Tuesday 5th April 2016University of Bristol, Queen’s Building, University Walk,
Bristol, BS8 1TR, UK
5th ANNUAL CONFERENCE OF THE
CDT IN ADVANCED COMPOSITES FOR INNOVATION AND SCIENCE
POSTER BOOKLET
Multifunctional
Composites and Novel
Microstructures
Advanced curing for on-platform repair of aerospace composite components by external
magnetic fieldsGiampaolo Ariu, Bhrami Jegatheeswarampillai, Ian Hamerton, Dmitry Ivanov
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 short fibres such as carbonnanotubes (CNTs) through external magnetic fields for advanced curing purposes.
Methodology
• Creation of “high conductivity connections”within composite structure.
• Localised heating for more uniform overallcuring process.
• High conductivity connectors: nanotubes
aligned towards applied field.Schematic of composite inner structure for fibre alignment byexternal energy fields.
Modelling
Modelling• Abaqus/Python model: modelling of realistic
clustered CNT configurations.• COMSOL 3D model for MWNT distribution.
Experimental• Magnetic analysis of Ni/Co/Fe plated MWNTs
(VSM and AC setup at Cardiff University).
Future work
MATLAB: CNTalignment in epoxy
Cylindrical fibres.
Stokes flow before cure. Gravity neglected.
Uniform DC field.
Higher 𝐵𝑂𝑚𝑖𝑛 for increasingar (<100).
COMSOL: Thermal + AC induction heating
AC cooled coil.HexPly® 8552 + metal coated MWNT (ar =10).No external heat source.
AC design parameters: I = 100 A; f = 180 kHz.Model shows a uniform T-field generated in CNT composite solely bymagnetic field.
MATLAB results (left) and COMSOL induction heating model(right: I = 100 A, f = 180 kHz and t = 1h).
Experimental
Magnetic MWNT alignment in epoxy
DC electromagnet (no
cooling): B = 0.5 T. PRIME 20LV + 1 vol.% of
as-received MWNTs
(ar>1000 or ≈ 10).
Relevant agglomeration. Higher alignment at low ar.
Metal coating of MWNTs
TEM of commercial Ni-coated MWNT andNi-plated MWNT.
Commercial coating: inefficient and weak. Plating: more uniform wall coating, but dominantagglomeration.Ni-plated MWNTs can align under lower DC fields.
DC electromagnet (a); SEM of low aspect ratio MWNT in epoxy after DC field (b);commercial Ni-coated (c) and Ni-plated (d, e) MWNTs; (f) Ni-plated and COOH-MWCNT alignment after different applied DC fields.
(a) (b)
H
(c)
200 μm
Unit
cell
Copper
coil
Water
cooling
channel
High
conductivity
connections Field
aligned
fibres
Field
aligned
fibres
Composite
fibres (e.g.
0-90˚
orientation)
Randomly
arranged fibres
in resin
(d) (e)
(f)
www.bristol.ac.uk/composites
Supported by
www.bristol.ac.uk/composites
4D materials are materials that shapechange in response to a stimuli. This stimulicould be temperature, light, chemical or timeitself. This work uses hydrogels, high watercontent plastics, to create shape changingmaterials with pre-programmable and re-programmable transformations. Thesesoft and wet shape changing materials areideally suited to applications involvinginteractions with biological systems,including the fields of biomedical, soft-roboticsand biological sensors.
4D MaterialsProgramming shape change into hydrogels
Anna Baker*, Duncan Wass+ and Richard TraskϮ*[email protected]
+Chemistry (University of Bristol), ϮMechanical Engineering (University of Bath)
Supported by
Programming
XY PlotterCation Pen
+3
+3
+3
+3
+3
Concept
LocalisedPatterning of Metal Cations
No Swelling in this Area
Fold Created as the Rest
Swells
Smart Hydrogel
Hot
Metal Cation
Cold
Water
Future Work
More ComplexShape Change
4D Printing
Demonstration
HotPrinted Cold
www.bristol.ac.uk/composites
3D printed elastic honeycombs with tailorable shock absorbing properties
University of Bristol: Simon Bates*, Ian Farrow, Richard Trask
RNLI: Holly Phillips, Iain Wallbridge
Supported by
To ensure crew members of small high speed craft do not suffer from dangerouslevels of whole body vibration (WBV), the unpredictable oscillations and waveimpact loads must be attenuated. In such vessels, mechanical spring-dampersystems cannot be retrofitted and foam paddings provide insufficient protection tocrew members who are required to kneel on deck. This work describes thedevelopment and experimental analysis of thermoplastic polyurethane (TPU)honeycomb structures which effectively absorb the energy from impact loads andprotect individual crew members, taking into account their weight and positioningwithin the craft.
Multiple densities
3D printed TPU honeycombs
Auxetic honeycombs
Hexagonal honeycombs FDM 3D printer
Experimental data
*0.5
*0.37
*0.26
*0.5
*0.37
*0.26
*0.5
*0.37
*0.26
*relative density, ρrel
a) The design and; b) collapse behavior of a 3-stage graded honeycomb. c) The stress strain behavior; d) energy absorption profile and; e) efficiency of this structure are shown alongside structures with uniform density. The average
relative density of the graded structure is 0.37a)
b)
c) d) e)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Str
ess (
Mpa)
Strain
Foam sample
Ninjaflex hexagonal RD=0.27
Conclusions
Optimum energy absorption
Optimum energy absorption
• The design freedom of 3D printingallows for functional tailoring
• Grading structures allows for atailored energy absorption profile
• Superior energy absorption tobenchmark closed cell foam
Honeycomb absorbs more energy whilst transferring
lower stress
www.bristol.ac.uk/composites
UV-Responsive Thermoplastic Liquid Crystal Elastomer
Future Work
• Full characterisation of polymeric material.
• Attempt extrusion of filament.
• Measurement of UV-triggered shape change.
Programmed shape change by UV-responsive liquid crystal elastomers
Laura Beckett, Richard Trask, Annela Seddon, George Whittell and
Ian Manners
Supported by
Liquid Crystal Elastomers
Liquid crystal elastomers (LCEs) are materials capable of programmed shapechange on exposure to an external stimulus. Consisting of liquid crystal mesogensattached to a polymer backbone, a change of order on a molecular level inducesdeformation. A thermoplastic LCE should be possible to extrude, giving a route toUV-active filaments that could be utilised in 3D printing.
Nematic Isotropic
Overall a macroscopic contraction/elongation is seen.
x=133y=2z=124
The liquid crystal mesophase switches from an ordered nematic, to a disordered isotropic phase.
When mesogens are attached to a flexible polymer backbone, the polymer chains transition from a stretched to a spherical conformation as order decreases.
LC =
A reversible change in configuration of the mesogen from its rod-like trans isomer to its bent cis isomer can be induced by UV irradiation.
UV-on
UV-off
• A synthetic route to the polymer shown has beendeveloped.
• Unlike the majority of LCEs no covalentcrosslinking is required – meaning processing byextrusion to form a fibre is possible.
• UV-irradiation should lead to reversiblecontraction along the fibre direction.
www.bristol.ac.uk/composites
Photonic crystals are periodic ordered microstructures, built from dielectricmaterials, with a periodicity in the scale of visible light wavelength (~200-700 nm).Through rational design and smart tuning of the PC periodicity it is possible to tailorthe color exhibited by these materials. The main objective of this work is to designand assemble photonic crystal structures based on colloidal self assembly and silicasol-gel chemistry.
Polychromatic composite structures
Diego Bracho, Richard Trask, Annela Seddon
Supported by
20°C1-2 weeks
400°C5h
Deposition Calcination
Figure 1: Schematic illustration of inverse opal assembly by colloidal self assembly
Evaporation
Figure 2: SEM imagedisplaying cross section of aSiO2 inverse opal (1000 nm)
10 μm
Conclusions and future work
• Silica inverse opals of different pore sizes were fabricated using a vertical depositionmethod in a single-step co-assembly of polystyrene colloids in a silica precursor solution.
• These exhibit a face-centered cubic structure (FCC), with the (111) plane oriented at thesurface of the structure.
• Future work will include a detailed study on the photonic bandgap tuning by liquidinfiltration, using different refractive index liquids, and stimuli responsive polymer gels.
Figure 3: Photographs of prepared silica inverse opals and silver coated silica inverse opals
240 nm 500 nm 1000 nm
Inv.
Opal
Inv.
Opal
+ A
g c
oating
Experimental
Figure 4: SEM images from SiO2 inverse structurestemplated from different colloid diameters (φ)
10 μm
φ=240 nm φ=500 nm
φ=1000 nm φ=1000 nm
www.bristol.ac.uk/composites
Use this area for Introduction or Abstract, delete if not required.
Use WHITE text, 36pt Verdana, fully justified and non-bold (except for highlightingwords)
Composite protection
Mark Hazzard, Paul Curtis a, Lorenzo Iannucci b, Stephen Hallett and
Richard Trask c
Supported by
a, b: Imperial College Londonc: University of Bath
The in-plane mechanical response of a Dyneema® based composite has beeninvestigated at varying strain rates and hot-press consolidation pressures. Shearand tensile strength both increased at higher strain rate, whilst consolidationpressure caused an increase in maximum shear strength. Due to the low shearstiffness of the material, strain variation was observed in the tensile gauge regionand is thought to be the cause of large variation in open literature stiffness values.
ManufacturingGel spun ultra-high molecular weightpolyethylene fibres produced by DSM werecross-plied into a 0/90/0/90 configuration.Plies were then stacked and hot-pressed at120°C at 10 MPa, 20 MPa, and 30 MPa.Microstructural investigation revealed plywaviness and fibre indentation. Specimens arefinally water-jet cut for testing.
0/90/0/90 Cross Ply Hot Pressed Cross Section Hot Press Indentation
0/90 Tensile Testing
• Custom specimens to avoid slip and delamination at grips.
• Testing dominated by intra-laminar slip, causing strainvariation in the gauge region, confirmed by FEA.
20 MPa
20 MPa
10 MPa
30 MPa30 MPa
10 MPa
0
100
200
300
400
500
600
700
800
0 1 2 3 4 5
Str
ess
(MP
a)
Ɛs (%)
20 MPa
20 MPa
0.1 mm/s
1 mm/s
Fibre pull-in at rear of loading
tab
Intra-laminar shear and fibre re-alignment
Ɛc
Ɛs
Future WorkTensile and shear properties will be input into aballistic model in LS-DYNA and compared with testresults. A homogenised model with elastic-plasticcriteria and element deletion will be used andcompared with results. Taking inspiration fromnature, novel hierarchical fibre architectures willbe trialled and investigated to improve impactperformance.
Classical Impact Behaviour
Model with Boundary Capture Modes of Failure
±45 Shear Testing
• Classical shear failure over a large length of the gaugeregion due to large amounts of delamination.
• Causes a highly non-linear shear response, largely causedby fibre re-alignment to loading axis.
10 MPa
20 MPa
30 MPa
10 MPa
30 MPa
30 MPa
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2
τ1
2[M
Pa
]
ɣ12 [rad]
1
2
3
45
6
θ = 65° after spring-back
Through thickness
www.bristol.ac.uk/composites
3D printing with ultrasonically arranged microfibre reinforcement
Thomas Llewellyn-Jones, Bruce Drinkwater, Richard Trask
Aims
• To manipulate glass microfibres within a viscous UV curable resin system.
• To selectively cure regions of the resin.
• To remove an intact part from the resin tank after curing.
Supported by
Results
• Glass microfibres align along acousticpressure nodal planes.
• Selective resin curing achieved.
• Aligned fibres extend to edge of printedpart.
3D Printing Process
• Ultrasonicmanipulation rigattached to FDMstyle printerbed.
• Printer extruderhead replacedwith focusedviolet (405nm)laser module.
Alignment Process
• Fibres dispersed in UV curing resin.
• 2MHz counter-propagating wavefrontsproduce standing wave field.
• Glass microfibres align along theacoustic pressure nodes. Conclusions
• Acoustic manipulation combined with SLAstyle 3D printer can produce parts withpatterned microfibres.
• Complex microstructures can beimplemented.
• Dynamic rearrangement ofmicrostructures can be performed mid-layer.
Glass microfibres aligned within 3D printed part.
Schematic representation of printing and alignment processes
Optical microscopy of glass microfibres before (left) during (middle) and after (right) ultrasonic alignment.
Ultrasonic manipulation was used to arrange glass microfibres within a UV curableresin tank. A 3-axis controller was then used with a UV light source to selectivelycure regions of the resin to produce 3D printed parts with oriented short fibrereinforcement.
www.bristol.ac.uk/composites
4D fibrous materials: characterising the deployment of paper architectures
Manu Mulakkal, Richard Trask, Annela Seddon, George Whittell and
Ian Manners
Diffusion (dominant) and capillary driven deployment in different kinds of paperfolds were investigated and characterised. The results show the clear role ofhydration, water transport and the interaction of hydrogen bonds within the fibrousarchitecture driving the deployment of the folded regions. The importance of fibrevolume fraction and functional fillers in shape recovery upon deployment was alsoobserved and confirmed. The design guidelines arising from this study will helpinform the development of synthetic fibrous actuators for repeated deployment.
Affiliations: ACCIS, School of Physics and School of Chemistry
Supported by
Origami Deployment Sequence
0
500
1000
1500
2000
2500
15 25 35 45 55 65 75
Actu
ation T
ime (
s)
Temperature (°C)
Printer paper 90 gsm Lokta 60 gsm Lokta 30 gsm Seki 30 gsm
0
50
100
150
200
15 20 25 30 35 40 45 50 55
Fold lines
Fold Recovery on Drying
Printer paper
(Filler )
Hand made
(Filler )
*for both directions* Average std.dev
1 44.60 12.89
2 42.83 8.67
3 33.31 9.18
4 39.05 14.66
5 39.02 7.22
6 44.82 11.30
0 s 15 s 22 s 34 s
Deployment sequence (L-R) of the folded profile.
Cracks formed in printer paper and development of low resistance flow paths
Microscopic histology of fold creation in handmade paper
Paper architecture with filler Paper architecture without filler
20µm 100µm50µm
15 mm
90 gsm 60 gsm 30 gsm 30 gsm
www.bristol.ac.uk/composites
Flexible pressure sensors are crucial components of next generation wearabledevices to monitor human physiological conditions. This paper investigatesoptimisation designs of a capacitive pressure sensor to improve its sensitivity andtactility. The effects of different electrode structures on capacitance are comparedto obtain an optimal pattern. Then, a pyramid dielectric structure is designed toimprove pressure sensitivity as well as tactile sensation. Finally, a sensor array isfabricated and using human skin as the other electrode is demonstrated to bemore sensitive to applied displacement.
Designs of capacitive pressure sensors for wearable device: patterns and sensitivity
Rujie Sun, Jonathan Rossiter, Richard Trask
Supported by
• Optimal electrode configuration;
• Pyramidal-shaped dielectric;
• Sensor array fabrication.Fig. 1. Schematic of the designed capacitive pressure sensor.
ElectrodePressure
Skin
Fig. 2. The pressure sensitivity basedon different sensor configurations.
Fig. 3. Sensor array with human skin as theother electrode (a), test results over time undertwo electrode sizes (b).
Micro scale manufacturing techniques; different structural patterns and parameter
optimization for the dielectric; resistive pressure sensor for comparative study.
(a)
0 1 2 3 4 5 60
0.5
1
1.5
2
2.5
3
3.5
Time/s
Cap/p
F
Small electrode
Large electrode(b)
Sensor Designs
Experiments and Results
Future Work
Design, Analysis and
Failure
www.bristol.ac.uk/composites
Aeroelastic performance controls wing shape in flight and its behaviour undermanoeuvre and gust loads. Controlling the wing’s aeroelastic performance cantherefore offer weight and fuel savings. In this work, the rib orientation and thecrenellated skin concept are used to control the wing deformation. Bothexperimental and modelling results show that the rib and crenellation orientationcan influence the wing’s bend-twist coupling and its natural frequencies.
Exploring bend-twist coupling due to geometric features on un-tapered wings
Guillaume Francois, Jonathan Cooper, Paul Weaver
Supported by
The impact of varying the rib/crenellation orientation on the tip twist and tip displacement under static loading is investigated using:
•High Fidelity Finite Element (Modelling)
•3D Printed Wing and DIC measurementmethod (Experiment)
Concepts Explored
Structural Arrangement: Rib/Spar Orientation
Crenellated skin: Skin of varying thickness
Methodology & Results Results - Static Tip Load
Tip
Tw
ist
(Degre
es)
Avera
ge T
ip D
eflection (
mm
)A A
RibSpar
Rib/Crenellation Orientation (Degrees)
Rib/Crenellation Orientation (Degrees)
www.bristol.ac.uk/composites
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 visualisationsTesting procedure
Impacted laminates: low speed (top left) and high speed (top right)1 mm thick high speed impacted laminates: hit at 45°to LE (bottom
left) and TE (bottom right)Experimental setup: high speed impact (left)
and low speed impact (right)
Results and discussion
0
200
400
600
800
1000
1200
0 5 10 15
Failu
re s
tress/
MP
a
Impact energy/ J
High speed
Low speed
Baseline
• 59.8% knockdown in residual tensile strength for 45°LE impact on 1mm thick laminates
• Difference in threshold impact energies between the high/low speed impact conditions
• Influence of specimen and test configurations on delamination size along the laminate
• Normalisation parameter between the two impact conditions – impact energy/force?
• Future work on machined notches, fatigue test post-impact, finite element modelling
0
200
400
600
800
1000
1200
0 10 20 30 40 50
Failu
re s
tress/
MP
a
Delamination length/mm
1mm thick
2mm thick
45° LE impacts
Impact configuration at 45°to the LE
Trailing edge (TE)Leading edge (LE)
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Performing rapid multidisciplinary evaluations—involving aerodynamics, structuraland flight mechanics—at the early stages of aircraft wing design is currently achallenge. Ongoing research focuses on developing a robust, multilevel optimisationstrategy for the aeroelastic tailoring of composite wings, including uncertainties inthe design parameter space.
Two-level aeroelastic tailoring for composite aircraft wings
Muhammad Othman, Jonathan Cooper, Alberto Pirrera, Paul Weaver
Supported by
Approach OverviewA two-level aeroelastic tailoring approach is adopted. The first level aims at minimising thestructural weight with the wing subjected to multiple load cases, with stress, buckling andaeroelastic constraints. The design space is then expanded in the second level to includeuncertainties in the parameters defining the structural and material properties.
2nd Level Tailoring
• Polynomial Chaos Expansion enables efficientquantification of uncertainty in wing design.
• Objective: Minimisation of probability foroccurrence of instability at design airspeed.
• Deterministic and robust design comparison.
• Design cases:i. Flutter/Divergence only.ii. Flutter/Divergence and gust response.
Analysis Mean instability speed (m/s) Prob. of failure
Monte Carlo Simulation (MCS)
371.4 0.0291
Deterministic design 374.0 0.0334
Robust design 544.3 1.0e-6
Optimal thickness variation Buckling results Stress tensor variation for optimal design
Comparison of instability speed PDFs
Benchmark wing model
Mean instability speed and probability of failure at design speed
VD=330 m/s
1) Deterministic design
2) Robust design
• Benchmark wing model with aspect ratio 10.• Static manoeuvre load cases.• Wing skin and spar laminates optimisation.• 328 design variables (ply thickness, t, and angle, θ).• Optimised solution used as input to 2nd level tailoring.
1st Level Tailoring
• Optimisation problem:
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Single Fibre Response
• Very high strain of 15%
• Metallic-like ductility
Carbon fibre composites commonly exhibit lower failure strains in compressionthan they do in tension. This is in spite of the inherent properties of carbon fibres,which can be ductile and achieve impressive strains in compression. The aim ofthe project is to overcome the mechanisms causing early failures in compression.
Realising the potential of carbon fibrecomposites in compression
Jakub Rycerz, Michael Wisnom, Kevin Potter
Carbon Composites Strength
• Composite up to twice as strong in tension
• Compressive strength has apparent limit
• Compression strength seems quiteindependent of tensile performance
• Suggestion of a different failure mechanism
• Low compressive strain not a fibre property
Supported by
Stability Governs Failure
• Fibres never perfectly aligned
• Shear and misalignment increase with load
• Loss of equilibrium causes critical instability
Objectives:• Develop a test to investigate non-linearity at high strains• Model the behaviour to establish the parameters affecting the instability• Explore materials that suppress the instability
[1] M. Ueda, W. Saito, R. Imahori, D. Kanazawa, and T.-K. Jeong, “Longitudinal direct compression test of a single carbon fiber in a scanning electron microscope,”Compos. Part A Appl. Sci. Manuf., vol. 67, pp. 96–101, Dec. 2014.
[2] M. Wisnom, “The effect of fibre misalignment on the compressive strength of unidirectional carbon fibre/epoxy,” Composites, vol. 21, no. 5, pp. 403–407, Sep. 1990.
Sourc
e: [1
]
Sourc
e: [1
]
Source: [2]
www.bristol.ac.uk/composites
The aim of this study is to experimentally investigate the open-hole tensileresponse of pseudo-ductile thin-ply angle-ply laminates. It is shown that withproper selection of pseudo-ductile strain to initial strain ratio, notch sensitivity isreduced and at least 96% of unnotched yield strength can be attained.
Open-hole response of pseudo-ductile thin-ply angle-ply laminates
Xun Wu, Jonathan Fuller, Michael Wisnom
Supported by
Initial Design:
Improved Design:
Background:
Pseudo-ductile tensile stress-strain responses havebeen achieved in using thin-ply angle-ply withcentral unidirectional plies concept. Periodic fibrefragmentation in the central 0° plies and theirdispersed local delamination introduce pseudo-ductile strains.
• Skyflex USN020 prepreg with layup (±265,0)s.
• Pseudo-ductile to initial strain ratio: 1
• Attained 65% unnotched yield strength
• Brittle net-section failure
• Insufficient stress and strain redistribution
• Pseudo-ductile to initial strain ratio: 3.5
• Attained 96% unnotched yield strength
• Non-linear stress-strain responseobserved
• Fragmented central UD plies anddispersed delamination released stressconcentration and redistributed strain.
Incre
ase p
seudo-d
uctile
stra
in ra
tio
• Angle ply (Skyflex UIN020) and UD ply(YSH70) with layup (±252,0)s
Loading Direction
Loading Direction
(J.D.Fuller, 2014)
Notch Sensitive
Notch Insensitive
Initial strain
1
Pseudo-ductile strain3.5
Net-section strength: 620 MPa, 96% of unnotched yield strength,
Kstress = 1.03.“Notch Insensitive”
Intelligent Structures
www.bristol.ac.uk/composites
Design optimization is carried out for a morphing trailing edge using honeycombcore of axial variable stiffness. Introducing variable stiffness materials intomorphing structures leads to a reduction in the actuation requirement and enablestailoring of the geometry of the deflected morphing trailing edge. Enhancedaerodynamic and aeroacoustic performance of aerofoils fitted with such devices isachieved. The optimization process successfully identifies the required stiffnessvariation in the honeycomb core to obtain the desired morphing profiles.
Design optimization of a morphing trailing edge using variable stiffness materials
Qing Ai, Paul Weaver, Mahdi Azarpeyvand
Supported by
Background
• Extended design space of morphingtrailing edge and enhanced aerodynamicand aeroacoustic performance of aerofoilscan be obtained using variable stiffnessmaterials
• Design optimization scheme seemsnecessary to bridge the morphing profileand structural design
Methodology
• An efficient beam model based on Rao’slayer-wise sandwich beam [1] model isdeveloped to facilitate the designoptimization process
• A hybrid optimization formulation basedon Matlab combining Genetic algorithmand Nelder-Mead algorithm to search theoptimal solution
• Fluid structure interaction is considered toaccount for the effects of the aerodynamicload on the structure design
Results
• The current model provides accurateprediction of the desired stiffnessvariation in the honeycomb core forprescribed optimal morphing profile
Future work
A hardware proof-of-concept demonstratorwill be built for furthermechanical tests.
Reference
[1] Rao D.K. Static response of stiff-cored unsymmetricsandwich beams. Journal of Manufacturing Science andEngineering 1976; 98:391-396.
Figure 1. The staticaeroelastic analysisprocedure
(a)
Figure 2. Optimization results of given morphingprofiles: (a) the optimised deformation shape ofthe morphing trailing edge; (b) the optimised corestiffness variation
(b)
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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.
Design optimization of a multistable composite compliant actuator for wearable robotics
Chrysoula Aza, Lorenzo Masia, Paul Weaver, Alberto Pirrera
Compliant actuator
Supported by
Composite structure
Motor
ReAct
Bowden cables
Timing belts
front back
stripspoke
L
H=
2R
Ζ
φ
θ Δℓ
X
W
ℓ
Results
Design requirements
• Minimising dimensions for space& weight limitations.
• Composite transmission in stableequilibrium at pitch θ = ±45°.(See figure below)
• Maximum axial force F = 50N.
Conclusions
A Pareto front of optimal designs obtained, suggesting:
• Use of anti-symmetric lay-up.
• Fewer plies smaller diameter of transmission.
• Smaller diameter of transmission higher axial forces.
• Plies <3 or >6 are less likely to satisfy all theobjectives equally.
Optimization process
Multi-objective optimization using genetic algorithm.
• Decision variables:
• Composite layup.
• Strips’ stress-free curvatures.
• Diameter of transmission.
• Strips’ length.
• Strips’ width.
• Conventional mechatronictechnology.
• Multistable compositetransmission i.e. doublehelix architecture.
optim
um
www.bris.ac.uk/composites
Intelligent self-actuating composite structures
Michael Dicker, Ian Bond, Paul Weaver, Jonathan Rossiter and Charl Faul
Supported by
a. b. c.
This project is concerned with the development of self-actuating structures fromchemically activated hydrogel composites. The project goes on to examine themanipulation of such structures with sensing and control inputs generated bychemical reactions. The aim of doing so is to create new classes of sentientstructures which can intelligently change their orientation or configuration inresponse to their environment. Such devices would mimic the distributed sensingand solid-state actuation so often seen in Nature, resulting in robust, highlyreliable multifunctional structures. In the future such devices could find applicationin solar power generation, efficient aerospace structures and soft robotics.
d. e.
www.bristol.ac.uk/composites
Shape-changing structures can reconfigure to provide extended/enhancedfunctionalities, thereby facilitating mass, volume and part count reduction, aperpetual objective across multiple industries. This project develops work onmulti-stable cylindrical lattices capable of adaptive shape change, by investigatingellipsoidal lattices. It is demonstrated numerically that the deformation mechanicsand kinematics of multi-stable cylindrical lattices are applicable to alternativegeometric configurations with non-zero Gaussian curvature, specifically ellipsoids.
Ellipsoidal lattice structures
Maximillian Dixon, Isaac Chenchiah, Alberto Pirrera
Supported by
• Enclosed volume – Capture/containment• Variable aperture – Flow regulating nozzle• Adaptive geometry – Spherical antenna• Tailorable stiffness – Spring/energy absorber
2. Pre-stress 3. Relaxed
Pre-stressed (black) and relaxed (coloured)configurations showing von Mises stress fora lattice of constant pre-curvature.
1. Initial 2. Pre-stress
Initial (black) and pre-stressed (coloured)configurations showing von Mises stress fora spiral of constant pre-curvature.
3. Relaxed 4. Operation
Axial extension of 250 mm
Radial contraction of 200 mm
SHAPE ADAPTATION
Cylindrical Lattice Application Examples
ALTERNATIVE GEOMETRY =ADDITIONAL EXPLOITABLE BEHAVIOUR
Quadrifilar Antenna1
Device Assembly Stages
1. Initial – Spirals manufactured profile2. Pre-stress – Deformation to lattice profile3. Relaxed – Relaxation of assembled lattice4. Operation – Shape Adaptation
1. GM Olson, 2013, doi:10.2514/6.2013-16712. BK Dinh, 2015, doi:10.1109/ICORR.2015.7281244
Robotic Actuator2
Potential Ellipsoidal Lattice Applications
www.bristol.ac.uk/composites
a. b. c.
Stimuli-responsive hydrogels are typically characterised by slow swelling speeds,limited by the rate of water diffusion through the material. This severely hinderstheir potential application in mechanical actuators. One method to increase thespeed of response is to introduce porosity into the material; however, this alsoresults in a decrease in the stresses that the gel can generate. In this study, theeffect of different levels of porosity on the swelling speed and force-strokecapability of a pH-responsive hydrogel are investigated. Power outputs of each gelcan then be determined, allowing optimisation of gel microstructure.
Hydrogel actuators: Porosity and power outputRob Iredale, Michael Dicker, Paul Weaver, Ian Bond, Jonathan Rossiter and Charl Faul
Supported by
Porous, pH-responsive Hydrogels
• Semi-interpenetrating polyurethane/poly(acrylicacid) double network hydrogels synthesized via UVcrosslinking.
• Gel swells in basic solutions. Swelling is reversible.
• NaCl particles of varyingsizes used to create poresin a salt leaching method.
Fig. 1 Schematic describing gel synthesis.
Fig. 2 Explanation of gel swelling process.Fig. 3 SEM images of hydrogel with 220μm pores.
Fig. 4 Stress-strain-power plots for gels of different porosities.
Gel Performance
• The introduction ofporosity (13 μmporogen size) leadsto 31% increase inpeak power.
• However, the stressgenerated is muchlower than the non-porous reference.
Porogen sizePeak power density
(W/m3)Stress (kPa)
Strain (%)
Time (mins)
a. Non-porous 1.16 33.4 40 180
b. 13 μm 1.52 9.3 90 90
c. 220 μm 1.09 6.3 95 90
Conclusion: A hydrogel’s microstructure can be tailored to optimise its performance in terms of stress, strain or swelling time.
.Mat Tolladay, Dmitry Ivanov, Neil Allan and Fabrizio Scarpa
Composites Processing
and Characterisation
www.bristol.ac.uk/composites
Kissing bonds are hard to detect with current ultrasound techniques, which relyupon interfaces causing reflection or scattering, since the two bond faces are inintimate contact. These interfaces are less stiff in tension than in compression sothey behave nonlinearly, which allows another route to detection. This work isfocused on developing the nonlinear method of non-collinear beam mixing tocreate parametric surfaces, called ‘fingerprints’. The features in these fingerprintsmight allow for weak bonds to be identified which would be very useful forproviding confidence in bonded joints.
Nonlinear ultrasonic detection of kissing bonds in composite structures
Jonathan Alston, Anthony Croxford, Jack Potter
Supported by
Frequency ratio
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Frequency ratio
Inte
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[deg]
0.6 0.8 1 1.2 1.4
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[deg]
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
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Left:2024-T351 aluminium with loaded interfaceRight: Same but with water in the interface
60 65 70 75 80 85 90 95 100 105 1100.02
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Interaction Angles
2Nm
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Sample
Detection array
Input transducer
Scattered beam
In the experiment the angles of the input beams andtheir frequencies are varied. The colour of each pixel inthe fingerprint is related to the intensity of the scatteredbeam produced by the combination of those twovariables. The patterns produced are independent of theinput beam intensities, as shown in the solid aluminiumfingerprints above.
Frequency ratio
Inte
raction a
ngle
[deg]
Max intensity
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
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100
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Maximum intensity
Bolted interface sample andmodelling of interface loading.
CFRP with weakened interface.
Left: 6082 T6solid aluminium Right: Single frequency ratio with varying interface load
www.bristol.ac.uk/composites
Porosity is a common manufacturing defect in composite materials. It can be caused by ineffective debulking or inadequate autoclave curing which leads to air being trapped within the laminate. Porosity has significant effects on the matrix-dominated properties of a composite. Many researchers have investigated the influence of porosity content on the mechanical performance of composites. However the size, shape and location of voids are important parameters often not characterised. The aim of this work was to characterise these parameters and investigate their correlation to interlaminar shear strength.
Effects of porosity on the interlaminar behaviourof carbon/epoxy composites
Iryna Gagauz, Luiz Kawashita, Stephen Hallett
Supported by
10 mm
2 mm
5 10 15 20 2536
38
40
42
44
46
48
50
Max dimension, mm
ILS
S, M
Pa
Batch 1 (temperature = 30C)Batch 2 (temperature = 90C)
r=-0.808
0.2 0.4 0.6 0.8 1 1.236
38
40
42
44
46
48
50
Max effective radius, mm
ILS
S, M
Pa
Batch 1 (temperature = 30C)Batch 2 (temperature = 90C)
r=-0.863
0 2 4 6 836
38
40
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46
48
50
Void content, %
Inte
rlam
inar
She
ar S
treng
th, M
Pa
Batch 1 (temperature = 30C)Batch 2 (temperature = 90C)
r=-0.858
0 10 20 30 4036
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Peak of void volume fraction in a layer,%
Inte
rlam
inar
She
ar S
treng
th, M
Pa
Batch 1 (temperature = 30C)Batch 2 (temperature = 90C)
r=-0.896
Pressure and temperature controlled curing using hot plates in a testing machine• Batch 1: pressure 0.3 MPa, T=30°C,
post-cure @ 100°C for 17 hours• Batch 2: pressure 0.3 MPa, T=90°C,
post-cure @ 100°C for 17 hours
RESULTS AND DISCUSSIONS
MANUFACTURE DETECTION TEST
Excellent correlation(a) optical micrograph (b) μCT-imaging
Cracks nucleate from and coalesce between voids
Effect of void volume fraction on ILSS
The maximum void volume fraction in a ply provides the best correlation with ILSS
Effect of void features on ILSS
1 2 3 4 5 6 7 8 9 101112131415160
0.1
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Ply number
Voi
d vo
lum
e, m
m3
Peak void volume
Void volume (i.e. effective radius) showeda much stronger correlation than maximumdiameter of a circumscribed sphere.
Effective radius, based on void volume:
Short beam shear test for interlaminar shear strength (ILSS) testing
www.bristol.ac.uk/composites
Understanding the behaviour of tufted sandwich structures in edgewise compression
Jamie Hartley, James Kratz, Carwyn Ward and Ivana Partridge
A major challenge for automotive manufacturers is reducing weight whilstmaintaining enough strength to protect the occupants in a crash. Compositesandwich structures with through-thickness reinforcement in the form of tuftingare seen as one possible solution to this problem. However, currently there is littleunderstanding of how tufts behave or the way the design parameters andmanufacturing process can affect performance.
Supported by
3. Key Findings
• Loop length appears to have no effect onperformance (SEA), but increasing thenumber of threads does.
1. Tufting
• Through-thickness reinforcement for drypreforms, where friction of preform holdsreinforcement in place before infusion.
Future Work
• Further analysis of column drifting effects,and the effect on energy absorption.
• Develop supporting modelling approach tohelp characterise tuft behaviour.
2. Test Development
• Novel coupon design created to testindividual tuft experimentally.
• Number and length of tufts chosen as testvariables.
Background
• Side impact is a critical design case,particularly for modern battery poweredvehicles.
• Need to avoid buckling or disbonding offace sheets to use sandwich structures inthese energy absorbing applications.
BMW i3 Euro NCAP pole impact test
Tufting manufacturing process
Tuft loops Single tuft test coupon
Single tuft test results
A B C
Tuft Columns before testing
Column DriftColumn stacking
and failure
Drifting behaviour of columns during crushing
• Drifting of resin columns observed,potentially leading to secondary energyabsorption mechanism.
www.bristol.ac.uk/composites
Currently the composites industry is struggling to integrate knowledge from production into design. The industry is operating with an incomplete learning cycle and this is problematic as the industry is looking to grow. This research has focussed on the manual forming process, hand lay-up, performed by a laminator. This process is very often reliant on a laminator’s tacit knowledge. To integrate a laminator’s knowledge, this research is aiming to describe what the interface between manufacture and design could look like.
Using a knowledge base on hand lay-up to describe the interface between design and
manufactureHelene Jones, Carwyn Ward, Kevin Potter
Supported by
Hand lay-up Hand lay-up (Fig.1) is a manual process that involves forming plies to a mould geometry. Ingrained in this process are manual tools that support the hand to form particular geometries. !
Figure 1: The manual process of hand lay-up
Hand lay-up knowledge base From previous research on hand lay-up [1,2,3,4] four variables to describe the knowledge base on hand lay-up have been extracted: • Mould Geometry• Material• Lay-up Task• Tool (Fig.1)
Design: Manufacture interface Currently the design process does not integrate the knowledge base around tools (Fig.2). Fig.3 proposes this knowledge base is integrated using geometry coupling.
Figure 3: Proposed interaction
Figure 2: Current interaction
Design for manufacture There is a need to design aids to incorporate a laminator’s knowledge into the design process. Fig.4 is a prototype for a visualisation to support the interaction proposed in Fig.3. Geometry coupling defines how a tool and mould geometry interact. This visualisation informs a designer when a tool is required to support the hand to form a geometry.
Figure 4: Visualisation to support a designer selecting a tool to form a particular mould geometry
1. L. D. Bloom (2015) On the relationship between lay-up time,material properties and mould geometry in the manufacture ofcomposite components, PhD Thesis, University of Bristol. 2. M. Elkington (2015) The future of sheet prepreg layup, PhDThesis, University of Bristol. 3. R. Dixon (2015) Quantifying the hand lay-up process of wovenpre-impregnated composite sheets to improve productivity, Masters Research Project, University of Bristol.
4. M. Such, C. Ward, W. Hutabarat and A. Tiwari (2014) Intelligent composite lay-up by the application of low cost tracking and projection technologies. In 8th Int. Conf. on Digital Enterprise Technologies.
www.bristol.ac.uk/composites
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 layup
Shashitha Kularatna, Carwyn Ward, and Kevin Potter
STAGE 1
Laying Up a Flat Panel in Virtual Reality (VR)
STAGE 2
Simulation of Prepreg Shear and Layup Tools
STAGE 3
Complex 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
Tra
inin
g
VR Tra
inin
g
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
WORK IN PROGRESSDesign of VR simulators for complex shapes and use of Microsoft Kinect to provide Real-Time feedback to
laminators
Virtual Pin Jointed Net Leap Motion Controller
Supported by
www.bristol.ac.uk/composites
Tufting thread
Resin pocket
Ply-by-ply composite
Cohesive contact
Tufting belongs to the class of Through-the-Thickness Reinforcement (TTR) techniques developed to improve the delamination resistance of 2D composites. It is a single sided stitching technique in which a dry thread is inserted into a dry preform and forms a microfastener once impregnated with resin and cured.This project aims at establishing a complete modelling framework for tufted composites by adopting a multi-scale modelling approach.
Multi-scale characterisation and modelling of tufted composite structures
Camilla Osmiani, Ivana Partridge, Galal Mohamed, *Giuliano Allegri
Supported by
Fig.1 – X-Ray image of single carbon tuft tested in pull-out (NCF composite) and corresponding experimental bridging law and
failure mechanisms.
Fig.2 – High fidelity FE model of a single carbon tuft in 0/90 NCF composite.
Tufted rows
Bridged crack
Fibre bridging
Fig.4 – Double Cantilever Beam (DCB) test of a tufted coupon with 1% areal density of
carbon tufts. Fig.5 – Tufted DCB specimen: FE analysis in LS-DYNA v971 R7.1.2.
Saw-tooth behaviour along tufted interface
Tuft bridging law
Ply-ply interface
Debonding
Tuft fracturesurface
Fig.3 – Calibrated analytical prediction of single carbon-tuft in mode I pull-out.
Single-Tuft Testing
Coupon Tests for Arrays
Micro-Scale FE Models
Meso-Scale FE Models
Analytical Modelling
CohesiveInterface Elements
Elastic deformationof tuft and composite
Debonding andfrictional sliding
Failure
Tuft made of two segmentsof a 2-yarn thread
*Imperial College London
Pre-crackCohesive elements
v
v
Analytical model
Envelopesexp. data
www.bristol.ac.uk/composites
Continuous fibre composites encounter problems with geometrically complexcomponent production due to induced wrinkling and bridging defects arising fromrestrictive deformation modes. These defects restrict productivity and play a keyrole in the structural response of a component which limits the design envelope forengineers. Discontinuous fibre composites may alleviate these problems, owing tothe ability of the material to extend in the fibre direction and localised deformationfor features instead of a global material response. A greater body of work isneeded to understand advantages and limitations of highly-aligned discontinuousfibre composites.
Investigation of formability of highly-aligned discontinuous fibre composites
Matthew Such, Carwyn Ward, Kevin Potter
Supported by
A tetrahedron tool with a highly complex double curved feature has been chosen to assessthe formability of various material systems with double diaphragm forming of an 8 ply QIlayup in order to represent the creation of a corner bracket component. The resultinglaminate is cured in an autoclave and inspected qualitatively for defects.
Discontinuous
Layup heated to ~80°C and held between two silicone
diaphragms
Tool drawn into layup and secondary vacuum applied
Layup cooled and bagged for autoclave cure
The resulting aim is to develop a more quantitative measure of formability. Curved beamstrength samples conforming to ASTM D6415 will be extracted from the laminate andcompared to pristine samples in order to understand the effect of defects in this component.This investigation will inform further development and utilisation of highly-aligneddiscontinuous fibre composites, a greater uptake of which should allow for a higher level ofautomation in composite production.
Excessive wrinkling trapped
autoclave consumables
Continuous
~210mm
Large degree of localised extension
Wrinkling minimised with respect to
continuous component but still
problematic
Large amount of waviness across both
samples
Further Work
Method
www.bristol.ac.uk/composites
Secondary recycling can give composite materials a second operative life as a highvalue product, reclaiming most of the value of the virgin constituents. This projectworked towards developing the first closed-loop recycling method for carbon fibrecomposites. The process involves the separation of thermoplastic matrix andcarbon fibre reinforcement, fibre re-alignment and subsequent consolidation of thereclaimed thermoplastic and fibres. Solvent processing of matrix and fibresresulted in composite tape-type prepreg fabrication however process optimizationis required for improved mechanical properties.
Towards a closed-loop recycling method for short carbon fibre composites
Rhys Tapper, Marco Longana, HaNa Yu, Kevin Potter
Closed-Loop Recycling Process - A cycle which requires no additional material input
after initiation.
Supported by
Impact
Gives end-of-life composites a secondary life in a high value application.
[1] Yu H, Potter KD, Wisnom MR. Composites: Part A (2014).
Figure 1 – Flow diagram of the closed-loop methodology.
Figure 2 – Schematic of the automated part of the recycling process.
Figure 3 – Preform.
Figure 5 – Prepreg.
Figure 4 – Film stacking Impregnation.
• Thermoplastics and Short (3 mm)carbon fibres lend themselves torecycling due to a lack of cross-linking and short length, respectively.
• HiPerDiF alignment method is usedto produce a high level of alignmentfrom liquid dispersion [1].
• Dispersion of fibres in polymersolution introduced to alignmenthead of machine.
Significantly increases carbon fibre composite desirability in industry i.e. automotive.
Fibres from pyrolysis can be incorporated –many tonnes of unused carbon fibre.
www.bristol.ac.uk/composites
Diaphragm forming is a cost-effective method that has been used to manufactureaircraft structures (e.g. wing spar). This technique improves production rate bylaying multiple prepregs to create an uncured laminate first and then forming itinto a desired shape later. However, the ply slippage resistance results in defectsduring this forming method. In this research, a new method using interleavingmaterials to reduce the interply friction was developed, which could effectivelyminimise the wrinkle during low temperature forming, as well as increase thefracture toughness.
Improvement of composite drape forming quality by enhancing interply lubrication
Wei-Ting Wang, HaNa Yu, Kevin Potter, Byung Chul Kim
Supported by
Background: HDF process
Multiple prepregs
Uncured laminate
Place laminate on top of tool
Shape with heat and external pressure
High interfacial friction
Out-of-plane wrinkleWrinkling mechanism
Improvement method
Laminate
Interleaving lubricant
Forming Consolidation
Challenge
ResultsPromote ply slippage
Powder interleaving
Veil interleaving
Non-interleaving
Interply frictional resistance test Drape forming test
Frictional test rig
Increase fracture toughness
Mode-I fracture toughness test
DCB test
Future work• Precision lubrication material deposition
methods.
• Focus on forming complex shape.
• Combine with existing automatedmanufacture processes.
• Transfer this concept to other compositesheet forming methods.
www.bristol.ac.uk/composites
Dijkstra’s algorithm is widely used in weighted shortest path problems in graphtheory. This has been applied in such disciplines as network optimisation andsatellite navigation. Here is presented the application of the algorithm to findingultrasonic ray paths and the corresponding arrival times in composite materials,which can be subject to complex steering due to variations in the fibre direction.This allows the construction of an image via the total focussing method in order tofind defects.
Dijkstra’s algorithm for ultrasonic ray tracing in composite materials
Callum White*, Paul Wilcox, Fabrizio Scarpa
Supported by
FE Dijkstra
Figure 3 Arrival times calculatedfrom FE and Dijkstra
Conclusion
• Dijkstra’s algorithm is a good candidate for calculating arrival times in non-planar anisotropiccomponents
• This should allow the accurate imaging of composite components of non-planar shapes, toallow the detection of defects
• Simulation shows the nature of beamsteering in composite materials
Figure 2 Elastic waves in acomposite cross section
Force input
• Create network approximation ofcomposite material
• Determine edges based on an allowablehop radius and velocity profile (Fig. 1)
• Use Dijkstra’s algorithm to find arrivaltime at each node Figure 1 Velocity phase diagram for
high strength carbon fibre/epoxy
• Using finite element-calculated velocity andarrival times (Fig. 1, 2) can see a closeagreement with Dijkstra’s algorithm (Fig. 3)
Results
Steps
www.bristol.ac.uk/composites
Through-thickness-reinforcement (TTR) is a method for limiting the delaminationseen in composite components and the debonding experienced by sandwich panelsduring edgewise compression. Tufting is one such TTR with the potential toinfluence failure. Understanding the quality implications of tufting parameters andthe manufacturing process is necessary, but this is not trivial as the tufts areembedded within the panel and have so far been difficult to analyse.
Tufting visualisation and analysisEmily Withers, James Kratz, Ian Hamerton, Ivana Partridge, Carwyn Ward
Objectives• Identify parameters of the tufting process
and their influence• Define tuft quality and if possible an ideal
tuft• Improve/control tuft quality through the
parameters identified
Supported by
Tuft technology
Dry fibre preform mounted on sacrificialfoam
Presser foot compacts preform Needle inserts thread at low tension Friction resists thread retraction causing a
loop to be formed in the preform
MethodologyDevelop test bed to permit visibility of needle
insertion and its effect on the preform
Transparent casing used to make loop
formation visible
Needle insertion controlled by Instron rates
of 100-1000mm/min
1kN load cell measures penetration and
retraction forces
Findings
Aspects of tufting quality:
o fragmentation of the carbon skin filaments
o fragmentation of the foam core
o non-uniformity of the needle path
dimensions
o fibre breakage/movement out-of-plane
Figure 2: Infused, tufted sandwich panel
Figure 3: Test bed in position on Instron
Needle
Figure 1: Loop variation seen in tufted panel
Figure 4: Loop formation in test bed
Results•Tuft formation visible in situ
•Force of penetration seen to vary with the
needle contours and sandwich interfaces
•A quality matrix was developed based on
the characteristic aspects observed
•This as-measured tuft quality correlates to
variation in rate of needle insertion
Further work required to identify additional
quality aspects and control in agreement
with the commercial tufting robot process.Figure 5: Insertion and retraction force data
www.bristol.ac.uk/composites
Automated high-volume production of complex composite parts: Continuous multi-tow shearing
Evangelos Zympeloudis, Kevin Potter, Paul Weaver, Byung Chul Kim
In an attempt to improve the productivity of composites manufacturing, theindustry has pioneered the use of automated material placement machines.Although these machines excel in placing fibres in straight lines, their ability toproduce curved paths is extremely limited. The concept of CMTS removes thislimitation while maintaining the potential for high production rates.
Tow Steering
• Structural efficiency through variablestiffness structures
• Lay-up in complex doubly curved moulds
[1] [2]
Limitations of Current Technology
Fibre Buckling Width affects steering abilities[3] [4]
• In plane bending of tapes Defects:
• Minimum steering radius:
• ATL: 6000 mm for 150 mm wide tape
• AFP: 630 mm for 3.175 mm wide tow [3]
Continuous Multi-Tow Shearing
• Exploit material shear deformation
Aim: Develop a material placement head which can produce high quality tow steered laminates at high production rates
Evaluation of Different Materials for CMTS
• Minimum steering radius:
• CMTS: 260 mm for 90 mm wide tape
[1] Coburn et al. 2015 [2] Chauncey Wu et al. 2009
[3] M. H. Nagelsmit et al, 2013 [4] K. D. Potter, 2009
0.0
1.0
2.0
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4.0
5.0
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9.0
10.0
-230 -170 -110 -50 0 50 110 170 230
Percen
tag
e o
f R
esin
Area (
%)
X Position (mm)
Resin Pocket Areas vs Position
Tows 1-10
Tows 11-30
Tows 31-40
{Fusible weft yarns cause excessive wrinkling at high shear angles}
{Weft yarns with low tension cause areas of resin pockets}
50 deg40 deg30 deg
200 m
m
50 deg30 deg
• Defect generation- Resin pockets- Local wrinkling- Tow thickness variation
• Process Accuracy- Tape path deviation- Tape boundaries variation
0
Supported by
Design, Build and Test
www.bristol.ac.uk/composites
The aim of this project was to design, manufacture and test a compositeundercarriage beam subjected to compression and an offset-vertical load. Thedesign must consist of a monolithic open-section beam with integral bushes for pinjoints.
The cohort has been split into two teams (Iceman & Maverick) who will compete todesign, build and test the structurally most efficient beam.
Design, Build & Test:Monolithic undercarriage beam
ACCIS CDT Cohort 2015
Structural & Manufacturing Requirements:
• The Y depth must taper by at least 30% at the ends.
• Beam shall not deflect by more than 20mm at limit load.
• Beam shall not rotate more than 5° at limit load.
• Fibre dominated or interlaminar failures shall not occur below ultimate load.
• Global or local buckling must not occur below ultimate load.
• The design shall allow for an impact up to 15J at any random position by ensuringadequate reserve factors.
• Any material or manufacturing route permitted.
• The critical design drivers are mass, cost and ease of manufacture within the timeconstraints of the project.
Supported by
Supervisors: Ian Farrow, Carwyn Ward
Team MaverickTeam Iceman
www.bristol.ac.uk/composites
Key Features• C beam
• Made from unidirectional and woven prepreg
• 5mm maximum thickness
• 10mm inner-radius of curvature
• 30% taper on one side of web
Team Iceman: Undercarriage beam
Andrés Rivero, Olivia Leão, Robert Worboys, Tamas Rev,
Vincent Maes and Yanjun He
Design
• Analytically and numerically calculated
• Beam is stability driven
• Local ‘pad-up’ sections around the holes
• Steel bushings at centre and end holes
Manufacturing
Supported by
Male Mould Hand Layup Autoclave Cured
• Styrofoam trial mould
• Tool block final mould
• 100⁰C for 3 hours
• 7 bar pressure
RF = 1.08
Deformation Analysis Buckling Analysis Stress Analysis
Pin Design
RF = 1.09
www.bristol.ac.uk/composites
Team Maverick: Undercarriage beam
Behjat Ansari, Lourens Blok, Aewis Hii, Tom Hounsell,
Arjun Radhakrishnan and Beth Russell
Supported by
Design
• Symmetric cross sectional design.
• Ply-drops along the length and crosssection to increase structural efficiency.
• High strength carbon fibre is usedthroughout, with woven fabric used for all
±45° plies and unidirectional fibres in the0° and 90° directions.
Build
• Off-the-shelf mould to minimise overall costs.
• Hand lay-up of 54 plies over a male tool.
• Vacuum bagging and autoclave curing process.
• Post trimming of beam to final dimensions and fitbushings into hole cut-outs for pinned attachments.Layup trial over stainless
steel mould
Material test samples
Team Maverick has adopted an unconventional design approach. An upside downU-beam configuration was chosen to improve manufacturability, reduce costs andprevent eccentric loadings, but it requires a cut-out in the flange to apply thevertical load.
Critical buckling mode: 2.05 x ultimate load
Stress analysis Stability analysis
YZ
X
Impression of final lay-up on male mould
Stress in X-direction (MPa)
328
246
169
91.6
14.5
-62.5
-140
-217
-294
-371
-447
Deflection at limit load: 19 mm
Failure load: 1.0 x ultimate load
Stiffness per weight: 11.9 mm/kg
Test
• Material coupon testing carried out to derive materialproperties.
• Full scale test planned to assess final beamperformance.
EPSRC Centre for Doctoral Training in Advanced Composites for Innovation and Science
University of Bristol, Queen’s Building, University Walk,
Bristol, BS8 1TR, UK
www.bristol.ac.uk/composites/cdt
Front cover photo credits:Jamie Hartley (top left), Yoho Media (top right and bottom left), Logan Wang (bottom right)