http://hdl.handle.net/10985/190 Sun, 05 Apr 2026 16:17:03 GMT 2026-04-05T16:17:03Z https://sam.ensam.eu:443/bitstream/id/4f20832b-25ad-47db-bde8-29565ee8975c/ http://hdl.handle.net/10985/190 http://hdl.handle.net/10985/19755 Microstructure investigation of hydrothermal damage of aged SMC composites using Micro-computed tomography and scanning electron microscopy ABDESSALEM, Abir; TAMBOURA, Sahbi; FITOUSSI, Joseph; DALY, Hachmi Ben; TCHARKHTCHI, Abbas; MERAGHNI, Fodil This paper presents an investigation on the effects of hydrothermal aging on Sheet Molding Compound (SMC) composite. Two different techniques were carried out to study the inner structure of aged SMC composite. Firstly, X-ray micro computed tomography (XμCT) was used to evaluate the changes using 3D images. The results showed cracks in all the composite structure with different shapes and volume in response to the hydrothermal conditions. The cracks results from the build up of an osmotic pressure in microcavities, which is proportional to water con­centration. However, it was not possible to quantify separately the hydrothermal induced damage in the studied SMC composite material. Therefore, the XμCT analyzes were supplemented by a microscopic study. This step has been studied in terms of crack density evolution and crack propagation rate. The results obtained by XμCT technique and SEM observations show that the damage increases continuously with time and temperature during aging. The damage was found to be located in the voids contained in the matrix at early stage of aging. Then it is mostly developed into the fiber interface in the form of fiber/matrix interfacial debonding. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/19755 2021-01-01T00:00:00Z ABDESSALEM, Abir TAMBOURA, Sahbi FITOUSSI, Joseph DALY, Hachmi Ben TCHARKHTCHI, Abbas MERAGHNI, Fodil This paper presents an investigation on the effects of hydrothermal aging on Sheet Molding Compound (SMC) composite. Two different techniques were carried out to study the inner structure of aged SMC composite. Firstly, X-ray micro computed tomography (XμCT) was used to evaluate the changes using 3D images. The results showed cracks in all the composite structure with different shapes and volume in response to the hydrothermal conditions. The cracks results from the build up of an osmotic pressure in microcavities, which is proportional to water con­centration. However, it was not possible to quantify separately the hydrothermal induced damage in the studied SMC composite material. Therefore, the XμCT analyzes were supplemented by a microscopic study. This step has been studied in terms of crack density evolution and crack propagation rate. The results obtained by XμCT technique and SEM observations show that the damage increases continuously with time and temperature during aging. The damage was found to be located in the voids contained in the matrix at early stage of aging. Then it is mostly developed into the fiber interface in the form of fiber/matrix interfacial debonding. http://hdl.handle.net/10985/19934 Microstructure investigation of hydrothermal damage of aged SMC composites using Micro-computed tomography and scanning electron microscopy ABDESSALEM, Abir; TAMBOURA, Sahbi; FITOUSSI, Joseph; DALY, Hachmi Ben; TCHARKHTCHI, Abbas; MERAGHNI, Fodil This paper presents an investigation on the effects of hydrothermal aging on Sheet Molding Compound (SMC) composite. Two different techniques were carried out to study the inner structure of aged SMC composite. Firstly, X-ray micro computed tomography (XµCT) was used to evaluate the changes using 3D images. The results showed cracks in all the composite structure with different shapes and volume in response to the hydrothermal conditions. The cracks results from the build up of an osmotic pressure in microcavities, which is proportional to water concentration. However, it was not possible to quantify separately the hydrothermal induced damage in the studied SMC composite material. Therefore, the XµCT analyzes were supplemented by a microscopic study. This step has been studied in terms of crack density evolution and crack propagation rate. The results obtained by XµCT technique and SEM observations show that the damage increases continuously with time and temperature during aging. The damage was found to be located in the voids contained in the matrix at early stage of aging. Then it is mostly developed into the fiber interface in the form of fiber/matrix interfacial debonding. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/19934 2021-01-01T00:00:00Z ABDESSALEM, Abir TAMBOURA, Sahbi FITOUSSI, Joseph DALY, Hachmi Ben TCHARKHTCHI, Abbas MERAGHNI, Fodil This paper presents an investigation on the effects of hydrothermal aging on Sheet Molding Compound (SMC) composite. Two different techniques were carried out to study the inner structure of aged SMC composite. Firstly, X-ray micro computed tomography (XµCT) was used to evaluate the changes using 3D images. The results showed cracks in all the composite structure with different shapes and volume in response to the hydrothermal conditions. The cracks results from the build up of an osmotic pressure in microcavities, which is proportional to water concentration. However, it was not possible to quantify separately the hydrothermal induced damage in the studied SMC composite material. Therefore, the XµCT analyzes were supplemented by a microscopic study. This step has been studied in terms of crack density evolution and crack propagation rate. The results obtained by XµCT technique and SEM observations show that the damage increases continuously with time and temperature during aging. The damage was found to be located in the voids contained in the matrix at early stage of aging. Then it is mostly developed into the fiber interface in the form of fiber/matrix interfacial debonding. http://hdl.handle.net/10985/10192 Assumed-strain solid-shell formulation for the six-node finite element SHB6: Evaluation on non-linear benchmark problems ABED-MERAIM, Farid; TRINH, Vuong-Dieu; COMBESCURE, Alain The current contribution proposes a six-node prismatic solid-shell denoted as (SHB6). The formulation is extended to geometric and material non-linearities, and focus will be placed on its validation on non-linear benchmark problems. The resulting derivation only involves displacement DOF, as it is based on a fully 3D approach. The motivation behind this is to allow a natural mesh connexion in problems where both structural and continuum elements need to be used. Another major interest is to complement meshes that use hexahedral finite element, especially when free mesh generation tools are employed. The assumed-strain method is combined with an in-plane one-point quadrature scheme in order to reduce both locking phenomena and computational cost. A careful analysis of possible stiffness matrix rank deficiencies shows that this reduced integration does not induce hourglass modes. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10985/10192 2012-01-01T00:00:00Z ABED-MERAIM, Farid TRINH, Vuong-Dieu COMBESCURE, Alain The current contribution proposes a six-node prismatic solid-shell denoted as (SHB6). The formulation is extended to geometric and material non-linearities, and focus will be placed on its validation on non-linear benchmark problems. The resulting derivation only involves displacement DOF, as it is based on a fully 3D approach. The motivation behind this is to allow a natural mesh connexion in problems where both structural and continuum elements need to be used. Another major interest is to complement meshes that use hexahedral finite element, especially when free mesh generation tools are employed. The assumed-strain method is combined with an in-plane one-point quadrature scheme in order to reduce both locking phenomena and computational cost. A careful analysis of possible stiffness matrix rank deficiencies shows that this reduced integration does not induce hourglass modes. http://hdl.handle.net/10985/10458 New quadratic solid-shell elements and their evaluation on popular benchmark problems ABED-MERAIM, Farid; TRINH, Vuong-Dieu; COMBESCURE, Alain In recent years, considerable effort has been devoted to the development of 3D finite elements able to model thin structures (Cho et al., 1998; Sze and Yao, 2000; Abed-Meraim and Combescure, 2002; Vu-Quoc and Tan, 2003; Chen and Wu, 2004). To this end, coupling solid and shell formulations proved to be an interesting strategy, providing continuum finite element models that can be efficiently used for structural applications. In the present work, two solid-shell elements are formulated (a 20-node and a 15-node element) based on a purely three-dimensional approach. The advantages of these elements are shown through the analysis of various structural problems. Note that their main advantage is to allow complex structural shapes to be simulated without classical problems of connecting zones meshed with different element types. These solid-shell elements have a special direction called the “thickness”, along which a set of integration points are located. Reduced integration is also used to prevent some locking phenomena and to increase computational efficiency. Focus will be placed here on linear benchmark problems, where it is shown that these solid-shell elements perform much better than their counterparts, conventional solid elements. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10985/10458 2012-01-01T00:00:00Z ABED-MERAIM, Farid TRINH, Vuong-Dieu COMBESCURE, Alain In recent years, considerable effort has been devoted to the development of 3D finite elements able to model thin structures (Cho et al., 1998; Sze and Yao, 2000; Abed-Meraim and Combescure, 2002; Vu-Quoc and Tan, 2003; Chen and Wu, 2004). To this end, coupling solid and shell formulations proved to be an interesting strategy, providing continuum finite element models that can be efficiently used for structural applications. In the present work, two solid-shell elements are formulated (a 20-node and a 15-node element) based on a purely three-dimensional approach. The advantages of these elements are shown through the analysis of various structural problems. Note that their main advantage is to allow complex structural shapes to be simulated without classical problems of connecting zones meshed with different element types. These solid-shell elements have a special direction called the “thickness”, along which a set of integration points are located. Reduced integration is also used to prevent some locking phenomena and to increase computational efficiency. Focus will be placed here on linear benchmark problems, where it is shown that these solid-shell elements perform much better than their counterparts, conventional solid elements. http://hdl.handle.net/10985/10370 Analyse de stabilité des évolutions quasi-statiques de systèmes standard dissipatifs ABED-MERAIM, Farid; NGUYEN, Quoc Son Cette étude est consacrée à la stabilité de la réponse quasi-statique de systèmes standard dissipatifs (visco-élastiques, visco-plastiques ou élasto-plastiques). Dans le cas de solides visqueux (visco-élastiques ou visco-plastiques), pour lesquels la réponse à une sollicitation est en partie différée dans le temps, l’absence d’équilibre nous suggère naturellement d’étudier la stabilité de leurs évolutions quasi-statiques. Dans le cas de solides élasto-plastiques, cette approche est motivée par le fait que, bien souvent, nous sommes en présence d’une réponse quasi-statique pour un trajet de chargement donné ; même si cette évolution représente une succession d’états d’équilibres. Cette notion de stabilité au sens des trajectoires est donc plus générale que celle d’un équilibre, plus communément étudiée en mécanique. Elle généralise d’ailleurs l’étude de stabilité d’un état d’équilibre, qui peut être vu comme un cas particulier de trajectoires. La principale difficulté rencontrée dans l’analyse de stabilité de solutions non-stationnaires vient du caractère non autonome des équations différentielles gouvernant leur évolution. Quelques résultats partiels, mais beaucoup moins généraux que le théorème de stabilité de Lyapunov pour un équilibre, peuvent être trouvés pour des systèmes linéaires non autonomes. Ainsi, l’application de la méthode de linéarisation de Lyapunov ne donne qu’une réponse partielle, car elle ne s’applique que pour des systèmes suffisamment réguliers, d’une part, et conduit à des équations non autonomes, d’autre part. Pour les solides visco-élastiques, nous appliquons cette méthode de linéarisation qui nous donne une condition de stabilité asymptotique basée sur la définie positivité de la seconde variation de l’énergie. Pour des solides à potentiel de dissipation moins régulier, élasto-plastiques ou visco-plastiques, une approche par estimations directes est appliquée et nous donne une condition suffisante de stabilité basée sur la positivité de la seconde variation de l’énergie le long de la réponse considérée. Ce critère unifié représente une extension du critère de seconde variation, bien connu en théorie de stabilité élastique, au cas de stabilité d’évolutions quasi-statiques. Plus récemment, une version étendue de l’équation d’évolution de Biot a été considérée pour discuter la stabilité d’une réponse quasi-statique dans le cadre de matériaux standard généralisés. On montre également que pour les théories à gradients cette équation reste valide, puisque les gradients d’ordres supérieurs peuvent être introduits dans les expressions des deux potentiels (énergie libre et dissipation). Ainsi, l’étude de stabilité d’une évolution quasi-statique gouvernée par l’équation de Biot étendue a été discutée, nous permettant de faire une généralisation du critère de stabilité de seconde variation de l’énergie. Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/10985/10370 2007-01-01T00:00:00Z ABED-MERAIM, Farid NGUYEN, Quoc Son Cette étude est consacrée à la stabilité de la réponse quasi-statique de systèmes standard dissipatifs (visco-élastiques, visco-plastiques ou élasto-plastiques). Dans le cas de solides visqueux (visco-élastiques ou visco-plastiques), pour lesquels la réponse à une sollicitation est en partie différée dans le temps, l’absence d’équilibre nous suggère naturellement d’étudier la stabilité de leurs évolutions quasi-statiques. Dans le cas de solides élasto-plastiques, cette approche est motivée par le fait que, bien souvent, nous sommes en présence d’une réponse quasi-statique pour un trajet de chargement donné ; même si cette évolution représente une succession d’états d’équilibres. Cette notion de stabilité au sens des trajectoires est donc plus générale que celle d’un équilibre, plus communément étudiée en mécanique. Elle généralise d’ailleurs l’étude de stabilité d’un état d’équilibre, qui peut être vu comme un cas particulier de trajectoires. La principale difficulté rencontrée dans l’analyse de stabilité de solutions non-stationnaires vient du caractère non autonome des équations différentielles gouvernant leur évolution. Quelques résultats partiels, mais beaucoup moins généraux que le théorème de stabilité de Lyapunov pour un équilibre, peuvent être trouvés pour des systèmes linéaires non autonomes. Ainsi, l’application de la méthode de linéarisation de Lyapunov ne donne qu’une réponse partielle, car elle ne s’applique que pour des systèmes suffisamment réguliers, d’une part, et conduit à des équations non autonomes, d’autre part. Pour les solides visco-élastiques, nous appliquons cette méthode de linéarisation qui nous donne une condition de stabilité asymptotique basée sur la définie positivité de la seconde variation de l’énergie. Pour des solides à potentiel de dissipation moins régulier, élasto-plastiques ou visco-plastiques, une approche par estimations directes est appliquée et nous donne une condition suffisante de stabilité basée sur la positivité de la seconde variation de l’énergie le long de la réponse considérée. Ce critère unifié représente une extension du critère de seconde variation, bien connu en théorie de stabilité élastique, au cas de stabilité d’évolutions quasi-statiques. Plus récemment, une version étendue de l’équation d’évolution de Biot a été considérée pour discuter la stabilité d’une réponse quasi-statique dans le cadre de matériaux standard généralisés. On montre également que pour les théories à gradients cette équation reste valide, puisque les gradients d’ordres supérieurs peuvent être introduits dans les expressions des deux potentiels (énergie libre et dissipation). Ainsi, l’étude de stabilité d’une évolution quasi-statique gouvernée par l’équation de Biot étendue a été discutée, nous permettant de faire une généralisation du critère de stabilité de seconde variation de l’énergie. http://hdl.handle.net/10985/10335 A quasi-static stability analysis for Biot’s equation and standard dissipative systems ABED-MERAIM, Farid; NGUYEN, Quoc Son In this paper, an extended version of Biot's differential equation is considered in order to discuss the quasi-static stability of a response for a solid in the framework of generalized standard materials. The same equation also holds for gradient theories since the gradients of arbitrary order of the state variables and of their rates can be introduced in the expression of the energy and of the dissipation potentials. The stability of a quasi-static response of a system governed by Biot's equations is discussed. Two approaches are considered, by direct estimates and by linearizations. The approach by direct estimates can be applied in visco-plasticity as well as in plasticity. A sufficient condition of stability is proposed and based upon the positivity of the second variation of energy along the considered response. This is an extension of the criterion of second variation, well known in elastic buckling, into the study of the stability of a response. The linearization approach is available only for smooth dissipation potentials, i.e. for the study of visco-elastic solids and leads to a result on asymptotic stability. The paper is illustrated by a simple example. Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/10985/10335 2007-01-01T00:00:00Z ABED-MERAIM, Farid NGUYEN, Quoc Son In this paper, an extended version of Biot's differential equation is considered in order to discuss the quasi-static stability of a response for a solid in the framework of generalized standard materials. The same equation also holds for gradient theories since the gradients of arbitrary order of the state variables and of their rates can be introduced in the expression of the energy and of the dissipation potentials. The stability of a quasi-static response of a system governed by Biot's equations is discussed. Two approaches are considered, by direct estimates and by linearizations. The approach by direct estimates can be applied in visco-plasticity as well as in plasticity. A sufficient condition of stability is proposed and based upon the positivity of the second variation of energy along the considered response. This is an extension of the criterion of second variation, well known in elastic buckling, into the study of the stability of a response. The linearization approach is available only for smooth dissipation potentials, i.e. for the study of visco-elastic solids and leads to a result on asymptotic stability. The paper is illustrated by a simple example. http://hdl.handle.net/10985/20357 Prediction of material ductility and sheet metal formability in relation to plastic instabilities ABED-MERAIM, Farid In the literature dealing with plastic instabilities in general, many instability criteria have been developed, and some of them have been extensively applied to sheet metals to investigate their formability limits. Exhaustively reviewing these criteria is difficult, considering the multitude of variants deriving from some of these approaches. However, a review of the literature reveals that thecriteria can be classified into at least four distinct categories depending on their fundamental basis and theoretical or physical background. For stretched sheet metals, two forms of necking, namely diffuse and localized necking, may occur. It has been shown that diffuse necking occurs prior to localized necking, and it is now well recognized that the maximum allowable straining in sheet metal forming is determined by localized necking. For this reason, forming limit diagrams (FLDs) are commonly determined at localization in most of the current formability approaches. Early instability criteria were based on the maximum force principle (Considère, 1885), and its two-dimensional extension (Swift, 1952) for application to sheet metals. In their original form, these criteria were intended to allow for the prediction of diffuse necking. Later, these maximum-force-based criteria were extended to the prediction of localized necking, and some enhanced versions were developed to account for some key features (Hora, 1996; Mattiason, 2006). Note also that Hill’s zero-extension criterion (Hill, 1952), which predicts localized necking on the left-hand side of the FLD, was developed during the same time as Swift’s diffuse necking criterion. Another approach, which postulates a pre-existing defect in the material sheet, was proposed by Marciniak and Kuczynski (1967). This M–K model can be regarded as a complementary approach to Hill’s zero-extension criterion, which is only applicable to the left-hand side of the FLD, as no zero-extension direction exists for positive biaxial stretching. However, because localized necking in biaxial stretching is observed in practice, a pre-existing defect has to be introduced in the M–K model to capture this phenomenon, which may provide some justification for this imperfection theory. In addition to the aforementioned engineering approaches, another category of plastic instability criteria was developed based on a more fundamental background. Drucker and Hill’s theory (Drucker, 1956; Hill, 1958), also referred to as the general bifurcation criterion, represents another class of approaches for necking prediction. This condition of positiveness of the second-order work provides a lower bound for all of the bifurcation-based criteria in this category. In the same class of criteria, Valanis (1989) suggested using a limit-point bifurcation criterion, which is less conservative than the general bifurcation criterion but coincides with it within the framework of associative plasticity and small strains. With regard to localized modes of deformation, Stören and Rice (1975) proposed a bifurcation criterion characterized by the singularity of the acoustic tensor, also known as discontinuous bifurcation. It has been shown that this criterion corresponds to the loss of ellipticity of the partial differential equations governing the associated boundary value problem. In the same manner, some authors (e.g., Bigoni and Hueckel, 1991) have suggested the use of the more conservative condition of strong ellipticity, which has been shown to coincide with Rice’s criterion within the framework of associative plasticity and small strains. This condition of loss of strong ellipticity is also a special case of Drucker’s general bifurcation criterion, in which the bifurcation mode is restricted to localized (compatible) deformation modes. From this overview of the various approaches pertaining to strain localization criteria and indicators, an interesting observation can be made. While M–K analysis has been widely used in the literature, few applications of Rice’s ellipticity loss theory, mainly restricted to plane-stress assumptions, particular loading paths, and simple behavior models, have been attempted in sheet metal forming for quantifying metals in terms of their formability. In this presentation, various results relating to the prediction of plastic flow localization based on bifurcation theory will be shown for different constitutive modeling approaches. Also, comparisons will be conducted for the different approaches of plastic instability prediction. For some approaches, a classification of the criteria will be established, in terms of their conservative nature of prediction. Moreover, similarities or relationships between some approaches and associated criteria will be emphasized, whenever their underlying formulations make it possible. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10985/20357 2018-01-01T00:00:00Z ABED-MERAIM, Farid In the literature dealing with plastic instabilities in general, many instability criteria have been developed, and some of them have been extensively applied to sheet metals to investigate their formability limits. Exhaustively reviewing these criteria is difficult, considering the multitude of variants deriving from some of these approaches. However, a review of the literature reveals that thecriteria can be classified into at least four distinct categories depending on their fundamental basis and theoretical or physical background. For stretched sheet metals, two forms of necking, namely diffuse and localized necking, may occur. It has been shown that diffuse necking occurs prior to localized necking, and it is now well recognized that the maximum allowable straining in sheet metal forming is determined by localized necking. For this reason, forming limit diagrams (FLDs) are commonly determined at localization in most of the current formability approaches. Early instability criteria were based on the maximum force principle (Considère, 1885), and its two-dimensional extension (Swift, 1952) for application to sheet metals. In their original form, these criteria were intended to allow for the prediction of diffuse necking. Later, these maximum-force-based criteria were extended to the prediction of localized necking, and some enhanced versions were developed to account for some key features (Hora, 1996; Mattiason, 2006). Note also that Hill’s zero-extension criterion (Hill, 1952), which predicts localized necking on the left-hand side of the FLD, was developed during the same time as Swift’s diffuse necking criterion. Another approach, which postulates a pre-existing defect in the material sheet, was proposed by Marciniak and Kuczynski (1967). This M–K model can be regarded as a complementary approach to Hill’s zero-extension criterion, which is only applicable to the left-hand side of the FLD, as no zero-extension direction exists for positive biaxial stretching. However, because localized necking in biaxial stretching is observed in practice, a pre-existing defect has to be introduced in the M–K model to capture this phenomenon, which may provide some justification for this imperfection theory. In addition to the aforementioned engineering approaches, another category of plastic instability criteria was developed based on a more fundamental background. Drucker and Hill’s theory (Drucker, 1956; Hill, 1958), also referred to as the general bifurcation criterion, represents another class of approaches for necking prediction. This condition of positiveness of the second-order work provides a lower bound for all of the bifurcation-based criteria in this category. In the same class of criteria, Valanis (1989) suggested using a limit-point bifurcation criterion, which is less conservative than the general bifurcation criterion but coincides with it within the framework of associative plasticity and small strains. With regard to localized modes of deformation, Stören and Rice (1975) proposed a bifurcation criterion characterized by the singularity of the acoustic tensor, also known as discontinuous bifurcation. It has been shown that this criterion corresponds to the loss of ellipticity of the partial differential equations governing the associated boundary value problem. In the same manner, some authors (e.g., Bigoni and Hueckel, 1991) have suggested the use of the more conservative condition of strong ellipticity, which has been shown to coincide with Rice’s criterion within the framework of associative plasticity and small strains. This condition of loss of strong ellipticity is also a special case of Drucker’s general bifurcation criterion, in which the bifurcation mode is restricted to localized (compatible) deformation modes. From this overview of the various approaches pertaining to strain localization criteria and indicators, an interesting observation can be made. While M–K analysis has been widely used in the literature, few applications of Rice’s ellipticity loss theory, mainly restricted to plane-stress assumptions, particular loading paths, and simple behavior models, have been attempted in sheet metal forming for quantifying metals in terms of their formability. In this presentation, various results relating to the prediction of plastic flow localization based on bifurcation theory will be shown for different constitutive modeling approaches. Also, comparisons will be conducted for the different approaches of plastic instability prediction. For some approaches, a classification of the criteria will be established, in terms of their conservative nature of prediction. Moreover, similarities or relationships between some approaches and associated criteria will be emphasized, whenever their underlying formulations make it possible. http://hdl.handle.net/10985/10204 An improved assumed strain solid-shell element formulation with physical stabilization for geometric non-linear applications and elastic-plastic stability analysis ABED-MERAIM, Farid; COMBESCURE, Alain In this paper, the earlier formulation of the SHB8PS finite element is revised in order to eliminate some persistent membrane and shear locking phenomena. This new formulation consists of a solid-shell element based on a purely three-dimensional approach. More specifically, the element has eight nodes, with displacements as the only degrees of freedom, as well as an arbitrary number of integration points, with a minimum number of two, distributed along the 'thickness' direction. The resulting derivation, which is computationally efficient, can then be used for the modeling of thin structures, while providing an accurate description of the various through-thickness phenomena. A reduced integration scheme is used to prevent some locking phenomena and to achieve an attractive, low-cost formulation. The spurious zero-energy modes due to this in-plane one-point quadrature are efficiently controlled using a physical stabilization procedure, whereas the strain components corresponding to locking modes are eliminated with a projection technique following the assumed strain method. In addition to the extended and detailed formulation presented in this paper, particular attention has been focused on providing full justification regarding the identification of hourglass modes in relation to rank deficiencies. Moreover, an attempt has been made to provide a sound foundation to the derivation of the co-rotational coordinate frame, on which the calculations of the stabilization stiffness matrix and internal load vector are based. Finally to assess the effectiveness and performance of this new formulation, a set of popular benchmark problems is investigated, involving geometric non-linear analyses as well as elastic-plastic stability issues. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/10985/10204 2009-01-01T00:00:00Z ABED-MERAIM, Farid COMBESCURE, Alain In this paper, the earlier formulation of the SHB8PS finite element is revised in order to eliminate some persistent membrane and shear locking phenomena. This new formulation consists of a solid-shell element based on a purely three-dimensional approach. More specifically, the element has eight nodes, with displacements as the only degrees of freedom, as well as an arbitrary number of integration points, with a minimum number of two, distributed along the 'thickness' direction. The resulting derivation, which is computationally efficient, can then be used for the modeling of thin structures, while providing an accurate description of the various through-thickness phenomena. A reduced integration scheme is used to prevent some locking phenomena and to achieve an attractive, low-cost formulation. The spurious zero-energy modes due to this in-plane one-point quadrature are efficiently controlled using a physical stabilization procedure, whereas the strain components corresponding to locking modes are eliminated with a projection technique following the assumed strain method. In addition to the extended and detailed formulation presented in this paper, particular attention has been focused on providing full justification regarding the identification of hourglass modes in relation to rank deficiencies. Moreover, an attempt has been made to provide a sound foundation to the derivation of the co-rotational coordinate frame, on which the calculations of the stabilization stiffness matrix and internal load vector are based. Finally to assess the effectiveness and performance of this new formulation, a set of popular benchmark problems is investigated, involving geometric non-linear analyses as well as elastic-plastic stability issues. http://hdl.handle.net/10985/10396 Investigation and comparative analysis of plastic instability criteria: Application to forming limit diagrams ABED-MERAIM, Farid; BALAN, Tudor; ALTMEYER, Guillaume The prediction of forming limit diagrams (FLDs) is of significant interest to the sheet metal forming industry. Although a large variety of plastic instability criteria have been developed during the previous decades, there is still a lack of comparison of their respective theoretical bases. The aim of this paper is to present the theoretical formulations of a representative selection of diffuse necking and strain localization criteria based on the maximum force principle, the Marciniak-Kuczyński method and the bifurcation approach. The theoretical foundations and underlying assumptions for each criterion are specified prior to their application to several materials to determine the associated FLDs. The capability of the criteria to predict the formability of thin metal sheets is discussed and a classification of some of the criteria is attempted according to their order of occurrence in terms of the localization prediction. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/10396 2014-01-01T00:00:00Z ABED-MERAIM, Farid BALAN, Tudor ALTMEYER, Guillaume The prediction of forming limit diagrams (FLDs) is of significant interest to the sheet metal forming industry. Although a large variety of plastic instability criteria have been developed during the previous decades, there is still a lack of comparison of their respective theoretical bases. The aim of this paper is to present the theoretical formulations of a representative selection of diffuse necking and strain localization criteria based on the maximum force principle, the Marciniak-Kuczyński method and the bifurcation approach. The theoretical foundations and underlying assumptions for each criterion are specified prior to their application to several materials to determine the associated FLDs. The capability of the criteria to predict the formability of thin metal sheets is discussed and a classification of some of the criteria is attempted according to their order of occurrence in terms of the localization prediction. http://hdl.handle.net/10985/10240 A physically stabilized and locking-free formulation of the (SHB8PS) solid-shell element ABED-MERAIM, Farid; COMBESCURE, Alain In this work, the formulation of the SHB8PS finite element is reviewed in order to eliminate some persistent membrane and shear locking phenomena. This is a solid-shell element based on a purely three-dimensional formulation. In fact, the element has eight nodes as well as five integration points, all distributed along the "thickness" direction. Consequently, it can be used for the modeling 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 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.; Dans cette étude, la formulation de l’élément SHB8PS est revisitée dans le but d’éliminer certains blocages persistants en membrane et cisaillement transverse. Rappelons que cet élément est de type coque épaisse obtenue à partir d’une formulation purement tridimensionnelle. Il possède donc huit noeuds et cinq points d’intégration répartis selon la direction de l’épaisseur. Ainsi, il peut être utilisé pour modéliser des structures minces tout en prenant correctement en compte les différents phénomènes à travers l’épaisseur. Afin d’améliorer ses performances de calcul et d’éviter certains blocages, l’intégration réduite a été employée. Les modes de hourglass générés par la sous-intégration sont efficacement stabilisés et les modes de blocages persistants sont éliminés par une technique de projection pouvant se mettre sous le formalisme de la « méthode de déformation postulée ». Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/10985/10240 2007-01-01T00:00:00Z ABED-MERAIM, Farid COMBESCURE, Alain In this work, the formulation of the SHB8PS finite element is reviewed in order to eliminate some persistent membrane and shear locking phenomena. This is a solid-shell element based on a purely three-dimensional formulation. In fact, the element has eight nodes as well as five integration points, all distributed along the "thickness" direction. Consequently, it can be used for the modeling 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 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. Dans cette étude, la formulation de l’élément SHB8PS est revisitée dans le but d’éliminer certains blocages persistants en membrane et cisaillement transverse. Rappelons que cet élément est de type coque épaisse obtenue à partir d’une formulation purement tridimensionnelle. Il possède donc huit noeuds et cinq points d’intégration répartis selon la direction de l’épaisseur. Ainsi, il peut être utilisé pour modéliser des structures minces tout en prenant correctement en compte les différents phénomènes à travers l’épaisseur. Afin d’améliorer ses performances de calcul et d’éviter certains blocages, l’intégration réduite a été employée. Les modes de hourglass générés par la sous-intégration sont efficacement stabilisés et les modes de blocages persistants sont éliminés par une technique de projection pouvant se mettre sous le formalisme de la « méthode de déformation postulée ».