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SAM captures, stores, indexes, preserves, and distributes digital research material.Mon, 09 Jul 2018 06:02:58 GMT2018-07-09T06:02:58ZNew prismatic solid-shell element : Assumed strain formulation and hourglass mode analysis
http://hdl.handle.net/10985/10198
ABED-MERAIM, Farid; COMBESCURE, Alain
Structural Engineering and Mechanics
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.
Tue, 25 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/101982011-01-25T00:00:00ZABED-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.Contact of a Finger on Rigid Surfaces and Textiles: Friction Coefficient and Induced Vibrations
http://hdl.handle.net/10985/8982
FAGIANI, Ramona; MASSI, Francesco; CHATELET, Eric; COSTES, Jean-Philippe; BERTHIER, Yves
Tribology Letters
The tactile information about object surfaces is
obtained through perceived contact stresses and frictioninduced
vibrations generated by the relative motion
between the fingertip and the touched object. The friction
forces affect the skin stress-state distribution during surface
scanning, while the sliding contact generates vibrations that
propagate in the finger skin activating the receptors (mechanoreceptors)
and allowing the brain to identify objects
and perceive information about their properties. In this
article, the friction coefficient between a real human finger
and both rigid surfaces and fabrics is retrieved as a function
of the contact parameters (load and scanning speed). Then,
the analysis of the vibration spectra is carried out to
investigate the features of the induced vibrations, measured
on the fingernail, as a function of surface textures and
contact parameters. While the friction coefficient measurements
on rigid surfaces agree with empirical laws
found in literature, the behaviour of the friction coefficient
when touching a fabric is more complex, and is mainly the
function of the textile constructional properties. Results
show that frequency spectrum distribution, when touching
a rigid surface, is mainly determined by the relative
geometry of the two contact surfaces and by the contact
parameters. On the contrary, when scanning a fabric, the
structure and the deformation of the textile itself largely
affect the spectrum of the induced vibration. Finally, some
major features of the measured vibrations (frequency distribution
and amplitude) are found to be representative of
tactile perception compared to psychophysical and neurophysiologic
works in literature.
Tue, 12 Jun 2012 00:00:00 GMThttp://hdl.handle.net/10985/89822012-06-12T00:00:00ZFAGIANI, RamonaMASSI, FrancescoCHATELET, EricCOSTES, Jean-PhilippeBERTHIER, YvesThe tactile information about object surfaces is
obtained through perceived contact stresses and frictioninduced
vibrations generated by the relative motion
between the fingertip and the touched object. The friction
forces affect the skin stress-state distribution during surface
scanning, while the sliding contact generates vibrations that
propagate in the finger skin activating the receptors (mechanoreceptors)
and allowing the brain to identify objects
and perceive information about their properties. In this
article, the friction coefficient between a real human finger
and both rigid surfaces and fabrics is retrieved as a function
of the contact parameters (load and scanning speed). Then,
the analysis of the vibration spectra is carried out to
investigate the features of the induced vibrations, measured
on the fingernail, as a function of surface textures and
contact parameters. While the friction coefficient measurements
on rigid surfaces agree with empirical laws
found in literature, the behaviour of the friction coefficient
when touching a fabric is more complex, and is mainly the
function of the textile constructional properties. Results
show that frequency spectrum distribution, when touching
a rigid surface, is mainly determined by the relative
geometry of the two contact surfaces and by the contact
parameters. On the contrary, when scanning a fabric, the
structure and the deformation of the textile itself largely
affect the spectrum of the induced vibration. Finally, some
major features of the measured vibrations (frequency distribution
and amplitude) are found to be representative of
tactile perception compared to psychophysical and neurophysiologic
works in literature.Analysis of green wood chip formation mechanisms at high cutting speed
http://hdl.handle.net/10985/10218
PFEIFFER, Renaud; MAIGRE, Hubert; COLLET, Robert; DENAUD, Louis; POT, Guillaume
During the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability.
Thus, this study aims at better understanding and predicting chips production in wood milling.
The different mechanisms of their formation are studied through orthogonal cutting experiments at high cutting speed. Chipping observations are carried out on a Chardin's pendulum. This experimental setup, similar to a Charpy's pendulum, was designed to measure cutting forces in sawing. A piezoelectric force transducer records the cutting forces. It is synchronized with a high speed camera to observe the formation of chips. In this experimental campaign, wood specimens are machined with fresh and saturated beech and Douglas fir.
Within these conditions, ejection of free water inside wood can be observed during fragmentation, particularly on saturated beech. As previously seen in quasi-static experiments, chip thickness is proportional to the nominal cut thickness. Moreover, the grain orientation has a great influence on the cutting mechanisms, so as the nominal cut and the grow circles widths. Digital image correlation is carried out in order to observe the strains fields during the cut for different cutting mechanisms.
This chip fragmentation study finally allows the improvement of the cutting conditions in rough milling for slabber manufacturers.
Sun, 14 Jun 2015 00:00:00 GMThttp://hdl.handle.net/10985/102182015-06-14T00:00:00ZPFEIFFER, RenaudMAIGRE, HubertCOLLET, RobertDENAUD, LouisPOT, GuillaumeDuring the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability.
Thus, this study aims at better understanding and predicting chips production in wood milling.
The different mechanisms of their formation are studied through orthogonal cutting experiments at high cutting speed. Chipping observations are carried out on a Chardin's pendulum. This experimental setup, similar to a Charpy's pendulum, was designed to measure cutting forces in sawing. A piezoelectric force transducer records the cutting forces. It is synchronized with a high speed camera to observe the formation of chips. In this experimental campaign, wood specimens are machined with fresh and saturated beech and Douglas fir.
Within these conditions, ejection of free water inside wood can be observed during fragmentation, particularly on saturated beech. As previously seen in quasi-static experiments, chip thickness is proportional to the nominal cut thickness. Moreover, the grain orientation has a great influence on the cutting mechanisms, so as the nominal cut and the grow circles widths. Digital image correlation is carried out in order to observe the strains fields during the cut for different cutting mechanisms.
This chip fragmentation study finally allows the improvement of the cutting conditions in rough milling for slabber manufacturers.Formulation d’éléments finis quadratiques de type solide-coque et leur évaluation sur des cas tests standards
http://hdl.handle.net/10985/10356
TRINH, Vuong-Dieu; ABED-MERAIM, Farid; COMBESCURE, Alain
Dans cet article, la formulation de deux éléments finis de type coque volumique sera présentée. Il s’agit d’un hexaèdre à vingt nœuds et d’un prisme à quinze nœuds 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.
Mon, 13 May 2013 00:00:00 GMThttp://hdl.handle.net/10985/103562013-05-13T00:00:00ZTRINH, Vuong-DieuABED-MERAIM, FaridCOMBESCURE, AlainDans cet article, la formulation de deux éléments finis de type coque volumique sera présentée. Il s’agit d’un hexaèdre à vingt nœuds et d’un prisme à quinze nœuds 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.Développement d’un nouvel élément fini prismatique « SHB6 » de type solide–coque : formulation et évaluation à travers des cas tests
http://hdl.handle.net/10985/10441
TRINH, Vuong-Dieu; ABED-MERAIM, Farid; COMBESCURE, Alain
Cet article décrit le développement d’un nouvel élément fini prismatique SHB6 de type solide-coque, obtenu à partir d’une formulation purement tridimensionnelle. Cet élément possède six nœuds et cinq points d’intégration répartis selon la direction de l’épaisseur. L’objectif étant d’avoir des éléments à géométrie volumique capables de 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. On montre d’abord que cette sous-intégration ne génère pas de modes de hourglass. Ensuite, on met en évidence que l’élément SHB6, sans aucune modification ou projection de son opérateur gradient discrétisé, peut souffrir de certains verrouillages de type cisaillement transverse ou membrane.; This paper presents the development of a new solid-shell finite element “SHB6” derived from a purely three-dimensional formulation. It has six nodes as well as five integration points, all distributed along the “thickness” direction. The main goal of this research is to develop low-order solid elements that are able to model thin structures while correctly taking into account the various through-thickness phenomena. In order to improve its calculation performances and to prevent some locking phenomena, reduced integration was used. We demonstrate first that there are no hourglass modes generated by the reduced integration. On the other hand, we show that, without any modification or projection of its discrete gradient operator, the SHB6 element could suffer from some membrane and shear locking phenomena.
Mon, 21 May 2007 00:00:00 GMThttp://hdl.handle.net/10985/104412007-05-21T00:00:00ZTRINH, Vuong-DieuABED-MERAIM, FaridCOMBESCURE, AlainCet article décrit le développement d’un nouvel élément fini prismatique SHB6 de type solide-coque, obtenu à partir d’une formulation purement tridimensionnelle. Cet élément possède six nœuds et cinq points d’intégration répartis selon la direction de l’épaisseur. L’objectif étant d’avoir des éléments à géométrie volumique capables de 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. On montre d’abord que cette sous-intégration ne génère pas de modes de hourglass. Ensuite, on met en évidence que l’élément SHB6, sans aucune modification ou projection de son opérateur gradient discrétisé, peut souffrir de certains verrouillages de type cisaillement transverse ou membrane.
This paper presents the development of a new solid-shell finite element “SHB6” derived from a purely three-dimensional formulation. It has six nodes as well as five integration points, all distributed along the “thickness” direction. The main goal of this research is to develop low-order solid elements that are able to model thin structures while correctly taking into account the various through-thickness phenomena. In order to improve its calculation performances and to prevent some locking phenomena, reduced integration was used. We demonstrate first that there are no hourglass modes generated by the reduced integration. On the other hand, we show that, without any modification or projection of its discrete gradient operator, the SHB6 element could suffer from some membrane and shear locking phenomena.New quadratic solid-shell elements and their evaluation on popular benchmark problems
http://hdl.handle.net/10985/10458
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.
Mon, 25 Jun 2012 00:00:00 GMThttp://hdl.handle.net/10985/104582012-06-25T00:00:00ZABED-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.Les simulations numériques de la mise en forme sont-elles fiables ?
http://hdl.handle.net/10985/10475
COMBESCURE, Alain; BRUNET, Michel; MAUREL, Bertrand; NEFUSSI, Germaine; ABED-MERAIM, Farid
Cette présentation porte un regard critique quant aux capacités des simulations actuelles (utilisant les logiciels de calcul par éléments finis disponibles) à prédire de manière fiable les phénomènes observés lors de la mise en forme des matériaux métalliques et dans les procédés de fabrication associés.
Mon, 28 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10985/104752008-01-28T00:00:00ZCOMBESCURE, AlainBRUNET, MichelMAUREL, BertrandNEFUSSI, GermaineABED-MERAIM, FaridCette présentation porte un regard critique quant aux capacités des simulations actuelles (utilisant les logiciels de calcul par éléments finis disponibles) à prédire de manière fiable les phénomènes observés lors de la mise en forme des matériaux métalliques et dans les procédés de fabrication associés.Space–time proper generalized decompositions for the resolution of transient elastodynamic models
http://hdl.handle.net/10985/8461
BOUCINHA, Lucas; GRAVOUIL, Anthony; AMMAR, Amine
Computer Methods in Applied Mechanics and Engineering
In this paper, we investigate ability of proper generalized decomposition (PGD) to solve transient elastodynamic models in space–time domain. Classical methods use time integration schemes and an incremental resolution process. We propose here to use standard time integration methods in a non-incremental strategy. As a result, PGD gives a separated representation of the space–time solution as a sum of tensorial products of space and time vectors, that we interpret as space–time modes. Recent time integration schemes are based on multi-field formulations. In this case, separated representation can be constructed using state vectors in space and same vectors in time. However, we have experienced bad convergence order using this decomposition. Furthermore, temporal approximation must be the same for all fields. Thus, we propose an extension of classical separated representation for multi-field problems. This multi-field PGD (MF-PGD) uses space and time vectors that are different for each field. Calculation of decomposition is done using a monolithic approach in space and time, potentially allowing the use of different approximations in space and time. Finally, several simulations are performed with the transient elastodynamic problem with one dimension in space. Different approximations in time are investigated: Newmark scheme, single field time discontinuous Galerkin method and two fields time continuous and discontinuous Galerkin methods.
Fri, 01 Mar 2013 00:00:00 GMThttp://hdl.handle.net/10985/84612013-03-01T00:00:00ZBOUCINHA, LucasGRAVOUIL, AnthonyAMMAR, AmineIn this paper, we investigate ability of proper generalized decomposition (PGD) to solve transient elastodynamic models in space–time domain. Classical methods use time integration schemes and an incremental resolution process. We propose here to use standard time integration methods in a non-incremental strategy. As a result, PGD gives a separated representation of the space–time solution as a sum of tensorial products of space and time vectors, that we interpret as space–time modes. Recent time integration schemes are based on multi-field formulations. In this case, separated representation can be constructed using state vectors in space and same vectors in time. However, we have experienced bad convergence order using this decomposition. Furthermore, temporal approximation must be the same for all fields. Thus, we propose an extension of classical separated representation for multi-field problems. This multi-field PGD (MF-PGD) uses space and time vectors that are different for each field. Calculation of decomposition is done using a monolithic approach in space and time, potentially allowing the use of different approximations in space and time. Finally, several simulations are performed with the transient elastodynamic problem with one dimension in space. Different approximations in time are investigated: Newmark scheme, single field time discontinuous Galerkin method and two fields time continuous and discontinuous Galerkin methods.Ideal minimal residual-based proper generalized decomposition for non-symmetric multi-field models – Application to transient elastodynamics in space-time domain
http://hdl.handle.net/10985/8456
BOUCINHA, Lucas; AMMAR, Amine; GRAVOUIL, Anthony; NOUY, Anthony
Computer Methods in Applied Mechanics and Engineering
It is now well established that separated representations built with the help of proper generalized decomposition (PGD) can drastically reduce computational costs associated with solution of a wide variety of problems. However, it is still an open question to know if separated representations can be efficiently used to approximate solutions of hyperbolic evolution problems in space-time domain. In this paper, we numerically address this issue and concentrate on transient elastodynamic models. For such models, the operator associated with the space-time problem is non-symmetric and low-rank approximations are classically computed by minimizing the space-time residual in a natural L2 sense, yet leading to non optimal approximations in usual solution norms. Therefore, a new algorithm has been recently introduced by one of the authors and allows to find a quasi-optimal low-rank approximation a priori with respect to a target norm. We presently extend this new algorithm to multi-field models. The proposed algorithm is applied to elastodynamics formulated over space-time domain with the Time Discontinuous Galerkin method in displacement and velocity. Numerical examples demonstrate convergence of the proposed algorithm and comparisons are made with classical a posteriori and a priori approaches.
Thu, 01 May 2014 00:00:00 GMThttp://hdl.handle.net/10985/84562014-05-01T00:00:00ZBOUCINHA, LucasAMMAR, AmineGRAVOUIL, AnthonyNOUY, AnthonyIt is now well established that separated representations built with the help of proper generalized decomposition (PGD) can drastically reduce computational costs associated with solution of a wide variety of problems. However, it is still an open question to know if separated representations can be efficiently used to approximate solutions of hyperbolic evolution problems in space-time domain. In this paper, we numerically address this issue and concentrate on transient elastodynamic models. For such models, the operator associated with the space-time problem is non-symmetric and low-rank approximations are classically computed by minimizing the space-time residual in a natural L2 sense, yet leading to non optimal approximations in usual solution norms. Therefore, a new algorithm has been recently introduced by one of the authors and allows to find a quasi-optimal low-rank approximation a priori with respect to a target norm. We presently extend this new algorithm to multi-field models. The proposed algorithm is applied to elastodynamics formulated over space-time domain with the Time Discontinuous Galerkin method in displacement and velocity. Numerical examples demonstrate convergence of the proposed algorithm and comparisons are made with classical a posteriori and a priori approaches.On the selection of Johnson-Cook constitutive model parameters for Ti-6Al-4V using three types of numerical models of orthogonal cutting
http://hdl.handle.net/10985/9863
ZHANG, Yancheng; OUTEIRO, José; MABROUKI, Tarek
Johnson-Cook constitutive model is still the most used model in metal cutting simulation, although several drawbacks reported in the literature. A high number of Johnson-Cook model parameters can be found in the literature for the same work material. One question that may arise is “What is the most suitable set of Johnson-Cook model parameters for a given material?”. The present paper puts in evidence some issues related with the selection of these parameters from the literature.
In this contribution, two sets of Johnson-Cook model parameters for Ti-6A-4V are evaluated, using three types of metal cutting models. These models are based on three different formulations: Lagrangian, Arbitrary Eulerian-Lagrangian (ALE) and Couple Lagrangian-Eulerian (CEL). This evaluation is based on the comparison between measured and predicted chip geometry, chip compression ratio, forces, plastic deformation and temperature distributions.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/98632015-01-01T00:00:00ZZHANG, YanchengOUTEIRO, JoséMABROUKI, TarekJohnson-Cook constitutive model is still the most used model in metal cutting simulation, although several drawbacks reported in the literature. A high number of Johnson-Cook model parameters can be found in the literature for the same work material. One question that may arise is “What is the most suitable set of Johnson-Cook model parameters for a given material?”. The present paper puts in evidence some issues related with the selection of these parameters from the literature.
In this contribution, two sets of Johnson-Cook model parameters for Ti-6A-4V are evaluated, using three types of metal cutting models. These models are based on three different formulations: Lagrangian, Arbitrary Eulerian-Lagrangian (ALE) and Couple Lagrangian-Eulerian (CEL). This evaluation is based on the comparison between measured and predicted chip geometry, chip compression ratio, forces, plastic deformation and temperature distributions.