Publications
269 results found
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.
Pascoe JA, Pimenta S, Pinho ST, 2020, Interlocking thin-ply reinforcements for the improvement of CAI strength
A new reinforcement concept for improving compression after impact strength of carbon fibre reinforced polymers is explored. The concept consists of manufacturing interlocked reinforcement units from thin-ply prepreg, which are inserted at the interlaminar interfaces within a regular ply-thickness laminate. Compression after impact tests following ASTM standards were performed on both reinforced and baseline specimens. The reinforced specimens showed a 11.4 % reduction in post-impact delamination area. The strength results will be presented at the conference.
Pascoe JA, Pimenta S, Pinho ST, 2020, Interlocking thin-ply reinforcements for the improvement of CAI strength
© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. A new reinforcement concept for improving compression after impact strength of carbon fibre reinforced polymers is explored. The concept consists of manufacturing interlocked reinforcement units from thin-ply prepreg, which are inserted at the interlaminar interfaces within a regular ply-thickness laminate. Compression after impact tests following ASTM standards were performed on both reinforced and baseline specimens. The reinforced specimens showed a 11.4 % reduction in post-impact delamination area. The strength results will be presented at the conference.
Häsä R, Pinho ST, 2020, Improving the damage tolerance of CFRP using a biomimetic crossed-lamellar microstructure
© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. 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.
Pascoe JA, Pimenta S, Pinho ST, 2020, Interlocking thin-ply reinforcements for the improvement of CAI strength
© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. A new reinforcement concept for improving compression after impact strength of carbon fibre reinforced polymers is explored. The concept consists of manufacturing interlocked reinforcement units from thin-ply prepreg, which are inserted at the interlaminar interfaces within a regular ply-thickness laminate. Compression after impact tests following ASTM standards were performed on both reinforced and baseline specimens. The reinforced specimens showed a 11.4 % reduction in post-impact delamination area. The strength results will be presented at the conference.
Mencattelli L, Pinho ST, 2020, Low velocity impact and compression after impact of thin-ply CFRP Bouligand structures
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.
Tang J, Swolfs Y, Aslani A, et al., 2019, Engineering tensile behavior of hybrid carbon fiber/self-reinforced polypropylene composites by bio-inspired fiber discontinuities, Composites Part B: Engineering, Vol: 178, ISSN: 1359-8368
Carbon fiber layer failure is vital for the tensile behavior of interlayer hybrid carbon fiber (CF)/self-reinforced polypropylene (SRPP) composites. Introducing cuts, termed here as discontinuities, into the carbon layer is a promising way to tailor its failure behavior. Inspired by structural features of biological composites, we designed and produced hybrid composites with hierarchical and polygonal arrangements of discontinuities in the carbon layer. Increasing the number of levels in the hierarchical patterns delayed the onset of carbon layer failure, hence improving the damage resistance of the hybrid composites. A progressive carbon layer failure was achieved with the polygonal patterns by creating a transition from fiber bundle pull-out to fiber bundle fracture. Spreading the polygonal patterns throughout the specimen resulted in a unique diffused delamination distribution that has not been reported in the literature. Pseudo-ductile behavior was achieved by creating dispersed fiber bundle pull-out with the fully dispersed polygonal patterns. The resulting hybrid CF/SRPP composites demonstrated a rare combination of stiffness (10 GPa) and ductility (~16% failure strain) with a pseudo-ductile strain over 14%. This paper delivers and proves the concept of utilizing discontinuities to engineer the tensile behavior of hybrid composites.
Häsä R, Pinho ST, 2019, A three-level hybrid metal/in-plane-CFRP/crossed-lamellar microstructure concept for containment applications, Composites Part A: Applied Science and Manufacturing, Vol: 126, ISSN: 1359-835X
This paper proposes a novel hybrid metal/Carbon Fibre Reinforced Polymer (CFRP) microstructure which includes a bio-mimetic crossed-lamellar CFRP layer (with out-of-plane fibres) as well as traditional CFRP layers (with in-plane fibres). We show that this microstructure is capable of preserving its structural integrity due to the crossed-lamellar and metal layers while the in-plane fibres provides it stiffness and strength. We studied numerically and experimentally a metal hybrid/crossed lamellar block in isolation, both with aluminium and titanium for the metal. We then proceeded to create the full microstructure, including a quasi-isotropic block. Our results show that these structures can withstand very large curvatures in a pseudo-ductile way. This makes them attractive for engineering applications where structural integrity is paramount, such as for containment structures.
Canturri C, Greenhalgh ES, Asp LE, et al., 2019, Fractographic study to characterise the interaction between intralaminar and interlaminar fracture from embedded defects under compression loading, Composites Part A: Applied Science and Manufacturing, Vol: 125, ISSN: 1359-835X
This paper describes the fractographic observations from the study of embedded defects subject to compression. The fractographic observations aim to characterise the interaction between intralaminar and interlaminar fracture and to understand their role in the delamination growth and the delamination migration. The influence of the stacking sequence orientation on the damage modes is studied in eight different configurations. A detailed fractographic study led to the identification of the different failure modes and failure sequence. It was also possible to establish the stacking sequences more prone to delamination migration and the failure modes more critical for damage tolerance.
Tang J, Aslani A, Swolfs Y, et al., 2019, Staggered ply discontinuities for tailoring the tensile behavior of hybrid carbon fiber/self-reinforced polypropylene composites: A study of pattern parameters, Composites Part A: Applied Science and Manufacturing, Vol: 125, Pages: 1-13, ISSN: 1359-835X
This work explores the potential of discontinuities combined with hybridization in controlling the failure mechanisms of composite materials. Laser cuts, termed as discontinuities, with a predefined staggered pattern were introduced into the carbon layer of hybrid carbon fiber (CF)/self-reinforced polypropylene (SRPP) composites. Three geometrical parameters were used to define the staggered pattern: cut fraction, cut length and step length. The effects of these three parameters on the failure mechanisms of the hybrid CF/SRPP composites under tensile loading were investigated. The three geometrical parameters can be successfully used to: (1) trigger more diffused damage; (2) delay onset of carbon layer fracture; and (3) promote a transition between fiber bundle pull-out and fiber bundle fracture. Comparing to hybrids with continuous fibers, hybrids with the staggered ply discontinuities exhibited a rich diversity of failure mechanisms. The enrichment of failure mechanisms is beneficial for expanding the design space for tailoring the mechanical response of interlayer hybrid composites.
Mencattelli L, Pinho ST, 2019, Realising bio-inspired impact damage-tolerant thin-ply CFRP Bouligand structures via promoting diffused sub-critical helicoidal damage, Composites Science and Technology, Vol: 182, Pages: 1-13, ISSN: 0266-3538
In this work, we manufactured bio-inspired thin-ply Carbon Fibre Reinforced Plastic (CFRP) laminates, mimicking the helicoidal architecture of the mantis shrimp's dactyl club periodic region, with the smallest inter-ply (pitch) angle in the literature (2.5∘), thus better mimicking the actual micro-structure of the dactyl club. We conducted Low Velocity Impact (LVI) tests on a wide range of pitch angles (2.5∘, 5∘, 10∘, 20∘, 45∘), thus demonstrating that decreasing the pitch angle leads to a progressively smoother double helicoidal evolution of damage, reduces delamination areas, diffuses sub-critical damage, and enhances damage tolerance. We then conducted Compression After Impact (CAI) tests, thereby demonstrating that the residual strength and failure strain are preserved as the pitch angle is reduced, even though there is a steep decrease in the proportion of 0∘-plies (plies aligned with the loading direction) as the pitch angle decreases. Via detailed modelling, we then developed and proposed an explanation for why very small pitch angles are required to achieve the beneficial damage mechanisms exhibited by biological Bouligand structures.
Häsä R, Pinho ST, 2019, A novel aluminium/CFRP hybrid composite with a bio-inspired crossed-lamellar microstructure for preservation of structural integrity, Composites Science and Technology, Vol: 182, ISSN: 0266-3538
In this paper, we demonstrate that a novel hybrid composite of aluminium and Carbon Fibre Reinforced Polymer (CFRP) with a microstructure inspired by a biological crossed-lamellar microstructure is an attractive alternative for applications where structural integrity is paramount. Composites with such microstructure are prototyped and tested using both standard and thin-ply CFRP prepreg. Three-point bend tests are carried out in an SEM environment, showing extensive diffuse damage in the CFRP and yielding in the aluminium. This is the first hybrid crossed-lamellar-inspired microstructure in the literature and the results demonstrate that this novel microstructure can be loaded up to record large curvatures (in comparison with other CFRPs and hybrid CFRPs) while retaining its structural integrity and dissipating energy under stable conditions.
Swolfs Y, Pinho S, 2019, 3D printed continuous fibre-reinforced composites: bio-inspired microstructures for improving the translaminar fracture toughness, Composites Science and Technology, Vol: 182, Pages: 1-8, ISSN: 0266-3538
Translaminar fracture toughness is a vital property governing the notch sensitivity and damage tolerance of composites. Nature has shown that incorporating material transitions can increase toughness significantly. This work presents finite element models demonstrating that such transitions can indeed increase the translaminar fracture toughness. The designed microstructures were then 3D printed using continuous glass and carbon fibres. The specimens consisted primarily of glass fibres, but with local carbon fibre strips. A new compact tension specimen with a side groove was designed to ensure proper failure. When the strips were sufficiently large, toughness improvements of 20–60% were found after the crack had grown through the strips. These results reveal a powerful strategy for locally increasing the toughness in areas where it is needed the most.
Pascoe J-A, Pimenta S, Pinho ST, 2019, Interlocking thin-ply reinforcement concept for improved fracture toughness and damage tolerance, Composites Science and Technology, Vol: 181, ISSN: 0266-3538
An original concept for improving the delamination resistance and damage tolerance of a composite laminate is proposed. The concept is to insert interlocked thin-ply reinforcement units between the laminae. Each reinforcement unit consists of two thin-ply layers with tabs cut into one layer, and slits cut into the other layer. The slits, and the long axis of the tabs, are parallel to the fibre direction in their respective layers. The two thin-ply layers are placed together, and the tabs are inserted through the slits, creating an interlocked reinforcement unit.The effect of the reinforcement units was quantified via mode I (DCB) and mode II (4ENF) fracture toughness tests, as well as compression after impact tests. Mode I propagation fracture toughness was increased by 77.6%, while mode II fracture toughness was not affected. In the compression after impact tests, an 11.4% reduction in delamination area was achieved but this only resulted in a 5.1% increase in CAI strength.
Morais MVC, Oliva-Avilés AI, Matos MAS, et al., 2019, On the effect of electric field application during the curing process on the electrical conductivity of single-walled carbon nanotubes–epoxy composites, Carbon, Vol: 150, Pages: 153-167, ISSN: 0008-6223
Single-walled carbon nanotube (SWCNT)/epoxy composites were cured under external electric fields and the influence of the processing parameters (electric field magnitude and frequency, SWCNT concentration and curing temperature)on the electrical response of the system was evaluated. A mold for the electric field application was designed and manufactured, allowing in situ measurements of the electrical resistivity of the composite, during and after the curing process. The resulting electrical properties revealed a strong dependence on the processing parameters. By rising the curing temperature, the solid bulk resistivity was decreased by one order of magnitude. Further reduction was observed with electric fields, up to an additional order of magnitude. Such improvements can be related with the decrease in viscosity and improvement of interconnected-nanotube paths within the polymer matrix. The effect of the electric field on the rotation and interconnection of the SWCNTs was investigated using a classical mechanics model based on the dielectrophoretic theory for the liquid state. The influence of inter-nanotube distances on the bulk electrical properties was calculated at different particle concentrations, using finite element models of the microstructure. This processing technique presents promising results for enhancing the electrical conductivity of polymer composites with carbon-based nanoparticles.
Hasa R, Pinho ST, 2019, Erratum to ‘Failure mechanisms of biological crossed-lamellar microstructures applied to synthetic high-performance fibre-reinforced composites’ [Journal of the Mechanics and Physics of Solids 125C (2019) 53–73], Journal of the Mechanics and Physics of Solids, Vol: 128, Pages: 255-255, ISSN: 0022-5096
Mencattelli L, Tang J, Swolfs Y, et al., 2019, Bio-inspired design for enhanced damage tolerance of self-reinforced polypropylene/carbon fibre polypropylene hybrid composites, Composites Part A: Applied Science and Manufacturing, Vol: 121, Pages: 341-352, ISSN: 1359-835X
In this work, we investigate the toughness of an inter-layer Self-Reinforced Polypropylene/Carbon Fibre Polypropylene (SRPP/CFPP) cross-ply hybrid composite and devise strategies to improve two aspects of its damage tolerance: (i) increasing the energy dissipation capability and (ii) enhancing the impact damage tolerance. To this end, we introduced discontinuities in the form of laser-cuts across the fibres of the CFPP plies, tailoring two patterns of laser-cuts to meet each specific damage tolerance requirement. We conducted penetration impact and Double Edge Notched Tensile (DEN-T) tests. The DEN-T tests, analysed via the Essential Work of Fracture method, show that engineering the microstructure successfully diffused damage. This resulted in a great increase in energy dissipation capability — 90% higher than a reference non-engineered structure. Engineering the microstructure of impact samples has led to enhanced impact damage tolerance with increased energy dissipation at a sub-critical level and delayed critical failure.
Matos MAS, Pinho ST, Tagarielli VL, 2019, Predictions of the electrical conductivity of composites of polymers and carbon nanotubes by an artificial neural network, Scripta Materialia, Vol: 166, Pages: 117-121, ISSN: 1359-6462
Industrial applications of conductive polymer composites with carbon nanotubes require precise tailoring of their electrical properties. While existing theoretical methods to predict the bulk conductivity require fitting to experiments and often employ power-laws valid only in the vicinity of the percolation threshold, the accuracy of numerical methods is accompanied with substantial computational efforts. In this paper we use recently developed physically-based finite element analyses to successfully train an artificial neural network to make predictions of the bulk conductivity of carbon nanotube-polymer composites at negligible computational cost.
Albuquerque Da Silva Matos M, Pinho S, Tagarielli V, 2019, Application of machine learning to predict the multiaxial strain-sensing response of CNT-polymer composites, Carbon, Vol: 146, Pages: 265-275, ISSN: 0008-6223
We present predictive multiscale models of the multiaxial strain-sensing response of conductive CNT-polymer composites. Detailed physically-based finite element (FE) models at the micron scale are used to produce training data for an artificial neural network; the latter is then used, at macroscopic scale, to predict the electro-mechanical response of components of arbitrary shape subject to a non-uniform, multiaxial strain field, allowing savings in computational time of six orders of magnitude. We apply this methodology to explore the application of CNT-polymer composites to the construction of different types of sensors and to damage detection.
Kocaman ES, Chen BY, Pinho ST, 2019, A polymorphic element formulation towards multiscale modelling of composite structures, Computer Methods in Applied Mechanics and Engineering, Vol: 346, Pages: 359-387, ISSN: 0045-7825
This paper presents a new polymorphic element modelling approach for multi-scale simulation, with an application to fracture in composite structures. We propose the concept of polymorphic elements; these are elements that exist as an evolving superposition of various states, each representing the relevant physics with the required level of fidelity.During a numerical simulation, polymorphic elements can change their formulation to more effectively represent the structural state or to improve computational efficiency. This change is achieved by transitioning progressively between states and by repartitioning each state on-the-fly as required at any given instant during the analysis. In this way, polymorphic elements offer the possibility to carry out a multiscale simulation without having to define a priori where the local model should be located.Polymorphic elements can be implemented as simple user-defined elements which can be readily integrated in a Finite Element code. Each individual user-defined polymorphic element contains all the relevant superposed states (and their coupling), as well as the ability to self-refine.We implemented a polymorphic element with continuum (plain strain) and structural (beam) states for the multiscale simulation of crack propagation. To verify the formulation, we applied it to the multiscale simulation of known mode I, mode II andmixed-mode I and II crack propagation scenarios, obtaining good accuracy and up to 70% reduction in computational time —the reduction in computational time can potentially be even more significant for large engineering structures where the local model is a small portion of the total.We further applied our polymorphic element formulation to the multiscale simulation of a more complex problem involving interaction between cracks (delamination migration), thereby demonstrating the potential impact of the proposed multiscale modelling approach for realistic engineering problems.
Häsä R, Pinho ST, 2019, Failure mechanisms of biological crossed-lamellar microstructures applied to synthetic high-performance fibre-reinforced composites, Journal of the Mechanics and Physics of Solids, Vol: 125, Pages: 53-73, ISSN: 0022-5096
This paper investigates whether the toughening mechanisms of a biological crossed-lamellar microstructure can be reproduced in a synthetic high-performance carbon fibre/epoxy matrix composite. The mechanics of the failure process in synthetic crossed-lamellar microstructures was investigated using the Finite Element Method. This enabled the design of a high-performance carbon-fibre reinforced polymer (CFRP) with such microstructure. Two different procedures were then developed to synthesise the first crossed-lamellar microstructures in CFRP in the literature. Test specimens were subsequently manufactured. Three-point bend tests were carried out in an SEM environment, showcasing the damage diffusion capability of the microstructure under stable conditions. The results show that the crossed-lamellar microstructure can be synthesised in CFRP with good accuracy, and that the mechanical toughening mechanisms associated with the natural crossed-lamellar microstructures can be reproduced in this synthetic material.
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