Papers by Farid ABED-MERAIM
HAL (Le Centre pour la Communication Scientifique Directe), Dec 17, 2018
In many engineering applications (automotive, computer and mobile device industries, etc.), magne... more In many engineering applications (automotive, computer and mobile device industries, etc.), magnesium alloys have been widely used owing to their interesting physical and mechanical parameters. However, magnesium alloys are identified by the low ductility at room temperature, due to their strong plastic anisotropy and the yielding asymmetry between tension and compression. In this work, the ductility limit of a rolled magnesium AZ31 sheet metal at room temperature is numerically investigated. This investigation is based on the coupling between a reduced-order crystal plasticity model and the Marciniak-Kuczyński localized necking approach. This reduced-order model is used to describe the anisotropic behavior of this material taking into account the strong plastic anisotropy (e.g., yielding asymmetry between tension and compression) due to the limited number of slip systems (i.e., twinning mode). To accurately describe the plastic anisotropy due to slip and twinning modes, a combination of two separate yield functions (according to Barlat and Cazacu) is used. The coupling between the adopted constitutive framework and the Marciniak-Kuczyński instability approach is numerically implemented via an implicit algorithm. Comparisons between experimental results from the literature and numerical results obtained by using our calculation tool are carried out to validate the choice of the reducedorder crystal plasticity model.
HAL (Le Centre pour la Communication Scientifique Directe), 1999
L'étude de la stabilité d'une évolution quasi-statique visco-élastique ou visco-plastique est pro... more L'étude de la stabilité d'une évolution quasi-statique visco-élastique ou visco-plastique est proposée. Cette stabilité au sens des trajectoires est moins classique que celle relative aux équilibres et conduit à des problèmes complexes car non autonomes. Dans le cas d'un potentiel de dissipation quadratique, on montre que la définie positivité de la seconde variation de l'énergie libre totale du système assure l'uniforme et asymptotique stabilité de son évolution. Cette condition suffisante de stabilité sera comparée au critère de non-bifurcation de Hill.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 27, 2018
Springer eBooks, 2019
Due to their lightness, low stiffness and high strength, Hexagonal Closed Packed (HCP) materials ... more Due to their lightness, low stiffness and high strength, Hexagonal Closed Packed (HCP) materials are widely used in aeronautic and aerospace industries. In this paper, the ductility limit of HCP sheet materials at room temperature (25° C) is predicted by coupling the Cazacu yield function and the Marciniak and Kuczyński (MK) necking criterion. Based on transformed principal stresses, the phenomenological constitutive model of Cazacu is used to take into account the initial plastic anisotropy and strength differential (SD) effects. For plane stress and orthotropic symmetry, two linear transformations are required to use a number of anisotropy coefficients which are more suitable for practical applications. Under these circumstances, a prediction of formability for HCP sheet materials with more than one linear transformation is performed using the numerical tool Mathematica.
HAL (Le Centre pour la Communication Scientifique Directe), Apr 23, 2013
Ce travail concerne le développement d'une nouvelle famille d'éléments finis (EF) de type coques ... more Ce travail concerne le développement d'une nouvelle famille d'éléments finis (EF) de type coques volumiques quadratiques. Deux éléments seront présentés, un hexaèdre à vingt noeuds et un prisme à quinze noeuds, qui sont formulés à partir d'une approche purement tridimensionnelle. La performance de ces éléments sera montrée à travers l'analyse de problèmes structuraux variés.
Engineering With Computers, Jul 17, 2020
In numerical strategies developed for determining the effective macroscopic properties of heterog... more In numerical strategies developed for determining the effective macroscopic properties of heterogeneous media, the efficient and robust computation of macroscopic tangent moduli represents an essential step to achieve. Indeed, these tangent moduli are usually required in several numerical applications, such as the FE 2 method and the prediction of the onset of material and structural instabilities in heterogeneous media by loss of ellipticity approaches. This paper presents a comparative study of three numerical techniques for the computation of such tangent moduli in the context of periodic homogenization: the perturbation technique, the condensation technique and the fluctuation technique. The practical implementations of these techniques within ABAQUS/Standard finite element (FE) code are especially underlined. These implementations are based on the development of a set of Python scripts, which are connected to the finite element computations to handle the computation of the tangent moduli. The extension of these techniques to mechanical problems exhibiting symmetry properties is also detailed in this contribution. The reliability, accuracy and ease of implementation of these techniques are evaluated through some typical numerical examples. It is shown from this numerical and technical study that the condensation method reveals to be the most reliable and efficient. Also, this paper provides valuable reference guidelines to ABAQUS/Standard users for the determination of the homogenized tangent moduli of linear or nonlinear heterogeneous materials, such as composites, polycrystalline aggregates and porous solids.
HAL (Le Centre pour la Communication Scientifique Directe), May 13, 2019
The robust and efficient computation of the macroscopic tangent moduli represents a challenging n... more The robust and efficient computation of the macroscopic tangent moduli represents a challenging numerical task in the process of the determination of the effective macroscopic properties of heterogeneous media. The aim of the present contribution is to compare the performances of three numerical techniques for the computation of the tangent moduli via the periodic homogenization multiscale scheme: the condensation technique, the fluctuation technique and the perturbation technique. A total Lagrangian approach is adopted in the formulation of the equations governing the periodic homogenization scheme as well as in the derivation of the macroscopic tangent moduli. Through a comparative study, the condensation technique is shown to have better performance as compared to the two other techniques. Keywords-representative volume element, periodic homogenization, macroscopic tangent moduli.
HAL (Le Centre pour la Communication Scientifique Directe), Sep 7, 2011
In this contribution, the formulation of the SHB8PS continuum shell finite element is extended to... more In this contribution, the formulation of the SHB8PS continuum shell finite element is extended to anisotropic elastic-plastic behavior models with combined isotropic-kinematic hardening at large deformations. The resulting element is then implemented into the commercial implicit finite element code Abaqus/Standard via the UEL subroutine. The SHB8PS element is an eight-node, three-dimensional brick with displacements as the only degrees of freedom and a preferential direction called the thickness. A reduced integration scheme is adopted using an arbitrary number of integration points along the thickness direction and only one integration point in the other directions. The hourglass modes due to this reduced integration are controlled using a physical stabilization technique together with an assumed strain method for the elimination of locking. Therefore, the element can be used to model thin structures while providing an accurate description of the various throughthickness phenomena. Its performance is assessed through several applications involving different types of non-linearities: geometric, material and that induced by contact. Particular attention is given to springback prediction for a Numisheet benchmark problem.
HAL (Le Centre pour la Communication Scientifique Directe), Jan 28, 2008
HAL (Le Centre pour la Communication Scientifique Directe), Jan 3, 2020
HAL (Le Centre pour la Communication Scientifique Directe), 1999
HAL (Le Centre pour la Communication Scientifique Directe), May 25, 2009
-Une nouvelle formulation de l'élément solide-coque SHB6 est décrite. Il s'agit d'un élément isop... more -Une nouvelle formulation de l'élément solide-coque SHB6 est décrite. Il s'agit d'un élément isoparamétrique prismatique à 6 noeuds, interpolation linéaire et intégration réduite dans le plan moyen. Les déplacements sont les seuls d.d.l. et les points d'intégration sont distribués à travers l'épaisseur. L'analyse de hourglass a révélé qu'il n'y a pas de modes à énergie nulle à stabiliser ; néanmoins, la méthode "assumed strain" est adoptée pour améliorer sa convergence. Les performances du nouvel élément, ainsi obtenu, sont évaluées à travers des cas tests standard. Mots clés-Solide-coque SHB6, verrouillage, hourglass, méthode « assumed strain », cas tests.
HAL (Le Centre pour la Communication Scientifique Directe), Jan 28, 2008
HAL (Le Centre pour la Communication Scientifique Directe), May 28, 2008
This paper presents the development of a six-node solid-shell finite element called (SHB6) and ba... more This paper presents the development of a six-node solid-shell finite element called (SHB6) and based on the assumed strain method adopted by Belytschko et al. [2]. It is integrated with a set of five Gauss points along a special direction, denoted "thickness", and with only one point in the other in-plane directions. Its discrete gradient is modified in order to attenuate shear and membrane locking. A series of popular linear benchmark problems has been carried out with comparisons to geometrically similar, low-order three-dimensional elements.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 19, 2007
In this study, the formulation of the SHB8PS solid-shell element is reviewed in order to eliminat... more In this study, the formulation of the SHB8PS solid-shell element is reviewed in order to eliminate some persistent membrane and shear locking phenomena. The resulting physically stabilized and locking-free finite element consists in a continuum mechanics shell element based on a purely three-dimensional formulation. In fact, this is a hexahedral element with eight nodes as well as five integration points, all distributed along the "thickness" direction. Consequently, it can be used for the modelling of thin structures, while providing an accurate description of the various through-thickness phenomena. The reduced integration has been used in order to prevent some locking phenomena and to increase computational efficiency. The spurious zero-energy deformation modes due to the reduced integration are efficiently stabilized, whereas the strain components corresponding to locking modes are eliminated with a projection technique following the Enhanced Assumed Strain (EAS) method.
Fluid-structure interaction is especially challenging when thin, lightweight structures have to b... more Fluid-structure interaction is especially challenging when thin, lightweight structures have to be coupled to incompressible flows, which makes this topic still a very active area of research. In this talk we will present some of our recent advances in the development of general, robust, efficient and accurate approaches to tackle this problem class. Besides referring to classical Arbitrary-Lagrangean-Eulerian (ALE) based formulations we will mainly cover a new fixed-grid approach for fluid-structure interaction [2] that is able to avoid limitations most existing fixed-grid approaches are suffering from so far [6]. We will demonstrate our recent advances in the development of this approach and show the individual building blocks needed to empower this approach to deal with thin-walled structures as well as realistic three-dimensional fluid-structure interaction examples.
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2018
HAL (Le Centre pour la Communication Scientifique Directe), Aug 29, 2011
Le phénomène de localisation des déformations plastiques, qui apparait lors d'opérations de mise ... more Le phénomène de localisation des déformations plastiques, qui apparait lors d'opérations de mise en forme des tôles, représente l'une des principales causes de rebut des pièces produites dans l'industrie. Plusieurs critères d'instabilités ont été développés dans la littérature afin de prédire le moment d'apparition de ce phénomène. Le travail proposé ici consiste à coupler un modèle d'endommagement de type Gurson au critère de localisation de Rice. L'implantation est réalisée sous forme d'une routine utilisateur (UMAT) dans Abaqus/std via un schéma d'intégration explicite de type Runge-Kutta. Enfin, l'efficacité de la modélisation utilisée, pour la prédire les limites de formage des tôles est explorée.
HAL (Le Centre pour la Communication Scientifique Directe), May 13, 2013
-Dans cet article, la formulation de deux éléments finis de type coque volumique sera présentée. ... more -Dans cet article, la formulation de deux éléments finis de type coque volumique sera présentée. Il s'agit d'un hexaèdre à vingt noeuds et d'un prisme à quinze noeuds obtenus à partir d'une approche purement tridimensionnelle. Ce concept solide−coque procure de nombreux avantages par rapport aux éléments finis traditionnels solides ou coques, puisqu'il consiste à combiner en une seule formulation certaines bonnes caractéristiques des coques avec quelques bonnes propriétés des solides. A noter que les éléments coques volumiques ainsi obtenus possèdent une direction privilégiée, le long de laquelle les points d'intégration sont disposés, et une intégration réduite dans le plan de l'élément est adoptée pour réduire un certain nombre de verrouillages et pour augmenter l'efficacité de calcul de ces éléments. Au travers de cas tests représentatifs, les performances de ces éléments sont montrées. Mots clés-élément fini solide−coque, principe variationnel mixte, phénomènes de verrouillage, intégration réduite, modes à énergie nulle, cas tests standards
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Papers by Farid ABED-MERAIM