Publications
217 results found
Wisnom MR, Pimenta S, Shaffer MSP, et al., 2024, High performance ductile and pseudo-ductile polymer matrix composites: A review, Composites Part A: Applied Science and Manufacturing, Vol: 181, ISSN: 1359-835X
The ability of fibre reinforced composites to deform with a non-linear stress–strain response and gradual, rather than sudden, catastrophic failure is reviewed. The principal mechanisms by which this behaviour can be achieved are discussed, including ductile fibres, progressive fibre fracture and fragmentation, fibre reorientation, and slip between discontinuous elements. It is shown that all these mechanisms allow additional strain to be achieved, enabling a yield-like behaviour to be generated. In some cases, the response is ductile and in others pseudo-ductile. Mechanisms can also be combined, and composites which give significant pseudo-ductile strain can be produced. Notch sensitivity is reduced, and there is the prospect of increasing design strains whilst also improving damage tolerance. The change in stiffness or visual indications of damage can be exploited to give warning that strain limits have been exceeded. Load carrying capacity is still maintained, allowing continued operation until repairs can be made. Areas for further work are identified which can contribute to creating structures made from high performance ductile or pseudo-ductile composites that fail gradually.
Kazemi ME, Medeau V, Chen Y, et al., 2024, Ballistic performance of bio-inspired hybrid interleaved composite structures suitable for aerospace applications, Composites Part A: Applied Science and Manufacturing, Vol: 179, ISSN: 1359-835X
We investigate the ballistic performance of an aircraft engine containment casing demonstrator, made of composite materials with a novel bio-inspired hybrid interleaved design, under high-velocity impact (HVI) at a specific angle. Firstly, we apply a bio-inspired (BI) helicoidal design to develop a large-scale monolithic laminate concept made of carbon fibre-reinforced polymer (CFRP). Then, we hybridise the developed BI laminate concept with interleaved blocks of Zylon fibre (PBO)-reinforced polymer to develop a large-scale BI hybrid interleaved laminate concept. We then further hybridise the developed BI hybrid concept with titanium (Ti) foils (located at the impact face) so that in total we have three large-scale laminate concepts. We manufacture 6 large-scale laminates from each concept with dimensions of 225 × 225 mm and a target areal weight of 0.95 g/cm2. We then test them (perpendicularly) under HVI ranging from 150 to 300 m/s to obtain the ballistic limit and energy dissipation. Secondly, after selecting the best-performing developed laminate concept, we scale it up to develop industrial demonstrator panels with a target areal weight of 1.5 g/cm2 and dimensions of 550 × 360 mm. We test the panels under HVI at an angle of 55° with a larger and heavier projectile, to more closely represent a fan blade-off event onto the engine casing. The results of the large-scale laminate concept tests show that the BI hybrid interleaved CFRP/PBO concept outperformed the rest of the concepts with 54% and 34% improvement in energy dissipation compared to that of quasi-isotropic (QI) and the BI monolithic CFRP, respectively. Our results show that small-scale designs for HVI-resistant CFRP-based laminates cannot be simply assumed to exhibit an equivalent performance for industrial applications with thicker laminates, heavier projectiles and impacts at an angle.
Kazemi ME, Medeau V, Greenhalgh E, et al., 2023, Bio-inspired interleaved hybrids: Novel solutions for improving the high-velocity impact response of carbon fibre-reinforced polymers (CFRP), Composites Part B: Engineering, Vol: 264, Pages: 1-11, ISSN: 1359-8368
We propose a novel design methodology consisting of bio-inspired (BI) and interleaved layups to develop hybrid carbon fibre-reinforced polymer (CFRP) composite structures for improved high-velocity impact (HVI) performance. Firstly, we apply a BI helicoidal design method consisting of various pitch angles (considering both thick- and thin-ply CFRP) to develop BI monolithic CFRP laminates. Secondly, we apply the interleaving design method to develop BI hybrid CFRP-based laminates interleaved with blocks of BI Zylon fibre-reinforced polymers through the thickness. We evaluate their response and compare it with traditional quasi-isotropic (QI) hybrid bulk layups. In addition to hybridising with Zylon, we apply titanium (Ti) foils to both the monolithic and hybrid CFRP-based laminates to investigate and compare their response. For all our hybrids, we kept the ratio of the hybridising material(s) to be less than 50% to ensure suitable in-plane mechanical properties and aimed at a target areal weight of 0.95 g/cm2. We also manufactured QI thick- and thin-ply monolithic CFRP laminates as baselines. We tested all laminates at 170 and 210 m/s and studied their response and failure modes. Our results show that the average energy dissipation of the QI monolithic thin-ply baseline improved by up to 22% by changing the layup from QI to BI, and by about 118% by changing the baseline QI layup to BI hybrid interleaved. Post-mortem analysis reveals that there are additional failure mechanisms activated in the BI hybrid interleaved layup with respect to the baseline.
Kazemi ME, Medeau V, Mencattelli L, et al., 2023, Novel zone-based hybrid laminate structures for high-velocity impact (HVI) in carbon fibre-reinforced polymer (CFRP) composites, Composites Science and Technology, Vol: 241, Pages: 1-10, ISSN: 0266-3538
We propose novel zone-based hybrid laminate concepts for improving the high-velocity impact (HVI) response of baseline carbon fibre-reinforced polymer (CFRP) composites while maintaining similar areal weights and retaining substantial in-plane mechanical properties by requiring that about 80% (by mass) of the baseline CFRP is kept in the hybrid concepts. We identify three zones along the thickness of the laminate according to their role during HVI and implemented tailored materials in these zones to improve the HVI response. We studied a wide range of materials, including: fibre reinforcements of carbon (thin- and thick-plies), glass, Zylon and ultra-high molecular weight polyethylene (UHMWPE); a shape memory alloy/carbon fabric; and ceramic, alumina and titanium sheets. All laminate concepts have similar areal weights for a meaningful comparison. After defining the various concepts, we manufactured and measured their specific dissipated energy under HVI, and finally carried out post-mortem analysis (including C-scan and microscopy). The results show up to 95% improvement in energy dissipation over the baseline quasi-isotropic (QI) CFRP configuration.
Quino G, Gargiuli J, Pimenta S, et al., 2023, Experimental characterisation of the dilation angle of polymers, Polymer Testing, Vol: 125, Pages: 1-7, ISSN: 0142-9418
Despite the wide use of Drucker-Prager plasticity-based models on polymers, the experimental measurement of the dilation angle, a critical parameter to fully describe the plastic potential, has been rarely reported in existing literature. This paper shows, for the first time, the experimental characterisation of the dilation angle of polymers over a wide range of plastic strain. These measurements were obtained from uniaxial compression experiments conducted on poly(methyl methacrylate) (PMMA) and an untoughened epoxy resin. The calculation of the dilation angle relied on the measurements of the compressive force and the strain components obtained via Digital Image Correlation (DIC). Lower values of dilation angle were obtained for the epoxy resin, suggesting that resistance to volumetric change during plastic deformation could be associated to molecular structure and internal forces. The methodology and results presented in this study can be applied to different types of materials and employed for developing and validating constitutive models that incorporate plastic dilation.
Hamid WLHWA, Hamid A, Iannucci L, et al., 2023, Flexural behaviour of 3D-printed carbon fibre composites: Experimental and virtual tests- application to composite adaptive structure, COMPOSITES PART C: OPEN ACCESS, Vol: 10, ISSN: 2666-6820
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- Citations: 2
Anthony D, Woodgate C, Shaw C, et al., 2023, Hierarchical solutions to compressive problems in fibre-reinforced composites, ECCM20 - The 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab), Pages: 1512-1517
Currently, the useable compressive properties of a composite are restricted by set design limits well below the expected intrinsic performance of the materials contained within. The next generation of high-performance fibre-reinforced polymer composites will need to address the challenge of improving the absolute performance of composites in compression. This task requires a rethink of the whole system; not only to address practical limitations of current materials, but their combination, interface, and their architecture. The mechanisms involved do not simply act over the nano-, macro-, or meso-level independently, but are mutually related at the system level, complicating the approach.
Thorn TDS, Liu Y, Yao X, et al., 2023, Smart and repeatable easy-repairing and self-sensing composites with enhanced mechanical performance for extended components life, COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING, Vol: 165, ISSN: 1359-835X
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- Citations: 2
Pimenta S, Patni M, Bikos D, et al., 2023, The role of constituents on the compressive strength of composites
Bikos D, Trask R, Robinson P, et al., 2023, COMPUTATIONALLY OMPUTATIONALLYOMPUTATIONALLY OMPUTATIONALLYEFFICIENT EFFICIENT FE MICROMECHANICAL MICROMECHANICAL MICROMECHANICAL MICROMECHANICALMICROMECHANICALMODELLING MODELLING OF UNIDIRECTIONAL UNIDIRECTIONAL COMPOSITES UNDER LONGITUDINAL
Zhang B, Quino G, Robinson P, et al., 2023, SHEAR AND COMPRESSION-SHEAR CHARACTERISATION OF A POLYMER MATRIX FOR CARBON FIBRE COMPOSITES
The compression behaviour of unidirectional carbon fibre/epoxy composites has been widely investigated. The poor compression properties of the material relate to the material instability which leads to the formation of fibre kinkbands. At high fibre volume fractions, this instability results from the polymer matrix which is sheared due to the misalignment of the compressed fibres, culminating in yielding or fracture of the matrix or failure at the matrix-fibre interface. In this study, the shear response of an epoxy polymer matrix under pure shear and shear-compression deformation was investigated. Hollow, thin-walled Prime 27 epoxy specimens were manufactured by machining from cured epoxy cylinders. Experimental results showed that the specimens exhibited a uniform in-plane shear strain in the gauge section in both test modes. The average yield stress of the compression-shear specimens (51.0 MPa) was slightly lower than that of the pure-shear specimens (54.9 MPa), due to the applied compression stress. The shear moduli of the specimens for both test modes were consistent with only 3.8% difference. The applied compression stress delayed the specimen failure and achieved a higher fracture strain. The data collected in these tests will be used in finite element (FE) modelling to explore how the compression behaviour of unidirectional composites can be improved.
Quino G, Gargiuli J, Pimenta S, et al., 2023, EXPERIMENTAL CHARACTERISATION OF THE DILATION ANGLE OF POLYMERS
Kazemi ME, Médeau V, Greenhalgh E, et al., 2023, BIO-INSPIRED INTERLEAVED COMPOSITE STRUCTURES FOR HIGH-VELOCITY IMPACT APPLICATIONS
We propose a novel design for improving the high-velocity impact (HVI) performance of hybrid carbon fibre-reinforced polymer (CFRP) composite structures. Our novel design consists of a non-conventional bio-inspired hybrid interleaved layup that significantly enhances damage diffusion and energy dissipation in CFRP composite structures. In our design, we retain more than 50% mass of the structure as CFRP to keep in-plane mechanical properties substantial and also aim to maintain the areal weight (compared to the monolithic CFRP baseline). We applied this design methodology to develop laminate concepts made of thin- and thick-ply CFRPs, hybridised with aramid fibre-reinforced polymer (AFRP) for one of the concepts, and also titanium foils for another concept. We tested the laminate concepts under HVI from 150 to 300 m/s and investigated their response in terms of energy dissipation, ballistic limit and failure modes. The results demonstrate a strong increase in ballistic limit and specific energy dissipation for the developed laminate concepts. The bio-inspired monolithic thin- and thick-ply CFRP laminate concepts exhibit about 15% improvement in specific energy dissipation compared to their QI monolithic baselines. Implementing interleaved blocks of AFRP into the bio-inspired monolithic CFRP laminate concepts shows an improvement in specific energy dissipation by up to 54% for the thick-ply and by up to 135% for the thin-ply, compared to their monolithic QI baselines.
Quino G, Robinson P, Trask RS, 2022, Design of a bending experiment for mechanical characterisation of pultruded rods under compression, 20th European Conference on Composite Materials, Publisher: EPFL Lausanne, Composite Construction Laboratory
Carbon fibre pultruded rods are used in structural applications across a wide range of industries due to their lightweight, corrosion/fatigue resistance and outstanding properties in the axial direction. While there is available literature on the mechanical characterisation of pultruded rods under tension and bending, very little has been reported about their compression response. The characterisation of the mechanical performance of pultruded rods under uniaxial direct compression is challenging due to the high sensitivity to alignment, stress concentrations in the gripping zone, and the complexity of specimen manufacturing, especially when the rodscan be of small diameter (~1mm).Existing literature reports the use of the compression side of a beam under bending to test materials with high axial stiffness and strength such as carbon fibre laminates. In this work, we show the applicability of such idea on pultruded rods. We report on the design of a novel bendingexperiment to characterise the compression behaviour of pultruded rods, ensuring low strain gradient and consistent failure within the gauge section.
Jones MP, Murali GG, Laurin F, et al., 2022, Functional flexibility: The potential of morphing composites, Composites Science and Technology, Vol: 230, Pages: 1-12, ISSN: 0266-3538
From plants tracking the sun to the aerodynamics of bird wings, shape change is key to the performance of natural structures. After years of reliance on mechanical joints, human engineering now focuses on improving aerodynamic efficiency through smooth, full form changes in material geometry, achieved using technologies such as morphing composites. Promising improved power generation and efficiency in wind turbines and safer more sustainable aircraft and cars, these materials can achieve both large geometric changes with low energy requirements by cycling between several stable physical states and more gradual changes in geometry by exploiting coefficient of thermal expansion mismatch and structural anisotropy, shape memory polymers and 4D printing. The merits and limitations of these various shape change systems are the subject of extensive and ongoing academic research and both commercial and defence industry trials to improve the viability of these technologies for widespread adoption. Shape change capabilities are often associated with problems in material cost, mass, mechanical properties, manufacturability, and energy requirements. Nonetheless, the considerable and rapid advances in this technology, already resulting in successful trials in advanced civilian and military aircraft and high-performance cars, indicate that future research and development of this materials platform could revolutionise many of our most critical power generation, defence and transport systems.
Murali GG, Robinson P, Bismarck A, et al., 2022, DEPLOYABLE COMPOSITE MESHES - MODELLING, MANUFACTURE AND CHARACTERISATION, Pages: 1183-1190
This paper describes the design and manufacture of a laminate which, when heated, will deploy into an expanded mesh. The design exploits the bending and/or twisting curvature that results when a non-symmetric laminate is subjected to a temperature change. To ensure the mesh laminate is almost flat after curing (i.e. prior to deployment), layups consisting of non-symmetric sublaminates separated by thermoplastic interleaves have been developed. When such a laminate is subsequently heated above the Tg of the thermoplastic layers, the mesh deploys. Two different layups are investigated; one deploys into a planar mesh and the other deploys into a mesh which forms a curved surface.
Katafiasz T, Greenhalgh ES, Allegri G, et 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.
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
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- Citations: 1
Zhang B, Bacarreza O, Robinson P, et 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.
Robinson P, Zhang B, Bismarck A, et 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.
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.
Zhang B, Bacarreza O, Robinson P, et 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.
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.
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%.
Sun J, Pernice MF, Bacarreza O, et 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.
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%.
Zhang B, Bacarreza O, Robinson P, et 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.
Sun J, Pernice MF, Bacarreza O, et 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.
Robinson P, Zhang B, Bismarck A, et 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.
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.
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