Papers by Author: M.H. Aliabadi

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Authors: Ivano Benedetti, M.H. Aliabadi
Abstract: A 3D grain boundary formulation is presented for the analysis of polycrystalline microstructures. The formulation is expressed in terms of intergranular displacements and tractions, that play an important role in polycrystalline micromechanics, micro-damage and micro-cracking. The artificial morphology is generated by Hardcore Voronoi tessellation, which embodies the main statistical features of polycrystalline microstructures. Each crystal is modeled as an anisotropic elastic region and the integrity of the aggregate is restored by enforcing interface continuity and equilibrium between contiguous grains. The developed technique has been applied to the numerical homogenization of cubic polycrystals and the obtained results agree well with available data.
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Authors: Ivano Benedetti, M.H. Aliabadi
Abstract: A two-scale three-dimensional approach for degradation and failure in polycrystalline materials is presented. The method involves the component level and the grain scale. The damage-induced softening at the macroscale is modelled employing an initial stress boundary element approach. The microscopic degradation is explicitly modelled associating Representative Volume Elements (RVEs) to relevant points of the macro continuum and employing a cohesive-frictional 3D grain-boundary formulation to simulate intergranular degradation and failure in the Voronoi morphology. Macro-strains are downscaled as RVEs' periodic boundary conditions, while overall macro-stresses are obtained upscaling the micro-stress field via volume averages. The comparison between effective macro-stresses for the damaged and undamaged RVEs allows to define a macroscopic measure of local material degradation. Some attention is devoted to avoiding pathological damage localization at the macro-scale. The multiscale processing algorithm is described and some preliminary results are illustrated.
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Authors: Tore Lucht, M.H. Aliabadi
Abstract: In an incremental crack extension analysis each crack increment is in general modelled with a straight extension. In order to avoid introduction of an error when the local crack growth criterion is used with an incremental formulation, each straight crack extension would have to be infinitesimal as the crack growth direction changes when the crack grows. A correction procedure to correct the extension direction of the increment can however be applied to ensure that a unique crack path is achieved with different analyses of the same problem performed with different size of the crack-extension increments. A proposed correction procedure and an reference correction procedure are demonstrated by solving a computational crack growth example. The demonstration shows that analyses of the crack path performed with big crack extensions and the proposed crack correction procedure are in excellent agreement with analyses of the crack path performed with very small crack extensions. Furthermore it is shown that the reference correction procedure has a tendency to overcorrect the crack growth direction if the stop criterion for the iterative correction procedure is not specified for each new crack growth analysis.
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Authors: Omar Bacarreza, M.H. Aliabadi
Abstract: A novel methodology for analysis of fatigue delamination growth, capable of dealing with complex delamination shapes and mixed-modes in a computationally efficient way, is proposed. It combines the VCCT to find the energy release rates and the XFEM to update the geometry during the progressive failure, thus making it very robust and computationally efficient. The methodology is demonstrated at coupon level.
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Authors: P.H. Wen, M.H. Aliabadi
Abstract: A variational technique has been developed to evaluate the static stress intensity factors of mixed mode problems with mesh free method in this paper. The stiffness is evaluated by regular domain integrals and shape functions are determined by both radial basis function (RBF) interpolation and moving least-square (MLS) method. The stress intensity factors are obtained by two boundary integrals with variation of crack length. The applications of proposed technique to two-dimensional fracture mechanics have been presented with several examples. Comparisons are made with benchmark solutions.
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Authors: P.H. Wen, M.H. Aliabadi
Abstract: . In this paper a variational technique is developed to calculate stress intensity factors with high accuracy using the element free Glerkin method. The stiffness and mass matrices are evaluated by regular domain integrals and the shape functions to determine displacements in the domain are calculated with radial basis function interpolation. Stress intensity factors were obtained by a boundary integral with a variation of crack length along the crack front. Based on a static reference solution, the transformed stress intensity factors in the Laplace space are obtained and Durbin inversion method is utilised in order to determine the physical values in time domain. The applications of proposed technique to two and three dimensional fracture mechanics are presented. Comparisons are made with benchmark solutions and indirect boundary element method.
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Authors: Luis Rodríguez-Tembleque, M.H. Aliabadi, R. Abascal
Abstract: Wear is present in all mechanical interface interaction problems –contact, fretting, orrolling-contact–, and it is one of the main reasons for inoperability in mechanical components. Thepresented work is a review of recent research carried out by the authors [1, 2, 3]. A boundary-element-based methodology to compute anisotropic wear on 3D contact, fretting, or rolling-contact conditionsis presented. Damage on the geometries of the solids and the contact pressures evolution under or-thotropic tribological properties can be predicted using this contact framework, where the formulationuses the Boundary Element Method to compute the elastic inuence coefcients. Contact problem isbased on an Augmented Lagrangian formulation, and restrictions fullment is established by a set ofprojection functions. The boundary element anisotropic wear formulation presented is illustrated withsome examples, in which some studies about the inuence of anisotropic wear on contact variablesevolution are shown.
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Authors: M. Thiene, Ugo Galvanetto, Marco Gherlone, M.H. Aliabadi
Abstract: Damage detection is a wide field of research and different approaches can be used to monitor structure integrity. Continuous monitoring of critical components is of vital importance to guarantee the safety of a structure. Variations in the dynamic response, in particular the curvature of mode shapes, are considered good indicators of the presence of possible defects. However noise, which often affects data, can lead to an erroneous calculation of the curvature, preventing the location of possible damage. The aim of this paper is to investigate the capability of the proper orthogonal decomposition (POD) to overcome noise, computing the curvature of proper orthogonal modes with a modified Laplacian operator. A numerical investigation on a cracked beam is compared to an analytical case present in literature. An extension of the mono-dimensional modified Laplacian scheme is introduced to study also plate-like structures. An experimental application on a vibrating composite plate will be presented in order to validate the numerical model.
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Authors: P.H. Wen, M.H. Aliabadi
Abstract: A computational method for the micro-mechanical material model of woven fabric composite material was developed in this paper based on a repeated unit cell approach and two smooth fibre modes were presented. The stiffness matrix was evaluated with a domain integral by the use of radial basis function interpolations without element mesh. The applications of mesh free method to evaluate woven fabric composite elastic moduli have been presented and good accuracy has been achieved compared with the results by other approaches.
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Authors: C. Di Pisa, M.H. Aliabadi, A. Young
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