Publications
259 results found
da Costa ROSS, Pinho ST, 2023, Topology optimisation for robust design of large composite structures, Composite Structures, Vol: 321, ISSN: 0263-8223
The manufacturing of composite structures can lead to material defects. Some of these defects, due to their small size, can go undetected by current non-destructive testing techniques; especially in very large and geometrically complex components. Therefore, it is of paramount importance to design composite components to resist defects by accounting for them as early as possible. Topology optimisation is a methodology whereby complex features, such as cracks and debonds, can be accounted for in the design. Therefore, this work proposes a new approach for the design of very large composite structures. This new approach is enabled by a solid shell element formulation with boundary tracking capabilities (through the floating node and the level-set methods) and optimisation capabilities (through design sensitivity analysis of an energy release rate objective function). Furthermore, this work proposes a new algorithm and modelling workflow that has the ability to handle large multi-scale models. The proposed methodology shows advantages as the ability to track the topology explicitly, and the ability to increase defect tolerance of the design. This works shows the new methodology is capable of handling complex structures, such as a multi-scale stringer run-out model from an aircraft wing-box, while a kissing bond defect is present.
Garulli T, Katafiasz TJ, Greenhalgh ES, et al., 2023, A novel bio-inspired microstructure for improved compressive performance of multidirectional CFRP laminates, Composites Part B: Engineering, Vol: 264, ISSN: 1359-8368
In this work, we design, manufacture, test and discuss the first bio-inspired microstructural concept to enhance longitudinal compressive performance of multidirectional (MD) Carbon Fibre Reinforced Polymer (CFRP) laminates. To do so, we take inspiration from biologically occurring layered materials; one remarkable example being the anchoring spicula of the deep-sea glass sponge Monoraphis chuni. We designed numerically various concepts and then devised a strategy to reproduce, in a MD CFRP laminate, the characteristic alternation of stiff and soft regions observed in this material, followed by a bespoke procedure to manufacture the laminate. We evaluated their performances by means of small-scale notched compression tests and direct comparison with an industrially relevant baseline laminate. Our results show that the proposed concept led to a statistically significant increase in the failure load and in the average ligament specific stress at failure. Furthermore, the designed microstructure showed potential to delay damage initiation from a stress concentration and to arrest damage propagation. We conclude that the presented microstructural concept is potentially of great value for the design of lightweight structures undergoing compression loading.
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.
Whitehouse AD, Medeau V, Mencattelli L, et al., 2023, A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite joints, Composites Part B: Engineering, Vol: 261, Pages: 1-15, ISSN: 0961-9526
Traditional adhesive joints with straight edged adherends suffer from a significant stress concentration in the composite coincident with the edge of the metal adherend, which can lead to accelerated translaminar failure of the substrate. In this work, we developed a novel profiling concept which improves the mechanical performance of adhesive joints between metallic adherends and composite substrates. We conducted quasi-static four-point bending (4PB) tests which showed that profiling the edge of the metallic adherend could improve the peak load by at least 27%, and that the stability of failure was simultaneously improved. We investigated varying the profile parameters and were able to conclude that further significant mechanical performance gains could be achieved by increasing any of the profile: amplitude, frequency, or number of fractal length-scales. By analysing in-situ acoustic emission (AE) monitoring data we were able to observe that profiling of the metallic adherend results in failure initiation occurring at higher loads, which suggests that the concept is successful in providing better stress distributions and lowering peak stresses. By analysing the fracture surfaces, it is apparent that the profiling concept is successful in deflecting the translaminar fracture path; and additionally that a debonding mechanism occurs at the profile tips which is thought to be an important additional mechanism for creating damage tolerant joints.
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.
Yu B, Katafiasz TJ, Nguyen S, et al., 2023, Characterising and predicting the relationship between translaminar fracture toughness and pull-out length distributions under distinct temperatures, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 381, ISSN: 1364-503X
The translaminar fracture toughness reflects the damage tolerance of a fibre-reinforced composite under longitudinal tension, which often governs the final failure of structures. One of the main energy-dissipation mechanisms that contributes to the translaminar toughness of composites is the fibre pull-out process. The present study aims to quantify and model the statistical distribution of fibre pull-out lengths formed on the translaminar fracture surface of composites, for the first time in the literature; this is done under different temperatures, so that the relationship between pull-out length distributions, micromechanical properties and the translaminar fracture toughness can be established. The fracture surfaces of cross-ply compact tension specimens tested under three different temperatures have been scanned through X-ray computed tomography to quantify the extent of fibre pull-out on the fracture surfaces; the distribution of pull-out lengths showed alarger average and larger variability with an increase in temperature, which also lead to an increase in translaminar fracture toughness. A similar trend has been captured by the proposed analytical model, which predicts the pull-out length distribution based on the analysis of quasi-fractal idealizations of the fracture surface, yielding an overall accuracy of more than 85%.This article is part of the theme issue 'Ageing and durability of composite materials'.
Medeau V, Kazemi ME, Greenhalgh E, et al., 2022, Helicoidal layups and interleaved hybrids: a novel design methodology for impact-resistant composite structures, ECCM20 - The 20th European Conference on Composite Materials
Whitehouse A, Medeau V, Mencattelli L, et al., 2022, A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite joints, ECCM20 - The 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab)
In this work, we designed metal-CFRP joints with a profiled adherend termination to improve the mechanical performance. We have applied several profiles to the edge of titanium adherends which were adhesively bonded to CFRP substrates. We conducted finite element modelling and experimental 4PB (4-Point-Bend) testing to investigate how the geometry of the adherend edge profile effects the mechanical performance of the joint. This work shows that profiling of the metal adherend can result in increases of at least 27% in the peak load, and of at least 272% in the energy dissipated up to critical failure normalised by the mechanical energy.
Silva Sampaio Da Costa R, Pinho S, 2022, A novel topology optimisation methodology for robust design of structural components considering material defects, 20th European Conference on Composite Materials, Publisher: Composite Construction Laboratory (CCLab)
This work outlines a new Topology Optimisation methodology whereby material defects are introduced at the earliest stage of the structural design process, leading to more robust final design solutions. We couple the Levelset Method and the Floating Node Method to capture a moving material boundary explicitly on the Finite Element mesh. A continuum designsensitivity analysis scheme based on a measure of the energy release rate is used to quantify the impact of the defect. We show how the structure is optimised to reduce this measure and mitigate the impact of the material defect on the overall response.
Kazemi M, Medeau V, Greenhalgh E, et al., 2022, Implementing structural fuses in CFRP components via microstructurally-engineered crack paths, 20th European Conference on Composite Materials, ECCM20. 26-30 June, 2022, Lausanne, Switzerland, Publisher: Composite Construction Laboratory (CCLab)
This study aims to develop and implement actual carbon fibre-reinforced polymer (CFRP) solutions for realising structural fuses in real components. To this end, we have developed various concepts for structural fuses, applied to generic idealised components and aimed at engaging different in-plane and through-the-thickness damage propagation mechanisms. Micro-cut patterns (MCPs) / crack path combinations have been engraved on thin-ply CFRP prepregs (by using a laser cut machine) for manufacturing CFRP specimens. Afterwards, we have carried out a series of experimental studies to evaluate the fracture properties of various MCPs under three-point bending (3PB). Then, 3PB results were used to refine and down-select ourconcepts, for use in our generic idealised component design to test them under indentation test using a cantilever beam rig. The test results demonstrated that MCPs can provide significant control over the fracture locus and path, additionally allowing the failure initiation load and energy dissipation to be tailored.
Garulli T, Greenhalgh E, Pinho S, 2022, A novel bio-inspired microstructure for progressive compressive failure in multidirectional composite laminates, 20th European Conference on Composite Materials, ECCM 2022, Publisher: Composite Construction Laboratory (CCLab)
n this study we take inspiration from biological materials to design a modified microstructure for laminated multidirectional (MD) carbon fiber reinforced polymers (CFRP), with the objective of mitigating their compressive failure behavior. We introduce soft inclusions in the form of thin longitudinal strips of foam in 0° load bearing layers, aiming at arresting kinkband propagation. We conceived a bespoke stacking sequence and developed a tailored procedure for manufacturing the microstructure. We then performed in-situ tests on small scale notched specimens from a baseline laminate and a modified one. Results are presented and discussed.
Pinho ST, Costa ROSS, Matos M, et al., 2022, Multiscale analysis of an aircraft wingbox, Pages: 348-355
This paper presents results of a methodology for structural simulation of very large structures. It does not assume the use of a specific failure model, but rather focuses on establishing a framework that enables failure analyses on full-wing models with a complexity comparable to real wings in large passenger aircraft.
Yu B, Katafiasz TJ, Nguyen S, et al., 2021, Hygrothermal effects on the translaminar fracture toughness of a highly toughened aerospace CFRP: Experimental characterisation and model prediction, Composites Part A: Applied Science and Manufacturing, Vol: 150, Pages: 1-12, ISSN: 1359-835X
The translaminar fracture toughness and its dependence on the environmental condition are key considerations in designing aerospace-grade composites with a high damage tolerance to severe service conditions in terms of temperature and moisture. The present work characterises and models the hygrothermal effects on the translaminar fracture toughness of an interlaminar toughened aerospace carbon/epoxy composite under six environmental conditions: −55 °C, 23 °C, and 90 °C, for both ‘dry’ (i.e. moisture free) and ‘wet’ (fully moisture-saturated) specimens. Cross-ply compact-tension experiments show that the translaminar fracture toughness increases with the rise of temperature for both dry and wet conditions with the latter exhibiting a much greater increase. A model to predict the effect of moisture and temperature on the translaminar fracture toughness is here proposed and developed. This approach yields good agreement with experimental results, and it allows an improved understanding of the complex synergistic effects of interfacial properties on the overall translaminar toughening mechanisms.
Plocher J, Mencattelli L, Narducci F, et al., 2021, Learning from nature: Bio-Inspiration for damage-tolerant high-performance fibre-reinforced composites, Composites Science and Technology, Vol: 208, ISSN: 0266-3538
Over millions of years Nature has attained highly optimized structural designs with remarkable toughness, strength, damage resistance and damage tolerance - properties that are so far difficult to combine in artificial high-performance fibre-reinforced polymers (HPFRPs). Recent studies, which have successfully replicated the structures and especially the toughening mechanisms found in flora and fauna, are reviewed in this work. At the core of the manufacturing of damage-tolerant bio-inspired composites, an understanding of the design principles and mechanisms is key. Universal and naturally-inherent design features, such as hierarchical- and organic-inorganic-structures as well as helical or fibrous arrangements of building blocks were found to promote numerous toughening mechanisms. Common to these features, the outstanding ability of diffusing damage at a sub-critical state has been identified as a powerful and effective mechanism to achieve high damage tolerance. Novel manufacturing processes suitable for HPFRP (such as tailored high-precision tape placement, micro-moulding, laser-engraving and additive manufacturing) have recently gained immense traction in the research community. This stems from the achievable and required geometrical complexity for HPFRPs and the replication of subtly balanced interaction between the material constituents. Even though trends in the literature clearly show that a bio-inspired material design philosophy is a successful strategy to design more efficient composite structures with enhanced damage tolerance and mechanical performance, Nature continues to offer new challenging opportunities yet to be explored, which could lead to a new era of HPFRP composites.
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.
Kocaman ES, Chen BY, Pinho ST, 2020, A floating connector element formulation for multi-level modelling of composite structures, Composite Structures, Vol: 251, Pages: 1-13, ISSN: 0263-8223
Design and optimisation of large structures, including the positioning of lower-level components, typically require extensive user involvement and sequential mechanical analysis/optimisation iterations. This paper presents an original method that enables adaptive positioning of lower-level models (such as components) within higher level-models (such as large structures), and that achieves a combined mechanical/optimisation problem for the design of structures with various hierarchical levels (such as the positioning of stiffeners within a wingbox). As the position of the lower-level model evolves, our proposed method does not require re-generating of the geometry, remeshing or modifying the stiffness matrix of the elements corresponding to the various hierarchical levels. Instead, we achieve the adaptive positioning via an original concept that we propose here: Floating Connector (FC) elements. In this paper, we validate the FC elements against reference purely-mechanical solutions, show that they can be combined with gradient-descent method and genetic algorithms, and that they can be applied to optimise the positioning of a stiffener runout taking into account a debonding manufacturing defect.
Häsä R, Pinho ST, 2020, Bio-inspired armour: CFRP with scales for perforation resistance, Materials Letters, Vol: 273, Pages: 1-4, ISSN: 0167-577X
This paper proposes a novel biomimetic Carbon Fibre Reinforced Polymer (CFRP) with a microstructure inspired by fish scales. The aim of the novel microstructure is to improve the perforation resistance of CFRP without compromising its flexibility. To this end, we prototype the first ever CFRP laminate with scales and test it in quasi-static indentation on a soft backing material. We compare the mechanical behaviour of the CFRP with scales to two baseline configurations with conventional lay-ups. The results presented in this paper suggest that the CFRP with scales significantly outperforms the two baseline configurations in terms of force and displacement at penetration, while being flexible. This makes CFRPs with scales an attractive alternative for applications where perforation resistance is paramount, such as body armour against low velocity strikes.
da Costa ROSS, Pinho ST, 2020, A novel formulation for the explicit discretisation of evolving boundaries with application to topology optimisation, Computer Methods in Applied Mechanics and Engineering, Vol: 367, Pages: 1-30, ISSN: 0045-7825
Evolving boundaries are an intrinsic part of many physical processes and numerical methods. Most efforts to model evolving boundaries rely on implicit schemes, such as the level-set method (LSM). LSM provides the means to efficiently model the evolution of a boundary, but lacks the ability to transmit information or provide information directly at the boundary. Explicit alternatives based on remeshing or partial-remeshing are often computationally expensive and inherently complex to implement. This work proposes a solution to this dichotomy: a novel finite element method (FEM) based formulation capable of explicitly discretising moving boundaries in an accurate and numerically-efficient way. It couples the floating node method (FNM) with LSM for the first time, which yield a methodology suitable for implementation as user-element in a generic FEM package. The explicitly discretised boundary allows for a new velocity-extension methodology, and a new LSM-reinitialisation procedure, which show benefits in accuracy and efficiency. The potential of this formulation is showcased within topology optimisation, showing greater geometrical accuracy and improvements in the optimum solution attained when compared to implicit methods.
Pascoe JA, Pimenta S, Pinho ST, 2020, The effect of tab orientation on the toughening mechanisms produced by interlocked interlaminar thin-ply CFRP reinforcements, Composite Structures, Vol: 238, Pages: 1-12, ISSN: 0263-8223
The use of interlaminar reinforcement units, containing an interlocked tab-and-slit geometry, is a new concept for improving interlaminar fracture toughness. It was recently shown that such reinforcement units are capable of substantially increasing mode I fracture toughness, but mode II fracture toughness was unaffected.This paper presents an investigation into the effect of tab orientation on the toughening mechanisms, comparing the experimentally determined Mode I and II interlaminar fracture toughness for different tab orientations.The results show that the previously reported lack of mode II toughness increase was due to an unsuitable tab orientation. With a better choice of tab orientation a mode II propagation toughness increase (of 23.5%) could be obtained, while simultaneously increasing the mode I propagation toughness further than previously reported (up to a 109% improvement).Fractography was used to investigate the toughening mechanisms. It was found that the two main toughening mechanisms are crack bridging (in mode I) and deflection of the delamination path (in both mode I and II). The relationship between the tab orientation and the obtained increase of fracture toughness can be explained by the effect of tab orientation on these mechanisms.
Mencattelli L, Pinho ST, 2020, Herringbone-Bouligand CFRP structures: A new tailorable damage-tolerant solution for damage containment and reduced delaminations, Composites Science and Technology, Vol: 190, Pages: 1-13, ISSN: 0266-3538
In this work, we design, prototype, test and analyse the first high-performance Herringbone-Bouligand microstructure (with Carbon Fibre Reinforced Plastic (CFRP)) inspired to the high-impact-resistant mantis shrimp's dactyl club. To this end, we devised the first prototyping procedure to manufacture point-by-point tailorable Herringbone-Bouligand CFRP microstructures; this was based on the micro-moulding of uncured CFRP prepreg, and led to mimicking features of the club microstructure never achieved before with CFRPs. We investigated the damage tolerance of the prototyped Herringbone-Bouligand CFRP laminates, compared against ‘classical’ Bouligand CFRP laminates, using quasi-static indentation tests. Our test results show that the Herringbone-Bouligand microstructure resulted in delayed onset of delaminations, reduced in-plane spreading of damage, increased energy dissipation capability, and in the containment of damage within the tailored Herringbone-Bouligand region. We conclude that Herringbone-Bouligand CFRP microstructures offer an excellent tailorable damage-tolerant solution with great potential for composite applications where resistance to through-the-thickness loads is paramount.
Bullegas G, Moledo Lamela J, Pimenta S, et al., 2020, On the role of dynamic stress concentrations and fracture mechanics in the longitudinal tensile failure of fibre-reinforced composites, Engineering Fracture Mechanics, Vol: 228, Pages: 1-31, ISSN: 0013-7944
This paper investigates the role of dynamic stress concentrations, and of fracture mechanics-driven growth of critical clusters of fibres, on the longitudinal tensile failure of fibre-reinforced composites. For this purpose, we developed a semi-analytical fibre bundle model to simulate the longitudinal tensile failure of large composite bundles of continuous fibres. The model uses shear-lag to calculate the stress recovery along broken fibres, and an efficient field superposition method to calculate the stress concentration on the intact fibres, which has been validated against analytical and Finite Element (FE) results from the literature.The baseline version of the model uses static equilibrium stress states, and considers fibre failure driven by strength of materials (stress overload) as the only damage theory which can drive bundle failure. Like other models in the literature, the baseline model fails to capture the correct size effect (decreasing composite strength with bundle size) shown by experimental results.Two model variants have been developed which include dynamics stress concentrations and a fracture mechanics failure criterion respectively. To the knowledge of the authors, it is the first attempt in the literature to investigate these two effects in a fibre bundle model by direct simulation of large composite bundles. It is shown that, although the dynamic stress concentration significantly decreases the predicted bundle strength, it does not allow to predict the correct trend of the size effect. Finally, the results suggest that fracture mechanics may be the physical mechanism which is necessary to include to correctly predict the decreasing composite strength with bundle size shown by experimental results.
Albuquerque Da Silva Matos M, Tagarielli V, Pinho S, 2020, On the electrical conductivity of composites with a polymeric matrix and a non-uniform concentration of carbon nanotubes, Composites Science and Technology, Vol: 188, ISSN: 0266-3538
We present a multiscale modelling approach to explore the effects of a non-uniform concentration of carbon nanotubes (CNTs) on the electrical conductivity of CNT-polymer composites. Realistic three-dimensional representative volume elements (RVEs) are generated from a two-dimensional CNT concentration map, obtained via microscopy techniques. The RVEs capture the measured probability density function of the CNT concentration and include a length-scale to represent the details of the spatial distribution of the concentration. The homogenized conductivity of the RVEs is computed via multiscale FE analyses for different values of such length-scale, and it is compared to measurements. The modelling strategy is then used to explore the effects of the microstructural features of these materials on their electrical conductivity.
Mencattelli L, Pinho ST, 2020, Ultra-thin-ply CFRP Bouligand bio-inspired structures with enhanced load-bearing capacity, delayed catastrophic failure and high energy dissipation capability, Composites Part A: Applied Science and Manufacturing, Vol: 129, Pages: 1-15, ISSN: 1359-835X
In this work, we demonstrate for the first time that the inherent low performance to out-of-plane loading of thin-ply Carbon Fibre Reinforced Plastics (CFRPs) can be overcome with tailored bio-inspired Bouligand microstructures. To this end, we designed, manufactured ultra-thin-ply CFRP Bouligand laminates and conducted an original study which combines full-penetration quasi-static indentation tests, in-situ three-point bending tests conducted under a SEM and detailed analytical modelling. We investigated a wide range of mismatch (pitch) angles [2.5°, 5°, 10°, 20°, 45°], showing that decreasing pitch angles simultaneously achieved a larger (i) load-bearing capability, (ii) delay in catastrophic failure and (iii) total dissipated energy. We then investigated the role of the pitch angle on the activation of the highly dissipative sub-critical failure mechanisms responsible for the high mechanical performances achieved by small pitch angles laminates. Our investigation clearly shows that, with ultra-thin-ply CFRP, smaller pitch angles achieve higher damage tolerance and structural integrity.
Pascoe J-A, Pimenta S, Pinho S, 2020, Example analysis input files for CZM analysis of delamination growth in a DCB specimens
The files in this collection accompany the paper 'How to set up a cohesive zone model for an LEFM dominated problem: a detailed analysis for first time users', submitted to Applied Mechanics Reviews. The files comprise input files that allow reproduction of the example analyses shown in that paper. The purpose of the paper is to show how to determine appropriate values of various numerical parameters required when setting up a cohesive zone model analysis of an LEFM dominated crack propagation problem. These parameters can be determined by running a series of convergence studies. The input files for those convergence studies as well as the final prediction are included in this collection.The example analyses for the paper were run using Abaqus/Standard 6.14, and the included files will work for that software version.
Pinho ST, Narducci F, Lee KY, 2020, Damage-tolerant nacre-inspired CFRP
© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. In this paper, a carbon/epoxy composite with nacre-inspired micro-structure is designed, synthesised and tested. A nacre-like discontinuous micro-structure of interlocking tiles is designed via original analytical and numerical models, and then laser-engraved in the laminate plies. Firstly, three-point bending (3PB) tests are carried out on the nacre-like carbon/epoxy composite, demonstrating its capability in deflecting cracks and avoiding localised failure in the specimen, with some amount of damage diffusion. Subsequently, the laminate interfaces are toughened by film-casting thin (0.3 µm) patches of poly(lactic acid) (PLA), in order to promote a more extensive pull-out of tiles and increase the damage-diffusion capability of the material. Finally, continuous layers of glass-fibre/epoxy, similar to the thick protein interlayers that separate layers of ceramic tiles in real nacre, are introduced in the laminate, in order to act as crack stoppers in case of unstable crack propagation in the micro-structure.
Mencattelli L, Pinho ST, 2020, Low velocity impact and compression after impact of thin-ply CFRP Bouligand structures
© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. In this work, several bio-inspired thin-ply CFRP laminates mimicking the helicoidal architecture of the mantis shrimp's dactyl club periodic region have been modelled and tested under low velocity impact (LVI) and compression after impact (CAI), investigating the effect of the inter-ply angle (pitch angle) on the mechanical response and damage characterization of the biomimetic laminate. The use of thin-ply technology has allowed for the first time to explore the effect of very small inter-ply angles, down to 2.5°, better mimicking the microstructure of the dactyl club and achieving failure mechanisms akin those observed in the natural microstructure. Tests conducted for a wide range of pitch angles (2.5°, 5°, 10°, 20°, 45°) show that, by decreasing the pitch angle, is it possible to better mimic the failure mechanisms observed in the biological microstructure.
Pinho ST, Narducci F, Lee KY, 2020, Damage-tolerant nacre-inspired CFRP
In this paper, a carbon/epoxy composite with nacre-inspired micro-structure is designed, synthesised and tested. A nacre-like discontinuous micro-structure of interlocking tiles is designed via original analytical and numerical models, and then laser-engraved in the laminate plies. Firstly, three-point bending (3PB) tests are carried out on the nacre-like carbon/epoxy composite, demonstrating its capability in deflecting cracks and avoiding localised failure in the specimen, with some amount of damage diffusion. Subsequently, the laminate interfaces are toughened by film-casting thin (0.3 µm) patches of poly(lactic acid) (PLA), in order to promote a more extensive pull-out of tiles and increase the damage-diffusion capability of the material. Finally, continuous layers of glass-fibre/epoxy, similar to the thick protein interlayers that separate layers of ceramic tiles in real nacre, are introduced in the laminate, in order to act as crack stoppers in case of unstable crack propagation in the micro-structure.
Pinho ST, Narducci F, Lee KY, 2020, Damage-tolerant nacre-inspired CFRP
© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. In this paper, a carbon/epoxy composite with nacre-inspired micro-structure is designed, synthesised and tested. A nacre-like discontinuous micro-structure of interlocking tiles is designed via original analytical and numerical models, and then laser-engraved in the laminate plies. Firstly, three-point bending (3PB) tests are carried out on the nacre-like carbon/epoxy composite, demonstrating its capability in deflecting cracks and avoiding localised failure in the specimen, with some amount of damage diffusion. Subsequently, the laminate interfaces are toughened by film-casting thin (0.3 µm) patches of poly(lactic acid) (PLA), in order to promote a more extensive pull-out of tiles and increase the damage-diffusion capability of the material. Finally, continuous layers of glass-fibre/epoxy, similar to the thick protein interlayers that separate layers of ceramic tiles in real nacre, are introduced in the laminate, in order to act as crack stoppers in case of unstable crack propagation in the micro-structure.
Häsä R, Pinho ST, 2020, Improving the damage tolerance of CFRP using a biomimetic crossed-lamellar microstructure
The damage tolerance of composites can be enhanced by bio-inspired microstructural designs. The crossed-lamellar microstructure is the toughest microstructure found in molluscs, despite consisting almost entirely of brittle ceramic. In this work, we investigate microstructures for CFRPs inspired by the crossed-lamellar microstructure in order to improve the damage diffusion capability of the former. This includes exploring two different prototyping procedures with different interface properties. The results indicate that the investigated configurations have the potential to significantly increase the damage dissipation capability of CFRP. The microstructures diffuse damage in a stable manner while preserving their structural integrity up to large curvatures under bending load. We demonstrate that composites with crossed-lamellar microstructures have very attractive properties in terms of damage diffusion.
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