Publications
269 results found
Gigliotti L, Pinho ST, 2015, Damage Tolerance of Sandwich Foam Cores: Experimental Characterization and Numerical Modelling, 30th Technical Conference of the American-Society-for-Composites, Publisher: DESTECH PUBLICATIONS, INC, Pages: 1573-1589
De Carvalho NV, Pinho ST, 2015, MECHANICAL RESPONSE AND FAILURE OF 2D WOVEN COMPOSITES UNDER COMPRESSION, WOVEN COMPOSITES, Vol: 6, Pages: 75-107
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- Citations: 2
Gigliotti L, Pinho ST, 2015, ENABLING FASTER STRUCTURAL DESIGN: EFFICIENT MULTISCALE SIMULATION OF LARGE COMPOSITE STRUCTURES, 20th International Conference on Composite Materials (ICCM), Publisher: AALBORG UNIV PRESS
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- Citations: 1
Pinho ST, Wilmes AAR, 2015, MODELLING NANOSCALE GRAPHENE STRUCTURES USING A MULTI-PHYSICS MOLECULAR-DYNAMICS FINITE-ELEMENT METHOD, 20th International Conference on Composite Materials (ICCM), Publisher: AALBORG UNIV PRESS
Grail G, Coq M, Pimenta S, et al., 2015, EXPLORING THE POTENTIAL OF HIERARCHICAL COMPOSITE FIBRE BUNDLES TO IMPROVE THE TENSILE PERFORMANCE OF UNIDIRECTIONAL COMPOSITES, 20th International Conference on Composite Materials (ICCM), Publisher: AALBORG UNIV PRESS
Bullegas G, Pinho ST, Pimenta S, 2015, BIO-INSPIRED MICROSTRUCTURE DESIGN TO IMPROVE TRANSLAMINAR FRACTURE TOUGHNESS OF THIN-PLY COMPOSITES, 20th International Conference on Composite Materials (ICCM), Publisher: AALBORG UNIV PRESS
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- Citations: 1
Wehrkamp-Richter T, Pinho ST, Hinterhoelzl R, 2015, MODELLING THE NON-LINEAR MECHANCIAL BEHAVIOUR OF TRIAXIAL BRAIDED COMPOSITES, 20th International Conference on Composite Materials (ICCM), Publisher: AALBORG UNIV PRESS
Canturri C, Greenhalgh ES, Pinho ST, 2014, The relationship between mixed-mode II/III delamination and delamination migration in composite laminates, Composites Science and Technology, Vol: 105, Pages: 102-109, ISSN: 0266-3538
Predictive models have struggled to accurately simulate progressive delamination growth in composite structures, often due to the challenges associated with modelling delamination migration phenomenon. This paper presents a methodology with which to model such migration. Firstly, the interlaminar shear at a delamination front were partitioned into axial and transverse modes, the mode-mixity of which was controlled by the mismatch between this front and the ply directions. An element formulation was presented which utilised this mismatch. Consequently, delamination migration was shown to have ensued when the transverse mode exceeded a critical mode-mixity Giii/GT = 0.22. This approach was verified against experimental studies on width tapered end loaded split coupons by correlating the fracture morphology against mode-mixity. In particular, the orientation of the cusps on the delamination surface were shown to be controlled by the relative dominance of the axial and transverse modes. This methodology provides a means to accurately and robustly model progressive delamination growth processes in composite structures.
Blanco N, Trias D, Pinho ST, et al., 2014, Intralaminar fracture toughness characterisation of woven composite laminates. Part I: Design and analysis of a compact tension (CT) specimen, ENGINEERING FRACTURE MECHANICS, Vol: 131, Pages: 349-360, ISSN: 0013-7944
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- Citations: 29
Blanco N, Trias D, Pinho ST, et al., 2014, Intralaminar fracture toughness characterisation of woven composite laminates. Part II: Experimental characterisation, ENGINEERING FRACTURE MECHANICS, Vol: 131, Pages: 361-370, ISSN: 0013-7944
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- Citations: 29
Wilmes AAR, Pinho ST, 2014, A coupled mechanical-charge/dipole molecular dynamics finite element method, with multi-scale applications to the design of graphene nano-devices, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 100, Pages: 243-276, ISSN: 0029-5981
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- Citations: 7
Grail G, Pimenta S, Pinho ST, et al., 2014, Exploring the potential of interleaving to delay catastrophic failure in unidirectional composites
Canturri Gispert C, Greenhalgh ES, Pinho ST, 2014, A methodology for realistic delamination growth prediction based on fractographic observations, American Society of Composites
Gutkin R, Pinho ST, 2014, Combining damage and friction to model compressive damage growth in fibre-reinforced composites, Journal of Composite Materials, Vol: 49, Pages: 2483-2495, ISSN: 1530-793X
A material model for unidirectional fibre-reinforced composites coupling damage to the friction acting on newly created microcracks is developed. While existing material models accounting for progressive damage assume that microcracks remain traction free under compressive load, the present model accounts for contact and friction at microcrack closure. The model is validated against experimental data and it is shown that friction can account for part of the non-linear response and the hysteresis loops typically observed in the shear response of composites. Further validation against simple crushing tests is performed and shows that the physics behind crushing is well captured.
Chen BY, Pinho ST, De Carvalho NV, et al., 2014, A floating node method for the modelling of discontinuities in composites, Engineering Fracture Mechanics, Vol: 127, Pages: 104-134, ISSN: 0013-7944
This paper presents a new method suitable for modelling multiple discontinuities within a finite element. The architecture of the proposed method is similar to that of the phantom node method (which is equivalent to XFEM with Heaviside enrichment), and the solution of it is equivalent to local remeshing within the cracked element. The new method shows several advantages over the phantom node method, such as avoiding errors in the mapping of the crack geometry from the physical to the natural space and avoiding performing integrations over only part of an element. Compared to remeshing, the proposed method enables the representation of discontinuities through relatively closed FE codes (such as user-defined elements) without modifying the initial mesh and geometry, thus making it computationally more efficient. Additionally, the proposed method is particularly suited for modelling weak and cohesive discontinuities and for the representation of complex crack networks; it can model multiple plies and interfaces of a composite laminate, and both matrix crack and delamination, within a user-defined element; the information is shared between the plies and interfaces within such an element, allowing the direct implementation of interactive mechanisms. Verification examples show that the floating node method can predict stress intensity factors and crack propagation accurately. An application example shows that the proposed method can predict well the transition from matrix cracking to delamination and the subsequent saturation of matrix crack density in a cross-ply laminate.
Pimenta S, Pinho ST, 2014, An analytical model for the translaminar fracture toughness of fibre composites with stochastic quasi-fractal fracture surfaces, Journal of the Mechanics and Physics of Solids, Vol: 66, Pages: 78-102, ISSN: 0022-5096
The translaminar fracture toughness of fibre-reinforced composites is a size-dependent property which governs the damage tolerance and failure of these materials. This paper presents the development, implementation and validation of an original analytical model to predict the tensile translaminar (fibre-dominated) toughness of composite plies and bundles, as well as the associated size effect. The model considers, as energy dissipation mechanisms, debonding and pull-out of bundles from quasi-fractal fracture surfaces; the corresponding lengths are stochastic variables predicted by the model, based on the respective bundle strength distributions and fracture mechanics. Parametric studies show that composites are toughened by stronger fibres with large strength variability, and intermediate values of interfacial toughness and friction. Predictions are validated against four different composite ply systems tested in the literature, proving the model’s ability to capture not only size effects, but also the influence of different fibres and resins.
Gigliotti L, Pinho ST, 2014, On transition regions for the simulation of the mechanical response of composite materials at multiple length-scales
A novel Mesh Superposition Technique (MST) for the transition between differently-discretized subdomains is proposed and implemented in a FE code. The interfaces between these subdomains are replaced by transition regions where the corresponding meshes are superposed. As a result, the artificial stress wave reflections and stress concentrations at these interfaces are eliminated. The MST is applied to the low-velocity impact of a projectile on a composite plate. The use of the MST allows to retrieve the same results of a fully refined model, unlike a multi-scale approach with a sudden discretization-transition. Compared to the latter, the MST uses similar computational times. Furthermore, the MST is successfully utilized for a 3D-2D coupling, achieving a 73% computational time reduction with respect to the fully 3D model, even for a small component.
Laffan MJ, Pinho ST, Robinson P, 2014, Modelling mixed-mode translaminar fracture
The work that will be presented concerns the development of a damage model intended to capture the delamination failure exhibited by notched laminates under mixed-mode in-plane loading. The model will be validated against an experimental program which uses a new type of tensile specimen, designed to trigger the desired failure mode. The advantage of the model is that it is able to accurately represent delamination without ply-by-ply modelling or the use of cohesive elements, thus greatly reducing the computational cost of simulating this failure mode.
Wilmes AAR, Pinho ST, 2014, A new multi-physics molecular dynamics finite element method for designing graphene composite nano-structures to target property specifications
A new multi-physics and multi-scale Molecular Dynamics Finite Element Method (MDFEM) is proposed, which allows for advanced mechanical and multi-physics charge-dipole MD force fields to be implemented exactly in the computationally more favourable FEM. The proposed model has produced novel mechanical and electrical charge-dipole FEM results. In particular the homogenised mechanical in-plane and bending properties of Pillared Graphene Structures (PGS) as well as the fracture toughness properties of pristine graphene have been obtained. The presented MDFEM is well suited for the optimised virtual design of a wide range of electro-mechanical nano-devices or nano-structures, e.g. PGS, to either given device property or macroscopic target specifications.
Greenhalgh ES, Canturri C, Pinho ST, 2014, A methodology for realistic delamination growth prediction based on fractographic observations
Delamination has dominated aerostructures research for several decades but the development of robust delamination growth models is yet to be achieved. The complexity of the delamination processes from even relatively simple defects (such as from an embedded disbond) means predicting progressive damage propagation beyond initiation is very difficult. Consequently, this has hindered damage tolerant design, promoting an over-reliance on 'make and test' rather than predictive models to support certification of composite aerostructures. Recent research has highlighted that two underpinning phenomena dictate delamination processes; (i) directionality and (ii) migration. The former is the observation that delaminations tend to preferentially grow parallel to the fibers whilst the latter is a consequence of when conditions force delaminations to growth oblique to the fibers. In essence, delaminations have preferential growth directions, and will propagate through the thickness of a laminate to reach ply interfaces that are conducive to such preferential growth. The work reported here describes development of a modeling methodology based on the observed delamination phenomena. The paper first outlines detailed observations stemming from a study into delamination growth from embedded defects. Based on these, the work then utilized a bespoke width tapered end-loaded split (WTELS) test method, which provided high fidelity data from which to validate model predictions. For fractographic observations the mode II/III mixity was characterized by the relative in-plane orientation of the cusps with respect to the fibers. The relationship between mode II/III mixity (as determined using a transposed VCC formulation) and delamination migration was deduced. It was demonstrated that when a critical proportion of mode III was exceeded, delamination migration ensued. The paper concludes by presenting the implications of these observations and a revised model formulation for delamination mod
Wehrkamp-Richter T, Pinho ST, Hinterhölzl R, 2014, Non-linear mechanical response of triaxial braided composites under tension
The presented work investigates the non-linear mechanical response of different 2×2 triaxial braided composites under multi-axial loading. Straight-sided specimens were subjected to incremental tensile load cycles, which included loading, unloading and reloading up to final failure. This procedure allows characterizing the evolution of plastic strain and damage and hence provides an insight into the physical phenomena acting within the material. A total of three braid architectures were investigated, comprising braiding angles of 30°, 45° and 60° loaded in the axial and transverse direction. Digital image correlation (DIC) was used to identify and locate constituent failure mechanisms and investigate surface crack propagation. Micro-sections of the specimen were analysed for the purpose of geometrical material characterization and assessment of failure mechanisms in the thickness direction.
Pinho ST, Chen BY, De Carvalho NV, et al., 2014, Accurate numerical simulation of kinking cracks in composites
This paper presents a new method suitable for modelling kinking discontinuities within a finite element framework. The proposed method effectively implements local remeshing in terms of solution, but is computationally more efficient than remeshing; it can be readily implemented in relatively closed FE codes; and it allows (sub-)elements near a crack tip to readily share information. The finite element architecture of the new method is similar to that of the phantom node method. Validation examples show that the proposed method can predict stress intensity factors and crack propagation accurately. An application example shows that the proposed method can predict the transition from matrix cracking to delamination in cross-ply composite laminates by accurately representing T-shaped cracks inside an element.
Wilmes AAR, Pinho ST, 2014, A new multi-physics Molecular Dynamics Finite Element Method for designing graphene composite nano-structures to target property specifications
A new multi-physics and multi-scale Molecular Dynamics Finite Element Method (MDFEM) is proposed, which allows for advanced mechanical and multi-physics charge-dipole MD force fields to be implemented exactly in the computationally more favourable FEM. Moreover, new generalised Periodic Boundary Conditions (PBC) are developed, which can be used to readily obtain homogenised electro-mechanical properties for low-dimensional nano-structures under generic rotational deformations. The proposed model has produced novel mechanical, electrical charge-dipole as well as concurrently coupled MD-continuum FEM results. In particular, the homogenised mechanical in-plane and bending properties of Pillared Graphene Structures (PGS) as well as the fracture toughness properties of pristine graphene have been obtained. Additionally, eigenvalue-based analyses of nano-structures' exact energy Hessian allow for more in-depth and varied modelling opportunities (e.g. buckling, frequency, modal dynamics). The presented MDFEM is well suited for the optimised virtual design of a wide range of electro-mechanical nano-devices or nano-structures, e.g. PGS, to either given device property or macroscopic target specifications.
De Carvalho NV, Ratcliffe JG, Chen BY, et al., 2014, Modeling Quasi-static and fatigue-driven delamination migration
An approach was proposed and assessed for the high-fidelity modeling of progressive damage and failure in composite materials. It combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. Delamination, matrix cracking, and migration were captured using failure and migration criteria based on fracture mechanics. Quasi-static and fatigue loading were modeled within the same overall framework. The methodology proposed was illustrated by simulating the delamination migration test, showing good agreement with the available experimental data.
Gigliotti L, Pinho ST, 2014, A mesh superposition technique for the simulation of the mechanical response of composite materials at multiple length and time-scales
A Mesh Superposition Technique (MST) for the transition between differently-discretized subdomains is proposed and implemented in an FE code. The interfaces between these subdomains are replaced by transition regions where the corresponding meshes are superposed. The MST is applied to the low-velocity impact of a projectile on a composite plate. The use of the MST allows to retrieve the same results of a fully refined model, unlike a multiscale approach with a sudden discretization-transition. The MST is successfully utilized for a macro/meso-scale coupling, achieving a computational time reduction of approximately 23% if compared to a model with a sudden discretization-transition. Furthermore, when compared to the latter, the use of the proposed MST allows to strongly reduce (≈ 60%) the extension of the area modelled at the smallest length-scale.
Pimenta S, Pinho ST, 2014, The influence of micromechanical properties and reinforcement architecture on the mechanical response of recycled composites, COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING, Vol: 56, Pages: 213-225, ISSN: 1359-835X
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- Citations: 19
Wilmes AAR, Pinho ST, 2014, A new multi-physics Molecular Dynamics Finite Element Method for designing graphene composite nano-structures to target property specifications, Publisher: DEStech Publications
A new multi-physics and multi-scale Molecular Dynamics Finite Element Method (MDFEM) is proposed, which allows for advanced mechanical and multi-physics charge-dipole MD force fields to be implemented exactly in the computationally more favourable FEM. Moreover, new generalised Periodic Boundary Conditions (PBC) are developed, which can be used to readily obtain homogenised electro-mechanical properties for low-dimensional nano-structures under generic rotational deformations. The proposed model has produced novel mechanical, electrical charge-dipole as well as concurrently coupled MD-continuum FEM results. In particular, the homogenised mechanical in-plane and bending properties of Pillared Graphene Structures (PGS) as well as the fracture toughness properties of pristine graphene have been obtained. Additionally, eigenvalue-based analyses of nano-structures' exact energy Hessian allow for more in-depth and varied modelling opportunities (e.g. buckling, frequency, modal dynamics). The presented MDFEM is well suited for the optimised virtual design of a wide range of electro-mechanical nano-devices or nano-structures, e.g. PGS, to either given device property or macroscopic target specifications.
De Carvalho NV, Ratcliffe JG, Chen BY, et al., 2014, Modeling Quasi-static and fatigue-driven delamination migration, Publisher: DEStech Publications
An approach was proposed and assessed for the high-fidelity modeling of progressive damage and failure in composite materials. It combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. Delamination, matrix cracking, and migration were captured using failure and migration criteria based on fracture mechanics. Quasi-static and fatigue loading were modeled within the same overall framework. The methodology proposed was illustrated by simulating the delamination migration test, showing good agreement with the available experimental data.
Gigliotti L, Pinho ST, 2014, A mesh superposition technique for the simulation of the mechanical response of composite materials at multiple length and time-scales, Publisher: DEStech Publications
A Mesh Superposition Technique (MST) for the transition between differently-discretized subdomains is proposed and implemented in an FE code. The interfaces between these subdomains are replaced by transition regions where the corresponding meshes are superposed. The MST is applied to the low-velocity impact of a projectile on a composite plate. The use of the MST allows to retrieve the same results of a fully refined model, unlike a multiscale approach with a sudden discretization-transition. The MST is successfully utilized for a macro/meso-scale coupling, achieving a computational time reduction of approximately 23% if compared to a model with a sudden discretization-transition. Furthermore, when compared to the latter, the use of the proposed MST allows to strongly reduce (≈ 60%) the extension of the area modelled at the smallest length-scale.
Canturri C, GREENHALGH ES, Pinho ST, et al., 2013, Delamination growth directionality and the subsequent migration processes – The key to damage tolerant design, Composites Part A: Applied Science and Manufacturing, Vol: 54, Pages: 79-87
Delamination has been recognised as one of the most challenging hurdles in using laminated composites, and has been the focus of considerable research over the last three decades. The research reported in this paper investigated the influence of ply interface on the delamination propagation processes. Experimental evidence is presented which illustrates that delamination does not grow in a self-similar manner. Instead, delaminations were shown to propagate preferentially in the direction of one ply at the delaminating interface; which ply was dictated by the orientation of the principal delaminating stress at the ply interface. In conjunction with the experimental studies, an initial methodology for modelling delamination directionality is presented. The results of this study have considerable implications for tailoring stacking sequences to promote delamination migration and thus enhance damage tolerance.
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