Laboratoire d'Etude des Microstructures et de Mécanique des Matériaux (LEM3)
http://hdl.handle.net/10985/190
Sat, 03 Jun 2023 04:02:13 GMT2023-06-03T04:02:13ZLaboratoire d'Etude des Microstructures et de Mécanique des Matériaux (LEM3)https://sam.ensam.eu:443/bitstream/id/4f20832b-25ad-47db-bde8-29565ee8975c/
http://hdl.handle.net/10985/190
Microstructure investigation of hydrothermal damage of aged SMC composites using Micro-computed tomography and scanning electron microscopy
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 GMThttp://hdl.handle.net/10985/199342021-01-01T00:00:00ZABDESSALEM, AbirTAMBOURA, SahbiFITOUSSI, JosephDALY, Hachmi BenTCHARKHTCHI, AbbasMERAGHNI, FodilThis 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.Microstructure investigation of hydrothermal damage of aged SMC composites using Micro-computed tomography and scanning electron microscopy
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 GMThttp://hdl.handle.net/10985/197552021-01-01T00:00:00ZABDESSALEM, AbirTAMBOURA, SahbiFITOUSSI, JosephDALY, Hachmi BenTCHARKHTCHI, AbbasMERAGHNI, FodilThis 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.A new locking-free formulation for the SHB8PS solid–shell element: non-linear benchmark problems
http://hdl.handle.net/10985/10454
A new locking-free formulation for the SHB8PS solid–shell element: non-linear benchmark problems
ABED-MERAIM, Farid; COMBESCURE, Alain
In this work, a new physically stabilized and locking-free formulation of the SHB8PS element is presented. This is a solid-shell element based on a purely 3D formulation. It 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 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.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10985/104542007-01-01T00:00:00ZABED-MERAIM, FaridCOMBESCURE, AlainIn this work, a new physically stabilized and locking-free formulation of the SHB8PS element is presented. This is a solid-shell element based on a purely 3D formulation. It 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 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.Analyse de stabilité des évolutions quasi-statiques de systèmes standard dissipatifs
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 GMThttp://hdl.handle.net/10985/103702007-01-01T00:00:00ZABED-MERAIM, FaridNGUYEN, Quoc SonCette 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.Prediction of material ductility and sheet metal formability in relation to plastic instabilities
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 GMThttp://hdl.handle.net/10985/203572018-01-01T00:00:00ZABED-MERAIM, FaridIn 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.Comparison of bifurcation analysis and maximum force criteria in the prediction of necking in stretched metal sheets
http://hdl.handle.net/10985/10271
Comparison of bifurcation analysis and maximum force criteria in the prediction of necking in stretched metal sheets
ABED-MERAIM, Farid; PEERLINGS, Ron; GEERS, Marc
In the present work, diffuse necking is investigated for stretched metal sheets using two different approaches, namely bifurcation theory and maximum force principle. The contribution includes a critical analysis and a systematic comparison of their respective ability to predict necking. In particular it is shown that, in contrast to bifurcation theory, which is of quite general applicability, some restrictions are associated with the application of maximum force conditions. It is noteworthy that the well-known Swift diffuse necking criterion is recovered through bifurcation analysis. Recall that Swift’s criterion has long been attributed in the literature to the maximum force principle, while it is shown here to rather originate from the bifurcation analysis, which provides it with a sound theoretical justification.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/102712015-01-01T00:00:00ZABED-MERAIM, FaridPEERLINGS, RonGEERS, MarcIn the present work, diffuse necking is investigated for stretched metal sheets using two different approaches, namely bifurcation theory and maximum force principle. The contribution includes a critical analysis and a systematic comparison of their respective ability to predict necking. In particular it is shown that, in contrast to bifurcation theory, which is of quite general applicability, some restrictions are associated with the application of maximum force conditions. It is noteworthy that the well-known Swift diffuse necking criterion is recovered through bifurcation analysis. Recall that Swift’s criterion has long been attributed in the literature to the maximum force principle, while it is shown here to rather originate from the bifurcation analysis, which provides it with a sound theoretical justification.Assumed-strain solid-shell formulation for the six-node finite element SHB6: Evaluation on non-linear benchmark problems
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 GMThttp://hdl.handle.net/10985/101922012-01-01T00:00:00ZABED-MERAIM, FaridTRINH, Vuong-DieuCOMBESCURE, AlainThe 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.New quadratic solid-shell elements and their evaluation on popular benchmark problems
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 GMThttp://hdl.handle.net/10985/104582012-01-01T00:00:00ZABED-MERAIM, FaridTRINH, Vuong-DieuCOMBESCURE, AlainIn 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.New prismatic solid-shell element : Assumed strain formulation and hourglass mode analysis
http://hdl.handle.net/10985/10198
New prismatic solid-shell element : Assumed strain formulation and hourglass mode analysis
ABED-MERAIM, Farid; COMBESCURE, Alain
The formulation of a six-node solid-shell called SHB6, which is a linear, isoparametric element, is discussed. An eigenvalue analysis of the element stiffness matrix is first carried out. Several modifications are introduced into the formulation of the SHB6 element following the assumed strain method adopted by Belytschko and Bindeman. SHB6's coordinates and displacements are related to the nodal coordinates and displacements through the linear shape functions. Applying the simplified form of the Hu-Washizu nonlinear mixed variational principle, in which the assumed stress field is chosen to be orthogonal to the difference between the symmetric part of the displacement gradient and the assumed strain field, the formula is obtained. The newly developed SHB6 element was implemented into the finite element codes INCA and ASTER. It represents some improvement since it converges well and performs much better than the PRI6 six-node three-dimensional element in all of the benchmark problems tested.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/101982011-01-01T00:00:00ZABED-MERAIM, FaridCOMBESCURE, AlainThe formulation of a six-node solid-shell called SHB6, which is a linear, isoparametric element, is discussed. An eigenvalue analysis of the element stiffness matrix is first carried out. Several modifications are introduced into the formulation of the SHB6 element following the assumed strain method adopted by Belytschko and Bindeman. SHB6's coordinates and displacements are related to the nodal coordinates and displacements through the linear shape functions. Applying the simplified form of the Hu-Washizu nonlinear mixed variational principle, in which the assumed stress field is chosen to be orthogonal to the difference between the symmetric part of the displacement gradient and the assumed strain field, the formula is obtained. The newly developed SHB6 element was implemented into the finite element codes INCA and ASTER. It represents some improvement since it converges well and performs much better than the PRI6 six-node three-dimensional element in all of the benchmark problems tested.Validation d’une nouvelle version de l’élément solide/coque “SHB8PS” sur des cas tests non linéaires
http://hdl.handle.net/10985/10334
Validation d’une nouvelle version de l’élément solide/coque “SHB8PS” sur des cas tests non linéaires
ABED-MERAIM, Farid; COMBESCURE, Alain
L’intérêt de disposer d’éléments finis volumiques capables de modéliser des structures minces est motivé par de nombreux problèmes industriels. Ainsi, ces dernières années, plusieurs travaux ont été réalisés dans ce domaine. Ces éléments coques épaisses ont de nombreux avantages : ils sont capables de représenter le comportement de structures minces avec une bonne prise en compte des phénomènes à travers l’épaisseur et avec un gain de temps de calcul significatif, ils permettent de mailler des géométries complexes où coques et solides doivent cohabiter sans les problèmes connus de raccordement de maillages. L’élément SHB8PS a été développé dans ce sens à partir d’une formulation purement tridimensionnelle. Récemment, une nouvelle version, libre de verrouillage (en membrane et cisaillement), a été formulée et validée en linéaire. Dans la présente étude, cette version revisitée est validée à travers de nombreux cas tests non linéaires.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10985/103342007-01-01T00:00:00ZABED-MERAIM, FaridCOMBESCURE, AlainL’intérêt de disposer d’éléments finis volumiques capables de modéliser des structures minces est motivé par de nombreux problèmes industriels. Ainsi, ces dernières années, plusieurs travaux ont été réalisés dans ce domaine. Ces éléments coques épaisses ont de nombreux avantages : ils sont capables de représenter le comportement de structures minces avec une bonne prise en compte des phénomènes à travers l’épaisseur et avec un gain de temps de calcul significatif, ils permettent de mailler des géométries complexes où coques et solides doivent cohabiter sans les problèmes connus de raccordement de maillages. L’élément SHB8PS a été développé dans ce sens à partir d’une formulation purement tridimensionnelle. Récemment, une nouvelle version, libre de verrouillage (en membrane et cisaillement), a été formulée et validée en linéaire. Dans la présente étude, cette version revisitée est validée à travers de nombreux cas tests non linéaires.