Imperial College London

ProfessorPaulRobinson

Faculty of EngineeringDepartment of Aeronautics

Head of Department of Aeronautics
 
 
 
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Contact

 

+44 (0)20 7594 5073p.robinson

 
 
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Location

 

318City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

201 results found

Katafiasz T, Greenhalgh ES, Allegri G, Pinho ST, Robinson Pet al., 2021, The influence of temperature and moisture on the mode I fracture toughness and associated fracture morphology of a highly toughened aerospace CFRP, Composites Part A: Applied Science and Manufacturing, Vol: 142, ISSN: 1359-835X

This paper addresses the characterisation of the mode I interlaminar fracture toughness of a carbon fibre/epoxy composite material, toughened with thermoplastic particles in the ply interlayers. The characterisation is undertaken at −55 °C, 19 °C, and 90 °C, on both dry and fully moisture saturated coupons. Fractographic observations of the delamination surfaces allows identification of the failure mechanisms. The mode I propagation fracture toughness tested at wet/90 °C exhibits a 176% increase compared to the dry/19 °C specimens, due to enhanced plastic deformation of the interlayers and more prominent fibre bridging. Moisture-saturated coupons tested at −55 °C suffered a 57% reduction of mode I fracture toughness compared to those under dry/19 °C conditions. This is due to the dis-bond and consequent plucking of the thermoplastic particles from the surrounding matrix. This observation points to the fact that wet/cold conditions may represent the worst-case scenario for the interlaminar fracture performance of composite systems toughened with thermoplastic interleaves.

Journal article

Hamid WLHWA, Iannucci L, Robinson P, 2020, Finite-element modelling of NiTi shape-memory wires for morphing aerofoils, AERONAUTICAL JOURNAL, Vol: 124, Pages: 1740-1760, ISSN: 0001-9240

Journal article

Zhang B, Bacarreza O, Robinson P, Burgstaller Cet al., 2020, The investigation of modified 'brick and mortar' composite architecture with in-plane wavy segments for pseudo-ductility

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. Discontinuous 'brick and mortar' composite architectures can display limited pseudo-ductile behaviour in tension due to the localisation of failure at the weakest set of overlaps through the specimen thickness. A modified, continuous 'brick and mortar' composite architecture with in-plane wavy segments (in place of discontinuities), to overcome the localisation of failure, was produced and tested in tension. Failure of first overlap was observed at ~0.25% strain after which the wavy segments straightened and stiffened. The second overlap failed at ~0.85% strain and the specimen continued to straighten and stiffen until the ultimate tensile failure at ~1.8% strain. 'Brick and mortar' composites with wavy segments exhibited prolonged pseudo-ductility in tension with a failure strain which exceeded that of the pristine unidirectional carbon fibre/epoxy composite.

Conference paper

Robinson P, Zhang B, Bismarck A, Burgstaller Cet al., 2020, Development of an interleaved composite with a two-stage shape memory capability for deployable structure applications

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. A carbon fibre epoxy composite laminate containing thermoplastic interleaves has been shown to provide an easy route for the manufacture of an expanded composite mesh. A two-stage shape memory composite using two different interleaf materials has been developed and this has been used to create a mesh that can deploy from the flat state into an expanded state. Creep of one of the interleaf materials, during flattening and deployment, limited the extent of the deployment but a better choice of interleaf materials should overcome this shortcoming.

Conference paper

Francesca Pernice M, Robinson P, 2020, Experimental investigation of low-velocity impact damage in pseudo-ductile composite laminates containing ply weakening

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. The damage resistance of a composite laminate configuration, which exhibits a pseudo-ductile stress-strain curve under tensile loading, was investigated. Pseudo-ductility was achieved by weakening some of the 0° plies in the laminate stacking sequence, by means of equally spaced, discontinuous cuts perpendicular to the fibres. Plies containing fibre cuts were embedded within 0° plies, in order to promote delamination onset from the ply cuts and propagation along the 0° fibre direction. This damage mechanism was demonstrated to cause a pseudo-ductile response in both unidirectional and multidirectional specimens in tension. Low-velocity impact tests were performed on specimens containing the cut fibres and on baseline specimens, with the same stacking sequence. Results showed a similar response to an impact event and a similar extent of damage in the baseline specimens and in the specimens containing ply weakening. It can be concluded that the strategy to achieve pseudo-ductility in composite laminates through discontinuous cuts perpendicular to the 0° fibre preserves the damage resistance of the material to a low-velocity impact event.

Conference paper

Zhang B, Bacarreza O, Robinson P, Burgstaller Cet al., 2020, The investigation of modified 'brick and mortar' composite architecture with in-plane wavy segments for pseudo-ductility

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. Discontinuous 'brick and mortar' composite architectures can display limited pseudo-ductile behaviour in tension due to the localisation of failure at the weakest set of overlaps through the specimen thickness. A modified, continuous 'brick and mortar' composite architecture with in-plane wavy segments (in place of discontinuities), to overcome the localisation of failure, was produced and tested in tension. Failure of first overlap was observed at ~0.25% strain after which the wavy segments straightened and stiffened. The second overlap failed at ~0.85% strain and the specimen continued to straighten and stiffen until the ultimate tensile failure at ~1.8% strain. 'Brick and mortar' composites with wavy segments exhibited prolonged pseudo-ductility in tension with a failure strain which exceeded that of the pristine unidirectional carbon fibre/epoxy composite.

Conference paper

Francesca Pernice M, Robinson P, 2020, Experimental investigation of low-velocity impact damage in pseudo-ductile composite laminates containing ply weakening

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. The damage resistance of a composite laminate configuration, which exhibits a pseudo-ductile stress-strain curve under tensile loading, was investigated. Pseudo-ductility was achieved by weakening some of the 0° plies in the laminate stacking sequence, by means of equally spaced, discontinuous cuts perpendicular to the fibres. Plies containing fibre cuts were embedded within 0° plies, in order to promote delamination onset from the ply cuts and propagation along the 0° fibre direction. This damage mechanism was demonstrated to cause a pseudo-ductile response in both unidirectional and multidirectional specimens in tension. Low-velocity impact tests were performed on specimens containing the cut fibres and on baseline specimens, with the same stacking sequence. Results showed a similar response to an impact event and a similar extent of damage in the baseline specimens and in the specimens containing ply weakening. It can be concluded that the strategy to achieve pseudo-ductility in composite laminates through discontinuous cuts perpendicular to the 0° fibre preserves the damage resistance of the material to a low-velocity impact event.

Conference paper

Bacarreza O, Robinson P, Shaffer MSP, 2020, Optimisation of ductile interlocking composite structures

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. An investigation on how interlocking composite structures can be designed using a multiobjective optimisation algorithm is described and the trade-off between the ultimate stress and the associated strain of pseudo-ductile composite interlocking structures is illustrated. Parameters changing the geometry of the interlocking structure and the friction coefficient were varied during the optimisation. Finite element models have been used to study the behaviour of these configurations. Different behaviours can be observed ranging from models with ultimate stress and associated strain in the optimal solutions from 333 MPa and 4.5% to 146 MPa and 20.2%.

Conference paper

Sun J, Pernice MF, Bacarreza O, Robinson Pet al., 2020, Pseudo-ductility in 0-degree fibre dominated CFRP through ply weakening

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. Previous research has demonstrated pseudo-ductile tensile response can be achieved by introducing periodic across-width ply cuts, perpendicular to selected 0° plies, in both unidirectional (UD) and quasi-isotropic (QI) laminates. The inserted discontinuities initiate progressive delamination at the interface between the cut and pristine (uncut) plies. The tensile stress-strain curve consists of an initial almost linear stage with high modulus, a flat plateau stage and a final strain-hardening stage. This paper presents the enhanced pseudo-ductile performance achieved by introducing dispersed periodic short perforations in the UD laminates. Perforations with precisely controlled length were cut into the constituent prepregs using a laser milling machine. UD laminates containing perforations in selected plies exhibit high initial modulus, a softening stage prior to a final strain-hardening stage, all connected by smooth transitions. The dominant failure mechanism in this case was debonding surrounding the discontinuous perforated fibre bundles. This failure mechanism was successfully transferred to 0° fibre-dominated multi-directional (MD) laminates with perforations introduced in the middle 0° plies, and thereby provided pseudo-ductile performance.

Conference paper

Bacarreza O, Robinson P, Shaffer MSP, 2020, Optimisation of ductile interlocking composite structures

An investigation on how interlocking composite structures can be designed using a multiobjective optimisation algorithm is described and the trade-off between the ultimate stress and the associated strain of pseudo-ductile composite interlocking structures is illustrated. Parameters changing the geometry of the interlocking structure and the friction coefficient were varied during the optimisation. Finite element models have been used to study the behaviour of these configurations. Different behaviours can be observed ranging from models with ultimate stress and associated strain in the optimal solutions from 333 MPa and 4.5% to 146 MPa and 20.2%.

Conference paper

Zhang B, Bacarreza O, Robinson P, Burgstaller Cet al., 2020, The investigation of modified 'brick and mortar' composite architecture with in-plane wavy segments for pseudo-ductility

Discontinuous 'brick and mortar' composite architectures can display limited pseudo-ductile behaviour in tension due to the localisation of failure at the weakest set of overlaps through the specimen thickness. A modified, continuous 'brick and mortar' composite architecture with in-plane wavy segments (in place of discontinuities), to overcome the localisation of failure, was produced and tested in tension. Failure of first overlap was observed at ~0.25% strain after which the wavy segments straightened and stiffened. The second overlap failed at ~0.85% strain and the specimen continued to straighten and stiffen until the ultimate tensile failure at ~1.8% strain. 'Brick and mortar' composites with wavy segments exhibited prolonged pseudo-ductility in tension with a failure strain which exceeded that of the pristine unidirectional carbon fibre/epoxy composite.

Conference paper

Sun J, Pernice MF, Bacarreza O, Robinson Pet al., 2020, Pseudo-ductility in 0-degree fibre dominated CFRP through ply weakening

Previous research has demonstrated pseudo-ductile tensile response can be achieved by introducing periodic across-width ply cuts, perpendicular to selected 0° plies, in both unidirectional (UD) and quasi-isotropic (QI) laminates. The inserted discontinuities initiate progressive delamination at the interface between the cut and pristine (uncut) plies. The tensile stress-strain curve consists of an initial almost linear stage with high modulus, a flat plateau stage and a final strain-hardening stage. This paper presents the enhanced pseudo-ductile performance achieved by introducing dispersed periodic short perforations in the UD laminates. Perforations with precisely controlled length were cut into the constituent prepregs using a laser milling machine. UD laminates containing perforations in selected plies exhibit high initial modulus, a softening stage prior to a final strain-hardening stage, all connected by smooth transitions. The dominant failure mechanism in this case was debonding surrounding the discontinuous perforated fibre bundles. This failure mechanism was successfully transferred to 0° fibre-dominated multi-directional (MD) laminates with perforations introduced in the middle 0° plies, and thereby provided pseudo-ductile performance.

Conference paper

Robinson P, Zhang B, Bismarck A, Burgstaller Cet al., 2020, Development of an interleaved composite with a two-stage shape memory capability for deployable structure applications

A carbon fibre epoxy composite laminate containing thermoplastic interleaves has been shown to provide an easy route for the manufacture of an expanded composite mesh. A two-stage shape memory composite using two different interleaf materials has been developed and this has been used to create a mesh that can deploy from the flat state into an expanded state. Creep of one of the interleaf materials, during flattening and deployment, limited the extent of the deployment but a better choice of interleaf materials should overcome this shortcoming.

Conference paper

Francesca Pernice M, Robinson P, 2020, Experimental investigation of low-velocity impact damage in pseudo-ductile composite laminates containing ply weakening

The damage resistance of a composite laminate configuration, which exhibits a pseudo-ductile stress-strain curve under tensile loading, was investigated. Pseudo-ductility was achieved by weakening some of the 0° plies in the laminate stacking sequence, by means of equally spaced, discontinuous cuts perpendicular to the fibres. Plies containing fibre cuts were embedded within 0° plies, in order to promote delamination onset from the ply cuts and propagation along the 0° fibre direction. This damage mechanism was demonstrated to cause a pseudo-ductile response in both unidirectional and multidirectional specimens in tension. Low-velocity impact tests were performed on specimens containing the cut fibres and on baseline specimens, with the same stacking sequence. Results showed a similar response to an impact event and a similar extent of damage in the baseline specimens and in the specimens containing ply weakening. It can be concluded that the strategy to achieve pseudo-ductility in composite laminates through discontinuous cuts perpendicular to the 0° fibre preserves the damage resistance of the material to a low-velocity impact event.

Conference paper

Bacarreza O, Robinson P, Shaffer MSP, 2020, Optimisation of ductile interlocking composite structures

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. An investigation on how interlocking composite structures can be designed using a multiobjective optimisation algorithm is described and the trade-off between the ultimate stress and the associated strain of pseudo-ductile composite interlocking structures is illustrated. Parameters changing the geometry of the interlocking structure and the friction coefficient were varied during the optimisation. Finite element models have been used to study the behaviour of these configurations. Different behaviours can be observed ranging from models with ultimate stress and associated strain in the optimal solutions from 333 MPa and 4.5% to 146 MPa and 20.2%.

Conference paper

Sun J, Pernice MF, Bacarreza O, Robinson Pet al., 2020, Pseudo-ductility in 0-degree fibre dominated CFRP through ply weakening

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. Previous research has demonstrated pseudo-ductile tensile response can be achieved by introducing periodic across-width ply cuts, perpendicular to selected 0° plies, in both unidirectional (UD) and quasi-isotropic (QI) laminates. The inserted discontinuities initiate progressive delamination at the interface between the cut and pristine (uncut) plies. The tensile stress-strain curve consists of an initial almost linear stage with high modulus, a flat plateau stage and a final strain-hardening stage. This paper presents the enhanced pseudo-ductile performance achieved by introducing dispersed periodic short perforations in the UD laminates. Perforations with precisely controlled length were cut into the constituent prepregs using a laser milling machine. UD laminates containing perforations in selected plies exhibit high initial modulus, a softening stage prior to a final strain-hardening stage, all connected by smooth transitions. The dominant failure mechanism in this case was debonding surrounding the discontinuous perforated fibre bundles. This failure mechanism was successfully transferred to 0° fibre-dominated multi-directional (MD) laminates with perforations introduced in the middle 0° plies, and thereby provided pseudo-ductile performance.

Conference paper

Anthony DB, Bacarreza Nogales O, Shaffer M, Bismarck A, Robinson P, Pimenta Set al., 2018, Pseudo-ductile failure mechanism introduced into finger jointed thermoplastic PES interleaved CFRC, ECCM18 - 18th European Conference on Composite Materials

Pre-cut unidirectional carbon fibre prepreg composites, with an overlapped finger-joint architecture, were modified through the addition of polyethersulfone (PES) interleaves. The properties arising from these finger-jointed configurations were strongly dependent on the interply overlap region. When the tough thermoplastic interleaves spanned only the central portion of the overlap, a crack arresting failure mechanism was observed in tension. A pronounced plateau region or pseudo-ductile response was shown in conjunction with a strain hardening response after crack arrest. The local strain-to-failure of PES interleaved samples was ~3.2%, an increase of 85% compared to the pre-cut baseline (strain-to-failure 1.6%, pre-cut specimens without interleaves).

Conference paper

Sun J, Bacarreza O, Robinson P, 2017, Pseudo ductility in quasi-isotropic CFRP through ply weakening, 21st International Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. Conventional CFRP composites commonly exhibit brittle behaviour; failure is often catastrophic with little or no warning and poor residual load bearing capacity. Previous research in unidirectional (UD) carbon-epoxy composite laminates showed pseudo-ductility can be achieved through the introduction of ply cuts and this behaviour can be tailored by adjusting the position of the cuts. This paper examines the potential of implementing this cut-ply strategy in quasi-isotropic (QI) carbon-epoxy laminates. Tensile tests showed that a pseudo-ductile behaviour can be achieved in cut-ply QI laminates and open-hole specimens showed that the cut-ply architecture is notch insensitive.

Conference paper

Maples HA, Robinson P, Zhang B, Bismarck A, Li W, Burgstaller Cet al., 2017, Exploring deployable configurations using interleaved composite with shape memory capability, 21stInternational Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. An interleaved composite which exhibits shape memory capability controlled by heating has been developed. Trials of this material have been conducted to investigate the potential of using the interleaved composite for deployable structures. This paper reports on an investigation of the shape memory performance of a deployable spring made of the interleaved composite in tension. It is shown that the spring was easily re-shaped to a straight shape with little force and exhibited an excellent shape recovery (99.5%) upon re-heating. This spring may be suitable as a shape memory actuator for space applications.

Conference paper

Zhang B, Robinson P, Bismarck A, Maples HA, Burgstaller Cet al., 2017, An investigation of the viscoelastic behaviour of interleaved composite with shape memory capability, 21st International Conference on Composite Materials (!CCM-21)

© 2017 International Committee on Composite Materials. All rights reserved. A carbon fibre/epoxy composite with thermoplastic interleaves has been developed which exhibits shape memory capabilities upon heating. The shape memory capability was previously modelled using finite elements but the viscoelastic behaviour of the interleaf was not considered. This paper reports on an experimental and modelling investigation into the viscoelastic behaviour of the interleaved composite. This has a significant effect on the re-shaping of this interleaved composite and on the deployment time of structures made of this material.

Conference paper

Robinson P, Zhang B, Kanneganti S, Bismarck A, Maples HA, Burgstaller Cet al., 2017, Easy repair of interlaminar damage using interleaved carbon fibre/epoxy composites, 21st International Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. Laminated carbon fibre/epoxy composites are susceptible to interlaminar damage when impacted. An easy repair concept for such damage using an interleaving concept has been proposed. Trials of polylactide (PLA)-interleaved composite have previously been conducted to investigate the repair effectiveness of this material in three-point flexure testing and have shown a strength recovery of up to 90%. This paper reports on a further investigation of the PLA-interleaved composite for the repair of interlaminar damage caused in static indentation testing. Another interleaved composite using thermoplastic polyurthane (TPU) interleaves has been tested in three-point flexure has shown excellent strength recovery on repair.

Conference paper

Bacarreza O, Maidl S, Robinson P, Shaffer MSPet al., 2017, Exploring the use of friction to introduce ductility in composites, 21 st International Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. The use of friction mechanisms for introducing pseudo-ductility in brittle materials has been investigated. These mechanisms are inspired by nature, specifically by nacre. When nacre is loaded in tension, the aragonite tablets, making around 95 % of nacre, slide relatively to each other. The wedge shape of these tablets in combination with internal constraints, provided by the remaining 5 % of the organic interfaces, induces interlocking by frictional forces. This work investigates how this mechanism can be transferred to composite materials in order to increase their ductility in tension. Modelling is used to predict the tensile behaviour of interlocking configurations that exploit friction with either internal or external constraint. Two different design approaches of internally constrained specimens with various geometries are investigated using 3D printed materials. Externally constrained specimens, with different wedge angles are then investigated and finally this approach used with carbon composite structures.

Conference paper

Nguyen SN, Gispert CC, Greenhalgh ES, Robinson P, Allegri G, Brown KAet al., 2017, A new test method to characterize mixed mode II/III and I/II/III delamination, 21st International Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. Delamination is a critical damage mechanism in laminated composites, and currently represents the greatest limitation to achieving lightweight damage tolerant designs of primary aircraft structures. Current mode III delamination toughness tests often generate additional damage processes other than mode III delamination, such as intralaminar ply splits and crack migration to neighbouring ply interfaces, which invalidate the toughness measurements. In this study, a test rig capable of generating mode II/III and I/II/III delaminations over a range of mode mixities, up to a threshold proportion of mode III, and almost uniform mode III strain energy release rates, has been designed, developed, trialled and validated. Preliminary mixed-mode tests have been conducted on Hexcel IM7/8552 with 0°/0° and 0°/90° ply interfaces at the delamination plane. Fractography has been performed to elucidate and understand the failure mechanisms and characterize the fracture morphologies associated with mixed-mode II/III and I/II/III delamination. The fracture morphology of the IM7/8552 toughness coupons with a 0°/0° ply interface under pure mode II and mode II/III loading was exclusively delamination with little evidence of ply splitting or migration having had occurred. Directly ahead of the starter crack, the fracture morphology for both loading conditions presented a wedge of torn matrix, associated with the resin fillet. Beyond this fillet region, mode II/III loading presented slightly rotated cusps and a minor degree of fibre bridging. In summary, this paper presents a new mixed mode delamination test configuration, which still needs significant further development from the research community. In particular, the constraints applied to the specimen to achieve greater mode III components needs to be addressed. However, this new test method does offer a means to characterize delamin

Conference paper

Anthony DB, Bacarreza Nogales OR, Shaffer MSP, Bismarck A, Robinson P, Pimenta Set al., 2017, Crack arrest in finger jointed thermoplastic interleaved CFRC, 21st International Conference on Composite Materials, Publisher: Chinese Society for Composite Materials

Pre-cut unidirectional carbon fibre prepreg (M21/194/34%/T800S) composites were tested in tension with a 20 mm overlapped finger joint architectures. In between the overlapping finger jointed region the effect of introducing polyethersulfone (PES) interleaves is investigated. Samples with the addition of a thick PES interleave arrested the initial crack which formed at the pre-cut site. The strain-to-failure of the thick PES interleaved samples was over 3.2%, an increase of 85% compared to the baseline samples, and catastrophic failure was delayed in the majority of instances.

Conference paper

Robinson P, Bismarck A, Zhang B, Maples HAet al., 2017, Deployable, shape memory carbon fibre composites without shape memory constituents, Composites Science and Technology, Vol: 145, Pages: 96-104, ISSN: 0266-3538

Trials have been conducted to investigate the shape memory capability of an interleaved composite consisting of carbon fibre reinforced epoxy laminae and polystyrene interleaf layers. It has been shown that the composite can be readily re-shaped by deforming it at an elevated temperature and then cooling the composite in the deformed state. On re-heating, the composite almost fully returns to its original shape. One potential application of the shape memory capability of the interleaved composite is in deployable structures and a simple structure has been manufactured to demonstrate this possibility.

Journal article

Teixeira R, Pinho ST, Robinson P, 2016, Thickness-dependence of the translaminar fracture toughness: experimental study using thin-ply composites, Composites Part A: Applied Science and Manufacturing, Vol: 90, Pages: 33-44, ISSN: 1359-835X

The concept of translaminar fracture toughness of 0° plies has enabled the development of a considerable number of ply-level numerical models for structural failure of laminated composites. Using thin-ply pre-pregs, this paper demonstrates that this translaminar toughness is not an absolute, but rather in-situ, property and depends strongly on the 0° ply-block thickness, even in situations where delamination and diffuse damage are inhibited. We used two different grades of a thin-ply carbon-epoxy system to produce four different 0° ply-block thicknesses ranging from 0.03 mm to 0.12 mm, and measured the respective translaminar fracture toughness using compact tension tests. SEM and X-ray analysis showed no delamination nor diffuse damage. Yet, the translaminar fracture toughness increased from 46 to 104 kJ/m2 (initiation), and from 49 to 160 kJ/m2 (propagation), for the thickness range above. This finding has significant implications for the development and use of ply-level numerical failure models, for structural design with thin-ply composites, and for the development of thin-ply material systems.

Journal article

Anthony DB, bismarck A, blaker JJ, Qian H, Maples HA, Robinson P, Shaffer MSP, Greenhalgh ESet al., 2016, Development of novel composites through fibre and interface/interphase modification, 37th Risø International Symposium on Materials Science, Publisher: IOP, Pages: 012001-012001, ISSN: 1757-8981

We show how fibre/matrix interface (or interphase) modification can be used to develop a range of novel carbon fibre reinforced polymer (CFRP) composites that open up new applications far beyond those of standard CFRPs. For example, composites that undergo pseudo-ductile failure have been created through laser treatment of carbon fibres. Composites manufactured with thermo-responsive interphases can undergo significant reductions in stiffness at elevated temperatures. Additionally, structural supercapacitors have been developed through a process that involves encapsulating carbon fibres in carbon aerogel.

Conference paper

Anthony DB, Grail G, Bismarck A, Shaffer M, Robinson P, Pimenta Pet al., 2016, Exploring the tensile response in small carbon fibre composite bundles, ECCM17 - 17th European Conference on Composite Materials

Small composite bundles, AS4 carbon fibre epoxy, with a restricted number of reinforcing fibres, ca. 20, showed a progressive failure when tested in tension. In-situ acoustic emission observations under tensile load reveal that numerous fibres fail before ultimate failure of the small composite bundle, suggesting that isolated and individual fibre failures occur without compromising the integrity of the neighboring fibres or the small composite bundle’s overall mechanical performance. The average strength of the carbon fibres in small composite bundles was 9.6% higher than in standard lab-scale composite specimens using the same fibre type.

Conference paper

Maples HA, Smith O, Burgstaller C, Robinson P, Bismarck Aet al., 2016, Improving the ply/interleaf interface in carbon fibre reinforced composites with variable stiffness, Composites Science and Technology, Vol: 128, Pages: 185-192, ISSN: 0266-3538

Polystyrene-interleaved carbon fibre reinforced epoxy composites exhibiting controllable stiffness have been manufactured. These composites undergo reductions in flexural stiffness of up to 99% when heated above the glass transition temperature Tg of the interleaf layers. Potential applications for such materials include their use in morphing and deployable structures. Flexural tests at room temperature indicated that improvements in adhesion between the polystyrene and CFRP layers are required to prevent premature failure of the composites at low shear stresses. Here we investigate how modification of the interleaf layer improves the interlaminar shear strength of the laminates without affecting the stiffness loss at elevated temperatures. Two poly(styrene-co-maleic anhydride) (SMA) films with different maleic anhydride content were prepared and used as interleaf films. Thick adherend shear tests showed that the adhesion strength more than doubled, while flexural tests showed that composites containing SMA interleafs had more than twice the apparent flexural strength of composites containing pure polystyrene layers at 25 °C and yet still undergo significant reductions in stiffness at elevated temperature.

Journal article

Diao H, Robinson P, Wisnom MR, Bismarck Aet al., 2016, Unidirectional carbon fibre reinforced polyamide-12 composites with enhanced strain to tensile failure by introducing fibre waviness, Composites Part A: Applied Science and Manufacturing, Vol: 87, Pages: 186-193, ISSN: 1359-835X

Unidirectional (UD) carbon fibre reinforced polymers offer high specific strength and stiffness but they fail in a catastrophic manner with little warning. Gas-texturing and non-constrained annealing were used to introduce fibre waviness into UD polyamide 12 composites produced by wet-impregnation hoping to produce composites with a more gradual failure mode and increased failure strain. Both methods increased the variation of fibre alignment angle compared to the control samples. The composites containing wavy fibres exhibited a stepwise, gradual failure mode under strain controlled uniaxial tension rather than a catastrophic failure, observed in control samples. Gas-texturing damaged the fibres resulting in a decrease of the tensile strength and strain to failure, which resulted in composites with lower tensile strength and ultimate failure strain than the control composites. Non-constrained annealing of carbon fibre/PA-12 produced wavy fibre composites with ultimate failure strain of 2%, significantly higher than 1.6% of the control composite.

Journal article

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