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Materials
7th ANNUAL CONFERENCE OF THE
CDT IN ADVANCED COMPOSITES FOR INNOVATION AND SCIENCE
POSTER BOOKLET
Tuesday 10th April 2018 University of Bristol, Queen’s Building, University Walk,
Bristol, BS8 1TR, UK
Materials
High velocity impact on hemispherical composites made from Dyneema®
Behjat Ansari, Luiz Kawashita, Stephen Hallett, Ulrich Heisserer *
*DSM Materials Science Center, Geleen, The Netherlands.
30˚ frame angle
60˚ frame angle
Modelling Approach
1. To improve understanding of mode-I and mode-IIfracture of plates made from Dyneema®, thefollowing contact algorithms investigated:
• Mixed-mode cohesive zone model developed at theUniversity of Bristol
• Cohesive elements using LS-DYNA®'s built-incohesive formulation (MAT_138)
• Tie-break inter-laminar contact with a 'Dycoss' mixed-mode fracture mechanics algorithm.
Dyneema® is an ultrahigh molecular weight polyethylene, gel-spun to form fibres embedded within a thermoplasticmatrix to form pre-impregnated composites. Previous studies on the failure mechanisms of these composites underimpact have exclusively focused on flat plates. Certain armour applications however, require the use ofhemispherical 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.
2. These models are extended to assess theimpact behaviour of the material for various:
• Degrees of curvature
• Directions of impact
• Impact velocities.
Acknowledgements
Many thanks to the Engineering and Physical Sciences Research Council for their supportthrough the EPSRC Centre for Doctoral Training in Advanced Composites for Innovation andScience, and to DSM Dyneema for their continued support and funding for this research.
In-p
lane
she
ar s
trai
n O
ut-o
f-pl
ane
disp
lace
men
t
Experimental Approach
1. A picture frame rig isused to induce in-planeshear for manufacturingplates with 30º and 60ºangles of shear.
2. The effect of factors suchas displacement rate,frame clamping pressure,and temperature areinvestigated.
3. Plates will be testedunder ballistic impact todetermine the effect ofdegree of shear on theirballistic response. Thisrepresents the location ofimpact on a formedhemispherical surface.
Strain (%)
0 10 20 30 40
Nor
mal
ised
for
ce (
N/m
m2
)
10-3
0
1
2
3
4
5
6
7
830° at 21°C
30° at 80°C
60° at 21°C
Global Shear Angle (°)
0 10 20 30 40 50 60
Nor
mal
ised
She
ar F
orce
(N
/mm
)
0
0.5
1
1.5
2
2.5
3
3.51 Ply
2 Plies
2 Plies/2
4 Plies
4 Plies/430° at 21°C
with slip
(10mm/min)
60° at 21°C
with slip
(60mm/min)
30° frame angle
60° frame angle
Normalised global force-strain curves at 21°C and 80°C, and normalised global shear force-globalshear angle curves for single and multiple plies sheared at 21°C.
Displacement (mm)
0 10 20 30 40
Con
tact
For
ce (
N)
0
5000
10000
15000
Cohesive Baseline
ki= 60 000 MPa, Kii = 100 000 MPa
Cohesive Baseline
ki= 60 000 MPa, Kii = 122 MPa
Cohesive Baseline
ki= 240 MPa, Kii = 122 MPa
Tiebreak Baseline
ki= 60 000 MPa, Kii = 100 000 MPa
Tiebreak Baseline
ki= 60 000 MPa, Kii = 122 MPa
Tiebreak Baseline
ki= 240 MPa, Kii = 122 MPa
Contact
instabilities
leading to
perforationof laminate
Contact
instabilities
causing partial
pentration
of laminate
Investigating the effect of Mode I and Mode II interlaminar contact interface stiffness on the contactforce and displacement, for low velocity impact of 3.377 m·s-1 on a 2 mm thick Dyneema® plate.
15” radius 5” radius
3 m·s-1 365+ m·s-1
+ Accurate for up to 1000 m·s-1 without an equation of state.
Development of improved fibre reinforced feedstocks for high performance 3D printing
Lourens Blok, Marco Longana, HaNa Yu, Ben Woods
A 3D printing filament with recycled fibres above the critical fibre length, enabling low cost production of highly tailorable structures with excellent mechanical properties.
Fibre in flow dynamics
A numerical model using smoothed particle hydrodynamics is being developed to predict the flow behavior and fibre orientation during filament forming and 3D printing.
Fibres represented by linked particles
Matrix represented by free flowing particles
Consolidation module Filaforming moduleTensile properties of 3mm carbon fibre thermoplastic
preforms (Vf = 12%) after consolidation show a tenfold increase from baseline matrix properties.
Crucial step of transforming high quality flat preform into an uniform circular filament. Observation of fibre
movement, melt front and temperature profile, to study the rheological behavior of composite melt.
5 mm
2 mm
Short fibres above the critical fibre length are aligned using the HiPerDiFmethod [1].
A thermoplastic composite preform is made with high fibre volume fractions Vf .
The thermoplastic preform is shaped into an uniform filament, preserving fibre length.
The reinforced filament can be used with standard printing methods.
PLA Nylon
ABS PETG
[1] Yu, H., Potter, K. D., & Wisnom, M. R. (2014). A novel manufacturing method for aligned discontinuous fibre composites (High Performance-Discontinuous Fibre method). Comp. Part A.
Composite materials for optics and active colour tuning devicesDiego Bracho, Ian Hamerton, Richard Trask, Annela Seddon
Figure 3: Diffuse UV-vis spectra of SiO2 inverse opals(φ=240 nm) coated with 15 nm Ag in air (a), and infilled withethanol (b). Inset shows photographs of the devicedisplaying colour change
Figure 2: Diffuse UV-vis spectra of PS opals(φ=240, 310, 500 and 1000 nm)
Glasssubstrate
240 nm
310 nm
500 nm
1000 nm
Photonic crystals are periodic ordered microstructures, built from dielectric materials, with a periodicity in thescale of visible light wavelength (~200-700 nm). Through rational design and smart tuning of the PC periodicity itis possible to tailor the colour exhibited by these materials. The main objective of this work is to design andassemble photonic crystal structures based on colloidal self assembly and silica sol-gel chemistry for activecolour display devices.
Results
Polymer opals and silica inverse opals were prepared bycolloidal self-assembly and sol-gel chemistry. Theresulting species exhibit angle-dependant colourationcharacteristic of photonic structures (Fig. 1a). Theseexhibit a face-centered cubic (FCC) structure, with the(111) plane oriented at the surface of the structure (Fig.1b,c).
The exhibited colour can be tuned by altering one ormore physical parameters of the system, such as latticespacing (Fig. 2), symmetry, induction of defects, andrefractive index contrast (Fig. 3).
2 μmFigure 1:a) Photograph of SiO2 inverse opal coated withsilver (φ=1 µm)b) SEM image of a polymer direct opal (φ=240 nm)c) SEM image of SiO2 inverse opal (φ=500 nm)
2 μm
5 mm
(b)
(a)
(c)
Conclusions and Future Work
• Direct and inverse opals of different pore sizes were fabricated using a vertical deposition method in a single-step co-assembly of polystyrene colloids in a silica precursor solution.
• Tunability of the photonic bandgap within the visible spectrum is interesting for potential applications in photonicsand optics, such as colour display devices, active camouflage, sensors, etc. Future work will include theintegration of smart materials, aiming for complete tunability within the visible spectrum.
Covalent adaptable networks: from dynamic bonds to functional compositesCallum Branfoot, Tim Coope, Duncan Wass, Paul Pringle and Ian Bond
3. Covalent adaptable networks
Material – Future work
4.3 Repairable composites
Functional composite – Future work
a. b.
c. d.
4.2 Reformable composites
Functional composite – Future work
a. b.
c. d.
4.1 Recyclable composites
Functional composite – Future work
a. b.
c. d.
1. Dynamic bonds
Molecular
2. Selectively cleavable polymers
Macromolecular
Material – Future work
Mod
ulus
/ ar
b
Temperature / arb
Unusual thermomechanical behaviour
Theoreticalbehaviour
Macromolecular
OS
O O [Na2]Se2Se
Se + SO
OONaO
n2 equivs
OO
n n2 equivs
DMF
SeSeO
O
n n
LightSe SeO
O
n nTHF
Polymer synthesis
• Moulding• Adhesive properties• Rheology• Solubility studies• Tensile testing• Healing: e.g. compression after impact• Thermal analysis (TGA, DSC, DMA etc.)• Recyclability assessment (solution/melt)
Material – Future work
Polymer processing and testing
Covalent adaptable networks (CANs) are polymers that exploit dynamic bonds (crosslinks) to reversiblytransition between thermoset and thermoplastic materials. Upon stimulus (e.g. localised heating) the crosslinksbreak, affording the surrounding polymer very high levels of chain mobility. This mobility allows stress relaxationand plasticity which can be used in reforming (shape change), repair (intrinsic self-healing) and recycling. Theimplementation of CANs in fibre-reinforced polymer composites (FRPs) presents an opportunity to address someof their limitations: low toughness, difficult repair and limited recyclability. A wide range of chemistries have beeninvestigated for use as dynamic crosslinks, including, Diels-Alder, disulfide exchange and transesterification. Inthis project, we are investigating these materials from the molecular level (e.g. the exchange reactions of noveldynamic bonds) to the material level (e.g. thermomechanical analysis) with the aim of developing CAN-containing FRPs.
Molecular
Metathesis/exchange reactions
P PR
RP P
R'
R'P P
R'
R
R
R
R'
R'
R
R'
Cl
P PR
RP Se
R'
R
R
R
RSe Se
R'
R'
Light
S SR
RS S
R'
R'S S
R'
R
UV / Base
HeatDiels-Alder
Macromolecular
MALDI MS molecular weight analysis
2000 3000 4000 5000 6000
Inte
nsity
m/z
Selective cleavage ofPEG-Se–Se-PEG
Molecular
31P{1H} NMR biphosphine metathesis
0102030405060
0 1000 2000Mix
ed p
rodu
ct /
%
Time / min
Chloroform
Chloroform + Et3N
Chloroform + TTBP
Active thermal management via embedded vascular networksJim Cole, Ian Bond, Andrew Lawrie
Fig. 2: Layup of laminate using PTFE-coated wire pre-forms
Fig. 1: Variation of mechanical properties with temperature [1]
Coolant flow rates up to 10.0 l/min were tested, yielding average surface temperature reductions of up to 5.0°Cin a non-optimised network design. The results showed good agreement with a purpose-developed finite difference numerical model, and confirm the feasibility of active thermal management with air coolant.
This project forms the basis for further research into thermo-mechanical performance, manufacturing techniques and optimisation.
A simple vascular network was embedded in a carbon/epoxy laminate and supplied with compressed air at ambient temperature. The laminate was exposed to external airflow of up to 80°C and ~3.0 m/s, and the surface temperature was monitored by an infra-redcamera.
Fibre reinforced polymer composites are limited in high temperature applications by the matrix glass transition temperature, Tg. Above this temperature, mechanical strength is lost as the matrix softens (see Fig. 1).
A potential solution is active thermal management, which aims to reduce matrix temperatures. This can be achieved by circulating liquid or gaseous fluid through a network of internal passages, or vascules.
[1]: Chowdhury et al, “Mechanical Characterization of Fibre Reinforced Polymers Materials at High Temperature”, Fire Technol, 47, 1063-1080, 2011
Fig. 3: Comparison of experimental and simulation results for coolant flows of 0.0 l/min (top) and 10.0 l/min (bottom)
Soft robotic wing structuresCalum Gillespie, Professor Johnathan Rossiter, Dr Ben Woods, Dr Michael Dicker
Nature’s Inspiration
• Deployment / foldable structures
• Real time control
Name Weight (Kg)
Aspect ratio
Wing loading (gcm-2)
Albatross 8.5 18:1 1.37Vulture 7.27 6:1 0.69
Pterodactyl 22.7 13:1 0.66
Inflated Beam Structures
3D Printing
Pneumatic actuator muscles
Design SpaceSoft Robotic
Wing Structures
Material Tensile Modulus (Mpa) *
Ninjaflex (TPU) 12
PolyFlex (PLA) 29Armadillo (TPU) 396
𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹 = 𝐹𝐹𝐹𝐹𝐺𝐺𝐺𝐺 + 𝐹𝐹𝐹𝐹𝑏𝑏𝑏𝑏 − 𝐹𝐹𝐹𝐹𝑠𝑠𝑠𝑠 + 𝐹𝐹𝐹𝐹𝑓𝑓𝑓𝑓
Highly efficient aspect ratios with lower weight than traditional UAVs. Pterodactyl vs Proposed engineering design.
Unmanned Aerial Vehicles (UAVs) have seen a steady increase in use in both Military and Civil applications. This research looks to nature for inspiration for a wing structure with a highly adaptive flight envelope that incorporates the design solutions of soft robotics and the adaptive geometry of morphing aircraft. The membrane wings of the
Pterodactyl provide the basis for a soft robotic wing design utilising soft structural components and pneumatic actuators..
Numerical modelling was used to determine the parameter limitations of a soft robotic wing
resulting in a maximum wing length of 0.6m at a maximum pressurisation of 0.26MPa.
3D printing technology was utilised to design thermoplastic polyurethane
bladders and actuators which where pressure tested to determine their feasible use in a wing structure.
A pneumatic artificial muscle built using more traditional methods was characterised to determine the force versus displacement behaviour to inform and refine the design
envelope of the soft robotic wing structure.
Iterative design
Future Work
All combinations of particle/resin resulted in a similar residual stress state at the matrix interface (compressive radial stress,tensile hoop stress). To achieve toughening effect described by L. S. Sigl the inverse stress state is required. This can bedone by removing the cure shrinkage effect through using a benzoxazine resin.
Resin plaques of both epoxy and benzoxazine will be produced reinforced with the following particles:
• Ceramic• Silica• PMMA• Polystyrene• Core-shell rubber
Material Ep-Polyamide 66 Ep-PTFE Ep-SilicaRegion Matrix Particle Matrix Particle Matrix ParticleMax radial stress / MPa -42.35 -27.72 -28.9 -22.18 -2387 -1594Max hoop stress / MPa 44.53 -35.2 26.44 -22.18 1564 -1546Compressive strength / MPa 290 78 290 12 290 1105Tensile strength / MPa 120 56 120 28 120 48
Accurate prediction of the micro-level stress state that arises during the processing ofparticle toughened interleaved composites is key to understanding their fractureperformance. Work by L. S. Sigl[1] on toughening of brittle matrices with ductile particlesshowed that the toughness of the composite is improved by residual stresses aroundparticles arising from the thermal expansion (CTE) mismatch during processing betweenthe matrix and particle. In this work, a numerical model for the processing of epoxycomposites was developed and used in conjunction with a finite element model, toinvestigate the impact that particle material has on the residual stresses around them.
Micrograph of thermoplasticparticles in the interleaf region.
Modelling the process induced stress state around particles in the interleaf
Robin Hartley, James Kratz, Ivana Partridge and Ian Hamerton
Process modellingCure kinetics models for Hexcel 8552 epoxy resin wereused to track the degree of cure through a simulated curecycle. This was then used to calculate the development ofthe following parameters during processing; Tg, CTE,modulus and the thermal expansion/cure shrinkage strain:
Shrinkage strains exceed thermal expansion strains when particle/epoxy CTEs and moduli same order of magnitude.
Time / s
Tem
pera
ture
/°C
Str
ain
0 5000 10000 1500025
50
75
100
125
150
175
200
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04Temperature / °CThermal expansion strainChemical cure shrinkage strain
Finite Element ResultsThe process model was applied to a finite element singleparticle embedded in epoxy to determine the how theresidual stress varies if the particle material is changed:
Material Properties
Residual stresses*
[1] L. S. Sigl, Acta Metall., 1988
Material Young's modulus / GPa CTE / 10-6 °C-1
Uncured epoxy (Low) 144Cured epoxy 4.67 88Polyamide 66 1.49 130Silica 73 0.5PTFE 0.48 145
*-ve is compressive and +ve is tensile. Bold values exceed material strength.
Time / s
Tem
pera
ture
/°C
Deg
ree
ofcu
re
Cur
e-ra
te/s
-1
0 5000 10000 1500025
50
75
100
125
150
175
200
0
0.2
0.4
0.6
0.8
1
0
0.0001
0.0002
0.0003
0.0004
0.0005Temperature / °CDegree of cureCure-rate / s-1
SENB specimens Microtester In situ DIC strain analysis using SEM/optical microscope
Image courtesy of University of Alberta:https://www.eas.ualberta.ca/sem/
Image courtesy of Debenhttp://deben.co.uk/tensile-
testing/sem/mini-tensile-tester-200n-compression-horizontal-bending-stage/
Durability of composite materials in deployable space structures
Yanjun Hea, 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, Electron Building, Harwell Space Cluster, Harwell, OX11 0QR, 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 (e.g. sample mass loss,surface chemistry, glass transition temperature, and flexural stiffness) before and after exposure. The resultspresented in this work can act as a benchmark for the development of new composite systems or protectiontechnologies which can provide an extended service life for flexible deployable structures in LEO.
Conclusions
Key Results
Laminates tested (all contain toughened epoxy): - LAM01: Carbon PW (Medium fibre content)- LAM02: Carbon PW (Low fibre content)- LAM03: Hybrid Kevlar/Carbon PW (Low fibre content)
Mass loss after AO exposure for each laminate under a total flux of 3.92 X1020 atom/cm2
(a) (b)
FTIR results of LAM 02
Surface profile of LAM 02 before (a) and after (b) exposure
• During AO exposure, the mass loss of the laminate was primarily the result of matrix erosion. The epoxy used in the three laminates was similar. For this reason, the mass loss for each laminate was comparable.
• The FTIR results and surface profile of LAM 02 show that the resin on the exposed surface of LAM 02 was completely eroded and fibres were exposed. For LAM 01 and LAM 03 residual resin was detected on the exposed surface.
• However, AO resistance cannot be characterised only by mass loss and surface chemistry. Further work will focus on combining current results with retention of mechanical properties after exposure to examine the AO resistance of the selected laminates.
Supported by
Low temperature, vacuum infusion of BT resin/glass fibre compositesRobert J. Iredale, Carwyn Ward and Ian Hamerton
Resin development
20 40 60
100
1000
Com
plex
Vis
cosi
ty (
mP
a s)
Temperature (°C)
Viscosity at 30 °C 259 mPa sGel temperature 212 °C
0 50 100 150 200 250 300 350 400
Spe
cific
Hea
t flo
w
Temp (oC)
Reaction Onset T 150 °CProcessing window > 100 °C
150 200 250 300 350
100
1000
E' (
Pa)
Temperature (°C)
0 100 200 300 400 500 600 700 80040
50
60
70
80
90
100
Wei
ght (
%)
Temperature (°C)
T5% 417 °CChar yield 46 %
Tg (E’ onset) 251 °CTg (tan δ peak) 280 °C
• Liquid processable BT resin produced
• Range of desirable properties attained
• Need to test suitability to composites manufacture
Rheology
TGADSC
DMA
Fibre surfaces
Infusion strategy Short Beam Shear Results
Fibre type 𝑭𝑭𝑭𝑭𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 (MPa) Failure type Notes
GFun 54 ± 2 Tensile – incremental Difficult to handle
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁2 45 ± 3 Tensile – sudden Poor infusion quality
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 65 ± 2 Mixed ILSS/Tensile -
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Load
(N
)
Extension (mm)
GFun
GFNH2
GFval
• Significant difference in 𝐺𝐺𝐺𝐺𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 between fibre types
• Change in failure mechanism between samples
Resin inlet
Resin outlet
Fibre preforms
Peel ply Aluminium tool plate
Release film
Tacky tape/ vacuum bag
Distribution mesh
Infusion & curing
Well consolidated composite plates
• Three different surface treatments investigated
• Balance between interface properties and processability required
Functionalisation Expected reactivityUnsized (GFun)
Aminosilane (𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁2)
Volan (GFun)
NH2
Si
MeO
MeO
OMe
OO
Cr Cr
Cl
ClO
H
Cl
Cl
• Infusion carried out at room temperature
• Infusion of all three plates complete within 5 minutes
N
O
O
N C O
BMI
CE
Why MOFs in polymeric composites?• Powder MOFs contain nanoparticles which can
be toxic • High pressure is needed for a gas to flow
through powder• Composite MOF aerogels will be both easier
and safer to handle and low pressure will be sufficient for their application
HKUST-1 ZIF-8Examples of MOF aerogels
MIL-101 Synthesis and Functionalisation
Step 1[2]
Step 2[4] MIL-101 + Pentaethylenehexamine MIL-101-NH2
Infrared spectroscopy confirms the incorporation of the amine-containing molecule in MIL-101
Cr (III) +H2O
→230°C
[3]
Carbon Dioxide CaptureGas adsorption experiments confirm that:• MIL-101-NH2 has better carbon dioxide capture
properties compared to MIL-101• Both MIL-101 and MIL-101-NH2 can be used up
to 5 times with practically unchanged results
Improvement of CO2 capture in MOF composites by amine functionalisation
Konstantina Kanari, Duncan Wass, Valeska Ting
Metal-organic frameworks (MOFs) are materials that consist of metal-containing building units that are interlinkedby organic molecules and the main goal for their synthesis is to create a compound with a porous but solidframework. In this study, a chromium-based MOF, MIL-101, is synthesised by a simple solvothermal method andsubsequently modified to create a new amine incorporated MIL-101 (MIL-101-NH2) with enhanced carboncapturing abilities. The aim of this work is the incorporation of MIL-101-NH2 on a polymeric substrate forcomposite materials that can selectively capture and store carbon dioxide from flue gases.
Conclusions and Future work
• MIL-101 powder was synthesised and functionalised with pentaethylenehexaminemolecules (MIL-101-NH2)
• Both materials exhibit excellent CO2 capture capabilities, and were used 5 times with no change in their properties
• In the future, MIL-101-NH2 will be incorporated into tailored polymer composites which will enable their use in CO2 capture applications
References[1] J. Am. Chem. Soc., 2016, 138 (34), 10810
[2] Chem. Commun., 2016, 48, 12053[3] RSC Adv., 2013, 3, 10181
[4] Sci. Rep., 2013, 3, 1859[5] Microporous and Mesoporous Materials, 2015, 204, 242
80012001600200024002800320036004000
MIL-101
Inte
nsity
(a.u
.)
Wavelength (cm-1)
MIL-101-NH2
Double peak: aliphatic amine
C=C vibrations
C=O group
-NH stretching vibrations
-CH vibrations
0
5
10
15
20
25
30
35
0 200 400 600 800 1000
Cycle 1 Cycle 2 Cycle 3
CO
2 A
dsor
bed
(cm
³/g
ST
P)
Cycle 4
Absolute Pressure (mbar)
Cycle 5
MIL-101
MIL-101-NH2
[1][1]
Composite aerogel of MIL-101 and 2-hydroxyethyl methacrylate (38, 59 and 67 wt % of MIL-101(Cr))
[5]
→CH3OH, 160°C
MIL-101
Adsorption
Desorption
Adsorption
Desorption
Simulation of ultrasonic FMC data in curved compositesCallum Lanherne ([email protected]), Paul Wilcox
Phased array inspection is a large and growing method of non-destructing testing (NDT). Comprised of smallpiezoelectric crystals, they are versatile, allowing for complex beam forming, emulation of single crystal probes,and full matrix capture (FMC). This latter technique allows for very high fidelity reconstruction of discontinuities inisotropic materials such as mild steel and aluminium. However in composites, it can be more complex; the lack ofhomogeneity in multidirectional laminates causes backscatter, and non-planar shapes cause beam steering. Inorder to better design transducers and algorithms for the imaging of such specimens, a fast GPU-based finiteelement code known as Pogo has been used for the simulation of FMC data.
Phased array
Fig 2. Snapshots of displacement magnitude at four timeintervals for a single transducer element.
Initial pulsePly backscatter Backwall reflection
Crack reflection
Fig 3. Received signal for element situatedabove a crack for pristine (top) and horizontallycracked (bottom) specimens.
Fig 1. Curved phased array for pipe inspection.
Transducer properties32/64 elements0.6/0.3 mm pitch5MHz 5-cycle toneburstNormal surface node displacement in model
Fig 4. Reconstructed total focussing method imagesusing straight line (left) and ray-tracing corrections (right),angle limited at 20°. 40dB scale relative to backwall.
• Experimental validation• Immersion probes/wedges• Characterise different defect types and depths
Horizontal crackResults
Simulation setup
Pipe
Simulation properties6 million triangular elements3 million nodes0,45,90,−45 10𝑠𝑠𝑠𝑠 layup
Plane strain elements~3 minute runtime per PZT element (c.f. 1.5hr in Abaqus)
Simulation Field
Future work
0
2
4
6
8
10
12
0
2
4
6
8
10
12
0
2
4
6
8
10
12
0
2
4
6
8
10
12
(mm
)
(mm
)
(mm
)
(mm
)
-10 -5 0 5 10-10 -5 0 5 10
-10 -5 0 5 10 -10 -5 0 5 10𝑥𝑥𝑥𝑥 (mm)𝑥𝑥𝑥𝑥 (mm)
𝑥𝑥𝑥𝑥 (mm)𝑥𝑥𝑥𝑥 (mm)
Utilizing DC plasma assisted CVD diamond as nanofiller for polymeric compositesD. R. Palubiski, N. Fox, F. Scarpa, H. Harris
Diamond is well known as a very hard and tough material, and while using it as a replacement for other materials may be out of reach, utilizing nanodiamond powder to enhance polymer composite properties is a viable option.
Current nanodiamond polymer composites are based around utilizing High Temperature, High Pressure (HTHP) or Detonation Nano Diamond (DND). A new, relatively unexplored, type of diamond fabrication, Pulsed DC Plasma
Assisted CVD, promises high growth rates with variable growth outcomes, ranging from single crystal to nanodiamond growth.
PDC PA-CVD grown ND has the ability tobe very low impurity due to lack ofnitrogen in the reagents (DND) or iron tocatalyze the reaction (HTHP). The rate ofgrowth can also compete with the highrates of both DND and HTHP ND, unlikeother CVD methods.
Taguchi optimization allowed for both the perfection of the growing process, achieving up to 80 µm h-1, as well as showcasing different routes to different growth types. This ranged from nanocrystalline diamond (left), to single crystal spherical diamond with great uniformity (below)
Growth runs, whileplagued with arcing, produced stable enough growths to allow for full film formation after just 1 hour. This film can be grown onto metallic substrates to allow for rapid fabrication of diamond coated leading edges of drill bits. The produced diamond can also be broken up into ND to be used as nano-reinforcement in polymer composites
Taguchi optimization produced ideal conditions, to maximize quality, coincidentally the same as run 2. This is highlighted below along with all the other Taguchi runs that were undertaken.
Run #CH4[SCCM]
Ar [SCCM]
Frequency [kHz]
Set Point [Torr]
1 10 0 100 200
2 10 5 125 230
3 10 10 150 260
4 20 0 125 260
5 20 5 150 200
6 20 10 100 230
7 30 0 150 230
8 30 5 100 260
9 30 10 125 200
Future work:- Comparison of CVD ND against HPHT and DND diamond within
polymer composite structures- Analysis of current mixing methods with aims of improving ND
incorporation into polymer composite system.- Utilizing ND into polymer matrix with carbon fibre to produce full
working polymer composite model for comparison.
Novel matrix for GFRP wind turbine bladesBethany K. Russella, Carwyn Warda, Shinji Takedab, Ian Hamertona
a ACCIS, University of Bristol, b Hitachi Chemical Company Ltd.
The project aims to develop a novel resin system for use in fibre reinforced wind turbine blades.Previous work showed the resin system offers improved interlaminar properties than the baselineresin. This phase of work focuses upon determination of interfacial properties. Future work willexplore optimisation of the resin cure cycle and potential to use novel manufacturing techniques toensure uniform cure through a part with variable thickness.
Resin formulation
bisphenol A diglycidyl ether (DEGBA)
tetrahydrimethylphthalic anhydride (MTHPA)
ancamine K54 (tertiary amine)
Supported by
Interfacial properties
• The fibre resin interface is key to overall laminate performance. Microbond testing can be used todetermine Interfacial shear stress (IFSS).
• The epoxy-anhydride resin on H-glass fibre showed brittle resin failure rather than shear while the amine-cured epoxy (the baseline resin) showed interfacial failure with an ILSS of 19 MPa.
• It is known that the anhydride-cured epoxy resin IFSS > resin tensile strength (20 MPa) and better thanthe baseline; but need a method to be able to calculate this IFSS value.
• Need to examine the interface between the new resin and carbon fibre.
Figure 1: a) Anhydride-cured epoxy resin on H-glass fibre i) optical micrograph before testing ii) SEM image after testing. b) SEM image after testing of amine-cured epoxy. c) Schematic of microbond test setup.
ai) aii) b) c)
Cure optimisation
• 12 hours at 75 °C is excessive, as bothisothermal DSC and rheology show themaximum degree of cure is reachedafter 6 hours.
• A cure model is being developed toallow for better understanding of curekinetics.
• Low temperature + long duration curecycle may be prescribed due to curingchallenge of large volume structures.
Vascular curing
• Novel curing methods are being explored; and exploiting avascular network within a laminate, as an internal heatingsystem during cure, is one such approach.
• Aims to reduce thermalgradients through thicksections and preventstresses developing in thecured part.
• The author would like tothank Yusuf Mahadik andMatthew P. O’Donnell. Figure 2: Lab-scale setup for vascular
curing
Industrial scale nano-reinforced composite structures
Robert Worboys, Ian Hamerton, Stephen Hallett, Rob Backhouse, Luiz Kawashita
Interlayer Toughening
GlobalToughening
Material Characterisation
• Vertically aligned carbon nanotubes embedded in the interlaminar region.
• Available as a film of nanotubes within a user selected epoxy.
• ~100nm nano-silica particles embedded into carbon fibre epoxy prepreg.
• Approximate particle volume fraction within the resin of 30%.
Vertically aligned carbon nanotubes (VACNTs) and homogeneously dispersed nano-silica particles are investigated as interlayer and global reinforcement techniques respectively. The nano-materials have
been selected based on their upscaling capabilities to industrial rates using current manufacturing technologies. These alternatives to Z-pinning and stitching offer 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
FutureWork
Hybrid Reinforcement?
Forc
e
Displacement
VACNT Reinforced
Unreinforced
GIC
Crack Length, a
UnreinforcedResin Reinforced40um VACNTs Reinforced7um VACNTs ReinforcedG
IIC
Controllable Failure
Mec
hani
cal
Frac
togr
aphy
DCB, ELS and Fractography tests conducted on:(i) Unreinforced, (ii) Resin interleaved, (iii) VACNT interleaved
composite laminates.
VACNTs induce intralaminar failure and 10 – 20% enhancement in toughness properties relative to
an unreinforced laminate.
Abaqus© cohesive element model for ply dropped specimen with inclusion of VACNTs in the interlaminar regions.
VACNT reinforced interfaces Initial failure location driven towards surface
Unreinforced laminate Initial failure location
Controllable failure migration through VACNTs shown to be theoretically possible with 50% strength gain.
Requires experimental validation.
[2]
[1] Image captured using the SEM facilities at N12 Technologies in Boston, MA.[2] Image captured using the SEM facilities at Wolfson Bioimaging in Bristol, UK.
Silica Particles
VACNTs
Reinforced Region
Silica Particles
Clam
pPo
sitio
n
[1]
Structures
Structures
Multistable trusses of nonlinear morphing elements
Chrysoula Aza, Mark Schenk, Alberto Pirrera
A multistable, compliant truss-like mechanism is introduced that consists of nonlinear morphing elements. Thesehelical elements are able to change shape and undergo large deformations while maintaining load carryingcapability and structural integrity. Additionally, they exhibit tailorable nonlinear stiffness characteristics. This enablesthe mechanism to be tailored by tuning the inherent properties of its constituent members, as well as its geometricparameters, and a variety of behaviours to be developed.
Morphing element
• Carbon fibre strips: pre-stress introduced by flattening curved strips
• Variable geometry: helix angle θ ϵ [0°, 90°]
• Tailorable nonlinear stiffness characteristics
Compliant mechanism
Results
• Assembly of the double-helices in a truss-like configuration
• Analysis using: (i) energy landscapes(ii) path-following method (modified-Riks)
Conclusions
The mechanism characteristics can be varied significantly by altering the composite strip lay-up and/or the initial truss geometry:
• Quadristable behaviour is obtained for steep trusses and symmetric composite lay-ups of the form [β2/0/β2], with 0° < β < 90°
• For β = 0°, the mechanism becomes bistable, and for β = 90°, monostable
• For decreasing initial truss angle, the mechanism transitions from being quadristable to bistable
The equilibrium paths bifurcate, enabling all internal equilibria to be traversed just by applying a vertical load
Double-helices of L = 95 mm, R = 15 mm, Ri = 30 mm, W = 5 mm, with composite strips of a [β2/0/β2] lay-up with β ϵ [0°, 90°].
Points 1–4 denote stable equilibria, while points A–G identify positions of unstable equilibrium. Points I-IV denote stable boundary equilibria. Red points indicate the equilibrium paths of the apex under an applied vertical load (Ph = 0).
Points 1–4 are stable equilibrium points. Points A–G are unstable equilibrium points. Dashed lines represent areas of instability.
Strain energy landscapes
Load-displacement curves (Ph = 0)
Granular jamming as a variable stiffnessmechanism for morphing aerostructures
David Brigido, Stephen Burrow, Benjamin Woods
Granular jamming is a physical mechanism present in particulate materials that allows the material to undergo afast, repeatable state change, from a liquid-like state to a solid-like state and vice versa under the action of acontrollable external pressure field, which locks the particles together. If the external pressure field is continuouslyvariable, then granular jamming is also able to create proportional changes in stiffness, thereby creating a materialwith actively variable stiffness. The aim of this work is to develop a novel concept of morphing wing structure usinggranular jamming, with the objective to adjust stiffness and control shape. Further objectives are to reduce noiseand drag due to the discontinuities among the control surface and the wing.
Actuation through differential pressure and control for spinedeflection. Image a) No spine deflection. Image b) Positivedeflections on the spine (upper cell contraction and lower cellexpansion). Image c) Negative deflections on the spine (lower cellcontraction and upper cell expansion)
The bending tests show that the mechanism can actively increasestiffness until more than 540% by varying the vacuum level.
Nonlinear lattice structuresMaximillian Dixon, Isaac Chenchiah, Alberto Pirrera
Shape-changing structures can reconfigure to provide extended/enhanced functionalities, thereby facilitatingmass, volume and part-count reduction, a perpetual objective across multiple industries. This projectdevelops work on multi-stable cylindrical lattices capable of adaptive shape change by generalising themodelling approach so as to capture the behaviour of more complex lattices geometries. The need for amore generalised modelling approach has arisen from the additional exploitable behaviour seen in non-cylindrical lattices. The approach models the lattices as framed geometric space curves, their elasticresponse is derived from this geometric description through the use of a Rayleigh-Ritz approximation.
SHAPE ADAPTATION
Lattices exhibiting variable deformationkinematics are available in a wide range ofgeometries. Cylindrical and spherical are shownabove. Additional geometries provide an avenuefor additional exploitable behaviour.
The ability to exhibit shape adaptation depends onboth the geometry and manufacturing process.
Left: Rotation anglefrom the current, abeam and a solidelement FEA modelfor a rectangularcross-section relativeto the geometricframe for a helixclamped at �̃�𝑠𝑠𝑠 =0.5.
The flexural strain rates of the material frame 𝜅𝜅𝜅𝜅1,𝜅𝜅𝜅𝜅2 and 𝜙𝜙𝜙𝜙 are defined as the rate of rotation of thematerial frame around its axes as shown above.
The lattice is modelled as a connected grid offramed space curves. The geometric curvatureand torsion represent the rate of rotation of theorthonormal frame about its axes as it travelsalong the curve.
The material frame (above) is fixed relative tothe principal axis of the cross-section. Thegeometric and material frames both have an axistangent to the centreline of the curve d3(s). Thetwo frames differ by a rotation about this axis. ARayleigh-Ritz approximation is used to minimisethe potential energy subject to this angle.
1. Geometry 2. Behaviour
3. Modelling Approach
For a given C2 space curve and flexural stiffness matrix the material frame which minimises the
total potential energy can be found.
Towards the optimisation of manufacturable composite structures using lamination parameters Noémie Fedon, Terence Macquart, Alberto Pirrera, Paul Weaver
Results for single panel-optimisation
LAYLA: A deterministic optimiser to retrieve manufacturable LAY-ups of LAminates from lamination parameters
Group 1
Group 2
Group 3
Symmetric of group 3
Symmetric of group 2
Symmetric of group 1
Middle surface
• A large range of design constraints considered: symmetry, balance, 10% rule, ply-blocking rule, damage tolerance (outer plies acting as protective layers) anddisorientation (limitation of the difference of fibre orientation between two adjacentplies).
• Novelty in the optimiser principles: The problem is divided in sub-problems with fewerdesign variables each that are solved deterministically one after another.
Optimiser performance for unconstrainedlaminates with a processor Intel® Core™ i7-6700 and 16GB RAM
• Fast computational timescompared to a state-of-the-art meta-heuristicoptimiser.
• Improved convergencetowards target laminationparameters compared toa state-of-the-art meta-heuristic optimiser.
Future work
• Lamination parameters design spaceboundaries definition.
• Multi-panel structures with continuityrequirements between panels and plydrop design constraints.
• Variable stiffness designs with towsteering and/or curved structures.
The stacking sequence design problemObjective: lightweight structures
• Geometry fixed.• Many design variables: thickness, material and fibre orientation of each plies.• A plurality of non-linear design guidelines and certification requirements restricts the design.• Mixed-integer problem as the ply orientations usually take a discrete set of values: 0, ±45 and 90°.
The complete exploration of the design space is impossible (extreme computational cost) so meta-heuristic optimisers areoften used to solve this problem. However, they suffer from slow convergence, especially for large number of plies(>40). In addition, convergence towards local optima is difficult to avoid and might lead to poor quality of the results.
[ϴ1, ϴ2, ϴ3, ϴ4] ?4 design variables for the design of a monolithic plates of 4 plies
Two-step optimisation with lamination parameters
Stacking sequences
2nd level optimiser
Optimal lamination parameters
1st level optimiser
Advantages:
• 12 lamination parameters only , number of designvariables independent from the number of plies.
• Continuous and convex lamination-parameters design space: fast gradient-based optimisers can be used at thefirst level.
• Reduced calls of the problem global objective function (buckling resistance, natural frequency minimisation…)which are often costly (based on finite element analysis).
0
20
40
60
80
100
20 120 220 320Com
puta
tiona
l tim
es (s
)
Number of plies
Unit Cells [-]
|ε|[
-]
0 2 4 6 8 10
-0.2
0
0.2
0.4
0.6
0.8
1
L = 1 mmL = 5 mmL = 50 mmL = ∞ mm
Local actuation of tubular origamiSteven Grey, Fabrizio Scarpa, Mark Schenk
Understanding the decay of actuation in origami is essential for designingdeployable or morphing structures based on the folding of materials. Anexperimentally verified numerical model demonstrates the effect of the elasticstiffness of the facets and folds on the decay of local actuation.
Local actuation ‘squeezing’ unitcell at one end
The experimental and numerical models show elastic decay and a spring-back effect
A laser scanner is used to measure unit cell deformations
L∗ =Material Flexural Stiffness
Fold Stiffness (kF)
The ratio, L*, between facet and fold elastic stiffness affects the elastic decay
Decay reducing effectof actuation
A finite element model investigates the effect of facet and fold elastic stiffness
Unit Cells [-]
|ε|[
-]
0 2 4 6 8 10
-0.2
0
0.2
0.4
0.6
0.8
1kF = 2 N/radkF = 3 N/radExperimental MeanExperimental Data
E1 = 2300 MPaE2 = 6100 MPaν12 = 0.17ν21 = 0.4
Spring-back: local actuation results in a deformation of the opposite sense after decay
A Miura-ori tube is studied. Bending of the facets causes decay of actuation
1
3
2
Support materialCFRP
σ33 + τ13 due to simple stamp andfibre curvature
Stamp
Stamp
F11F11
F33
F331
3
2
Support materialCFRP F11F11
F33
σ33 + τ13 due to special stamp geometry
Stamp
Stamp
F33
-33 [MPa]
11* [
MP
a]
The influence of complex through-thickness stress states on in-plane fibre tensile strength of CFRP Kilian Gruebler, Michael Wisnom, Stephen R. Hallett
This PhD project will investigate the influence and interaction of combinations of through-thickness (primarilycompression) and shear stresses on the in-plane tensile strength of fibre reinforced composites. A bespoke testmethod is being developed to study the material behaviour and based on this a numerical model will be developed andvalidated. A successfully developed model and test method will give the opportunity to improve the design and thereliability of composite components. Such a model and test method can be applied to applications where compositesare subject to complex 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
τ31
1
3
2
𝝈𝝈𝝈𝝈𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓∗ = 𝝈𝝈𝝈𝝈𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊
∗ − 𝜶𝜶𝜶𝜶 ∗ 𝝈𝝈𝝈𝝈𝟑𝟑𝟑𝟑𝟑𝟑𝟑𝟑− − 𝜷𝜷𝜷𝜷 ∗ 𝝉𝝉𝝉𝝉𝟏𝟏𝟏𝟏𝟑𝟑𝟑𝟑
𝝈𝝈𝝈𝝈𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓∗ = 𝝈𝝈𝝈𝝈𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊𝒊
∗ − 𝜶𝜶𝜶𝜶 ∗ 𝝈𝝈𝝈𝝈𝟑𝟑𝟑𝟑𝟑𝟑𝟑𝟑−
Investigated stress state Possible fibre failure envelope for IM7/8552, in case 𝜶𝜶𝜶𝜶=1 and 𝜷𝜷𝜷𝜷=1
Strain will be measured with digital image correlation technique. Failure stress state will be predicted by numerical models.
Advanced shell models for 3D stress field analysis in layered structuresAewis K.W. Hii, Luiz Kawashita, Alberto Pirrera
The scope for early stage design and optimisation of thick composite aerospace components is limited by the expensivenumerical analysis of nonlinear dynamic phenomena. These analyses are often dominated by the use of three dimensionalcontinuum elements in the finite element method (FEM). For end-users of FEM structural elements such as 1D and 2Delements are often regarded as numerically efficient but inaccurate in stress solutions, thus limiting their applications inphenomena driven by 3D stress states.
In this work, we utilise the recent advances in computational mechanics to develop a displacement-based continuum shellfinite element formulation, capable of 3D stress field analysis in layered shell structures. The displacement fields areexpressed in terms of the unified formulation, where expressions of vectors/matrices in the principle of virtual work aregeneralised. This allows user to prescribe arbitrary forms and orders of axiomatic expansions in the shell kinematics.Consequently implementation for various orders of shear theories, layer-wise theories and zig-zag theories can beintegrated in a single piece of computer code. The formulation shows good accuracy and requires relatively low degree offreedoms compared to 3D FEM across a series of benchmarks we performed in linear static, nonlinear static, naturalfrequency and transient dynamic analysis for shell structures with heterogenous layups.
1 Hierarchy of displacement-based formulations:
Computational efficiency
Layer-wise theory
Kirchoff-Love theory3
Reissner-Mindlin theory2
Higher order shear theory
Zig-zag theory
Pro
blem
com
plex
ity
Direct 3D approach1
Capable of 3D
stress field
2 Static analysis: Accurate 3D stresses near BC
E11/E22 = E11/E33 = 25
Layup = (0°/90°)5
Pressure
𝜎𝜎𝜎𝜎11 3D FEM𝜎𝜎𝜎𝜎33 3D FEM
𝜎𝜎𝜎𝜎31 3D FEM𝜎𝜎𝜎𝜎11 3-Layerwise𝜎𝜎𝜎𝜎33 3-Layerwise
𝜎𝜎𝜎𝜎31 3-Layerwise4
Thi
ckne
ss lo
catio
n
Cauchy stresses
3 Geometrically nonlinear analysis:
4 Transient dynamic analysis:
• The shell element captures accurately the transientresponse for thick shell. We obtain a diagonal massmatrix naturally with Gauss-Lobatto integration scheme.
For
ce
Displacement at ‘x’
Reference4 3-Layerwise
E11/E22 = E11/E33 = 40
Layup = (90°/0°/90°)
Dis
plac
emen
t at ‘
x’
Reference5 3rd order shear
Time
Pressure impulse
E11/E22 = E11/E33 = 1
1-3 Commonly offered in commercial FEM codes.4 Layerwise theory with third order shear deformation.5 Payette and Reddy’s 7-parameter shell model.
• The shell element captures the large strain localisationand rotation in the ‘pinched’ hyperboloid shell, which areaccounted for by a Total Lagrangian formulation.
• In this work, we explore the potential of high fidelity 2Delements for industrial application, to improve thecomputational costs in numerical analysis.
5 Future work:• Develop capability for progressive damage
analysis.• Explore options to increase stability time
limit in explicit time marching.
Design, build, and testing of an automated winding machine
A three degree-of-freedom winding machine was designed and built to demonstrate the suitability of the manufacturing processfor automation.
WrapToR composite truss structuresChris Hunt, Prof Michael Wisnom, Dr Benjamin Woods
Truss geometry• Maximises second
moment of area • Removes weakening
bending moments by aligning forces along the member lengths
Composite Materials• High specific strengths and
stiffnesses• Anisotropy can be tailored
to prioritise material properties in the loading direction
Unique winding processSimilar to filament winding, the manufacturing process is:
• Automatable• Repeatable • Low-cost
Wrapped Tow Reinforced Truss Concept
AnalysisPrevious studies have concentrated on stiffness response. Continuing work will focus on strength analysis for prediction of failure.
Concept scalingDeveloping the ability to produce larger scale trusses will allow for the superlative properties of the trusses to be used in a wider range of applications.
OptimisationDevelopment of an optimiser that uses previous analysis methods to optimise truss geometry for given loading conditions will be an extremely useful design tool.
Testing Analysis methods require experimental verification under a range of loading conditions.
Future Work
Automating the winding process allowed faster and more consistent production of trusseswith improved control over process variables.
Effect of high velocity oblique impacts on thin composite plates
Ashwin R Kristnama, Michael R Wisnom, Stephen R Hallett, David Nowell*
*University of OxfordImpacts from small and hard bodies at high velocity cause foreign object damage (FOD). Understanding the effect of FOD on component strength and structural integrity is a critical activity. Impacts have been carried out for a range of velocities, and damage was investigated with X-ray CT scans. Impact induced damage was characterised in terms of amount of fibre fracture and projected delamination areas. The residual strength of impacted laminates was determined through quasi-static tensile tests. Finite element modelling of impacted laminates under tension was carried out using LS-DYNA.
Impact Post impact
Cantilever jig
Laminate
Material: IM7/8552 Projectile: 3mm steel cube of mass 0.22g
A – edge impactB – centre impact
Laminate configurationLength: 250 mmWidth: 40 mm
Thickness: 2 mm[45/90/-45/0]2S
Experiment
X-ray CT scan
Dynamic impact modelling
Residual tensile strength vs Delamination area
Residual tensile strength vs Fibre fracture width
Quasi-static FE modelling
Boundary conditions for quasi-static tension
Coarse mesh regions
Fine mesh region
Mesh based on a unit cell.Mesh density of 0.23 mm
Region of interest on impacted laminate is given finer mesh based on a unit cell. Delamination areas based on X-Ray CT scans are represented through cohesive interface elements. Laminate is then modelled for quasi-static tension
Delamination plays an important role in residual strength of impacted laminates, where centre impacts show larger delamination areas than edge impacts at high impact velocities.
The plot to the left is for edge impacts. FE models for machined notches give closer residual strength values to Test data at high impact velocities.
Initial work looking at normal edge impacts
Amount of fibre fracture
Deletion of cohesive interface elements represents delamination size for the 1st -45/0 interface
100 m/s
Structural efficiency via stiffness adaptationOlivia Leão, Rainer Groh, Alberto Pirrera
Nonlinearities have long been treated as a source of structural failure or as undesiredstructural design aberrations due to the complexities they add to the problem. However,restricting structures to behave linearly from initial design stages can withhold someinteresting capabilities that are only possible in the nonlinear regime. This work embracesgeometrical nonlinearities to present and explore the concept of structural efficiency viastiffness adaptation.
Sponsored by
Basic hypothesis Forcing structures to behave linearly may correspond to overdesigning them, as part of the stiffness they can provide remains unused. On the other hand, if a structure is allowed to operate in the nonlinear regime, but in a well-behaved and controlled manner, it can be tailored to provide only the strictly necessary stiffness under operation.
Conceptual modelL: length (fixed)w: flange widthh: web heighttf: flange thicknesstw: web thicknessN: number of half wavesa: half-wave amplitude
In a T-beam with sinusoidal web, the geometry makes the structure inherently nonlinear due to the hidden length mechanism it develops upon loading. Initially, for small bending deformations, the beam is relatively flexible as the web acts like a corrugation, i.e. it provides little resistance to being stretched. As deformation increases, membrane stresses develop in the web causing the beam to stiffen whilst locally converting bending to stretching strain energy.
MethodologyNonlinear finite elements were used coupled to a genetic algorithm optimisation to find the best models for certain target points in the force-displacement (F-D) curve. The objective is afunction of the beam mass and the distance of the curve from the point. Wavy beams and conventional straight T-beams are compared in terms of mass and stiffness at the target.
Preliminary resultsFor target points further away from the origin on the F-D curve, best wavy and best straight models converge to a similar mass. In practice, this means that by including nonlinearity in the design space, it is possible to achieve models as light as their straight counterparts with higher stiffness at the target.
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Min
imum
mas
s (g)
Target displacement (mm)
Straight beam
Wavy beam
y
xz
L
w
h
a
tf
tw
N
Design and manufacturing of bend-twist coupled wind-turbine blade demonstratorsVincent Maes, Terence Macquart, Paul Weaver, Alberto Pirrera
Sponsored by:
As the beams D1 and D2 are baseline cases, little to no disagreement is expected between the predicted twist distribution and the experimental data. Figure 2 shows the models agree well, except at the root of the beams, where the beam model formulation does not capture the constrained warping effects. As the beams are thin-walled, excellent agreement is seen between the shell and solid models, as would be expected.
The shell and solid models are made using ABAQUS and analysed using standard S4R and C3D8R elements with the enhanced hourglass control option. Cross-sectional properties for the beams are calculated in parallel using BECASand VABS.
Future demonstrators, including sandwich panels and bond-lines among other features, are planned to further test the cross-sectional analysers and the beam model approach.
Most design efforts in wind-turbine blades are carried out using beam models with the help of cross-sectional analysers, which provide the beam element stiffness coefficients. Investigating the accuracy of these cross-sectional modellers for BTC is paramount and requires a series of demonstrators with increasing complexity.
To this end, the demonstrators shown above in Fig. 1 have been designed and built as the first benchmark cases. Both are 1.7 meter long, prismatic beams made using E-glass/913. By building up the features from these basic beams to realistic wind-turbine blade sections the models can be tested sequentially for their ability to capture various key features.
Bend-Twist Coupling (BTC) promises improved cost efficiency of wind-turbine blades by introducing aero-elastic coupling. This reduces the severity of gust loading and fatigue loading, by making the blades self-regulating, allowing an increase in size or lifetime of the blades. The methods underlying the analysis of BTC blades, however, remain largely unvalidated. Effective comparison requires benchmark cases with accompanying test data, which this work aims to provide through a series of BTC demonstrators.
Demonstrators: D1 and D2
Fig. 1: D1 and D2 being de-bulked during lay-up at the NCC (left) and schematics of their cross-sectional dimensions in millimetres (right).
Analysis: Beams vs Shells vs Solids
Fig. 2: Predicted twist distribution using beams, shells, and solids, for both D1 and D2.
Exploiting thin-ply carbon composites to establish failure criteria under multi-axial loading conditionsTamas Rev, Gergely Czél, Ian Bond, Michael R. Wisnom([email protected], [email protected], [email protected], [email protected])
The failure prediction of composite materials is hindered by the development of accurate theoriesand generating reliable experimental data [1]. Accurately determining the strength of compositesunder multi-axial loadings is still a great scientific challenge. The utilization of thin-ply materialsallows for suppressing undesirable damage scenarios [2,3], hence the objective of this project: todevelop innovative test methods using thin materials and investigate the interaction of differentstress-components on the failure mechanisms of unidirectional composites. Understanding theseinteractions can enhance design performance while a safer operation in service 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.[4] M. Jalalvand, M. Fotouhi, M. C. Leong, and M. R. Wisnom, “A novel technique to accurately measure the fibre failure strain in composite laminates under a combined in-plane tension and shear stress state,” 21st Internetional Conference on Composite Materials, ICCM21, August, 2017.
• Classical Laminate Theory (CLT)
• Design of Experiments (DOE) methods
• Advanced Failurecriterion 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
• Establishing failure criteria
• Comparing with literature
• Microscopy• Acoustic Emission (AE)
• Digital Image Corr. (DIC)• X-Ray Computed Tomography
(XCT)
Pivots
Compression-buckling rig
Strain distribution on tensile faceLoad case
Longitudinal tension –Transverse compression
Longitudinal tension –Shear
Longitudinal compression –Transverse tension
• Almost independent to shear stress values
• Novel tensile test configuration• High transverse compressive stresses applied
[4]
• Laminates with fibre compressive failure in 90° ply
𝑉𝑉𝑉𝑉1𝐴𝐴𝐴𝐴
𝑉𝑉𝑉𝑉 3𝐴𝐴𝐴𝐴
90° 0° pliesmore
mor
e an
gle
plie
s
Design & manufacture of a composite FishBAC wind tunnel model
Andrés Rivero, Paul Weaver, Jonathan Cooper and Benjamin Woods
The Fishbone Active Camber (FishBAC) concept is a morphing trailing edge device capable ofgenerating large, smooth and continuous changes in aerofoil camber distribution from abiologically inspired compliant structure. It has already shown promising results in terms of itslarge lift control authority, with significantly lower drag penalty than traditional trailing edge flaps.This work presents progress on the design, analysis and manufacture of the first FishBAC windtunnel model made with fibre-reinforced composite laminates. The wind tunnel model wasdesigned using a previously developed novel analytical tool that models highly discontinuouscomposite plate structures using Rayleigh-Ritz Method and Classical Laminate Theory.
Fishbone Active Camber Device
Benefits
Solid Trailing Edge
Section
TendonsStringersElastomericSkin
Spine (Bending Plate)
Tendon Pulley &
Actuator
Rigid Wing:Front Section
Rigid Wing:Trailing Edge Box
Trailing Edge flap Camber Morphing
Smooth and continuous change in camber• Lower drag and noise• Higher ⁄𝐿𝐿𝐿𝐿 𝐷𝐷𝐷𝐷 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚
Design
Manufacture
Analytical
Analysis⃝ FEM
― Analytical
Finite Element Method
Presented at the 7th Annual EPSRC ACCIS CDT Conference, University of Bristol
Bristol, UK, 10th April 2018
Carbon Fibre Spine (FishBAC)
Assembly Test
10 % chord
In partnership withShape Adaptive Blades for Rotorcraft Efficiency
Aeroelastic tailoring of wind turbines through multi-disciplinary optimisation
Samuel Scott, Terence Macquart, Alberto Pirrera, David Langston, Paul Weaver
The challenge for wind turbine designers is to reduce the cost of wind energy, thereby improving economicviability. During design, it is crucial to capture the inherent aeroelastic couplings present in wind turbineblades, such that loads and energy production are predicted correctly.
Bend-twist coupling, or more generally aeroelastic tailoring, can provide passive load alleviation, which in turnoffers further design choices such as increasing blade radius for greater power capture or mass reductions forlower capital cost. This work presents a novel optimisation framework capable of efficiently and accuratelynavigating an expansive design space to minimise cost of energy through aeroelastic tailoring.
The optimisation framework
• Two nested sub-optimisation loops• Outer loop ensures aero-structural coupling• Gradient-based optimisation
Preliminary results
Figure 1. Graphical representation of the optimisation framework architecture
Figure 2. 7MW blade with swept planform
• Baseline wind turbine model: Siemensoffshore 7MW
• Aerodynamic:• Rearward sweep reduces AEY• Baseline blade has rearward sweep,
illustrating aeroelastic trade-off indesign
• Structural:• Rearward swept blade reduces
optimal blade mass due to passiveload alleviation
Figure 3. Free vortex wake convection from a lifting line simulation
1. Model setup• Aerodynamic models for curved blades –
BEM vs Lifting Line• Efficient structural feasibility assessment
2. Optimisation setup• Complete development of optimisation tool• Investigate multi-fidelity optimisation
techniques for speed vs accuracy
3. Design & optimise• Apply tool to evaluate benefits of aeroelastic
tailoring
Future work
PROTOTYPE MANUFACTURE• IM7-8552 prepreg + cylindrical tool plate• Post-warp geometry measured using laser scan• Large moisture effects: -65% twist (<1 week)
VAL
IDA
TE
TAPE SPRING THEORETICAL PREDICTIONS
Stiffness tailoring of thin composite shells via thermal prestress
Jonathan Staceya, Matt O’Donnella, Carwyn Warda, Just Herderb, Boudewijn Wissec , Mark Schenka
aBristol Composites Institute (ACCIS), University of Bristol, bTU Delft, cLaevo BV
Supported by:
Composite manufacture often leaves internal stresses in the structure after cooling from cure, which cansignificantly affect the behaviour of thin shell structures. The application of this thermal prestress is investigatedas a technique to reduce the torsional stiffness of cross-ply tape springs, with a view to enabling tailoredcomposite compliant mechanisms. One example application of such compliant mechanisms is passive medicalexoskeletons, where bending support could be provided to the patient while still allowing twisting freedom.
FINITE ELEMENT ANALYSIS• Abaqus/Standard with S4R shell elements• Application of temperature fields to model cure• Small fibre misalignment to break twist symmetry
NO THERMAL EFFECTS:• Monostable @ θ = 0°• Small low energy twist region
WITH THERMAL EFFECTS:• Bistable @ θ = 22° (0° unstable)• Large low energy twist region
Energy landscapes for [02/902] tape spring with 38mm tool radius
Sample Design Parameters Helix Radius (mm) Twist Angle (°)Layup Tool Radius (mm) Experiment ΔT (°C) Theory FE Experiment Theory FE Experiment
[0/90] 38 -162.7 48.1 50.6 50.9 22 21.8 16.9
[02/902] 38 -163.9 48.1 47.3 55.5 55 53.0 47.8
[1] – Guest et al., J. Mech. Mater. Struct., 6(1-4):203-212, 2011
• ASSUMPTION: Tape spring wrapped around an underlying cylinder throughout twist θ
[1]
• CALCULATION: Internal strain energy due to residual thermal stresses in cylindrical configuration
• Strain energylandscapespredict stable equilibria,cylinder radiiand shell twist
Kirigami stretchable strain sensors with enhanced piezoelectricity induced by topological electrodesRujie Sun, Bing Zhang, Wenjiao Zhang, Ian Farrow, Fabrizio Scarpa, Jonathan Rossiter
Piezoelectric materials have great potential for biomedical devices, because of their self-powered sensingcapacities. However, low stretchability has restricted their wider use on soft and highly deformable surfaces, whichare typical of the human body. Here, a Kirigami (Origami + cuts) topology with straight cut patterns has beenemployed to design a stretchable piezoelectric sensor with enhanced piezoelectricity. A novel inter-segmentelectrode connection approach is also proposed to further enhance the piezoelectric performance of the sensor. Aparametric Finite Element (FEA) study is first performed to investigate its mechanical behaviour, followed byexperiments. The voltage output shows a superior performance, with a 260% improvement compared toconventionally continuous electrodes. Dynamic tests with a range of frequencies and strains are performed tovalidate the sensor design. With its high performance in large strain measurements, this Kirigami-based sensingsystem shows promise for stretchable electronics in biomedical applications.
Mechanical analysisFig. 1. (a) Schematic of the Kirigamistructure where L, a, b and t indicate cutlength, hinge length, cut spacing, andfilm thickness. (b) Stress-strain curvesfor the pristine film, and Kirigamipatterned film obtained by numericalsimulations and experiments.
Fig. 2. (a) The inter-segment electrode pattern with reverse connections for adjacent parts through holes. (b)the electrode pattern using inter-segment connections within one unit strip of the Kirigami structures, scalebar 2 cm. (c) the time domain output of voltage using the electrode patterns in (b) from experimental tests.
Electrode design
Fig. 3 (a) Voltage output of theKirigami piezoelectric sensor under agiven frequency of 10 Hz and a strainrange from 2 % to 10 %; (b) thevoltage output under a given strainrange of 1 % and a frequency rangefrom 3 Hz to 24 Hz.
Dynamic test
(a) (b) (c)
(a) (b)
Manufacturing & Design
Cutting Characteristics Study (ongoing work)
Novel tow termination mechanism for high quality AFP production
Tharan Gordon, Stephen Hallett, Michael Wisnom and Byung Chul Kim
Key Advantages(i) Composite components formed using the AFP
process will have improved performance with respect to delamination onset load [2]
(ii) The process will allow for minimisation of the high computational expense of designing and analysing complex tapered laminates
(iii) New avenue of study opened for optimising tow end geometry to different loading scenarios
During conventional Automated Fibre Placement (AFP) production of tapered components, defects are built into the structure in the form of resin pockets at the terminated ply boundary. These can be critical in nature as they become crack initiation zones upon loading [1]. Conventionally such sites are accepted as an artefact of manufacture, with much work undertaken to accurately predict and account for their detrimental effect in the design stage. This is at great expense both computationally and in efficiency.
In this work, the feasibility of a novel tow termination method for AFP manufacture is explored. The project focuses on developing a new tow cutting mechanism that automatically tapers the tow ends during the AFP lay-up process in a controllable manner, and experimental investigation into the cutting characteristics of representative AFP materials.
Conventional Guillotine Cutting:• The formation of Resin Pockets a the ply
boundary
Novel Tow Termination• Complete removal of the defect
Discontinuous
Continuous
Tapered Tow
[1] Z. Petrossian and M. R. Wisnom, “Parametric study of delamination in composites with discontinuous plies using an analytical 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.
Fibre Compression
Fibre Cutting
Cutting Force Evolution
Cutting Angle Control at Tow End
Taper ratio comparison
Tow Cutting Test Rig
3° Angle
7° Angle
5° Angle
Example Cut Tow
Loadcell
LoadcellPrepreg
Blade
Resin Pocket
Compressed Area
Cut Face
Fibre CuttingFibre
Compression
Cutting Complete
α1 α2E1
Designing bend‐twist coupled blades for the segmented ultralight morphing rotor
Anatoly Koptelov, Alberto Pirrera, Terence Macquart, Paul Weaver, Todd Griffith
E-LT fiberglassTriax fiberglassBalsa
Current trends in the power generation industry show that companies are driven to build largerwind turbines capable of satisfying increasing demands in energy consumption, which leads tothe enlargement of main structural components including wind turbine blades.
The current research aims to demonstrate the effectiveness of bend-twist coupling (BTC) interms of load alleviation by incorporating it into one of the existing designs.
Blade model
The reference blade is a Sandia’s SNL100-3100-metre blade for 13.2 MW downwind windturbine.
The blade was modelled by means of a newoptimisation framework [1].
Interpolated wind turbine model
Types of the aerofoils along the blade
ResultsRoot bending moment (left) and average energyproduction (right) depending on the layup, E1
location is fixed at the optimal point
Dependence of root bending moment and powercoefficient on operating wind speeds
• Optimisation procedure for an existingstate-of-the-art project was carried out
• Load alleviation at the rated wind speeds of3.61% was achieved for the optimised design
• Consideration of additional design variables
• Smooth change of the fibre orientation
• Flutter and divergence study
E-LT fiberglassTriax fiberglass
UD carbonTriax fiberglass
E-LT fiberglassTriax fiberglass
Saertex fiberglassFoam
Conclusions and future work
[2] Capuzzi M, Pirrera A, Weaver P. Thin-Walled Structures. 2015;doi:10.1016/j.tws.2015.06.006.
[1] Macquart T, Maes V, Langston D, Pirrera A, Weaver P. A New OptimisationFramework for Investigating Wind Turbine Blade Designs. 2017.
Pow
er c
oeffi
cien
t
Wind speed, m/s
Root
ben
ding
mom
ent,
N*m
Wind speed, m/s
Optimisation problemOptimal energy production rate is achieved whenthe inner part of the blade twists to feather whilethe outer part conversely twists to stall
Root
ben
ding
mom
ent,
N*m
α1α2 α2
α1
PAV
Local grading of composite architecturesArjun Radhakrishnan+, Ian Hamerton+, Milo Shaffer*, Farbizio Scarpa+, Dmitry S Ivanov+
+University of Bristol, *Imperial College London
This research demonstrates feasibility of using local grading of composite structures to improve structuralperformance and functionality of composites. Combination of Liquid Resin Printing (LRP) andconsolidation programmes allows for controlled morphology of the graded patch.
A localised manipulation of material properties allows an increase in the loading of additives, decrease thecost of manufacturing properties compared to bulk modification of composites, creates greater stiffnesscontrast, improves structural performance and opens a larger material design space for optimisation.
Step 1: Liquid resin printing of enhanced matrix
Step 2: Thermal management and consolidation of patch
Step 3: Resin infusion of graded structure
Processing multi-matrix composites
Morphology of graded composites
❖ Distribution of additives is controlled through injectionparameters, filtration mechanisms (natural grading) andconsolidation programmes (controlled grading).
❖ Local enhancement of the properties (e.g. around the stress concentrator) is shown to improve mechanical performance of the material.
❖ Varying consolidation parameters results in differentpatch morphology.
❖ Chemo-viscous properties of the resin controls theprincipal flow mechanisms.
❖ Grading of composites is shown to affect stressdistribution in composite through a number ofmechanisms:
❖ Through thickness-electricalconductivity mapping showsthat various patchmorphologies and additivedistributions can be achieved.
Mechanical properties of graded composites
Processing of graded composites Stress distribution in graded composite
❖ Consolidation programmes are tailored to curekinetics and rheology of injected resin.
Evolution of patch(flow) with heatand compactionwith different CNTcontents.
Graded patchHost
CompositeGraded patchHost preform
Controlled flow
Applied pressure
❖ Various grading materials are considered.
❖ Increase of 17% and 24% of strain-to-failure andstrength respectively is observed in open holetensile tests by grading of glass-epoxy braidedsamples.
Str
ess
alon
g fib
re in
in
lay
yarn
s.
Local tuning of composite
structures
1.5 wt%
3 wt%
• Load flow is modifieddue to stiffness andpresence of internalinterfaces.
• Damage mechanismsis improved due tocombination ofdifferent matrices.
A closed-loop recycling method for short carbon fibre thermoplastic compositesRhys Tapper, Marco Longana, Hana Yu, Ian Hamerton, Kevin Potter
This project describes the proof-of-concept study of a closed-loop recycling method for carbon fibre composites. Closed-loop recycling can provide multiple use phases for CFRP material. In combination with the HiPerDiF alignment method, this process can produce a highly aligned, discontinuous, carbon
fibre thermoplastic prepreg that retains competitive mechanical properties over repeated recycling process loops. The resulting lightweighting benefits have the potential to offset the significant
environmental burden and fincancial cost of production.
Mild processing solvents and conditions
> 90 % material recovery
Highly aligned preforms
Compression moulding: 10 MPa
minimal matrix
degradation
Results
[1] Tapper R, Longana M, Yu H, Hamerton I, Potter K. Composites: Part B (2018).
• Polypropylene matrix and 3mm carbon fibres with a VfF = 26 %.
• Competitive mechanical properties retained after each loop: Et= 43 GPa, σt = 285 Mpa.
• Tensile strength showed an increase after the final loop; σt = 396 Mpa.
• Matrix residue left on fibres post recycling acts as a matrix-specific sizing, boosting adhesion.
Future Work
• Increase matrix range: Polyamide 6 & Polyamide 66.
• Life cycle assessment of recycling process to quantify energy demand, environmental impact andfinancial cost.
• Manufacture of bidirectional composite laminates for broader range of mechanical performance characterisation.
• Collaboration with industrial partner to produce demonstrator component.
Effect of voids on interlaminar behaviour of carbon/epoxy compositesIryna Tretiak, Luiz F. Kawashita, Stephen R. Hallett
Porosity is a common manufacturing defect in composite materials. It can be caused by ineffective debulkingor inadequate autoclave curing which lead to air being trapped within the laminate. Porosity has significanteffects on the matrix-dominated properties of a composite. Many researchers have investigated the influenceof porosity content on the mechanical performance of composites. However the size, shape and location ofvoids are important parameters often not characterised. The aim of this work was to characterise theseparameters and investigate their correlation to interlaminar shear strength (ILSS).
Pressure and temperature controlled curing using hot plates in a testing machine
Batch 1: pressure 0.3 MPa, T=30°C, Batch 2: pressure 0.3 MPa, T=90°C, Batch 3: pressure 0.3 MPa, T=120°C, Further curing in oven @180°C for 5 hourBatch 4: reference autoclave curing
Excellent correlation(a) optical micrograph (b) μCT-imaging
Short beam shear test for interlaminar shear strength (ILSS) testing
RESULTS AND DISCUSSIONS
Minimum ILSS difference 2MPa; Void content range of 0.08%
Void Feature Analysis (based on void volume & location)
Void content, %
0 1 2 3 4 5 6 7 8
Inte
rlam
inar
She
ar S
tren
gth,
MP
a
40
50
60
70
80
90
Batch 1 (temperature = 30C)
Batch 2 (temperature = 90C)
Batch 3 (temperature = 120C)
Batch 4 (Reference Autoclave)
Void content, %
0 1 2 3 4 5 6 7 8
Inte
rlam
inar
She
ar S
tren
gth,
MP
a
40
50
60
70
80
90
All tested samples
Selected pairs
Behaviour 1
Void number
1 2 3 4 5 6 7 8 9 10
Voi
d vo
lum
e, m
m3
0
1
2
3
4
5
6
7
8
9
ILSS=47.63MPa,Vv=7.47%
ILSS=50.2283MPa,Vv=7.46%
Void number
1 2 3 4 5 6 7 8 9 10
Voi
d vo
lum
e, m
m3
0
5
10
15
ILSS=49.9993MPa,Vv=7.06%
ILSS=55.3808MPa,Vv=7.04%
Before test
After test
• Cracks propagate from void to void
• Voids can alter crack direction
Behaviour 3Behaviour 2
Void number
1 2 3 4 5 6 7 8 9 10
Voi
d vo
lum
e, m
m3
0
1
2
3
4
5
6
7
ILSS=51.9103MPa,Vv=6.37%
ILSS=57.343MPa,Vv=6.37%
Void number
1 2 3 4 5 6 7 8 9 10
Voi
d vo
lum
e, m
m3
0
1
2
3
4
5
6
ILSS=49.9993MPa,Vv=7.06%
ILSS=55.3808MPa,Vv=7.04%
Void number
1 2 3 4 5 6 7 8 9 10
Voi
d vo
lum
e, m
m3
0
1
2
3
4
5
ILSS=51.9103MPa,Vv=6.37%
ILSS=57.343MPa,Vv=6.37%
10 largest voids in close proximity to mid-plane
Void location with respect to the critical region of the specimen has a significant effect on strength reduction
Large voids are more critical than an equivalent volume of smaller voids
10 largest voids through the thickness of samples
two samples, same average void content, different strength
Behaviour 2 Behaviour 3
DETECTION TESTMANUFACTURE
Minimising forming defects in the diaphragm forming process by reducing interply slip resistanceWei-Ting Wang, HaNa Yu, Kevin Potter, Byung Chul Kim
Diaphragm forming is a composite pre-forming technique that has been used to manufacture large aircraft structural parts. Compared to conventional ply-by-ply lay-up method, this method significantly shortens the processing time by forming a flat prepreg stack into a desired shape in a single step. However, the high tackiness resin on prepreg surface prevents slippage between each ply, which affects forming
quality. In this research, the interply slip resistance was reduced by using the dry lubrication materials at the interply regions, which minimise defect generation and enable formation at lower temperature. The interleaving materials also improve composite mechanical performance.
Apply vacuum pressure and heat to shape the laminate
Flat laminate and tool covered by a diaphragm
Diaphragm
Laminate
Tool
Pressure and heat
Curing process
Hot drape forming(Laminating Technology)
Generate out-of-plane wrinkles
Improvement Method : Interply Lubricant
Flat laminate
During formation
Ply slip resistance due to viscous resin
Laminate with interply lubricant
Laminate without interply lubricant
High slip resistance causes wrinkles
Wrinkle free
Lubricant layer promote ply slip
Mechanical performance
Force
Pressure
Mid ply
Fixed plies Lubricant
layer
Increase fracture
toughness
Mode-I fracture toughness
Preform
Interplyfriction test
Ply Slip Characterisation
Diaphragm Forming Test
Diaphragm forming rig
• Rig size 500*430 mm
• Single or double diaphragm
• Temperature range: Oven heating up to 60°C
Curved beam strength
Future work
• How does processing conditions influence lubrication effect?
• How to achieve high forming quality for complex parts using interleaving lubricants?
• How does lubrication materials affect composite structural performance?
Promote ply slip> 500 N
New experiments for in-plane shear characterisation of uncured prepreg
Yi Wang, Dmitry Ivanov, Jonathan Belnoue, James Kratz, BC Eric Kim, Stephen Hallett
Automated 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.
Related to:• In-plane behaviour
(shear/bending)• Surface characteristics
(tack, friction)
Shear band
grip area
grip area
α𝐹𝐹𝐹𝐹𝑡𝑡𝑡𝑡
𝐹𝐹𝐹𝐹𝜏𝜏𝜏𝜏𝐹𝐹𝐹𝐹
𝐹𝐹𝐹𝐹
𝐹𝐹𝐹𝐹
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
Relationships between shear stress, shear strain and rates
Stress/Strain curves with different layers
Test setup
Evolution of buckling load with temperature
DIC analysis results:
Design, Build and Test
Design, Build & Test: UAV box-spar demonstrator
ACCIS CDT Cohort 2017Supervisors: Ian Farrow, Carwyn Ward
The aim of this project is to design, build and test a UAV box-spar demonstrator based on a single critical design case. This will be created from a single, closed-
section monolithic composite beam. The cohort will be split into two teams, Wilbur and Orville, named after the pioneers of powered flight.
Structural Requirements:• Wing-spar beam must withstand 1000 N at limit load. • Design factor of 1.5 for the ultimate load.• The beam tip deflection shall not exceed 150mm at limit load.• The beam tip twist shall not exceed 0.5° at limit load.• No fibre dominated or interlaminar failures will occur below
ultimate load.• No global or local buckling shall occur below ultimate load.
Manufacture Requirements:• Single structure, hollow monolithic composite beam.• Cantilever beam bolted to wall fixtures on top and bottom flanges.• 20mm diameter lower flange inspection hole in the centre of the
beam.• Withstand 15J impact at any point without premature failure.
Team Orville: Design, Build & TestJoachim Paul Forna Kreutzer, Riccardo Manno, Chiara Petrillo, Jagan Selvaraj, Kirk Willicombe
The aim of this project is the design and manufacture of a UAV wing box-spar demonstrator to withstand a single critical load case. The geometry of the beam section is pre-defined by the specification. The section is designed to withstand a 1kN limit load case, offset from the
central axis in a whiffletree loading, with a maximum allowable twist and deformation.
Design• High Strength
Carbon Fibre used throughout
• Symmetric Lay-up• Ply-drops present in
flange sections
Analysis• ABAQUS FE Analysis
undertaken• Deformation within
allowable limits• Buckling modes
analysed
Future Work• Manufacture and test • Male mould tooling• Vacuum bagging and
autoclave curing
• Post-cure machining to finish
• Testing on whiffletree loading to assess final performance
Manufacture Trials• Multiple tooling sections cut• Testing of lay-up and cure• Wrapping, ply orientation, de-bulking etc.
PreparationMaterials Testing• Testing of Carbon
specimens• Tensile Testing: QI and UD• Open hole testing• DIC and video gauge
Team Wilbur: Design, Build & TestEileen Atieno, Francescogiuseppe Morabito, Hernaldo Mendoza Nava, Imad Ouachan, Usman Sikander
Aim: To design a composite box-beam suitable for a UAV tapered wing with a load carrying capability of 1kN.
Taper angle of 1.5°.
Bolted fixture at the root.
Inspection hole at mid-span.
Details
Limit load: 1kN (RFultimate=1.5)
δmax=150mm
θmax=0.5°
No buckling failure up to ultimate.
Finite Element Analysis
HSCFEP prepreg (SE 84-LV, UD / woven).
Oven cured (12 hrs at 80 °C, holding vacuum pressure).
Extruded polystyrene foam (FloormateTM 700-AP) mold.
Shrink-wrap to improve surface finish.
Materials Properties: E1, E2, ν12, G12.
Bearing Test.
DIC for V-Notch Test.
Manufacturing Trials
Mechanical Characterisation
uild
esig
nes
t
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
Front cover photo credits: Lourens Blok (top), Michael Dicker, NCC ImagesofResearch.com (bottom left), Maximillian Dixon (top right & bottom), Tom Hounsell (far left & far right), Callum Lanherne (bottom right), Dominic Palubiski (centre), Samuel Scott (top left).
