Dépouillements

Micromorphic approach for gradient elasticity, viscoplasticity, and damage / Samuel Forest in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 117-131 Titre : Micromorphic approach for gradient elasticity, viscoplasticity, and damage Type de document : texte imprimé Auteurs : Samuel Forest, Auteur Article en page(s) : pp. 117-131 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Elasticity  Damage  Viscoplasticity. Résumé : A unifying thermomechanical framework is presented that reconciles several classes of gradient elastoviscoplasticity and damage models proposed in the literature during the last 40 years. It is based on the introduction of the micromorphic counterpart chiphi of a selected state or internal variable phi in a standard constitutive model. In addition to the classical balance of momentum equation, a balance of micromorphic momentum is derived that involves generalized stress tensors. The corresponding additional boundary conditions are also deduced from the procedure. The power of generalized forces is assumed to contribute to the energy balance equation. The free energy density function is then chosen to depend on a relative generalized strain, typically phi-chiphi, and the microstrain gradient [del]chiphi. When applied to the deformation gradient itself, phi[equivalent][bold F][underaccent undertilde [below] , the method yields the micromorphic theory of Eringen and Mindlin together with its extension to finite deformation elastoviscoplasticity by Forest and Sievert. If the selected variable is the cumulative plastic strain, the theory reduces to the so-called “nonlocal implicit gradient-enhanced elastoplasticity model” by Engelen, Geers, and Peerlings, provided that simplified linear relationships are adopted between generalized stresses and strains. The same holds if the micromorphic variable coincides with a microdamage variable. If the internal constraint is introduced that the micromorphic variable chiphi remains as close as possible to the macroscopic variable phi, the micromorphic model reduces to the second gradient or gradient of internal variable approach as defined by Maugin. If the selected variable is the cumulative plastic strain or the full plastic strain tensor, the constrained micromorphic theory delivers Aifantis-like strain gradient plasticity models. The advantage of the micromorphic approach is that it provides the generalized balance equation under nonisothermal conditions and offers the setting for anisotropic nonlinear constitutive relations between generalized stress and strains in contrast to most existing models. In rate-independent plasticity, it is shown that there is generally no need for a variational formulation of the yield condition. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Micromorphic approach for gradient elasticity, viscoplasticity, and damage [texte imprimé] / Samuel Forest, Auteur . - pp. 117-131. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 117-131 Mots-clés : Elasticity  Damage  Viscoplasticity. Résumé : A unifying thermomechanical framework is presented that reconciles several classes of gradient elastoviscoplasticity and damage models proposed in the literature during the last 40 years. It is based on the introduction of the micromorphic counterpart chiphi of a selected state or internal variable phi in a standard constitutive model. In addition to the classical balance of momentum equation, a balance of micromorphic momentum is derived that involves generalized stress tensors. The corresponding additional boundary conditions are also deduced from the procedure. The power of generalized forces is assumed to contribute to the energy balance equation. The free energy density function is then chosen to depend on a relative generalized strain, typically phi-chiphi, and the microstrain gradient [del]chiphi. When applied to the deformation gradient itself, phi[equivalent][bold F][underaccent undertilde [below] , the method yields the micromorphic theory of Eringen and Mindlin together with its extension to finite deformation elastoviscoplasticity by Forest and Sievert. If the selected variable is the cumulative plastic strain, the theory reduces to the so-called “nonlocal implicit gradient-enhanced elastoplasticity model” by Engelen, Geers, and Peerlings, provided that simplified linear relationships are adopted between generalized stresses and strains. The same holds if the micromorphic variable coincides with a microdamage variable. If the internal constraint is introduced that the micromorphic variable chiphi remains as close as possible to the macroscopic variable phi, the micromorphic model reduces to the second gradient or gradient of internal variable approach as defined by Maugin. If the selected variable is the cumulative plastic strain or the full plastic strain tensor, the constrained micromorphic theory delivers Aifantis-like strain gradient plasticity models. The advantage of the micromorphic approach is that it provides the generalized balance equation under nonisothermal conditions and offers the setting for anisotropic nonlinear constitutive relations between generalized stress and strains in contrast to most existing models. In rate-independent plasticity, it is shown that there is generally no need for a variational formulation of the yield condition. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Study of plastic shear localization via the flow theory of mechanism-based strain gradient plasticity / Z. Shi in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 132-138 Titre : Study of plastic shear localization via the flow theory of mechanism-based strain gradient plasticity Type de document : texte imprimé Auteurs : Z. Shi, Auteur ; Y. Huang, Auteur ; J. Song, Auteur Article en page(s) : pp. 132-138 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Shear  flow  Plasticity  Material  properties. Résumé : The plastic shear localization is studied via the flow theory of mechanism-based strain gradient plasticity. The shear strain rate displays a rather sharp decrease from the center to the boundary of shear band, and gradually approaches the uniform remote shear strain rate outside the shear band. The shear band thickness obtained analytically is linearly proportional to the (length of) Burgers vector, and also depends on the softening modulus and mesoscale cell size. The maximum shear strain rate in the shear band, however, is sensitive to other material properties such as the ultimate tensile strength and intrinsic material length in strain gradient plasticity. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Study of plastic shear localization via the flow theory of mechanism-based strain gradient plasticity [texte imprimé] / Z. Shi, Auteur ; Y. Huang, Auteur ; J. Song, Auteur . - pp. 132-138. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 132-138 Mots-clés : Shear  flow  Plasticity  Material  properties. Résumé : The plastic shear localization is studied via the flow theory of mechanism-based strain gradient plasticity. The shear strain rate displays a rather sharp decrease from the center to the boundary of shear band, and gradually approaches the uniform remote shear strain rate outside the shear band. The shear band thickness obtained analytically is linearly proportional to the (length of) Burgers vector, and also depends on the softening modulus and mesoscale cell size. The maximum shear strain rate in the shear band, however, is sensitive to other material properties such as the ultimate tensile strength and intrinsic material length in strain gradient plasticity. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Variable material length scale associated with nanoindentation experiments / Voyiadjis, George Z. in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 139-148 Titre : Variable material length scale associated with nanoindentation experiments Type de document : texte imprimé Auteurs : Voyiadjis, George Z., Auteur ; Amin H. Almasri, Auteur Article en page(s) : pp. 139-148 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Metals  Material  tests  Experimentation  Length. Résumé : Material length scale that can be used in nonlocal gradient theories is obtained in this work based on experimental observations for two metals using nanoindentation experiments. The materials are cold rolled 1018 steel and oxygen free high conductivity copper. A fixed value of the material length scale is not always realistic and different problems under various conditions could require different values. Therefore, two models are proposed for a dynamic length scale that depends on strain rates and temperature. First the model is physically based, with parameters related to dislocation densities. This model introduces strain rate and temperature dependency in a coupled form. The second model is a phenomenological one that is based on hardness tests. Both models show that length scale decreases with increasing equivalent strain rate. The temperature effects are not studied in this work. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Variable material length scale associated with nanoindentation experiments [texte imprimé] / Voyiadjis, George Z., Auteur ; Amin H. Almasri, Auteur . - pp. 139-148. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 139-148 Mots-clés : Metals  Material  tests  Experimentation  Length. Résumé : Material length scale that can be used in nonlocal gradient theories is obtained in this work based on experimental observations for two metals using nanoindentation experiments. The materials are cold rolled 1018 steel and oxygen free high conductivity copper. A fixed value of the material length scale is not always realistic and different problems under various conditions could require different values. Therefore, two models are proposed for a dynamic length scale that depends on strain rates and temperature. First the model is physically based, with parameters related to dislocation densities. This model introduces strain rate and temperature dependency in a coupled form. The second model is a phenomenological one that is based on hardness tests. Both models show that length scale decreases with increasing equivalent strain rate. The temperature effects are not studied in this work. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

A generalized continuum theory and Its relation to micromorphic theory / Youping Chen in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 149-155 Titre : A generalized continuum theory and Its relation to micromorphic theory Type de document : texte imprimé Auteurs : Youping Chen, Auteur ; James Lee, Auteur ; Liming Xiong, Auteur Article en page(s) : pp. 149-155 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Continuum  mechanics  Theories. Résumé : Classic continuum mechanics views a crystal as a homogeneous and continuous medium, in which the basic structural unit of the crystal is taken without structure and is idealized as point mass. Micromorphic theory views a material as a continuous collection of deformable point particles; each particle has finite size and additional nine internal degrees of freedom describing the stretches and rotations of the particle. This paper presents a multiscale field theory that views a crystalline material as a continuous collection of lattice points, while embedded within each point is a group of discrete atoms. The atomistic formulation of the field theory is briefly introduced. Its relation with the well-known micromorphic theory is derived. The applicability of the classical continuum theory, micromorphic theory, and the generalized continuum field theory is discussed. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] A generalized continuum theory and Its relation to micromorphic theory [texte imprimé] / Youping Chen, Auteur ; James Lee, Auteur ; Liming Xiong, Auteur . - pp. 149-155. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 149-155 Mots-clés : Continuum  mechanics  Theories. Résumé : Classic continuum mechanics views a crystal as a homogeneous and continuous medium, in which the basic structural unit of the crystal is taken without structure and is idealized as point mass. Micromorphic theory views a material as a continuous collection of deformable point particles; each particle has finite size and additional nine internal degrees of freedom describing the stretches and rotations of the particle. This paper presents a multiscale field theory that views a crystalline material as a continuous collection of lattice points, while embedded within each point is a group of discrete atoms. The atomistic formulation of the field theory is briefly introduced. Its relation with the well-known micromorphic theory is derived. The applicability of the classical continuum theory, micromorphic theory, and the generalized continuum field theory is discussed. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Classification of concepts in thermodynamically consistent generalized plasticity / C. B. Hirschberger in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 156-170 Titre : Classification of concepts in thermodynamically consistent generalized plasticity Type de document : texte imprimé Auteurs : C. B. Hirschberger, Auteur ; P. Steinmann, Auteur Article en page(s) : pp. 156-170 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Classification  Thermodynamics  Plasticity. Résumé : A classification of various formulations coined as generalized plasticity is introduced. Thereby the authors present variants of both gradient and micromorphic plasticity, which prove thermodynamically consistent by fulfilling the second law of thermodynamics. In a structured manner, they vary key characteristic features of the formulation and compare their influence on the complexity and, in particular, on the benefit of the individual formulations. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Classification of concepts in thermodynamically consistent generalized plasticity [texte imprimé] / C. B. Hirschberger, Auteur ; P. Steinmann, Auteur . - pp. 156-170. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 156-170 Mots-clés : Classification  Thermodynamics  Plasticity. Résumé : A classification of various formulations coined as generalized plasticity is introduced. Thereby the authors present variants of both gradient and micromorphic plasticity, which prove thermodynamically consistent by fulfilling the second law of thermodynamics. In a structured manner, they vary key characteristic features of the formulation and compare their influence on the complexity and, in particular, on the benefit of the individual formulations. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Use of thermodynamic formalism in generalized continuum theories and a model for damage evolution / Amit Acharya in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 171-177 Titre : Use of thermodynamic formalism in generalized continuum theories and a model for damage evolution Type de document : texte imprimé Auteurs : Amit Acharya, Auteur Article en page(s) : pp. 171-177 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Thermodynamics  Damage  Methodology. Résumé : A technique for setting up generalized continuum theories based on a balance law and nonlocal thermodynamics is suggested. The methodology does not require the introduction of gradients of the internal variable in the free energy, while allowing for its possibility. Elements of a generalized (brittle) damage model with porosity as the internal variable are developed as an example. The notion of a flux of porosity arises, and we distinguish between the physical notion of a flux of voids (with underpinnings of corpuscular transport) and a flux of void volume that can arise merely due to void expansion. A hypothetical, local free energy function with classical limits for the damaged stress and modulus is constructed to show that the model admits a nonlinear diffusion-advection equation with positive diffusivity for the porosity as a governing equation. This equation is shown to be intimately related to Burgers equation of fluid dynamics, and an analytical solution of the corresponding constant-coefficient, semilinear equation without source term is solved by the Hopf–Cole transformation, that admits the Hopf–Lax entropy weak solution for the corresponding Hamilton–Jacobi equation in the limit of vanishing diffusion. Constraints on the class of admissible porosity and strain-dependent free energy functions arising from the mathematical structure of the theory are deduced. This work may be thought of as providing a continuum thermodynamic formalism for the internal variable gradient models proposed by Aifantis in 1984 in the context of local stress and free-energy functions. However, the degree of diffusive smoothing is not found to be arbitrarily specifiable as mechanical coupling produces an “antidiffusion” effect, and the model also inextricably links propagation of regions of high gradients with their diffusive smoothing. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Use of thermodynamic formalism in generalized continuum theories and a model for damage evolution [texte imprimé] / Amit Acharya, Auteur . - pp. 171-177. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 171-177 Mots-clés : Thermodynamics  Damage  Methodology. Résumé : A technique for setting up generalized continuum theories based on a balance law and nonlocal thermodynamics is suggested. The methodology does not require the introduction of gradients of the internal variable in the free energy, while allowing for its possibility. Elements of a generalized (brittle) damage model with porosity as the internal variable are developed as an example. The notion of a flux of porosity arises, and we distinguish between the physical notion of a flux of voids (with underpinnings of corpuscular transport) and a flux of void volume that can arise merely due to void expansion. A hypothetical, local free energy function with classical limits for the damaged stress and modulus is constructed to show that the model admits a nonlinear diffusion-advection equation with positive diffusivity for the porosity as a governing equation. This equation is shown to be intimately related to Burgers equation of fluid dynamics, and an analytical solution of the corresponding constant-coefficient, semilinear equation without source term is solved by the Hopf–Cole transformation, that admits the Hopf–Lax entropy weak solution for the corresponding Hamilton–Jacobi equation in the limit of vanishing diffusion. Constraints on the class of admissible porosity and strain-dependent free energy functions arising from the mathematical structure of the theory are deduced. This work may be thought of as providing a continuum thermodynamic formalism for the internal variable gradient models proposed by Aifantis in 1984 in the context of local stress and free-energy functions. However, the degree of diffusive smoothing is not found to be arbitrarily specifiable as mechanical coupling produces an “antidiffusion” effect, and the model also inextricably links propagation of regions of high gradients with their diffusive smoothing. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Finite strain micromorphic pressure-sensitive plasticity / R. A. Regueiro in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 178-191 Titre : Finite strain micromorphic pressure-sensitive plasticity Type de document : texte imprimé Auteurs : R. A. Regueiro, Auteur Article en page(s) : pp. 178-191 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Plasticity  Strain  Pressure  Thermodynamics  Microstructure. Résumé : A finite strain micromorphic pressure-sensitive plasticity model is formulated starting with thermodynamically conjugate stresses and plastic deformation rates in the reduced dissipation inequality, written in the intermediate configuration. Isotropic linear elasticity and nonassociative Drucker–Prager plasticity with cohesion hardening/softening are assumed for the constitutive equations. The reduced dissipation inequality dictates three levels of plastic evolution: (1) evolution of Fp, the plastic part of the deformation gradient; (2) evolution of chip, the plastic part of the microdeformation tensor; and (3) evolution of [overline [bold [del]]]chip, the covariant derivative of chip. A semi-implicit time integration of the stress and plastic evolution equations is outlined after assuming small elastic deformations and Cartesian coordinates for the current configuration. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Finite strain micromorphic pressure-sensitive plasticity [texte imprimé] / R. A. Regueiro, Auteur . - pp. 178-191. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 178-191 Mots-clés : Plasticity  Strain  Pressure  Thermodynamics  Microstructure. Résumé : A finite strain micromorphic pressure-sensitive plasticity model is formulated starting with thermodynamically conjugate stresses and plastic deformation rates in the reduced dissipation inequality, written in the intermediate configuration. Isotropic linear elasticity and nonassociative Drucker–Prager plasticity with cohesion hardening/softening are assumed for the constitutive equations. The reduced dissipation inequality dictates three levels of plastic evolution: (1) evolution of Fp, the plastic part of the deformation gradient; (2) evolution of chip, the plastic part of the microdeformation tensor; and (3) evolution of [overline [bold [del]]]chip, the covariant derivative of chip. A semi-implicit time integration of the stress and plastic evolution equations is outlined after assuming small elastic deformations and Cartesian coordinates for the current configuration. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Multiscale computation for nano/micromaterials / James D. Lee in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 192-202 Titre : Multiscale computation for nano/micromaterials Type de document : texte imprimé Auteurs : James D. Lee, Auteur ; Xianqiao Wang, Auteur ; Youping Chen, Auteur Article en page(s) : pp. 192-202 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Computation  Material  properties  Simulation. Résumé : This paper presents a multiscale field theory and its applications in modeling and simulation of atomistic systems. The theoretical construction of the multiscale field theory is briefly introduced. A single crystal is discretized into finite-element mesh as if it is a continuous medium. However, each node is a representative unit cell, which contains a specified number of distinctive atoms. Ordinary differential equations for each atom in all nodes are obtained. Material behaviors of a given atomistic system at nano/microscale, subject to the combination of mechanical loadings, electromagnetic field, and temperature field, can be obtained through numerical simulations. Sample problems on wave propagation and simple tension have been solved to demonstrate the advantage and applicability of this multiscale field theory. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Multiscale computation for nano/micromaterials [texte imprimé] / James D. Lee, Auteur ; Xianqiao Wang, Auteur ; Youping Chen, Auteur . - pp. 192-202. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 192-202 Mots-clés : Computation  Material  properties  Simulation. Résumé : This paper presents a multiscale field theory and its applications in modeling and simulation of atomistic systems. The theoretical construction of the multiscale field theory is briefly introduced. A single crystal is discretized into finite-element mesh as if it is a continuous medium. However, each node is a representative unit cell, which contains a specified number of distinctive atoms. Ordinary differential equations for each atom in all nodes are obtained. Material behaviors of a given atomistic system at nano/microscale, subject to the combination of mechanical loadings, electromagnetic field, and temperature field, can be obtained through numerical simulations. Sample problems on wave propagation and simple tension have been solved to demonstrate the advantage and applicability of this multiscale field theory. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Two finite-element discretizations for gradient elasticity / A. Zervos in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 203-213 Titre : Two finite-element discretizations for gradient elasticity Type de document : texte imprimé Auteurs : A. Zervos, Auteur ; S.-A. Papanicolopulos, Auteur ; I. Vardoulakis, Auteur Article en page(s) : pp. 203-213 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Finite  element  method  Elastic  analysis  Microstructures  Numerical  models. Résumé : We present and compare two different methods for numerically solving boundary value problems of gradient elasticity. The first method is based on a finite-element discretization using the displacement formulation, where elements that guarantee continuity of strains (i.e., C1 interpolation) are needed. Two such elements are presented and shown to converge: a triangle with straight edges and an isoparametric quadrilateral. The second method is based on a finite-element discretization of Mindlin's elasticity with microstructure, of which gradient elasticity is a special case. Two isoparametric elements are presented, a triangle and a quadrilateral, interpolating the displacement and microdeformation fields. It is shown that, using an appropriate selection of material parameters, they can provide approximate solutions to boundary value problems of gradient elasticity. Benchmark problems are solved using both methods, to assess their relative merits and shortcomings in terms of accuracy, simplicity and computational efficiency. C1 interpolation is shown to give generally superior results, although the approximate solutions obtained by elasticity with microstructure are also shown to be of very good quality. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Two finite-element discretizations for gradient elasticity [texte imprimé] / A. Zervos, Auteur ; S.-A. Papanicolopulos, Auteur ; I. Vardoulakis, Auteur . - pp. 203-213. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 203-213 Mots-clés : Finite  element  method  Elastic  analysis  Microstructures  Numerical  models. Résumé : We present and compare two different methods for numerically solving boundary value problems of gradient elasticity. The first method is based on a finite-element discretization using the displacement formulation, where elements that guarantee continuity of strains (i.e., C1 interpolation) are needed. Two such elements are presented and shown to converge: a triangle with straight edges and an isoparametric quadrilateral. The second method is based on a finite-element discretization of Mindlin's elasticity with microstructure, of which gradient elasticity is a special case. Two isoparametric elements are presented, a triangle and a quadrilateral, interpolating the displacement and microdeformation fields. It is shown that, using an appropriate selection of material parameters, they can provide approximate solutions to boundary value problems of gradient elasticity. Benchmark problems are solved using both methods, to assess their relative merits and shortcomings in terms of accuracy, simplicity and computational efficiency. C1 interpolation is shown to give generally superior results, although the approximate solutions obtained by elasticity with microstructure are also shown to be of very good quality. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Nonlocal thermoelastic damping in microelectromechanical resonators / Raffaele Ardito in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 214-220 Titre : Nonlocal thermoelastic damping in microelectromechanical resonators Type de document : texte imprimé Auteurs : Raffaele Ardito, Auteur ; Claudia Comi, Auteur Article en page(s) : pp. 214-220 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Structural  analysis  Micromechanics  Thermoelasticity  Constitutive  models  Damping. Résumé : The evaluation of loss mechanisms in microscale mechanical resonators is addressed. Among various dissipation causes, thermoelastic loss is considered as a fundamental dissipation mechanism in microbeam resonators packed in a near-vacuum environment. However, the standard thermoelastic analysis is unable to interpret the size effect experimentally evidenced in resonators when the dimensions become very small, below several microns. In this paper we propose an enhanced nonlocal thermoelastic model, based on a thermodynamical formulation, which incorporates internal characteristic material lengths. Analytical results obtained with this nonlocal theory are compared with experimental results reported in the literature. It is shown how nonlocality can better interpret the observed behavior, at least in a certain range of resonators dimensions. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Nonlocal thermoelastic damping in microelectromechanical resonators [texte imprimé] / Raffaele Ardito, Auteur ; Claudia Comi, Auteur . - pp. 214-220. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 214-220 Mots-clés : Structural  analysis  Micromechanics  Thermoelasticity  Constitutive  models  Damping. Résumé : The evaluation of loss mechanisms in microscale mechanical resonators is addressed. Among various dissipation causes, thermoelastic loss is considered as a fundamental dissipation mechanism in microbeam resonators packed in a near-vacuum environment. However, the standard thermoelastic analysis is unable to interpret the size effect experimentally evidenced in resonators when the dimensions become very small, below several microns. In this paper we propose an enhanced nonlocal thermoelastic model, based on a thermodynamical formulation, which incorporates internal characteristic material lengths. Analytical results obtained with this nonlocal theory are compared with experimental results reported in the literature. It is shown how nonlocality can better interpret the observed behavior, at least in a certain range of resonators dimensions. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

New model for the analysis of size-scale effects on the ductility of reinforced concrete elements in bending / A. Carpinteri in Journal of engineering mechanics, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 221-229 Titre : New model for the analysis of size-scale effects on the ductility of reinforced concrete elements in bending Type de document : texte imprimé Auteurs : A. Carpinteri, Auteur ; M. Corrado, Auteur ; M. Paggi, Auteur Article en page(s) : pp. 221-229 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Reinforced  concrete  Ductility  Size  effect  Crushing  Nonlinear  analysis  Finite  element  method  Bending. Résumé : The well-known cohesive crack model describes strain localization with a softening stress variation in concrete members subjected to tension. An analogous behavior is also observed in compression, when strain localization takes place in a damaged zone and the stress reaches the compression strength with surface energy dissipation. In the present paper, we propose the new concept of overlapping crack model, which is analogous to the cohesive one and permits us to simulate material interpenetration due to crushing. The two aforementioned elementary models are merged into a more complex algorithm able to describe both cracking and crushing growths during loading processes in reinforced concrete members. A numerical procedure based on elastic coefficients is developed, taking into account the proposed constitutive laws in tension and compression. With this algorithm, it is possible to effectively capture the flexural behavior of reinforced concrete beams by varying the reinforcement percentage and/or the beam depth. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] New model for the analysis of size-scale effects on the ductility of reinforced concrete elements in bending [texte imprimé] / A. Carpinteri, Auteur ; M. Corrado, Auteur ; M. Paggi, Auteur . - pp. 221-229. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°3 (Mars 2009) . - pp. 221-229 Mots-clés : Reinforced  concrete  Ductility  Size  effect  Crushing  Nonlinear  analysis  Finite  element  method  Bending. Résumé : The well-known cohesive crack model describes strain localization with a softening stress variation in concrete members subjected to tension. An analogous behavior is also observed in compression, when strain localization takes place in a damaged zone and the stress reaches the compression strength with surface energy dissipation. In the present paper, we propose the new concept of overlapping crack model, which is analogous to the cohesive one and permits us to simulate material interpenetration due to crushing. The two aforementioned elementary models are merged into a more complex algorithm able to describe both cracking and crushing growths during loading processes in reinforced concrete members. A numerical procedure based on elastic coefficients is developed, taking into account the proposed constitutive laws in tension and compression. With this algorithm, it is possible to effectively capture the flexural behavior of reinforced concrete beams by varying the reinforcement percentage and/or the beam depth. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

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