9th accis & 1st ncc annual conference 2016€¦ · morphing hybrid honeycomb (mohycomb) with...

9th ACCIS & 1st NCC

Annual Conference 2016

Tuesday 13th September 2016

National Composites Centre, Bristol & Bath Science Park, Emersons Green,

Front cover photo credits:

Main Image: Mike Elkington, robotic arm for automatic fibre placement.

Left: Logan Wang, high speed camera.

Centre: Stephen Hallett, Thompson 5HS shifted.

Right: Fabrizio Scarpa, cactus fibre microfibril.

Contents ACCIS Research

Adaptive structures for fluid flow regulation Gaetano Arena, Rainer Groh, Raf Theunissen, Paul Weaver, Alberto Pirrera

Predicting and understanding wrinkle formation in components made from toughened prepreg Jonathan Belnoue, Oliver Nixon-Pearson, Tassos Mesogitis, James Kratz, Dmitry Ivanov, Ivana Partridge, Kevin Potter, Stephen Hallett

Strong cellulose fibres manufactured using chemically tailored ionic liquids Jyoti Bhardwaj, Olga Kuzmina, Kevin D Potter, Sameer S Rahatekar, Tom Welton

Self-repair technologies for FRP composites Tim Coope, Rafael Luterbacher, Ian Bond

Virtual layup prediction Michael Elkington, Carwyn Ward

Morphing hybrid honeycomb (MOHYCOMB) with in-situ Poisson’s ratio modulation Callum Heath, Robin Neville, Fabrizio Scarpa, Ian Bond, Kevin Potter

Cure path dependency of interleaf prepregs James Kratz, Tassos Mesogitis, Alex Skordos, Ian Hamerton, Ivana Partridge

Design and optimization of composite structures through advanced high-fidelity models Sergio Minera, Mayank Patni, Paul M Weaver, Alberto Pirrera

Recycling manufacturing scrap for high value applications Jamie Snudden, Carwyn Ward, Kevin Potter

High fidelity modelling of the compaction behaviour of 2D woven fabrics Adam Thompson, Bassam El Said, Dmitry Ivanov, Jonathan Belnoue, Stephen Hallett

Meta-compliance and energy dissipation in cactus-based solids Ioannis Zampetakis, Alistair Hetherington, Adam Perriman, Fabrizio Scarpa

Nano-ink coated open cell PU foam with micro-architectured multilayer skeleton Xiao-Chong Zhang, Fabrizio Scarpa, Ronan McHale, Andrew P Limmack, Hua Xin-Peng

High modulus regenerated cellulose fibres spun from a low molecular weight microcrystalline cellulose solution Chenchen Zhu, Robert Richardson, Kevin Potter, Anastasia Koutsomitopoulou, Jeroen Van Duijneveldt, Sheril Vincent, Nandula Wanasekara, Stephen Eichhorn, Sameer Rahatekar

EPSRC Centre for Doctoral Training in Advanced Composites for Innovation and Science (CDT)

Composite compliant actuator for wearable robotics Chrysoula Aza, Lorenzo Masia, Paul Weaver, Alberto Pirrera

Embracing nonlinearities in structural design Bradley Cox, Rainer Groh, Daniele Avitabile, Alberto Pirrera

Development of liquid processable BT resins Robert Iredale, Carwyn Ward, Ian Hamerton

Gamification for improved layup Shashitha Kularatna, Carwyn Ward, Kevin Potter

The circular economy of composite materials Matthew Such, Carwyn Ward, Kevin Potter

Development of a closed-loop recycling method for short carbon fibre composites Rhys Tapper, Marco Longana, HaNa Yu, Ian Hamerton, Kevin Potter

HiPerDuCT Programme Grant

Fibre fragmentation detection in pseudo-ductile hybrid laminates by acoustic emission Mohamad Fotouhi, Putu Suwarta, Meisam Jalalvand, Gergely Czel, Michael R Wisnom

Combining fibre rotation and fragmentation to achieve optimised pseudo-ductile CFRP laminates Jonathan Fuller, Meisam Jalalvand, Michael R Wisnom

Pseudo-ductile quasi-isotropic hybrids Meisam Jalalvand, Mohammad Fotouhi, Gergely Czél, Michael R Wisnom

Development of high performance ductile composites by optimising the matrix Thomas Pozegic, Ian Hamerton, Michael Wisnom

Applications of the HiPerDiF method HaNa Yu, Marco L Longana, Kevin D Potter, Michael R Wisnom

Composites UTC, supported by Rolls-Royce

Advanced curing for on-platform repair of aerospace composite components by external magnetic fields Giampaolo Ariu, Ian Hamerton, Bhrami Jegatheeswaram Pillai, Dmitry Ivanov

Experimental testing for defects and features – ‘DF2’ test programme Mike Jones, Hafiz Ali, Stephen Hallett, Michael Wisnom

Effect of foreign object damage on composite aerofoils and structures Ashwin Kristnama, Michael Wisnom, Stephen Hallett, David Nowell

High cycle fatigue behaviour of composites for aero engine applications – fully reversed fatigue testing Rico Kuehlewind, Luiz F Kawashita, Stephen R Hallett

Identification and prediction of damage development in composites under HCF Fabrizio Magi, Dario Di Maio, Ibrahim Sever

Variable stiffness composite laminates for rotating pre-twisted plates Matthew Thomas, Paul Weaver, Stephen Hallett

Fatigue behaviour of CFRP under environmental conditions Georgios Voudouris, Dario Di Maio, Ibrahim Sever

Advanced experimental testing for Z-pinned composites Felix Warzok, Giuliano Allegri, Maik Gude, Stephen Hallett

ACCIS Research

Previous page photo credit: Jamie Snudden, 'Simulation of delamination progression through a quasi isotropic laminate under tension.'

www.bristol.ac.uk/composites

A design concept for an adaptive, variable geometry fluid inlet is presented. Theinlet’s shape adapts passively in response to varying flow conditions. In contrast totraditional designs, the inlet does not rely on separate mechanisms for actuation.Instead, the novelty of the present approach is that a variety of adaptive responsesare obtained by exploiting the nonlinear behaviour of post-buckled structures.

Adaptive structures for fluid flow regulationGaetano Arena, Rainer Groh, Raf Theunissen, Paul Weaver & Alberto Pirrera

Supported by

Coupled Eulerian-Lagrangian (CEL) fluid-structure interaction

Adaptive inlet with monostable snap-through behaviour

1) Open stable state 2) Snap-through occurs once acritical velocity is reached

3) Unstable closed state 4) Suction holds the inlet in itsclosed state.

INTERACTION

FLUID

Abaqus solves the Equation of State (EOS), plus the continuity and momentum equations.

p=pressure; pH=Hugoniot pressure; Γ=Grüneisen ratio; EH=Hugoniot specific energy; e=internal energy;ρ=density; v=velocity; f=body forces, σ=Cauchy stress tensor=-pI+σdev.

Precompression

Adaptive behaviour through nonlinear structural mechanics

Influence of pre-compression and pre-bending (1) on a post-buckled beam (2). When symmetry is broken (broken pitchfork), regions of bistability (3), monostability with snap-through behaviour (4) and simple monostability are identified.

Cen

tral

dis

plac

emen

t

(1)(2) (3)

(4)Bistability

STRUCTURE

Monostability with snap-through behaviour

Sim

ple

stab

ility

Forc

e

Snap-through

Unloading path

0

Central displacement

Forc

eSnap-through

Unloading path

0

Applications


Resin flow has a major impact on composites part quality. In the present study, anovel flow model for toughened prepreg systems was proposed. The new modelwas implemented in the finite element (FE) package Abaqus. The model wascoupled with existing cure simulation models for the description the full cure cycle.

Predicting and Understanding Wrinkle Formation in Components Made from Toughened Prepreg

Jonathan Belnoue, Oliver Nixon-Pearson, Tassos Mesogitis, James Kratz, Dmitry Ivanov, Ivana Partridge, Kevin Potter and Stephen Hallett

Supported by

Experimental Programme•Various load sequences (monotonic &ramp-dwell), load rates (up to 24.5N/s), and temperatures (30ºC to 90ºC).•Scale effects related to flow peculiaritieswere studied for samples of various sizes and configurations

Model for prepreg consolidation•The experimental programme showed:flow transition mechanism, strong scale effect and compaction limit phenomenon.•Model of effective ply behaviour based onmicro-structural considerations.

Prediction of wrinkle formation•The model capabilities were assessed on anumber of cases inspired by industry.

What next?• The ability of this new tool to predict wrinkles in full-

scale components is now being investigated.• The newly developed tool can be used in conjunction

with failure models to form a design tool able to takemanufacturing constraints into account.

CP BP SB

16plies15/30 mm

25/50 mm

Figure 1: Crucifix shaped samples compacted in a DMA

3D Hyper-viscoelastic model•Theoretical formulation of 3D hyper-viscoelastic model •Implemented in Abaqus/standard.•Good agreement of the model predictions withthe experimental data

200µm20µm

Figure 2: Micrograph of a BP specimen

Figure 3: Thickness evolution for CP and BP specimens (IM7/8552) under ramp-dwell loading (model

predictions)

Figure 4: Width evolution with temperature of BP baseline and scale-upspecimens (IM7/8552)

Figure 5: Consolidation and curing over an L-shaped tool. Good agreement between experiments (left) and model predictions (right).

Figure 6: Predictions for tapered laminate cured with hard tooling (bottom) agrees very well with experiments (top).


Strong Cellulose Fibres Manufactured using Chemically Tailored Ionic Liquids

Jyoti Bhardwaj1, Olga Kuzmina2, Kevin D Potter1, Sameer S Rahatekar1, Tom Welton2

1University of Bristol, 2Imperial College LondonThis project aims to carry out a systematic study of the influence of the cation’s and anion’s structure of thesuperbase ionic liquids (Fig. 2) to improve the dissolution of cellulose, fibre spinning process and theresulting fibre’s mechanical properties avoiding the known drawbacks. Acetate and diethylphosphate ILswere successfully able to dissolve cellulose to produce concentrated spinning solutions (dissolution timefrom 2.5 to 4 hours and temperature between 60-95 °C, cellulose concentration 4%).

Mechanical Properties Of Cellulose Fibres

0

50

100

150

200

250

300

0 0.05 0.1

Str

ess

Strain

Fibre Cross-section

BMIm Cl MP 80˚CNaCl MP 803˚C

BioEconomy

What are Ionic liquids ?

Biomass from Forest & AgricultureStrong Fibres

Manufactured from Biomass

Extruder

Types of Ionic liquids Currently Used

Bio-Economy for Composites Manufacturing

An ionic liquid is a salt which can be liquid below 1000 C or evenat room temp. The cation in ionic liquids is asymmetric whichcauses poor bonding with its anion resulting in low attractionbetween them and hence low melting point.

Ionic Liquid used for Fibre Spinning Young’s Modulus

Tensile Strength

1,5-Diazabicyclo[4.3.0]non-5-eniumacetate 4.6 (±1.1) 78.9 (±9.0)

1-Ethyl - 1,8-diazabicyclo[5.4.0]undec-7-enium diethyl phosphate 5.3 (±0.8) 81 (±8.5)

1-Ethyl -1,5-diazabicyclo[4.3.0]non-5-enium diethyl phosphate 7.5 (±1.4) 97.3

(±21.6)

1-ethyl-3-methyl imidazolium diethyl phosphate 20 (±2.3) 281.5

(±30.5)

Sustainable Composites

Common Salt Ionic liquid (asymmetric cation)

Winding unit

Coagulation bath

Ionic liquids are effective & benign solvents to dissolvecellulose, silk and range of natural bio polymer fibres.


Application

After 15000 cycles

Self-repair technologies for FRP composites Tim Coope*, Rafael Luterbacher and Ian Bond

*[email protected]

Self-healing technologies are developed to realise a new generation of smart fibre reinforced polymer (FRP) composites containing an in situ repair functionality, while operating in demanding environments.

Embedding self-healing functionalities into high performance polymer composites has the potential to afford further weight savings by reducing the required safety factors and to facilitate significant change to current composite material design parameters.

Supported by Self-HealIng POlymers for Concepts on self-Repaired AeronauticalcomposiTES (HIPOCRATES) The aim of the HIPOCRATES project is to serve as a platform for developing the required knowledge, technologies, procedures and strategies to deliver self-repairing composite aero-structures, while defining the roadmap to achieve the vision of self-repairing composite structures. (Grant agreement no: 605412)

‘Self-healing prepreg’ system†

• Upon heating (120-150°C, 5 minutes) the Diels-Alder (DA) functionalities disassociate to the two separate components • Cooling facilitates the ‘healing’ process

• Double cantilever beam (DCB) CFRP testspecimens with an integrated DA ‘self-healingprepreg’ on the central mid-plane

†material developed by TNO Materials, NL

Stringer run-out demonstrator • Embedded microvascular channels located on skin-stringer interface

• Stringer debonding during static testing to expose microvascules

• Epoxy resin injected via protruding vascules at run-out

• Promising results showing good recovery for stringer disbond

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Load

, N

Extension, mm

Baseline SE70 without SH SE70 SH DCB : Initial SE70 SH DCB : Healed (x1) SE70 SH DCB : Healed (x2) SE70 SH DCB : Healed (x3)

• 35% reduction ‘Baseline SE70without SH’ vs. ‘SE70 SH DCB :Initial’

• 45% healing (1st cycle)• 50% healing (2nd cycle)• 65% healing (3rd cycle)

• Potential for further healing

After 15000 cycles

Intrinsic

Thermo-reversible epoxy system

Damage to adhesively joined components

Skin-stiffener panel debonding

Microvascular

Embedded vascular channels

After 15000 cycles

Tech. solution 1 Tech. solution 2

Multifunctional Monomers

Thermoset behaviour

Thermoplastic behaviour

Healed

Damaged

Heating

Diels-Alder reaction


Hand layup is a very complex process which for some components can contributea significant amount of the manufacturing costs. Layup modelling software suchas ‘Virtual Fabric Placement’ (VFP) can already predict how a sheet of wovenmaterial will deform as it is laid up over a complex shape. This project takes thisa step further and processes the outputs from such programs to identify potentialdefects and areas which will be particularly difficult to layup either robotically orby hand. This will allow rapid optimisation of component designs for more efficientmanufacturing. Additionally, detailed instructions can be automatically generated,showing how to layup each part enabling faster, more consistent layup.

Virtual Layup PredictionMichael Elkington, Carwyn Ward.

Supported by

Bridging locations

Probable wrinkling locations:

Probable tension applications:

Complexity analysis

Componentshape

‘Secondary’ bridging

‘VFP’ Sheardiagram

Identify ‘easy’ areas

Identify ‘hard’ areas


Electrostatic adhesion can be used as a means of reversible attachment. Throughapplication of high voltage (~2kV) across closely spaced parallel plate electrodes,significant shear stresses (11 kPa) can be generated. Such reversible adhesion canprovide control of the internal connectivity of a cellular structure, and determinethe effective cell geometry. Such a structure offers the potential for tuneablevibration absorption (due to its variable stiffness properties), or as a smarthoneycomb with controllable curvature.

Morphing Hybrid Honeycomb (MOHYCOMB) with in-situ Poisson’s ratio Modulation

Callum Heath, Robin Neville, Fabrizio Scarpa, Ian Bond and Kevin Potter

The ConceptElectrostatic Adhesion provides a means of reversible coupling between structural elementsgenerated from closely spaced high voltage electrodes. Introducing this capability to cellularstructures allows for control of the effective cell morphology.

ImpactThe in situ modulation capability of MOHYCOMBis promising for use in adaptable structuresapplications. Modification of not only stiffness,but also Poisson’s ratio on demand allows forcontrol of both in-plane and out of planeproperties, such as secondary curvature.

ResultsVideo gauge tracking allowed for the demonstration of variablestiffness up to 450 % and Poisson’s ratio modulation between theregular and re-entrant honeycomb configurations.

ConfigurationStartWidth(mm)

StartHeight(mm)

∆x(mm)

∆y(mm)

Regular 130.8 73.8 -4.3 4.5 1.84 0.54

Re-entrant 132.6 73.8 3.2 4.0 -2.23 -0.45

All On 125.6 72.5 -2.6 4.0 2.67 0.37

*Heath, C.J., Neville, R.M., Scarpa, F., Bond, I.P. and Potter, K.D., 2016. Morphing hybrid honeycomb (MOHYCOMB) with in situ Poisson’s ratio modulation. Smart Materials and Structures, 25(8)


Interleaf toughened systems have been developed to improve the impactresistance of composite materials. Particles – often thermoplastics – are added tothe base epoxy matrix to improve delamination resistance. Here we investigatethe cure kinetics needed for degree-of-cure simulation.

Cure Path Dependency of Interleaf PrepregsJames Kratz¹, Tassos Mesogitis², Alex Skordos³, Ian Hamerton¹, Ivana Partridge¹

1 University of Bristol, 2 National Composites Centre, 3 Cranfield University

Supported by

Particle interleaved laminate100µm

Conventional laminate

Particle Interleaf Composite Materials• Thick resin layers between fibre plies

Heat Transfer Relationship

𝜌𝜌𝐶𝐶𝑝𝑝𝜕𝜕T𝜕𝜕𝑡𝑡 −

𝜕𝜕𝜕𝜕𝑧𝑧 𝑘𝑘𝑧𝑧

𝜕𝜕𝑇𝑇𝜕𝜕𝑦𝑦 = 𝜌𝜌 1 − 𝑉𝑉𝑓𝑓 Δ𝐻𝐻𝑅𝑅

𝑑𝑑𝑑𝑑𝑑𝑑𝑡𝑡

Heattransferred by the laminate

Heatabsorbed by the laminate

Heat generated by the resin cure

reaction

• Are these parameters obtaineddifferently from a non-particle system?

• What if the particles melt?

Glass Transition Temperature (Tg)• The DiBenedetto relationship has a single constant λ to describe Tg in conventional epoxies

• Rapidly quenching an isothermal hold or a dynamic ramp test (conventionally used todetermine ΔHR) at various times and measuring the Tg,Quench will indicate whether a curepath dependency exists

• Occurs above the recommended 180°C cure temperature

• Cure kinetics of the reaction exhibit no path dependency

𝑇𝑇𝑔𝑔 − 𝑇𝑇𝑔𝑔,i𝑇𝑇𝑔𝑔∞ − 𝑇𝑇𝑔𝑔0

= 𝜆𝜆𝑑𝑑1 − (1 − 𝜆𝜆)𝑑𝑑

where : uncured ∞: ultimate α: instantaneous degree-of-cure, λ: fitting parameter

Dynamic (left) and Isothermal (right) heating tests

• A cure path dependency of Tg is evident at highheating rates (5°C/min)

0

50

100

150

200

0 0.25 0.5 0.75 1

T g(

C)

Degree-of-cure

150°C 180°C 2°C/min 5°C/min

Glass transition temperature evolution

Points above 200°C

Tem

pera

ture

Time

Conventional Quenched test

Tg,i

Tg,Quench

ΔHR

Quenchpoint

Tem

pera

ture

Time

Conventional Quenched test

Tg,i

Quenchpoint

Tg,Quench

ΔHR


Taylor expansion

Lagrange expansion

Calculating accurate 3D stress fields for structural tailoring is often a complex,computationally expensive task. This is especially so for lightweight, thin-walledcomposite parts with stiffening elements such as stringers and ribs, and localisedfeatures such as stringer terminations and rib foot connectors. The so-calledUnified Formulation offers a computationally efficient means of capturing high-fidelity 3D stress fields and considerable scope to analyse such features in a robustand direct way.

Design and optimization of composite structures through advanced high-fidelity models

Sergio Minera, Mayank Patni, Paul M. Weaver, Alberto Pirrera

Introduction to FULLCOMPThis research project is conducted as part ofthe FULLCOMP consortium. FULLCOMP (FULLyintegrated analysis, design, manufacturingand health-monitoring of COMPositestructures) is funded by the EuropeanCommission under a Marie Skłodowska-CurieInnovative Training Networks programmewithin Horizon2020. The consortium iscomposed of seven Universities, one researchinstitute and one company[1] where 12 PhDstudents are working in an internationalframework to develop integrated analysis toolsto improve the design of composite structures.

ObjectiveOn the basis of the Unified Formulation, new,accurate and computationally cheap designand optimization methods are beingdeveloped, with particular attention paid toaerospace structures and the buckling analysisof thin-walled shells.

Supported by

H2020MSCAITN – ETN

3D structure Cross-sectional expansion

1D FE model

u(x,y,z) u(x,y,z)=uζ (y)Fζ (x,z) uζ (y)=uζi Ni (y)

Task 1: Development of advanced models forthin-walled structure buckling

Task 2: Development of enhanced models foraccurate 3D stress fields around complexgeometries.

Open square cross-section3D localized stress

C section beam Von Mises stress distribution

Plate Cross-section mesh

Beam First three modes

Bending modes

Twisting modes

Scordalis roof Shell buckling

Computational expansion of the displacement field

[1] www.fullcomp.net


An area of concern for the composites industry that is becoming increasinglyapparent as its popularity increases is how to recycle it. One particular source ofwaste that could be exploited for generating a new, cheap, material for high valueapplications is the manufacturing processes. With quoted buy – to – fly ratios ofup to 1.7-1, there is a huge quantity of otherwise useable material going to wastein landfill. A novel approach to reforming this waste has been developed forapplications such as energy absorption that demonstrates a high level of propertyretention compared with virgin material in both static testing and energyabsorption, showing that there are other options that sending the scrap to landfillas waste or grinding it up for use as filler or moulding compound.

Recycling Manufacturing Scrap for High Value Applications

Jamie Snudden ([email protected]), Carwyn Ward, Kevin Potter

• High property retention possible fromreforming scrap;

• Delamination and fibre fracture are principalfailure modes

• Automated manufacturing route creation andcostings analysis to be performed

Reforming Approach

Mechanical Property Retention

Ongoing project Conclusions and future work

Waste cut into patches

Secondary waste removed

Coupons laid up in regular

pattern

Coupons collected and

sorted

Next ply offset

Ply stack bagged and infused by VARTM

0102030405060708090100110120130140150

0100200300400500600700800900

100011001200130014001500

Stif

fnes

s (G

Pa)

Ulti

mat

e st

reng

th (

MPa

)

strength

stiffness

0

20

40

60

80

100

120

0

200

400

600

800

1000

1200

1400

Continuous Discontinuous

Flex

ural

Mod

ulus

(G

igap

asca

ls)

Ulti

mat

e fle

xura

l str

engt

h (M

egap

asca

ls)

strength stiffness

Failure modes

Offcuts taken and cut into patches of at least 50mm x 50mm, and reformed into an aligned discontinuous preform with the process shown. Example of material reformed into flat

plates Flow chart for the reforming process Layup diagram for an 8 ply Quasi Isotropic reformed laminate made up

of 100mm square patches

In UD reformed material, property retention in both tension & flexure is high. Tests were performed on large samples to ensure a high quantity of discontinuities within the gauge length.

Tensile property retention

Flexural property retention

A modelling approach has been created to accurately model the failure mechanismspresent in the reformed material using cohesive zone modelling.

The more angle plies present within a laminate, the greater the amount of delamination present. Cracks jump between plies at discontinuities in the 0° plies.

Failure surfaces in a quasi isotropic tensile sample with a [45,-45,0,90]s stacking sequence

Simulation of delamination progression through a quasi isotropic laminate under tension


A modelling approach has beendeveloped to predict the mechanicaland kinematic behavior of wovenfabrics during compaction. The keybenefit of this method is that thedependency on detailed geometricand mechanical examination of thephysical specimen is removed.Hence, the possibility of makingaccurate predictions without accessto the physical specimen is attained.

High fidelity modelling of the compaction behaviour of 2D woven fabrics

Adam Thompson, Bassam El Said, Dmitry Ivanov, Jonathan Belnoue, Stephen Hallett

Modelling Approach

The method uses a two step modellingframework -The first step uses a kinematic multi-chainelement method to generate the initial as-woven fabric geometry.The second step uses this geometry togenerate a 3D finite element model. This iscoupled with a hyper-elastic material modelwhich describes the behavior of a single yarn.

Modelling Single and Multi-Layer compaction

Single or multiple layers can then becompacted to examine and predict both thegeometrical changes and mechanicalresponse of the fabric or layup.

Comparisons with X-ray CT scans show themethod gives good predictions for both yarnpath and yarn cross-section deformations.

The method is also able to capture effects oflayer stacking and nesting on the mechanicalcompaction response as shown below.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65

Pres

sure

(MPa

)

Volume Fraction

Single Layer

6 Layer Aligned

6 Layer Arbitrary Shift

Supported by


Fig.1: Energy dissipation of Cacti fibre composites1

1. Bouakba, M. et al. Cactus fibre/polyester biocomposites: Manufacturing, quasi-static mechanical and fatigue characterisation. Composites Science and Technology 2013, 74, 150-15

Meta-compliance and energy dissipation in cactus-based solids

Ioannis Zampetakis, Alistair Hetherington, Adam Perriman, Fabrizio Scarpa

Cactus Fibres:

• High Specific properties, light in weight& significant composite reinforcementpotential.

• Excellent flexural modulus and fatiguetoughness under cyclic loading.

Supported by

Morphological Characterization1. Fractal Geometry Analysis:

• A fractal is an object that when subdividedinto parts each part is a reduced copy of thewhole.

• Box-Counting method for fractal orderestimation on optical microscopy and SEMimages.

• A Fractal Order of 1.8 was estimatedacross magnifications for the fiber sheets and fibre powder.

2. X-Ray CT:

• Images enable the mechanical modellingof the fibres to correlate their morphologyand mechanical properties.

Future Work:

• Modelling of Cactus fibres for mechanical property assessment and understanding.

• Polymer composite prototype fabrication.

Fig.2:Optical Microscopy & SEM images for fractalcharacterization

Fig.3: X-ray CT image and model

Global Objective: We aim to develop novel composite materials using Cactus fibresfor impact energy dissipation and bone tissue engineering applications. Cactus fibres,demonstrate unique deformation mechanisms and energy dissipation propertiesunder cyclic flexural loading as composite reinforcements. A multiscale morphologicalcharacterization of the cacti fibres on the nano, micro, meso, and macro scale willprovide insight into how their unique structure translates to their unprecedentedmechanical properties, in a sheet and a powdered format obtained via ball milling.Models will be developed and composites fabricated will be mechanicallycharacterized using static, dynamic and impact protocols with the aim to generate annew structural paradigm for energy dissipation applications.


660%330%

270%

Using CNT nano-ink, a simple dip-coating technique was developed to form amicroarchitecture similar to multilayer covering on each cell strut of PU foam.Significantly improved the foam electrical, mechanical and damping performance whencomparing with the pristine foam.

Nano-ink coated open cell PU foam with micro-architectured multilayer skeleton

Xiao-Chong Zhang, Fabrizio Scarpa, Ronan McHale, Andrew P. Limmack, Hua-Xin Peng

Supported by

Dip-coating technique

PU foam strut

PUD top coat

CNT

Foam strut

Illustration of one layer coating

SEM image showing skeleton of open cell PU

foam

Illustration of multi-layered coating at foam cross section

Isopropyl30min

Sonication

Silane treatment

Carbon nanotube ink (0.1wt%)

Silane treated foam

• ρ= 27kg/m3

• 2047-2244 pores/m

• MWNT-COOH• D= 20nm, L= 10’s of μm

O2 Plasma

Pure PUfoam

Step1:Nano-ink preparation

Step2:Foam preparation Water based PUD coating

Silanetreated

PUfoam

Drying

Drying + silane

CNT Ink coating

Step3:Multipayer coating processStep 1: MWNT-COOH added directly into IPA, followed by 30min ultrasonication with

dispersant.

Step2: Open cell PU foams were firstly O2

plasma treated and immediately immersed

in a silane solution. The silane acts as a

coupling agent to chemically bond the CNTs

onto the foam strut.

Step3: Silane-treated foams immersed

into the ink. Foam then removed for drying

at 80 °C for 12 hours. Water-based PUD

applied as sealant to form the sandwich

microstructure. Repeat this process to

create the multi layered microstructure. 0.01wt%

0.05wt%0.1wt%

0.2wt%

Surface Morphology and Electrical Conductivity

0.1wt%

• Heavily entangled CNTs observedwith increased ink concentration

• Electrical conductivity increaseswith increasing ink concentration

• Percolation threshold regionbetween 0.05wt% and 0.1wt%

• Conductivity reached 1S/m withjust 0.1wt% ink.

Static and Quasi-static Compression Dynamic Mechanical Analysis

• E’ and E” increased with increasingnumber of coating layers

• Nanotube-nanotube interfacialsliding contributed significantly tothe overall damping

• 4 layers of coating improved thestorage modulus by 330%, lossmodulus by 660%.

• ‘4MW’ exhibits 220% and 190%increments of E and σ10 respectively

• MWNTs core formed rigid sheatharound the flexible PU foam skeletonimproved the foam mechanicalperformance

~70% increment

~ 380%increment

• 380% increment indissipated energy, 70%increment in loss factor with4 coating layers (4MW).

• Damping in CNT core layercontributed significantly tothe overall performance.


High modulus regenerated cellulose fibres spun from a low molecular weight microcrystalline

cellulose solutionChenchen Zhu1, Robert Richardson2, Kevin Potter1,

Anastasia Koutsomitopoulou1, Jeroen van Duijneveldt3, Sheril Vincent1, Nandula Wanasekara4, Stephen Eichhorn4, Sameer Rahatekar1

1ACCIS, University of Bristol, 2H H Wills Physics Laboratory, University of Bristol, 3School of Chemistry, University of Bristol, 4College of Engineering, University of Exeter

Supported by

V2V1Air

gap

Extruder

Winding unit

Dry-jet Wet Fibre Spinning

18.0 wt% Cellulose Fibre

Published by ACS Sustainable Chemistry & Engineering,July 2016

Ionic Liquid (IL) as Benign SolventMicrocrystalline Cellulose

20 °C

Liquid Crystalline Phase Cellulose/IL Solution

EPSRC Centre for Doctoral Training in Advanced

Compositesfor Innovation and Science

(CDT)

Previous page photo credit: Leonardo Cappello and Lorenzo Masia, 'The Oculus Rift combined with the Leap Motion.'


Composite compliant actuator forwearable robotics

Chrysoula Aza, Lorenzo Masia1, Paul Weaver, Alberto Pirrera

Supported by

A novel actuator for a wearable robotic device assisting elbow motion has beendeveloped. The actuator combines current mechatronics with compositestructures with nonlinear stiffness characteristics. Nonlinearities are exploited toobtain compliance, force and position control authority, as well as powerefficiency; all key features for the successful design of robotic devices that involvedirect human-robot interaction.

Compliant actuatorComposite structure

Motor

ReAct

Bowden cables

Timing belts

front back

• Minimising dimensions for space& weight limitations.

• Composite transmission in stableequilibrium at pitch θ = ±45°.

• Maximum axial force F = 50N.

stripspoke

L

H=

2R

Ζ

φ

θ Δℓ

X

W

ℓ

• Multi-objective optimizationusing genetic algorithm.

• Decision variables:• Composite layup.

• Strips’ stress-free curvatures.

• Diameter of transmission.

• Strips’ length.

• Strips’ width.

Design requirements

FE model

Application

Manufacture & Test

Composite transmission

optim

um

Optimization process

(1) Pre-stress (2) Assembly –straight configuration

(3) Twisted stable configuration

(4) Coiled configuration

1 School of Mechanical & Aerospace Engineering,Nanyang Technological University, Singapore


Figure 3: Λ2 continuation; at the most efficientstructure of Λ3 = 0.99993, the total volume of the

structure varies from 200 (Λ2 = 1) to 1000 (Λ2 = 5);

(a)

(b)

Figure 2: Λ3 continuation (a) Equilibrium surface ofbeam problem with fixed average area Λ2 = 1 in multi-parameter space. The black line represents the most efficient structure; (b) Top-down view of Figure (a);

Blue, stable; Red, one eigenvalue unstable; Green, two eigenvalues unstable

Embracing nonlinearities in structural designBradley Cox1, Rainer Groh1, Daniele Avitabile2 and Alberto Pirrera1

IntroductionNonlinear phenomena are prevalent instructural and continuum mechanics, albeit notcommonly utilised. This general reluctance isdue to the lack of availability of sufficientlyrobust computational tools to solve thesecomplex problems. There appears to be littlequestion that the so-called incremental iterativemethods represent by far the most popularprocedures for the solution of nonlinearstructural mechanics. Of these, numericalcontinuation provides many advantages. Thenoteworthy, yet often overlooked, quality is itsapplication in optimising engineeringstructures.

Numerical continuation is coupled to anonlinear finite element analysis framework,where, for a benchmark nonlinear problem,arched beams are analysed using structuralbeam elements based on Timoshenkokinematics.

Future research

Numerical continuation

Results and discussion

Motivation

Model definition

Within the realm of nonlinear structuralanalysis it is generally understood that moststructures are somewhat overdesigned. This issimply to ensure that they respond linearly tothe externally applied loads. The motivationbehind the current research is to enableengineers to design new structures thatembrace well-behaved nonlinear deformationsthus potentially leading to significantly moreefficient structures, by removing redundant andunnecessary stiffness, and in turn mass.

Numerical continuation is a numerical methodused for computing solutions of a system ofparameterised nonlinear equations. Themethod is independent from the source ofnonlinearity - in terms of structural analysis - itcan be geometric, inertial, material, or it canarise from other physical phenomena such ascontact, damage, delamination, buckling drivendelamination, etc.

The numerical method offers a number ofadvantages. Most significantly, it allows for asystematic exploration of the design space, andit makes typically cumbersome and expensivenonlinear calculations, often requiring oneroususer intervention, relatively straightforward.

In essence, numerical continuation is builtaround the idea of the addition of someaugmenting conditions to the equilibriumequations. These conditions, specifying subsetsof equilibrium states with certain properties,will further allow the addition of the extracontrol parameters required [1] in any analysis.

Problem formulation

1 ACCIS, Queen’s Building, University of Bristol, Bristol, BS8 1TR, UK2 School of Mathematical Sciences, University of Nottingham, NG7 2RD, UK

The finite element equilibrium equations areformally expressed as

where 𝒇𝒇, the internal forces, are a function ofboth the current displacements, 𝒅𝒅 , andpossibly some other properties of the model,𝚲𝚲. This additional property parameter could intheory be anything from a change in geometry(area, length, height, etc.), to a change inmaterial properties (E, G, etc.) or auxiliaryload cases.

Model #1: Arched beam, Λ1

Model #2 & #3: Arched beam, Λ2 & Λ3

In order to illustrate the capabilities of numericalcontinuation a simple arched beam problem hasbeen evaluated.

Here, the vector 𝚲𝚲 = {Λ1, Λ2, Λ3, Λ4} comprises ofonly four parameters. The parameters are definedas follows:• Λ1 Externally applied load to centre-point of

arch.• Λ2 Average cross-sectional area (used to

evaluate total volume).• Λ3 Quadratic distribution of volume along

beam length (symmetric).• Λ4 Arch height.

This model delivers classic snap-through curvesas illustrated in Figure 1a.

The models presented herein are based on onefundamental load-displacement curve, where theload-factor 𝜆𝜆 = Λ1 is the first parameter evaluated– all other parameters remain fixed. This isnecessary due to the process involved incontinuing the parameters along an equilibriumpath. The solutions at each time-step on thisfundamental load-displacement path act as aninitial guess i.e. starting positions for theevaluation of other parameters.

Parameters Λ2 and Λ3 are once again solvedindependently of one another, but both arerelated to the change in cross-sectional areaalong the beam length, as illustrated in thefollowing expression:

Λ3 is physically limited to 0.99995 ≤ Λ3 ≤ 1.0002 toavoid elements containing zero or negativevolume (see Figure 1). Λ3 = 1 corresponds to aconstant cross-sectional area along the beamlength. Λ2 relates directly to the average area ofthe beam: when divided by the overall length it isused to evaluate the overall volume of the beamand hence mass.

References

To expand on our understanding of more complexnonlinear structures and to undertakecomprehensive imperfection sensitivity analyses.

Figure 1: Beam problem schematics; (a) Free-bodydiagram; (b) Parameter Λ3 with a maximum beamthickness at the centre; (c) Parameter Λ3 with the

maximum thickness at either end.

[1] C. Pacoste, A. Eriksson, A. Zdunek, Parameter dependence in the critical behaviour of shell structures: a numerical approach, IASS-IACM 2000

Figure 2a illustrates an equilibrium surface inwhich each load-displacement curve is solvedvarying the distribution of volume along thelength of the beam. Each curve corresponds to afixed load.

The most efficient design (Figure 2a: blackcurve) is found by evaluating each point on thesurface to find the best ratio of load-to-displacement. This design is found at Λ3 = 0.99993;which incidentally is the solution at which the first

bifurcation point and the first limit pointcoincide; this is illustrated graphically in Figure2b as the point where all three colours coincide.

The design of the arch is further evaluatedwith the continuation along parameter Λ2 whichessentially alters the solution into a 4th

dimension (see Figure 3). In this instance theequilibrium surface, and hence design space, isexpanded. Figure 3 can be used to designminimum weight structures for any given load orrequired displacement. The most importantfeature is the blue region. These solutionscorrespond to stable, and hence real, solutionsthat are physically observed.


0 50 100 150 200 250 300 350 400

Hea

t flo

w (e

xo u

p)

Temperature (°C)

BISMALEIMIDE

Melting Point = 160 °C

Uses toxic MDA as starting material


Eliminates use of MDA

CYANATE ESTER


Removing methyl group reduces molecular symmetry

Liquid at room temperature

Can be used as a solvent for BMI component

Bismaleimide-Triazine (BT) resins combine the beneficial properties ofbismaleimides (BMIs) and cyanate esters (CEs) to create systems with superiorattributes. These include high glass transition temperatures (Tg > 300 °C) and lowdielectric constants, making them excellent candidates for application as printedcircuit board substrates or radome materials. However, their adoption has beenhindered by high material cost, toxicity issues and poor processability. This projectaims to tackle these obstacles by creating novel, liquid processable systems thatmaintain or exceed the properties of current industry standards.

Development of liquid processable BT resinsRobert Iredale, Carwyn Ward, Ian Hamerton

Supported by

Replace with more beneficial monomers

Combine to form new BT

system

DSC(Uncured)

• No observable melting transition

• Liquid processing window > 100 °C

Initial data for 90:10 blend

(CE:BMI)

Homogeneous cured resin

0 50 100 150 200 250 300 350 400108

109

E' (

Pa)

Temperature (°C)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

tan(

delta

)

• Tg = 300 °C

• More properties still to be measured

DMA (Cured)

Exotherm peak


Hand layup of composites is still poorly understood, though this is improvingthrough the activities of EPSRC CIMComp. Even so, it is yet to be fullystandardised as even two expert laminators tend to layup very basicgeometries in different ways. This can lead to variations in the performanceof the final composite part. By using novel Augmented and Virtual Realitytechnologies, this project seeks to deliver a solution to this issue.

GAMIFICATION for improved layupShashitha Kularatna, Carwyn Ward, and Kevin Potter

Supported by

STAGE 1Laying Up a Flat Panel in Virtual Reality (VR)

STAGE 2Simulation of Prepreg Shear and Layup Tools

STAGE 3Complex Shapes and Real-Time Feedback

A VR training aid for composite layup, based in the ACCIS clean

room environment was designed and delivered to users

via a head mounted, smartphone based, VR system.

The tool was trialed against groups with different levels of experience in composite layup.

DELIVERY TO THE USER

Vid

eo

Trai

ning

VR Trai

ning

TESTINGVideo training vs. Virtual Reality training for novice laminators.

[A task was measured as completed if it was performed accurately and in the

same order as in the VR simulator]

Muscle memory reinforcement for laminators in deforming

Prepreg

The “Dibber” is a standardized multi-purpose layup tool designed by Helene Jones at the

University of Bristol

Tools play an important role in draping Prepreg over complex

shapes.

The Oculus Rift can be combined with the Leap Motion controller to train laminators and standardise the layup

procedure of complex composite parts

Virtual Pin Jointed Net Leap Motion Controller


There is an increasing drive to reduce greenhouse gas emission and resourceconsumption arising from the manufacture and use of products across a widerange of industries. The current economy is seen as linear, and inherentlyunsustainable, with a ‘take-make-dispose’ philosophy in which materials areextracted, manufactured into products, and discarded at end-of-life. The circulareconomy model aims for sustainability by reducing waste and keeping resourcesat their highest value where possible. Composite materials possess desirableproperties which enable emission reduction through lightweighting in automotiveand aerospace sectors. However, they are inherently difficult to recycle and oftenlandfilled at the end-of-life.

The circular economy of composite materialsMatthew Such, Carwyn Ward, Kevin Potter

Supported by

Figure 1: Simplified composite life cycleLandfill Energy recovery

Downcycle

Repair

Continuous fibre

Prepreg

Component

Assembly

Product

Resin

Moulding compound

Milled fibre

Short fibre

Composite Life Cycle• Composites are inherently difficult to recycle due

to their separate constituent phases• Large majority of composite is created at various

stages in constituent and component manufacture• Recycling methods are focused on recovering fibre

and discarded matrix phase by thermal orchemical processes

• Current processes downcycle end-of-life productsand in-process scrap, material value is heavilyreduced

Material

Component

Assembly

Product

Constituents

Landfill

Energy recovery

Recycle

Reuse

Repair

Environmental impactof operation

Embeddedvalue of goods

Figure 2: Idealised composite circular economy with qualitative ranking of

embedded value of goods and environmental impact of processes

• The focus is on automotive and consumergoods, it is unlikely to see applicability toaerospace in the near future due tolegislative barriers

• Ideal scenario will enable material valueretention by adequate repair, reuse, andrecycling strategy

• Use of composite materials in active productsmight enable greater emission reductionduring the use phase than manufacturingcompared with mono-materials

• Design for circular economy will incorporatelife cycle analysis alongside disassembly andrecycling route

• Aligned discontinuous fibre reinforcement willenable greater rates of fibre recycling andhigher property retention in comparison tounaligned short fibres

Future Scenario


Supported by

Development of a closed-loop recycling method for short carbon fibre composites

Rhys Tapper, Marco Longana, Hana Yu, Ian Hamerton, Kevin PotterSecondary recycling can give a composite material multiple operative lives as a highvalue product, reclaiming most of the value of the virgin constituents. This project aimsto develop the first closed-loop recycling method for carbon fibre composites, producinga highly aligned, discontinuous, carbon fibre tape-type prepreg that is able to retaincompetitive mechanical properties over repeated recycling process loops. The processinvolves the separation of thermoplastic matrix and carbon fibre reinforcement, fibre re-alignment and subsequent consolidation of the reclaimed constituents. The tape-typeprepregs can be used directly as feedstock for automated manufacturing techniques.

Closed Loop Recycling - A cycle which requires no additional material input after initiation.

• Thermoplastic matrix and short(3mm) carbon fibres lend themselvesto recycling due to a lack of cross-linking and short length, respectively.

• Shredded part is dissolved in solventthen the fibres are filtered out andthermoplastic is collected as precipitate.

• HiPerDiF alignment method is used toproduce a high level of alignment fromliquid dispersion [1].

Figure 6 – Preform.

Figure 5 – Schematic of the automated part of the recycling process.

[1] Yu H, Potter KD, Wisnom MR. Composites: Part A (2014).

Figure 1 – Flow diagram of the closed-loop methodology.

Figure 2 – Waste composite.

Figure 4 Reclaimed Fibres.

Figure 3 Thermoplastic precipitate.

SOLVENT DISSOLUTION

RECLAIMED CABRON FIBRE ALIGNMENT INTO HIGHLY ALIGNED PREFORMS

IMPREGNATION

Figure 7 – Prepreg.

Impact

Gives end-of-life composites multiple operative lives ina high value application.

Fibres from pyrolysis can be incorporated –

many tonnes of unused

recycled carbonfibre.

Significantly increases carbonfibre composite desirability in industry i.e. automotive.

HiPerDuCT Programme

Grant

Previous page photo credit: Marco Longana, 'Differences in the fragmentation of continuous S-glass and discontinuous carbon fibre interlaminated hybrid composite with the variation of the carbon fibre strength.'

Fibre fragmentation detection in Pseudo-ductile hybrid laminates by acoustic emission

Programme Grant

Mohamad Fotouhi, Putu Suwarta, Meisam Jalalvand, Gergely Czel, Michael R. WisnomThe aim of this work is to establish a direct connection between the observeddamage mechanisms and the Acoustic Emission (AE) signals originating from thedamage mechanisms in thin-ply hybrid composites which fail gradually with“pseudo-ductile” stress-strain response. Analysing the AE results showed thatthere were two types of events regarding the AE parameters; the high values ofEnergy and Amplitude, and the low values which were related to fragmentationand delamination, respectively. It was concluded that the applied methods can beused as a simple and sensitive device to estimate number and sequence of thefailure modes in the hybrid laminates.

Acoustic emissionInvestigated layups and their damage mode mapThe hybrid plates laid up in [G1/C/G1]sequence where G stands for S-glass plies and C for MR40 carbon plies. Tensile test were applied and the AE signals were recorded.

Experimental results

AE

sen

sors

F

F

AE characteristics for the failure modes

Sp

ecim

en

Damage mode map for [G1/C/G1]

Observed damage modes in different strains( Fragmentation & Delamnation)

Number & sequence of the damage modes obtained by AE

Different AE behaviour

Key Challenge• [±θm/0n]S laminates have been shown to exhibit considerable pseudo-ductility, via a

combination of fibre rotation and gradual failure of 0° plies, with a metal-like stress-strainresponse. This behaviour can be tailored, through the use of high and standard modulus fibresto achieve thin sub-laminates for use as a pseudo-ductile prepreg in multi-directional layups.

Combining fibre rotation and fragmentation to achieve optimised pseudo-ductile CFRP laminates

Programme Grant

Jonathan Fuller, Meisam Jalalvand, Michael R. Wisnom

Concept•

• For 𝒕𝒕𝟎𝟎/𝒕𝒕𝜽𝜽 ≤ 𝑩𝑩𝒎𝒎𝒎𝒎𝒎𝒎, large stiffnessmismatch required betweenthe 𝐸𝐸𝑥𝑥𝜃𝜃 and 𝐸𝐸11.

• Solution:Use high (YSH70A) and standard (TR30)modulus thin ply CFRP. Leads to a sub-laminatethickness of 0.150mm.

Standard modulus thin ply Skyflex with TR30 fibres, 𝜀𝜀11∗ = 1.9%

High modulus thin ply North TPT with YSH-70A fibres, 𝜀𝜀11∗ = 0.5%

E11 [GPa] E22 [GPa] G12 [GPa] ν12 tp [mm]Skyflex 102 6.0 2.4 0.3 0.03YSH70A 362 6.0 4.0 0.3 0.03

• Pseudo-ductile behaviour determined by material properties, thickness of 0° and ±θ plies and the ratio between the thicknesses, 𝒕𝒕𝟎𝟎/𝒕𝒕𝜽𝜽 = 𝑩𝑩. 𝐵𝐵𝑚𝑚𝑚𝑚𝑥𝑥 =

𝜎𝜎𝜃𝜃∗𝐾𝐾𝑡𝑡𝜎𝜎11∗

− 𝐸𝐸𝑥𝑥𝜃𝜃𝐸𝐸11

Maximum ratio given by:

Experimental validation

𝑡𝑡𝜃𝜃𝑡𝑡0 0

θ

θ

[±26/0]s±26° plies – TR300° plies - YSH70A

Initial fragmentation at 𝜀𝜀frag = 0.55%

Initial laminate modulus: 𝐸𝐸𝑥𝑥i = 105 GPa.

Pseudo-ductile strain:𝜀𝜀d = 1.6%.

Analytical modelling well-matched to experimental results.

10 mm

Confirmed by XCT scans of specimen removed from test

machine at 𝜀𝜀𝑥𝑥 = 1.7%.

Model predicts fragmentations only, with no delaminations.

[±265/0]sALL plies – TR30

Comparison with results from a different layup, shows the scope for tailoring the laminate

behaviour in terms of 𝐸𝐸𝑥𝑥i, 𝜀𝜀frag and 𝜀𝜀d.

Delaminations seen in XCT scans of specimen removed from test

machine at 𝜀𝜀𝑥𝑥 = 3.75%.

Fragmentations and delaminations predicted.

𝐸𝐸𝑥𝑥i = 41 GPa

𝜀𝜀d = 2.2%𝜀𝜀frag = 1.9%

Pseudo-ductile quasi-isotropic hybrids

Programme Grant

Meisam Jalalvand, Mohammad Fotouhi, Gergely Czél, Michael R Wisnom

Composite materials are light, strong, stiff and corrosion resistant but they sufferfrom an inherent lack of ductility. The aim of the HiPerDuCT programme is todesign new materials which fail gradually with “pseudo-ductile” stress-strainresponse. Thin-ply hybrid composites with two different types of fibres canproduce such a gradual failure process. In this study, quasi-isotropic hybridlaminates with pseudo-ductile response in all their fibre directions are tested andsuccessful nonlinear stress-strain responses have been achieved.

UD hybrid composites• Successful pseudo-ductility with a variety ofmechanical properties have been achieved using different combinations of fibres.

Free-edge delamination

Over-load sensor• The appearance of a glass/carbon hybridchanges from fully black to striped pattern if it is over-stretched beyond the carbon fibres failure strain.

Quasi-isotropic hybrid compositesTwo different QI laminates were tested along all their fibre orientations and very good pseudo-ductility has been achieved in all fibre directions.

060-60

060

-60

[60G/-60G/0G/0C/60C/-60C]S

0

9045-45

045

-45

90

[45G/90G/-45G/0G/0C/45C/-90C/45C]S

Gtot=0.59N/mm

Gtot=0.204N/mm

QIG45H

Glass

Carbon

x

z

90H-45H45H

Two methods of hybridisation for evenly dispersing (i) the materials or (ii) the fibre orientations through the thickness have been studied. Energy release rates at the free edges are significantly lower for fibre orientation dispersion method.

i) Materialdispersion

ii) Fibre orientationdispersion

Programme GrantDevelopment of high performance ductile

composites by optimising the matrixThomas Pozegic, Ian Hamerton and Michael Wisnom

Thermal Characterisation Prepare Polymer Films

Dissolvepolymerin DMAc

Hot plate

Rotary evaporator

Consolidation into Fibrous composite

Heat press

1 2

3 4

Methodology

Background

Exploration of alternative polymer matrices to develop ductile advanced composites by recuperating mechanical losses from fibre and lay-up configurations and eliminating

shear instability in compression

Polybenzimidazole – Highest tensile and compressive

strength of any

unfilled polymer

Other polymers: Polyetherimide,polycarbonate, Polyether ether ketone

Removal of other

species

Polymer Evaluation

Compressive properties arelimited by shear instabilityand will be studied bymodifying the polymer matrix.Examples include highperformance polymers withhigh strength and modulus. Inaddition, the ability ofpolymers to undergo strainhardening will be explored.

Polymers

Recuperate lossin strength and modulus

Compression Tensile

Programme Grant

The newly developed High Performance Discontinuous Fibre “HiPerDiF” method is a high speedprocess to produce highly aligned discontinuous fibres composites.This manufacturing method has been used to tailor the fibres organisation at ply level andcontrol the material mechanical response and to process reclaimed fibres.

Applications of the HiPerDiF method HaNa Yu, Marco L. Longana, Kevin D. Potter, Michael R. Wisnom

Hybrid ductile composites:

0.1 0.33 0.5

50 µm

Recycled fibres remanufacturing:• High level of alignment leads to a high fibre volume fraction and

therefore to high mechanical performances and high structuraland economical value.

• The HiPerDiF method is a valuable instrument to produced tapesthat are intrinsically easy to recycle and remanufacture recycledcarbon fibres.

Intermingled-hybrid aligned short fibre composites• Fibre type: High modulus carbon & E-glass (3 mm)

H. Yu, M.L. Longana, M. Jalalvand, M.R. Wisnom, K.D. Potter“Pseudo-ductility in intermingled carbon/glass hybrid composites with highly aligneddiscontinuous fibres” Composites Part A, 2015, Vol 73., pp. 35-44.

Carbon ratio

M.L. Longana, H. Yu, K.D. Potter“Multiple closed loop recycling of carbon fibre composites with the HiPerDiF (High PerformanceDiscontinuous Fibre) method” Composites Structures, 2016, Vol. 153, pp. 271-277.

The HiPerDiF method offers flexibility in shaping hybridcomposites with various fibre type, fibre length, preform pattern, resin type and fibre surface treatment.

Novel architectures of aligned discontinuous fibre can begenerated for ductile response in composite materials.

Scientific approaches

Interlaminated/intermingled carbon/glass hybrids

Continuous S-glass epoxy prepreg

Intermingled hybrid short fibre prepreg

Continuous S-glass

Low strain carbonHigh strain carbon

Fragmentation within the intermingled

layer(Low strain material)

Fragmentation and stable delamination

(Intermingled layer)

Composite recycling;Applications in Automated fibre placement, 3D printing...

Industrial approachesNew industrial applications of short fibre composites:1) Remanufacturing of recycled carbon fibres into Highstructural performance composites;2) Automated High-volume, defect-free manufacturing.

Intermingled virgin/recycling carbon hybrids

71 GPa (C.V. 7.5 %) at vf 38%

Smooth transition Sharp transition

Closed loop recycling

Composites UTCsupported by Rolls Royce

Previous page photo credit: Fabrizio Magi, 'Thermal image at initiation.'

www.bris.ac.uk/composites

The investigation of effective through service re-manufacturing technologies foron-platform repair of propulsion systems is of interest for aerospace applications.The research focuses on the manipulation of nanofillers such as carbon nanotubes(CNTs) through external magnetic fields for advanced curing purposes.

ADVANCED CURING FOR ON-PLATFORM REPAIR OF AEROSPACE COMPOSITE COMPONENTS BY

EXTERNAL MAGNETIC FIELDS Giampaolo Ariu, Ian Hamerton, Bhrami Jegatheeswaram Pillai, Dmitry Ivanov

Methodology• High conductivity CNT connections within

composite structure: magnetic CNT alignment.• Localised heating for more uniform overall

curing process.

Supported by

Schematic of composite inner structure for CNT magnetic alignment and translation.

Electroless metal plating onto CNTsProcess

COOH-CNTs subjected to:- Sensitisation with SnCl2;

- Activation with PdCl2;- Plating (specific pH and T).

Findings

More uniform and strong wall coating.CNT agglomeration.

Computerised Tomography (CT)

Specimens

Ni-MWCNTs (1 vol.%)embedded in PRIME 20LVand under DC field.

Findings

Alignment pattern at lower DC fields (0.25 T and 0.1 T): edge effects.

TEM: commercial Ni-coated (a), Ni-plated (b) and Co-plated MWNTs.

(a) (b) (c)

B = 0.25 T B = 0.5 T

Left: Ni-plated MWCNTs alignment pattern after DC field; Right: CT scans of PRIME 20LV + 1 vol.% Ni-plated MWCNTs under 0.25 T and 0.5 T.

Magnetic characterisationSpecimens

VibratingSample Magnetometer(VSM) on powdered metal-plated MWCNTs.

Findings

Cobalt-MWCNTs show highest magnetic moment and coercivity (high hysteresis.

Thermal & rheological analysisDifferential Scanning

Calorimetry (DSC)

20˚C to 180˚C; 5˚C/min.Metal coating: exothermicpeak shifts to lowertemperatures.

Cone/plate viscometer

Shear viscosity increase with nanotube addition.High shear rates: easier resin processability.

Left: VSM results for metal-plated MWCNTs; Right: VSM Co-MWCNT results (sonication vs. stirring).

Left: DSC results; Right: table of shear rates for 10 vol.% of COOH- and metal-plated MWCNTs.


This project aims to develop experimental data which will provide information on thefailure mechanisms occurring in composites structures with particular reference tothose containing manufacturing process induced defects. The data will be used forinput to and validation of finite element models and as an aid to the understandingof the basic phenomena.

EXPERIMENTAL TESTING FOR DEFECTS AND FEATURES – ‘DF2’ TEST PROGRAMME

Mike Jones, Hafiz Ali, Stephen Hallett and Michael Wisnom

Supported by

Background - The DF2 programme builds on previous experimental work (DF1) which involved in-planeuni-axial tests on specimens containing a single defect type. Recent work has focussed on the development of four new test procedures where specimens are subjected to bi-axial or out-of-plane stresses as shown below.

Interlaminar shear (S31,S32) with through-thickness compression (S33C)•‘Arcan’-type test fixture provides variable ratio of (S31,S32):S33•Initial tests at 4° and 20° show no significant strength knockdown for wrinkle specimen compared to pristine

Axial tension (S11T) with through-thickness compression (S33C)

r=20mm

w=30mm

‘Arcan’ test fixture

Axial tension (S11T) with through-thickness tension (S33T)•Aluminium T-pieces used to apply TT tensile stress field•Bonded to specimen using a high-strength epoxy paste adhesive•Tested in the same bi-axial test rig but with reversed TT displacement Test schematic

Wrinkle specimen failing away from the defect region

Failed pristine specimentested at 20° angle

Failed wrinkle specimen tested at 4° angle

IM7/8552 L-bend specimen- first failure

• Zwick® bi-axial test rig with four independently-controlled hydraulic actuators (100kN capacity)

• IM7/8552 pristine and wrinkle specimens tested• TT compressive stress inhibits failure at wrinkle

defect

Through-thickness tension (S33T)• L-bend specimen tested in 4-point bending• Original layup for IM7/8552: [04,(+452, 902, -452, 02)4]S

• Layup now modified to shift failure closer to specimenmid-plane where defects will be located in future tests.

• New stacking sequence:[04,(45/90/-45/0)2(452/902/-452/02)3]S

L-bend specimen in 4-point bending test rig


Ingestion of small and hard particles at high speed causes foreign object damagein gas turbine engines. With increasing usage of composite components and theirrecent introduction to aircraft engines, understanding the effect of FOD oncomponent strength and structural integrity has become a critical activity.

Effect of foreign object damage on composite aerofoils and structures

Ashwin Kristnama a, Michael Wisnom a, Stephen Hallett a, David Nowell b

aACCIS, University of Bristol, bUniversity of Oxford

Supported by

Impact damage visualisationsWork from XP

Impacted laminates under C-scan (1 mm thick; high speed): Hit at 45 to LE (left) and TE (right)

Discussion

0

200

400

600

800

1000

1200

0 2 4 6 8 10 12

Failu

re s

tres

s/M

Pa

Impact energy/ J

High speedLow speedBaseline

Impact configurations at 45 to the LE & TE and 90 to LE (top view)

Trailing edge (TE)

Leading edge (LE)

Impact configurations

• 59.8 % knockdown in residual tensile strength for45 leading edge (LE) impact on 1mm thick laminates.

• Difference in threshold impact energies between the high/lowspeed impact conditions.

• No damage detected under low speed impacts.

New impact configurations

Impact configurations at 45 to the LE and midspan (top view)

Fig 2: Typical specimen failure post tensile test. Impact speed: 250 m/s. Top: Edge impacted; Bottom: Midspan impacted

From XP to PhD

• Laminates were impacted at the leading edge andmidspan at 45 for a range of velocities.

• Differences in residual strength accounted for byamount of damage induced upon impacts atdifferent velocities and splits which can growlonger.

• Future work includes: damage characterizationunder CT-scan, FE models with characterizeddamage zones.

65% (midspan) & 61% (LE) reductions in residual strength

• High speed ~ 300m/s• Low speed: ~ 4.5 m/s• Thickness: 1 and 2 mm• Laminate size: 150 x

20 mm

• Thickness: 2 mm• Laminate size: 250 x 40 mm

Leading edge (LE)

Trailing edge (TE)


This project shall provide a thorough understanding of how fatigue-drivendelamination in composites is initiated and evolved. The delamination growth isinvestigated in practical tests using a newly developed test method. Materialdegradation is monitored in different test set ups. Future work will be conductedon the modelling of delamination for the usage with commercial finite elementsoftware.

HIGH CYCLE FATIGUE BEHAVIOUR OF COMPOSITES FOR AERO ENGINE APPLICATIONS

– FULLY REVERSED FATIGUE TESTINGRico Kuehlewind, Luiz F. Kawashita, Stephen R. Hallett

Fully reversed Fatigue• Development and verification of a new

test method• Allows full reversal of load case for

Mode-II delamination• Load reversal exhibits crack growth

rate nearly two orders of magnitudehigher compared to the non-reversecase

• Method has been expanded to mixedmode fatigue for more realistic loadcases on components

Supported by

Fatigue Mechanisms• Crack surfaces are investigated, show big differences for different load cases• Surfaces show ripples corresponding to cycles• Micrographs help identify the underlying mechanism

Outlook• Identification of the fatigue material degradation mechanisms in fully-reversed

loading• Extraction of material data for R=0.1, R=0 and R=-1• Development of a modelling strategy for implementation in commercial FE software

R = -1, low amplitude R = -1, high amplitude R = 0.1, high amplitude


Str

ain

Phas

e sh

ift

Time to failure

The aim of the project is to develop a method for testing composites to HCF.Guidelines are found for a complete testing procedure based on vibration fatigue.This method is cost efficient and it captures the dynamic and mechanical behavior ofcoupons and components as well as the initiation of delamination.

IDENTIFICATION AND PREDICTION OF DAMAGE DEVELOPMENT IN COMPOSITES UNDER HCF

Fabrizio Magi, Dario Di Maio, Ibrahim Sever

Testing methodSpecimens with ply-drops [0,0drop,90drop,0,(90,0)3]s were tested in first bending mode, at resonance. The testing method consisted in:

• Measuring the Frequency Response Function (FRF)

• Calibrating strain-vibration amplitude relationship

• Running the fatigue test at constant frequency and constantamplitude, up to the initiation of delamination

Ply drop

Fixture clamping the specimen

Important outcomes• Initiation is precisely identified by a gradient step change of the phase

over time and defined as1: the critical event that is able to change the rate of structural degradation for a given excitation level.

Supported by

Thermal image at initiation

• The testing technology wasvalidated on a real blade,proving that the physics behind the failure of coupons is the same as that behind the failure of real components.

For 1% of damping:1% stiffness reduction0.5% frequency drop34% phase change

S-N curve by means of strain

Safe zone

• The phase is more accurate than temperature, stiffness or frequencydecay due to the resonance phenomenon.

Rig setup for the real bladeMaximum temperature of the blade and resonance phase over time

The critical event has been modelled in ABAQUS byusing the VCCT in a dynamic environment.

• S-N curve can be built based onthe critical event and not anylonger on engineering judgements.

Nodes are bonded togetherby springs and springs areremoved to simulate thedelamination (Paris’ Law)

1Patent application filed

Number of cycles

Phase shift undergoing a gradient step change

Life in log scale

Number of cyclesVCCT


Variable Stiffness Composite Laminates For Rotating Pre-Twisted Plates

Matthew Thomas*, Paul Weaver and Stephen Hallett*ACCIS Centre for Doctoral Training, e-mail: [email protected]

Supported by

1. Byung Chul Kim, Kevin Potter, and Paul M. Weaver. Continuous tow shearing for manufacturing variable angle towcomposites. Composites Part A: Applied Science and manufacturing, 43(8):1347-1356, August 2012.

Rotating pre-twisted plates are frequently used within turbomachineryapplications. Due to the geometry and loading that is exerted on them fromcentrifugal and aerodynamic forces they untwist. As the optimal plate shape isdifferent at different running speeds, it would be beneficial to passively control itsshape. The aim of this investigation is to increase the untwist of a rotating pre-twisted composite plate by tailoring its stiffness using variable angle tow (VAT)and non-symmetric laminates.

● Pre-twisted plate dimensions: 1m span length, 0.5m chord width, 70 tip angle,rotating about an axis 0.415m away from the root at 2660 rpm.

● A genetic algorithm (GA) was used to select the 6 variables used to define each of the3 different VAT plies [1] as well as the proportion of each.

● The cost function comprised of maximising the amount of untwist, with 7 penalty termsused to penalise any designs where strain and chord-wise bending allowables wereexceeded.

● The optimal laminate, shown in figure 1, increased the amount of untwist whilesatisfying strain allowables that unidirectional equivalents failed to achieve.

Figure 1: Fibre angle variation for different VAT plies.


The main objective of this project is to generate understanding regarding the HighCycle Fatigue behaviour of CFRP under different Environmental Conditions,utilising a Dynamic Testing Method.

Fatigue Behaviour of CFRPunder Environmental Conditions Georgios Voudouris, Dario Di Maio, Ibrahim Sever

TESTING PROCEDURE

• The 1st Bending Mode, of CFRP Specimens,is tested close to Resonance Frequency.

• Sudden shift in phase indicates Damage Initiation– Critical Event –*

• Critical Event can also be capturedthrough the use of a Thermal Camera.

• During the Endurance Testing, the specimens are locatedinside an Environmental Chamber where the temperatureis controlled and maintained around the desired levels.

• Test are aimed to be carried out between – 60 OC to + 100 OC, which are representativefor in – service conditions.

OUTCOMES

• The Initial tests revealed: A change in the Critical Event

as the Temperature is increased. The delamination initiation appears earlier than

the one at the room temperature.

What is happening on the inside?

• It is difficult to capture the Temperature Distributionthrough the thickness of the component.

• An FE model is being built which uses contact elementsto simulate the energy dissipation due to ply by ply rubbing; taking into accountthe surround Temperature, the Self – Heating Effect and the Heat Generationdue to ply by ply rubbing.

• Correlation between simulated and measured Temperature data at the surface will becarried out.

*PATENT APPLICATION FILEDFOR THIS TECHNIQUE

Supported by

SCHEMATIC REPRESENTATION OFPLY DROP & CONTACT REGION

FRICTIONAL CONTACT STRESSES ON THE RESIN POCKET

SCHEMATIC REPRESENTATION

OF EXPERIMENT SET UP

DAMAGE INITIATION

AT 25 OC & 50 OC

THERMAL IMAGES BEFORE &AFTER THE CRITICAL EVENT

Supported by

www.bris.ac.uk/composites www.tu-dresden.de/mw/ilk

In collaboration with

• Quasi-static test interrupted byfatigue were performed

• Mode I:

• Large degradation of residualproperties for large fatigueamplitudes

• Insignificant effects forvibration like behaviour

• Mode II

• Minor effects for vibration likebehaviour

• Pin rupture for displacementsexceeding 0.25mm

• Findings transferred into a modelfor the prediction of residualproperties in fatigued Z-pins

Z-pinning has proved to be efficient in suppressing the propagation of cracks incomposites. However, research on operational loads, which are likely to includefatigue, is limited. Combining the strengths of the two RR partner institutes, ACCIS(UoB) and ILK (TUD), this project aims at characterising the fatigue behaviour ofZ-pinned composites as well as generating numerical design tools.

ADVANCED EXPERIMENTAL TESTING FOR Z-PINNED COMPOSITES

Felix Warzok*, Giuliano Allegri, Maik Gude* , Stephen Hallett - University of Bristol, * - TU Dresden

Microscale Single Pin Testing

Mesoscale Tests & Modelling

(a) Single Z-pin specimen; mode I (b) quasi-static pre- and post-fatigue results & (c) test rig; mode II (d) quasi-static pre- and post-fatigue results & (e) test rig

• Z-pinned DCB and ELS testscarried out

• Meso-scale test resultsconfirm the microscalefindings

• Very good agreementbetween experimental andnumerical curves

Experimental and numerical quasi-static pre- and post-fatigue load-displacement curves of Z-pinned (a) DCB and (c) ELS (results reduced by specimen compliance). Sketches of (b) DCB and (d) ELS specimen.

b) c)

d)

a)

e)

a) b)

c) d)

Advanced Composites Centre for Innovation and Science, University of Bristol, Queen’s Building,

University Walk, Bristol BS8 1TR, UK Tel: +44 (0)117 331 5311

Visit: bristol.ac.uk/compositesEmail: [email protected]

Twitter: @BristolUniACCIS

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