffness andmember strains.

Key findings

Modal nudging of stiffened structuresOlivia Leão, Rainer Groh, Alberto Pirrera

[1] Cox BS, Groh RMJ, Avitabile D, Pirrera A. Modal nudging in nonlinear elasticity: Tailoring the elastic post-buckling behaviour of engineering structures. J Mech Phys Solids 2018;116:135–49. doi:10.1016/j.jmps.2018.03.025.

The potential of using nonlinearities for new smart functionalities has become apparent in the recent literature.Modal nudging uses information from additional stable regions found in a structure's post-buckling regime totailor the nonlinear response [1]. Herein, the technique is used to improve the load-carrying capacity of astiffened panel. Focus is given to the role of symmetry on the design space exploration and how the processcan be adapted to tackle non-symmetric problems.

Methodology1. Identify disconnected stable region of interest in load-

displacement equilibrium curve and extract its deformationmode 𝐮𝐮state.

2. Superpose scaled 𝐮𝐮state to initial geometry 𝐱𝐱0 to nudge tothe desired region:

Compression buckling of a wing stiffened panel

Symmetry is broken by unbalanced laminate. Stable regions exist in the post-buckling regime with

higher load-carrying capacity than the natural path. Nudging to disconnected stable region improves the load

carrying capacity by ~2.6x without any significantchange in overall mass (Fig. 6).

Modal nudging

𝐱𝐱 = 𝐱𝐱0 + 𝜂𝜂 ഥ𝐮𝐮state𝜂𝜂: nudging factor, 𝜂𝜂~𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡; ഥ𝐮𝐮state: normalised 𝐮𝐮state.

Fig. 5. Nudged geometry (𝐱𝐱) with exaggerated nudge (𝜂𝜂=20)(Actual change to geometry is imperceptible to the eye (𝜂𝜂~thickness))

𝐮𝐮state

Sponsored by

Symmetry breaking and restorationNonlinear finite element + numerical continuation solver for modal nudging: Extensive information of the post-buckling

regime and critical points. Possibility of incrementally restoring/breaking

symmetry through navigation of the design space by controlling design parameter (e.g. mode, geometry).

Fig. 2. Geometrical restoration of symmetry Fig. 3. Laminate restoration of symmetry

Symmetric unbalanced

laminate

Equivalentbalancedlaminate

Fig. 1. Load-displacement bifurcation of compressed plate for simply-supported edges

Perfect pitchfork Easy to pinpoint bifurcation point Information from fundamental and

bifurcated paths

Broken pitchfork Information from natural path Uncertainty about broken away path Caused by geometrical (Fig. 2) or

material asymmetries (Fig.3)

StableUnstableLimit pointBifurcation point

Lateral deflection

Load

Fig. 6. Load-shortening curve showing improvement in load-carrying capacity for a nudging of 𝜂𝜂 = 1 (𝜂𝜂~thickness)

Naturalpath

Brokenpath

Perfectbifurcation

𝑢𝑢 𝑥𝑥 𝑦𝑦

𝑧𝑧Clamped edge

Fig. 4. Original geometry (𝐱𝐱0)

Clamped edge

Design and manufacturing of bend-twist coupled wind-turbine blade demonstratorsVincent Maes, Terence Macquart, Paul Weaver, Alberto Pirrera

Sponsored by:

Aeroelastic coupling, achieved using Bend-Twist Coupling (BTC), can reduce wind-turbine cost of energy, through load alleviation. Reductions in severity of gust and fatigue loads have been demonstrated in the literature by multiple authors. However, the analysis methods for BTC blades require further validation to ensure confidence in designs. Effective comparison between methods necessitates benchmark cases with test data, currently lacking in the literature, which this work aims to provide using BTC demonstrators.

To validate the stiffness coefficients calculated by cross-sectional analysers and 3D FEM, a sequence of demonstrators with varying cross-sectional geometries have been built, as shown in Figure 1. These are 1.7 meters prismatic beams, made from E-glass/913.

The demonstrators were tested under cantilevered conditions, and compared for twist predictions based on cross-sectional modellers (BECAS and VABS), as well as shell based Finite Element Method (FEM) models using S4R elements in ABAQUS. Final data comparison is still pending data processing.

Demonstrator Testing

Initial design studies for the demonstrators indicated complete agreement between the different modelling techniques, when comparing cross-sectional coefficients. Further numerical studies have, however, revealed significant sensitivity to modelling:

• Simplifications of geometrical features, seeFigure 2 (diff. of 5% in BTC Stiff. Coef.)

• Variations due to manufacturing tolerances,e.g. bond-lines, web placements, thicknesses.

Numerical Studies

Fig. 1: Schematics of demonstrator cross-sections with dimensions in millimetres.

Based on the findings so far, the following work has been identified:

• Final testing and post-correlation of data for the demonstrators, incl. location of flexural centre;

• Further detailed studies on influence of geometrical features and manufacturing tolerances;

• Confirming agreement between cross-sectional analysers and 3D FEM for all of the above trials, and

• Synthesis of modelling and manufacturing guidelines for achieving acceptable accuracy in prediction of BTC stiffness terms for wind-turbine blades.

Future Work

Inner corner Simplified

Fig. 2: Example of simplification commonly used in modelling.

Top-down of the “aeroelastic tymbal”Spanwise transverse cross-sectionHindwing Aeroelastic tymbalErmine moth

CT-scan

Two layer membrane, α-chitin reinforced protein

A one-dimensional snap-through model of the aeroelastic tymbal sound production in Yponomeutidae mothsHernaldo Mendoza Nava, Rainer Groh, Marc Holderied, Alberto Pirrera

Ermine moths (Yponomeutidae) produce bursts of clicks in the ultrasonic range to defend against bats. The biomechanical actuation of the sound production has been hypothesized as a series of buckling events in response to the aerodynamic forces exerted at a clear patch present in its hindwings (Aeroelastic tymbal)[1]. In this research a one-dimensional model resembling a single microtymbal has been investigated as the source of the sound production. Differences with respect to the experimental recordings were observed, signal decay and membrane pre-stress have been identified as further parameters to be explored.

Structural instabilities are identified relative to a rigid or hinge joint connection

Modal & Steady State DynamicsThe eigenvalues & Rayleigh damping parameters are computed

From the velocity output a FFT algorithm is used to calculate the frequency responseThe sound pressure level is calculated using the baffled-piston equationSpectrogram representation of the clicking sound

FE model assumptionsStatic and Dynamic:o Homogeneous isotropic

propertieso Constant thicknesses tbeam, tarcho Longitudinal cross-section with

clamped-SS boundary conditionso Arch subjected to a cyclic

concentrated loadAcoustics:o The measured tymbal area

equivalent to a circular piston geometry

Static Analysis Dynamic Analysis I

Dynamic Analysis II Acoustic model Future worko Pre-stress to supress the low

frequencieso Expansion to a 2d shell modelo Membrane properties

characterisationo Demonstrator to probe model

scalability

Beam Arch

JointBC-clamped

BC-SS

Window area

Microtymbals

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Damped response at the arch during cyclic loading (Explicit dynamics)The velocity at the middle of the beam is derived

[1] O’Reilly, 2019. Scientific Reports (9:1444)

Exploiting thin-ply materials to establish controlled failure in carbon compositesTamas Rev, Gergely Czél, Ian Bond, Michael R. Wisnom(tamas.rev@bristol.ac.uk, g.czel@bristol.ac.uk, i.p.bond@bristol.ac.uk, m.wisnom@bristol.ac.uk)

The failure prediction of composite materials is hindered by the lack of accurate theories anddifficulties in generating reliable experimental data [1]. Accurately determining the strength ofcomposites under multi-axial loadings is still a great scientific challenge. The utilization of thin-plymaterials allows for suppressing undesirable damage scenarios [2,3], hence the objective of thisproject: to develop innovative test methods using thin materials and investigate the interaction ofdifferent stress-components on the failure mechanisms of unidirectional composites.Understanding these interactions can enhance design performance while a safer operation inservice is ensured.

[1] M.R. Wisnom, The Challenge of Predicting Failure in Composites, 19th Int. Conf. Compos. Mater. (2013) 12–13[2] J.D. Fuller, M.R. Wisnom, Pseudo-ductility and damage suppression in thin ply CFRP angle-ply laminates, Compos. Part A Appl. Sci. Manuf. 69 (2015) 64–71. doi:10.1016/j.compositesa.2014.11.004.[3] S. Sihn, R.Y. Kim, K. Kawabe, S.W. Tsai, Experimental studies of thin-ply laminated composites, Compos. Sci. Technol. 67 (2007) 996–1008. doi:10.1016/j.compscitech.2006.06.008.

• Classical Laminate Theory (CLT)

• Design of Experiments (DOE) methods

• Advanced Failurecriteria Design and

optimizationManufacturing and Testing

Failure analysis– In-situ/post-mortem)

Syntheses

• Novel material characterisation• Precision manufacturing

(thin-plies)• Innovative test methods,

specimen configurations

• Constructingfailure envelopes

• Establishingfailure criteria

• Comparingwith literature

• Microscopy• Acoustic Emission (AE)

• Digital Image Corr. (DIC)• X-Ray Computed Tomography

(XCT)

Pivots

Compression-buckling rig

Strain distribution on tensile faceLoad cases under investigation

Longitudinal tension – Transverse compression Longitudinal compression –Transverse tension

• Novel tensile test configuration• High in-plane transverse compressive

stresses • Laminates with fibre compressive failure in 90° ply

𝑉𝑉1𝐴𝐴

𝑉𝑉 3𝐴𝐴

90° 0° pliesmore

mor

e an

gle

plie

s

• Overall transverse strains are higher than in a typical multi-directional laminate

• Negligible effect of high transverse stresses

Fluid-Structure Interaction of a composite FishBAC morphing deviceAndrés E. Rivero, Paul M. Weaver, Jonathan E. Cooper and Benjamin K.S. Woods

The Fish Bone Active Camber (FishBAC) concept is a morphing trailing edge device capable of generatinglarge, smooth and continuous changes in aerofoil camber from a biologically inspired compliant structure. Ithas already shown promising results in terms of its large lift control authority, and significantly lower dragpenalty than traditional trailing edge flaps. This work presents progress on the Fluid-Structure Interaction(FSI) analysis of a three-dimensional camber morphing composite FishBAC wing. The FSI routine is basedon a discontinuous Mindlin-Reissner plate model, that is loosely coupled with a three-dimensionalaerodynamic solver based on a viscous corrected 2D Panel Method and Lifting Line Theory. The resultingFSI routine will be key for future design and optimisation of composite FishBAC devices.

Nature’s approachBirds continuously adapt wings during flight

Our current approachRigid trailing edge flaps

Reduced Drag

Vortex Panel + Lifting Line

Fish Bone Active Camber (FishBAC)

Mindlin-Reissner Plate Model

Increased Fuel Efficiency

Reduced Noise

Fluid-Structure Interaction

• Classical Laminate Theory → Composite Analysis• Shape Functions → Orthogonal Polynomials (Chebyshev)• Structural Discontinuities → Artificial Penalty Springs

Experimental Validation

Structural Test Wind Tunnel Test

Future WorkRobust, fully coupled FSI routine

Future Design and Optimsiation of composite FishBACsExperimentally ValidatedFurther understanding of FishBAC’s benefits

[1] Laurence Whitehead (2012). Grey Backed Shy Albatross. Reproduced with Author’s permission[2] Alexandre Doumenjou (2014). ©Airbus S.A.S. Reproduced according to Airbus S.A.S. Copyright

[1] [2]

Shape Adaptive Blades for Rotorcraft Efficiency

Presented at the 8th Annual EPSRC ACCIS CDT Conference, University of Bristol

Bristol, United Kingdom16th April 2018 Video here!

Efficient non-linear wind blade modelling using high-order beam elements

Samuel Scott, Terence Macquart, Peter Greaves, Paul Weaver, and Alberto Pirrera

Upscaling wind turbines has resulted in levelised cost of energy (LCoE) reductions. However, largerturbine diameters pose significant design challenges, often with conflicting requirements. For example,the non-linear dynamics of aeroelastic tailored blades must be accurately predicted whilst, for the sakeof efficient gradient-based design, it is also desirable to minimise the computational effort of loadevaluations. This work presents the application of two structural modelling features appropriate for largewind turbines: high-order beam elements and the non-linear co-rotational framework.

High-order beam modelling• Long compliant/aeroelastic tailored blades

may exhibit large spanwise variations instructural properties

• High-order beam elements with three, four orfive nodes per element enable accurateprediction of stiffness variations with fewernodes

• Two-node elements require 151 nodes (150elements) to reach convergence of flapwise tipdisplacement, three-node elements requireonly 101 nodes (50 elements).

Static load test validation• 7 MW turbine, 83.5 m blade length (Samsung

Heavy Industries)

• Finite element (FE) beam model is standardstructural component for wind turbineaeroelastic analysis

• Comparison of linear vs non-linear beampredictions.

Test setup

Figure 1. Convergence flapwise tip displacement Figure 2. Measured vs predicted deflections for FlapMAX load case

Supported by

Adaptive mesh segmentation fordelamination initiation and propagationJagan Selvaraj, Luiz Kawashita, Giuliano Allegri and Stephen Hallett

A methodology is proposed for modelling dynamic delamination initiation and propagation in composites with multiple delamination paths. It adaptively segments the mesh with additional nodes which model the discontinuities in the displacement field caused by delamination. Besides, it also introduces cohesive segments between the newly created nodes so that delamination propagation is controlled by an energy criterion. These adaptations are performed in a dynamic explicit Finite Element solution and the mesh segmentation technique does not reduce the time increment size for solution stability. A technique to initialise cohesive tractions with minimal disturbances to the surrounding stress field is also presented.

Element 1

Element 2

Stress in Element 1 satisfies segmentation initiation criterion

Segmentation nodes areinitiated with the assignment ofmass using lumped mass matrix

Cohesive segments are initiated based oncohesive law and nodal force based tractions.

‘on-the-fly’ delaminationModelling discontinuity on continuum meshes according to physically based criteria and without direct user intervention.

Initial configuration of DCB Model

P

P

Segmentation nodes and displacement discontinuityare not visible from output of commercial FE solver.

Cohesive elements are formed adaptively asinterpreted from the output of user subroutine.

Benchmark in Mixed Mode case - FRMMDisplacement Discontinuity

Global NumberingLocal Numbering

Thermally-actuated composite helical lattices: prediction and validationJonathan P. Stacey, Mark Schenk, Carwyn Ward, Matthew P. O’DonnellBristol Composites Institute (ACCIS), University of Bristol, United Kingdom

Composite helical lattices can be tailored to createnovel cylindrical structures exhibiting large negativeaxial thermal expansions. By utilising geometry,material orientations and prestress, thesemechanisms could act as a thermally-controlledactuators or tuneable nonlinear springs within widermechanical systems.

A novel composite helical lattice has beenconstructed at the macroscopic length scale todemonstrate the predicted large negative thermalexpansion. Supporting finite element modellingshows good correlation with experiments, andthereby enables the development of such latticestructures with extreme behaviour.

INTRODUCTION CONCLUSION

21°C 135°C

Extreme CTE:-3285 · 10-6 K-1

PARAMETER SENSITIVITY• Transverse curvature important at macro-scale• Hinge friction and width variation less significant• Lattice behaviour robust to end-effects

Manufacturing & Design

Novel Termination for high quality AFPproduction

Tharan Gordon, Stephen Hallett, Michael Wisnom, Byung Chul Kim

Key Advantages

0.00

10.00

20.00

30.00

40.00

50.00

60.00

NS 1_8 1_20

Load

/ kN

Specimen Configuration

Delamination,kN

Ultimate, kN

Conventional 1:8 Ratio 1:20 Ratio

Material Testing• 3 Unidirectional specimen configurations tested:

a) Conventional ply drops

b) 1:8 taper ratio ply drops

c) 1:20 taper ratio ply drops

• IM7/8552 epoxy prepreg

Laminate Testing Resultshbj

During conventional Automated Fibre Placement (AFP) production oftapered components, discontinuities are built into the structure at the terminated ply boundaries. These can be critical in nature becoming crack initiation zones upon loading [1] that leads to delamination.

In this work, the feasibility of a novel tow termination method for AFPmanufacture is explored. The project focuses on developing a new cutting mechanism that automatically tapers the tape ends during the AFP lay-upprocess, and experimental investigation into its’ effect upon laminates.

Resin Pocket

Tapered End

Conventional

1:8 Ratio

1:20 Ratio

Effect of Novel Tow termination on Laminate

• Components formed will have improved performance with respect to delamination onset load [2]

• The process will allow for minimisation of the high computational expense of designing and analysing complextapered laminates

• New avenue of study opened for optimising plyend geometry to different loading scenarios

[1] Z. Petrossian and M. R. Wisnom, “Parametric study ofdelamination in composites with discontinuous plies using ananalytical solution based on fracture mechanics,” Compos.Part A Appl. Sci. Manuf., vol. 29, no. 4, pp. 403–414, 1998.

[2] B. Khan, K. Potter, and M. Wisnom, “Suppression ofDelamination at Ply Drops in Tapered Composites by PlyChamfering,” J. Compos. Mater., vol. 40, no. 2, pp. 157–174,2005.

A)

Delamination

Before Tensile Testing

B)

C)

AfterTensile Testing

Delamination

Taper ratio controllability

0°

0°

0°

0°

0°

0°

0°

0°

0°

0°

Half specimen geometry

1.25

mm

thic

k se

ctio

n

1mm

thin section

0.25

mm

disc

ontin

uous

[1] Z. Petrossian and M.R. Wisnom, “Parametric study of delamination in composites with discontinuous plies using ananalytical solution based on fracture mechanics,” Compos. Part A Appl. Sci. Manuf., vol. 29, no.4, pp. 403–414,1998.

[2] B. Khan, K. Potter, and M. Wisnom, “Suppression of Delamination at Ply Drops in Tapered Composites by Ply Chamfering,” J. Compos. Mater., vol. 40, no. 2, pp. 157–174, 2005.

Novel tow termination forhigh quality AFP production

Tharan Gordon, Stephen Hallett, Michael Wisnom, Byung Chul Kim

During conventional Automated Fibre Placement (AFP) production of tapered components, fibre discontinuities often referred to as resin pockets are built into the structure at the terminated ply boundaries. These can be structurally critical, becoming crack initiation zones upon loading [1,2] and leading to delamination.

In this work, the feasibility of a novel tow termination method for AFP manufacture is explored. The project focuses on developing a new cutting mechanism that automatically tapers the tape ends during the AFP lay-up process, and experimental investigation into its’ effect upon laminates.

Resin pocket

Tapered ply

Fibre Compression

Fibre Cutting

Cutting Force EvolutionCutting Fixture

Unidirectional Tensile Test Specimens

Cut Tape Quality

1:20 Ratio Tapered Ply Set Geometry

Measured Geometry

5mm

Discontinuous plies show clear

delamination under tension before ultimate

failure of specimen.

No indications of delamination under

tension. Failure mode of the specimen is

fibre failure.

0.25mm

[08]SThickness = 2mm

[010]SThickness = 2.5mm x

Line of Symmetry

Configuration X (mm)Conventional Ply Drop ~2

1:20 Tapered Ply 5

10mm

160mm

Conventional Drops Conventional Drops

1:20 Taper Ratio 1:20 Taper Ratio

As-formed: Obvious removal of discontinuity Test Behaviour

Key Advantages• Coupons have improved performance owing to

delamination suppression and a change of failure mode

• The method allows for minimisation of the highcomputational expense when designing complextapered laminates

• Potential avenue of study opened for optimising ply end geometry to different loading scenarios

1:20 Taper RatioConventional Drops

Fibre failureFibre

failureDelamination

Tensile Test Results

FEA

Machine-driven experimentation for solving challenging consolidation problems

Anatoly Koptelov, Jonathan Belnoue, Ioannis Georgilas, Stephen R. Hallett, Dmitry S. Ivanov.

Consolidation in composite manufacturing presents a serious challenge for defect mitigation,predicting dimensional tolerances, and optimization of composite morphology due to nonlinearity ofall the flow and deformation processes involved in it.The aim of this project is to develop a material testing system capable of designing loadingprogrammes and distinguishing between dominant deformation mechanisms rather than imposingrigid framework of arbitrarily selected models. This system should be self-developing, adaptableand capable of capturing the main characteristics of the consolidation process by interrogating thematerial in the way it independently decides.

Importance of consolidation Characterisation testing strategies for different materials

Project scheme

Processing Framework

Hardware

Consolidation sensor

Forc

e

Input load schedule, subject to definition

Time

Possible load

Chosen load

Thickness (time)

Based on the hardware’s output Processing framework produces adaptable loading schedule for the currenttimestep of the process

Consolidation sensor is capable of recognizing the flow/deformation modes by its characteristicsignatures

No universal testing procedure for compaction ofcomposite precursors

[3] Kelly et al.

Impregnated mat for liquid mouldingLow viscosity UD prepregs

Toughened prepregs

[1] Belnoue et al.

[1] J.P.-H. Belnoue, O.J. Nixon-Pearson, D. Ivanov and S.R. Hallett “A novel hyper-viscoelastic model for consolidation of toughenedprepregs under processing conditions”. Mechanics of Materials, Vol. 97, pp 118-134, 2016.[2] P. Hubert and A. Poursartip, “Aspects of the compaction of composite angle laminates: an experimental investigation”. Journal ofComposite Materials, Vol. 35, pp 2-26, 2001.[3] P.A. Kelly, “ A viscoelastic model for the compaction of fibrous materials”. Journal of the Textile Institute, 102(8), pp.689-699, 2011.

Importance of consolidation in defect formationConsolidation is influenced by resin flow modesExamples of different flow modes in the specimen. [1] Belnoue et al.

Cross section of samples showing the defects found [2] Hubert et al.

[2] Hubert et al.

Supported by

Micro-Scale Analysis of Progressive Static Damage in CMCs Riccardo Manno, Giuliano Allegri, Antonio Melro and Stephen Hallett

This PhD project investigates the damage behaviour of Ceramic Matrix Composites (CMCs) at the micro-scale.This level of analysis entails representative elementary volumes (RVES) located within single fibrous tows. In SiC-SiC CMCs both the fibres and the matrix have comparable failure strains, hence damage appears in complex“diffuse” patterns of micro-cracks, originating from defects such as voids. An RVE generation algorithm originallydeveloped for organic matrix composites has been adapted to CMC, including compliant fibre coatings that promotetoughness. A micro-scale homogenization framework, based on periodic boundary conditions (PBCs), has beenimplemented Abaqus. FE results are in good agreement with Mori-Tanaka theory for the linear elastic regime.

Random Fibres Placement Algorithm:

Generation of random seeds in the plane

L-BFGS-B Quasi-Newton optimization solver

Pathan, Tagarielli, Patsias and Baiz-Villafranca, Comp Part B 2016

Homogenisation Framework:

Finite Element Implementation:

Further works:• Further analyses will be performed to obtain the

homogeneous stiffness tensor for more complex RVE cases.• A more sophisticated CDM technique will be implemented to

have a better representation of the damage behaviour

Constitutive response trend with increasing the ratio:𝐿𝐿/𝑑𝑑 = 𝛿𝛿 → 𝛿𝛿 ∈ [0,∞].

The apparent stiffness tensor can be generated through six virtual tests:

Σ𝑖𝑖𝑖𝑖 = 𝐶𝐶𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑒𝑒𝑒𝑒𝑒𝑒E𝑖𝑖𝑖𝑖

Generation of a normal distribution of fibres radius and interphase thickness:

Generation of three different microstructures:

Damage Idealisation:Random planes of cohesive elements have been placed in the space for fibres and matrix:

Elastic Homogenisation:

Continuous trusstrusion of ultra-efficientWrapToR truss structures

Francescogiuseppe Morabito, Dr. Terence Macquart, Dr. Mark Schenk, Dr. Alberto Pirrera and Dr. Benjamin Woods

The Wrapped Tow Reinforced (WrapToR) truss concept is a family of ultra-efficientwound composite truss structures under development within ACCIS. These trusseshave been shown to provide an order of magnitude increase in structuralperformance compared to existing composite tubes. The TrussBot conceptproposed here is an alternative to the current filament winding based approach thatcombines pultrusion and bi-directional winding to create a continuous “Trusstusion”process. A prototype has been designed and built to show the basic viability of theconcept, and work continues to develop the manufacturing process and to quantifythe achievable performance benefits in comparison to traditional technologies.

TrussBot is able to work in both a fixed (left) or moving (right) configuration: causing the output truss to be moving or fixed respectively.

The manufactured TrussBot prototype mounted on the testing rail at University of Bristol.

TrussBot 1.0The first TrussBot prototype focused on proving the viability of the proposed concept, by winding shear webs in two directions onto a truss-shaped mandrel.

Exploded view of the winding system.

Video of TrussBot 1.0 in operation (video speed x10)

Two different working configurations:

1. Pultrusion of corners 2. Feeding forward of

corners by drive unit3. Winding of shear web

High throughput In-situ manufacturing

Moving forward, there are a number of manufacturing and analysis challenges which will be tackled:

• Consolidation and bonding of the shear web members: thermoplastic and thermosetting materials will be tested,with detailed consideration of cure kinetics and thermodynamic and mechanical aspects of material deposition.

• Analysis of mechanical properties (validated against experiments) will show the achievable performance of thesetruss structures, and will allow for design and optimisation of larger structures built up from them.

1) Pultrusion

2) Feeding

3) Winding

Finished Truss

Three stage manufacturing process:

A WrapToR Truss Structure

Local grading of composite architecturesArjun Radhakrishnan+, Ian Hamerton+, Milo Shaffer*, Farbizio Scarpa+, Dmitry S Ivanov+

+University of Bristol, *Imperial College London

Step 1: Liquid resin printing (LRP)

• Preform is injected with additive loaded polymer matrix.

• Consolidation pressure is applied at optimal resin viscosity to suppress the porosity in the patch.

Step 2: Cure and consolidation of patch Step 3: Resin infusion to form multi-matrix composite

• Remaining preform infused with host matrix via vacuum assisted resin infusion.

Structural design tool:

Effect of grading on composite performance

Process design tool:• Viscosity at point of consolidation in step 2 is critical to

suppressing porosity. • Closed loop processing is required to control the patch

morphology (Porosity & Shape).• Analytical design tools are being developed to predict the

morphology.

Switch in flow mechanisms from unsaturated to saturated patch observable from the difference in optical transparency of the patches

• A conductive network is formed by CNTs in a GFRP composite

• Through-thickness electrical conductivity of up to 0.26 S/m

• CNT patch introduces novel damage mechanisms in GFRP composites

• Open hole tensile test: increase of 17% and 24% of strain-to-failure and strength respectively.

Mechanical performance Through-thickness electrical conductivity

Printed multi-matrix carbon fibre composites

Conclusion:• Combination of process and structural design tool can be used to improve composite

performance for various applications.• Closed loop out-of-autoclave processing for multi-matrix multifunctional polymer

composites.

Stanier et al., 2019

• Grading is shown to affect stress distribution in composite through a number of mechanisms.

• Load flow modified due to stiffness gradients .

• Structural design tool helps in identifying the locations for printing to improve composite performance.

Overview of localised grading of polymer composites:

New experiments for in-plane shear characterisation of uncured prepreg

Yi Wang, Dmitry Ivanov, Jonathan Belnoue, James Kratz, BC Eric Kim, Stephen HallettAutomated Fibre Placement (AFP) is becoming one of the mainstream composites manufacturing techniques incommercial aerospace. However, one of the limitations is the occurrence of the defects generated in the towsteering process, e.g. wrinkles and tow pull off. Defect formation is closely related to the in- and out of planeproperties of uncured prepreg. This work focuses on the in-plane shear behaviour characterization of thermosetprepreg by a unidirectional off-axis tensile test, taking into account the layup speed and tow width, to betterunderstand and further simulate the AFP process.

Conclusions: This test allows extraction of the non-linear in-plane shear stress/strain relationship of uncured prepreg; The shear behaviour of uncured prepreg does not vary much with different thickness specimens; The stiffness of the material is heavily dependent on the test rates and temperatures.

Related to:• In-plane behaviour

(shear/bending)• Surface characteristics

(tack, friction)

Shear band

grip area

grip area

α𝐹𝐹𝑡𝑡

𝐹𝐹𝜏𝜏𝐹𝐹

𝐹𝐹

𝐹𝐹

Defects generated in AFP steering process [1]

Shear strain field

Method: 10˚ off-axis tensile test Hexcel IM7-8552 carbon/epoxy prepreg Shear strain extraction by DIC analysis

results Resolving local stress state for shear

stress

Temperature influence investigation

Test results in room temperature

In-plane shear characterisation

Reference: [1] Smith, R. P., et al. J. Reinf. Plast. Compos. 35.21 (2016)

Determination of buckling load Stress/Strain curves with different layers

DIC analysis results:

Evolution of buckling load with temperature The shear stress-strain curves under 0.001/s

The shear stress-strain curves under 0.1/s The shear stress-strain curves under 0.01/s

Exploring the feasibility of transportation shells for high volume preforming

Kirk Willicombe, Ian Hamerton, Sona Rusnakova, Mike Elkington, Carwyn Ward

The ever-increasing need for environmentally friendly methods of mass transportation has led to an increaseddemand for lightweight vehicles, and as such increased interest in high volume composite manufacture for theautomotive industry. As such, the development of new manufacturing methods and practices is an area ofsignificant interest. This project investigates a method by which this can be achieved, saving time in thepreforming process by utilising thermoplastic shells to transport the preforms and hold their shape, as opposedto the traditional, time-consuming approach using binder materials. This shell can then be heated andcompressed to form the matrix of the final part. An initial feasibility study has been undertaken, assessing theviability of achieving acceptable fibre impregnation and wet-out using this method.

6%

17%

34%

4%

9%

30%

Kit Cutting

Binder 'Activation'

Binder Cooling

Net Shape Cutting

Mould Evacuation

Cure

Time cost evaluation of stages of fabrication of an HP RTM automotive part [1]

WH

YH

OW

RES

ULT

S

• Preforming important for final part quality • Binder used to ensure preform holds shape; this allows

transportation and prevents geometric defects etc.• Binder shown to account for over 50% of the time cost

of a typical HP RTM automotive part

• Corollary: Removing binder from the preform process will significantly reduce manufacture cycle time

• Thermoplastic outer ‘clamshell’ to replace binder

• Shell provides preform shape• Shell matched to tool; heated and

compressed to form final part matrix• Shell benefits:

• Protects preform• Prevents defects• Allows easier transportation• Maintains geometric tolerances• Recyclable thermoplastics used

Dry surface fibres

Impregnated tows

• Trial samples manufactured of 6 ply UD Carbon and PLA shell over a range of compaction loads

• Lay-up: [0,90,0]s• Manufactured samples show good inter-tow and

intra-tow impregnation• Higher compaction loads led drier surfaces• Feasibility study successful; method should be

further refined• Larger manufacturing program with bespoke tooling

should follow

[1] L. Munshi and C. Ward, “Developing the UK High Volume Composites Supply Chain,” in JEC Automotive Forums, 2017.

Design, Build and Test

Design, Build & Test: UAV box-spar demonstrator

ACCIS CDT18Supervisors: Ian Farrow, Carwyn Ward, Kevin Potter

Two teams, Curiosity and Voyager, have been tasked with designing, building and testing a UAV box-spar demonstrator based on a single critical load case. The load case is applied through an offset-whiffle tree system, made to mimic a wing loading case. The beam shall be a closed-section monolithic, composite beam. This poster

details the key requirements as set by the client.

Structural requirements• Loads: Limit = 1000 N, safety factor of 1.5 → ultimate = 1500 N• Stiffness:

• Deflection, δ: 50 mm ≤ δ ≤ 150 mm at limit load• Tip rotation, θ: 0.25° ≤ θ ≤ 0.50° at limit load

• Strength: no fibre dominated failures or interlaminar failures below ultimate load

• Stability: no global or local buckling below ultimate load

Manufacturing requirements• Hollow monolithic, single structure beam• 20 mm diameter inspection hole at 750 mm from root• Mild steel fixture on top and bottom flange for cantilever• Must withstand a 15J impact at any location• Account for operating temperatures of -20°C up to + 50°C

Team Curiosity: Design, Build & TestMudan Chen, Callum Hill, Ali Kandemir, Sarthak Mahapatra, Michael O’Leary, Will Proud, Michelle Rautmann

Design• Lengthwise taper from a height of 60mm at x=150mm to 30mm at x=1500mm.

• 50mm < tip deflection < 150mm.

• 0.25° < tip rotation < 0.50°.

• Hand calculations were used in design. Initially simple, they evolved into

refined calculations of each section.

• Finite element analysis was additionally use as a design aide.

Build• Hand lay up of prepreg material around a male mould was used to

form the laminate.

• The mould consisted of two separate sections, joined together during

production, to ease its removal.

• The formed laminate was cured in an autoclave.

Test• Before the building stage, the glass/epoxy was tested to determine its properties.

• The beam will be tested by applying a 1kN transverse load using a wiffle tree

configuration.

• The beam will likely then be tested to failure to check if it has been overdesigned

– an undesirable trait for an aerospace component which should be as light as

possible.

Team curiosity has designed a tapered UAV wingbox solely from unidirectional E-glass fibre/ epoxy to satisfy set minimum and maximum requirements for both tip deflection and tip rotation. The use of a stiff, lightweight material has enabled a 1.5m long structure, weighing only 1.2kg, to withstand a 1kN transverse load.

Testing picture

Team Voyager: Design, Build & TestKnight Krajangsawasdi, Rafael Heeb, Eduardo Santana De Vega, Marcelle Hecker,

Gianni Comandini, Charles de Kergariou, Reece Lincoln

Team Voyager has been tasked with designing, building and testing a monolithic box-spar demonstrator based on a critical load case.

Requirements for stiffness, strength and stability have been outlined, along with geometry. The beam is to withstand a 1kN load case that is applied through an offset whiffletree loading that twists and deflects the beam.

• High strength carbon fibre (SE84 LV)• Antisymmetric lay-up, symmetric box• Stiffness/stability critical• Custom Matlab script for iterations

combined with Abaqus model

Design

• Hand lay-up on epoxy tooling board• Wax coating of tooling to melt away

for release of beam• Autoclave cure: 6 bar // 120 °C• Test piece shown on right

Build

• Offset whiffletree loading to mimic wing load case

• Strain gauges, DIC and high speed camera tocapture failure

Test

Epoxy tooling board

Wax layer

Cork

SE84 LV

EPSRC Centre for Doctoral Training in Advanced Composites for Innovation and Science

Bristol Composites Institute (ACCIS) University of Bristol, Queen’s Building, University Walk,

Bristol, BS8 1TR, UK

www.bristol.ac.uk/composites/cdt