Documents disponibles écrits par cet auteur

Convexity of yield surface with directional distortional hardening rules / Plesek, Jiri in Journal of engineering mechanics, Vol. 136 N° 4 (Avril 2010) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 136 N° 4 (Avril 2010) . - pp. 477-484 Titre : Convexity of yield surface with directional distortional hardening rules Type de document : texte imprimé Auteurs : Plesek, Jiri, Auteur ; Feigenbaum, Heidi P., Auteur ; Dafalias, Yannis F., Auteur Article en page(s) : pp. 477-484 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Plasticity  Elastoplasticity  Yield  Anisotropy. Résumé : The present paper examines the convexity of the yield surface in the directional distortional hardening models by Feigenbaum and Dafalias. In these models anisotropy develops through kinematic and directional distortional hardening, supplemented by the classical isotropic hardening, and the associative flow rule is used. However, the issue of convexity, which naturally arises due to the distortion of the yield surface, was not fully addressed. The present paper derives the necessary and sufficient conditions to ensure convexity of the yield surface for the simpler Feigenbaum and Dafalias models, but it is not as straightforward to derive corresponding conditions for convexity of the Feigenbaum and Dafalias model version which contains an evolving fourth-order tensor. In this case convexity will be addressed first in general and then at the limit state for which simple restrictions on the material constants to ensure convexity are derived. Numerical examples will show that some of the yield surfaces simulated in the original Feigenbaum and Dafalias publication will not stay convex if loaded beyond what was done in these publications. Therefore the material constants for these cases are recalibrated based on the derived relations for satisfaction of the convexity requirement, and the fitting of the yield surfaces is repeated with the new set of constants and compared with the previous case. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...] [article] Convexity of yield surface with directional distortional hardening rules [texte imprimé] / Plesek, Jiri, Auteur ; Feigenbaum, Heidi P., Auteur ; Dafalias, Yannis F., Auteur . - pp. 477-484. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 136 N° 4 (Avril 2010) . - pp. 477-484 Mots-clés : Plasticity  Elastoplasticity  Yield  Anisotropy. Résumé : The present paper examines the convexity of the yield surface in the directional distortional hardening models by Feigenbaum and Dafalias. In these models anisotropy develops through kinematic and directional distortional hardening, supplemented by the classical isotropic hardening, and the associative flow rule is used. However, the issue of convexity, which naturally arises due to the distortion of the yield surface, was not fully addressed. The present paper derives the necessary and sufficient conditions to ensure convexity of the yield surface for the simpler Feigenbaum and Dafalias models, but it is not as straightforward to derive corresponding conditions for convexity of the Feigenbaum and Dafalias model version which contains an evolving fourth-order tensor. In this case convexity will be addressed first in general and then at the limit state for which simple restrictions on the material constants to ensure convexity are derived. Numerical examples will show that some of the yield surfaces simulated in the original Feigenbaum and Dafalias publication will not stay convex if loaded beyond what was done in these publications. Therefore the material constants for these cases are recalibrated based on the derived relations for satisfaction of the convexity requirement, and the fitting of the yield surfaces is repeated with the new set of constants and compared with the previous case. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...]

Objective model for the fluctuating pressure-strain-rate correlations / Dafalias, Yannis F. in Journal of engineering mechanics, Vol. 135 N° 9 (Septembre 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N° 9 (Septembre 2009) . - pp. 1006-1014 Titre : Objective model for the fluctuating pressure-strain-rate correlations Type de document : texte imprimé Auteurs : Dafalias, Yannis F., Auteur ; Younis, Bassam A., Auteur Article en page(s) : pp. 1006-1014 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Strain  rates  Fluid  mechanics  Pressure  Turbulence. Résumé : Representation theorems for isotropic functions are used to construct a closure model for the fluctuating pressure-strain-rate correlation tensor. In contrast to alternative proposals in the literature, the present model does not include a dependence on the vorticity in inertial frames or on the intrinsic spin tensor in noninertial frames because it is shown that this dependence violates objectivity which has been previously suggested to be an essential property of a turbulence closure. The proposed model is calibrated using data from homogeneous shear flows in inertial frames and is tested against data from a variety of turbulent shear flow, in both fixed and rotating frames, with generally very encouraging results. In particular, the results conclusively demonstrate that the absence of dependence on vorticity and intrinsic spin in the model for the pressure-strain-rate correlations does not adversely impact its ability to accurately predict the effects of system rotation on the turbulence. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...] [article] Objective model for the fluctuating pressure-strain-rate correlations [texte imprimé] / Dafalias, Yannis F., Auteur ; Younis, Bassam A., Auteur . - pp. 1006-1014. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N° 9 (Septembre 2009) . - pp. 1006-1014 Mots-clés : Strain  rates  Fluid  mechanics  Pressure  Turbulence. Résumé : Representation theorems for isotropic functions are used to construct a closure model for the fluctuating pressure-strain-rate correlation tensor. In contrast to alternative proposals in the literature, the present model does not include a dependence on the vorticity in inertial frames or on the intrinsic spin tensor in noninertial frames because it is shown that this dependence violates objectivity which has been previously suggested to be an essential property of a turbulence closure. The proposed model is calibrated using data from homogeneous shear flows in inertial frames and is tested against data from a variety of turbulent shear flow, in both fixed and rotating frames, with generally very encouraging results. In particular, the results conclusively demonstrate that the absence of dependence on vorticity and intrinsic spin in the model for the pressure-strain-rate correlations does not adversely impact its ability to accurately predict the effects of system rotation on the turbulence. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...]

Objectivity in turbulence under change of reference frame and superposed rigid body motion / Dafalias, Yannis F. in Journal of engineering mechanics, Vol. 137 N° 10 (Octobre 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 10 (Octobre 2011) . - pp.699-707 Titre : Objectivity in turbulence under change of reference frame and superposed rigid body motion Type de document : texte imprimé Auteurs : Dafalias, Yannis F., Auteur Année de publication : 2012 Article en page(s) : pp.699-707 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Turbulence  Modeling  Rotating  frames  Theory  Objectivity  Superposed  rigid-body  motion Résumé : The validity of objectivity or frame-indifference in turbulence is examined simultaneously from the dual perspective of change of reference frame and superposed rigid-body motion. Similarities and differences arising from the two approaches and their effect on modeling in turbulence are discussed in detail. The use of the absolute spin for noninertial frames and of the net spin for superposed rigid-body motions in closure representations for the pressure-strain-rate correlations tensor are critically discussed. The enigmatic statement made by Speziale that the frame-indifference or objectivity of Reynolds stress does not establish the validity of material frame-indifference in turbulence and the subsequent case-study test of objectivity under superposed rigid-body mean motion within a rotating frame presented to prove it are investigated and fully explained. It is shown analytically that such apparently contrasting conclusions on the validity of objectivity result from the application of the objectivity test to the mean rather than the instantaneous motion, a case not encountered in classical continuum mechanics, which considers only one motion, the instantaneous. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i10/p699_s1?isAuthorized=no [article] Objectivity in turbulence under change of reference frame and superposed rigid body motion [texte imprimé] / Dafalias, Yannis F., Auteur . - 2012 . - pp.699-707. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 10 (Octobre 2011) . - pp.699-707 Mots-clés : Turbulence  Modeling  Rotating  frames  Theory  Objectivity  Superposed  rigid-body  motion Résumé : The validity of objectivity or frame-indifference in turbulence is examined simultaneously from the dual perspective of change of reference frame and superposed rigid-body motion. Similarities and differences arising from the two approaches and their effect on modeling in turbulence are discussed in detail. The use of the absolute spin for noninertial frames and of the net spin for superposed rigid-body motions in closure representations for the pressure-strain-rate correlations tensor are critically discussed. The enigmatic statement made by Speziale that the frame-indifference or objectivity of Reynolds stress does not establish the validity of material frame-indifference in turbulence and the subsequent case-study test of objectivity under superposed rigid-body mean motion within a rotating frame presented to prove it are investigated and fully explained. It is shown analytically that such apparently contrasting conclusions on the validity of objectivity result from the application of the objectivity test to the mean rather than the instantaneous motion, a case not encountered in classical continuum mechanics, which considers only one motion, the instantaneous. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i10/p699_s1?isAuthorized=no

Sand Plasticity Model Accounting for Inherent Fabric Anisotropy / Dafalias, Yannis F. in Journal of engineering mechanics, Vol. 130 N°11 (Novembre 2004) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 130 N°11 (Novembre 2004) . - 1319-1333 p. Titre : Sand Plasticity Model Accounting for Inherent Fabric Anisotropy Titre original : Anisotropie Inhérente d'Explication Modèle de Tissu de Plasticité de Sable Type de document : texte imprimé Auteurs : Dafalias, Yannis F., Auteur ; Papadimitriou, Achilleas G., Auteur ; Li, Xiang S. ; Kaliakin, Victor N., Editeur scientifique Article en page(s) : 1319-1333 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Anisotropy  Constitutive  models  Dilatancy  Sand  Plasticity  Fabrics  Anisotropie  Modèles  constitutifs  Epaississement  Sable  Plasticité  Tissus Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A sand plasticity constitutive model is presented herein, which accounts for the effect of inherent fabric anisotropy on the mechanical response. The anisotropy associated with particles’ orientation distribution, is represented by a second-order symmetric fabric tensor, and its effect is quantified via a scalar-valued anisotropic state variable, A. A is defined as the first joint isotropic invariant of the fabric tensor and a properly defined loading direction tensor, scaled by a function of a corresponding Lode angle. The hardening plastic modulus and the location of the critical state line in the void ratio—mean effective stress space, on which the dilatancy depends, are made functions of A. The incorporation of this dependence on A in a pre-existing stress-ratio driven, bounding surface plasticity constitutive model, achieves successful simulations of test results on sand for a wide variation of densities, pressures, loading manners, and directions. In particular, the drastic difference in material response observed experimentally for different directions of the principal stress axes with respect to the anisotropy axes, is well simulated by the model. The proposed definition and use of A has generic value, and can be incorporated in a large number of other constitutive models in order to account for inherent fabric anisotropy effects. Un modèle constitutif de plasticité de sable est présenté ci-dessus, qui explique l'effet de l'anisotropie inhérente de tissu sur la réponse mécanique. L'anisotropie liée distribution d'orientation à particules', est représentée par un tenseur symétrique de tissu du second degré, et son effet est mesuré par l'intermédiaire d'une variable anisotrope évaluée scalaire d'état, A. A est défini comme l'invariable isotrope du premier joint du tenseur de tissu et d'un tenseur de chargement correctement défini de direction, mesuré par une fonction d'un angle correspondant de filon. Le module en plastique durcissant et l'endroit de la frontière d'état critique dans l'espace efficace d'effort de moyen vide de rapport, duquel l'épaississement dépend, sont faits à des fonctions d'A. L'incorporation de cette dépendance à l'égard A dans un rapport préexistant d'effort conduit, modèle constitutif de bondissement de plasticité extérieure, réalise des simulations réussies des résultats d'essai sur le sable pour une grande variation des densités, des pressions, des façons de chargement, et des directions. En particulier, la différence énergique dans la réponse matérielle observée expérimentalement pour différentes directions de l'effort principal diminue en ce qui concerne les haches d'anisotropie, est bien simulée par le modèle. La définition et l'utilisation proposées d'A a la valeur générique, et peut être incorporée dans un grand nombre d'autres modèles constitutifs afin d'expliquer des effets inhérents d'anisotropie de tissu. DEWEY : 620.1 ISSN : 0733-9399 En ligne : yfdafalias@ucdavis.edu, loupapas@alum.mit.edu, xsli@ust.hk [article] Sand Plasticity Model Accounting for Inherent Fabric Anisotropy = Anisotropie Inhérente d'Explication Modèle de Tissu de Plasticité de Sable [texte imprimé] / Dafalias, Yannis F., Auteur ; Papadimitriou, Achilleas G., Auteur ; Li, Xiang S. ; Kaliakin, Victor N., Editeur scientifique . - 1319-1333 p. Génie Mécanique Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 130 N°11 (Novembre 2004) . - 1319-1333 p. Mots-clés : Anisotropy  Constitutive  models  Dilatancy  Sand  Plasticity  Fabrics  Anisotropie  Modèles  constitutifs  Epaississement  Sable  Plasticité  Tissus Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A sand plasticity constitutive model is presented herein, which accounts for the effect of inherent fabric anisotropy on the mechanical response. The anisotropy associated with particles’ orientation distribution, is represented by a second-order symmetric fabric tensor, and its effect is quantified via a scalar-valued anisotropic state variable, A. A is defined as the first joint isotropic invariant of the fabric tensor and a properly defined loading direction tensor, scaled by a function of a corresponding Lode angle. The hardening plastic modulus and the location of the critical state line in the void ratio—mean effective stress space, on which the dilatancy depends, are made functions of A. The incorporation of this dependence on A in a pre-existing stress-ratio driven, bounding surface plasticity constitutive model, achieves successful simulations of test results on sand for a wide variation of densities, pressures, loading manners, and directions. In particular, the drastic difference in material response observed experimentally for different directions of the principal stress axes with respect to the anisotropy axes, is well simulated by the model. The proposed definition and use of A has generic value, and can be incorporated in a large number of other constitutive models in order to account for inherent fabric anisotropy effects. Un modèle constitutif de plasticité de sable est présenté ci-dessus, qui explique l'effet de l'anisotropie inhérente de tissu sur la réponse mécanique. L'anisotropie liée distribution d'orientation à particules', est représentée par un tenseur symétrique de tissu du second degré, et son effet est mesuré par l'intermédiaire d'une variable anisotrope évaluée scalaire d'état, A. A est défini comme l'invariable isotrope du premier joint du tenseur de tissu et d'un tenseur de chargement correctement défini de direction, mesuré par une fonction d'un angle correspondant de filon. Le module en plastique durcissant et l'endroit de la frontière d'état critique dans l'espace efficace d'effort de moyen vide de rapport, duquel l'épaississement dépend, sont faits à des fonctions d'A. L'incorporation de cette dépendance à l'égard A dans un rapport préexistant d'effort conduit, modèle constitutif de bondissement de plasticité extérieure, réalise des simulations réussies des résultats d'essai sur le sable pour une grande variation des densités, des pressions, des façons de chargement, et des directions. En particulier, la différence énergique dans la réponse matérielle observée expérimentalement pour différentes directions de l'effort principal diminue en ce qui concerne les haches d'anisotropie, est bien simulée par le modèle. La définition et l'utilisation proposées d'A a la valeur générique, et peut être incorporée dans un grand nombre d'autres modèles constitutifs afin d'expliquer des effets inhérents d'anisotropie de tissu. DEWEY : 620.1 ISSN : 0733-9399 En ligne : yfdafalias@ucdavis.edu, loupapas@alum.mit.edu, xsli@ust.hk

SANISTEEL: Simple anisotropic steel plasticity model / Mark Mahan in Journal of structural engineering, Vol. 137 N° 2 (Fevrier 2011) 

Public ISBD [article]  in Journal of structural engineering > Vol. 137 N° 2 (Fevrier 2011) . - pp. 185-194 Titre : SANISTEEL: Simple anisotropic steel plasticity model Type de document : texte imprimé Auteurs : Mark Mahan, Auteur ; Dafalias, Yannis F., Auteur ; Mahdi Taiebat, Auteur Année de publication : 2011 Article en page(s) : pp. 185-194 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Steel  Anisotropy  Constitutive  model  Plateau  Perfect  plasticity  Bounding  surface Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : A simple constitutive model for the inelastic response of steel under monotonic and random cyclic loading conditions is developed within the framework of bounding surface plasticity. The particular feature that distinguishes this model from other similar ones is the ability of the bounding surface formulation to describe in a very simple way the initial “plateau” type of perfectly plastic response that many kinds of structural steels exhibit upon initial yield in tension or compression, before hardening begins. The key constitutive element is to assume a fixed nonhardening bounding surface during the plateau response until a cumulative plastic strain threshold is reached, while the yield surface softens isotropically and hardens kinematically. In this way not only monotonic but also cyclic loading within the plateau range can be easily described. Three kinematic hardening rules for the bounding surface are explored. The development is focused on uniaxial loading conditions that are typical in many structural engineering applications employing a fiber-based discretization of the cross section. Several simulations to demonstrate the effectiveness of the proposed model are presented. Finally, its extension to a multiaxial stress generalization is concisely presented for future use. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i2/p185_s1?isAuthorized=no [article] SANISTEEL: Simple anisotropic steel plasticity model [texte imprimé] / Mark Mahan, Auteur ; Dafalias, Yannis F., Auteur ; Mahdi Taiebat, Auteur . - 2011 . - pp. 185-194. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 137 N° 2 (Fevrier 2011) . - pp. 185-194 Mots-clés : Steel  Anisotropy  Constitutive  model  Plateau  Perfect  plasticity  Bounding  surface Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : A simple constitutive model for the inelastic response of steel under monotonic and random cyclic loading conditions is developed within the framework of bounding surface plasticity. The particular feature that distinguishes this model from other similar ones is the ability of the bounding surface formulation to describe in a very simple way the initial “plateau” type of perfectly plastic response that many kinds of structural steels exhibit upon initial yield in tension or compression, before hardening begins. The key constitutive element is to assume a fixed nonhardening bounding surface during the plateau response until a cumulative plastic strain threshold is reached, while the yield surface softens isotropically and hardens kinematically. In this way not only monotonic but also cyclic loading within the plateau range can be easily described. Three kinematic hardening rules for the bounding surface are explored. The development is focused on uniaxial loading conditions that are typical in many structural engineering applications employing a fiber-based discretization of the cross section. Several simulations to demonstrate the effectiveness of the proposed model are presented. Finally, its extension to a multiaxial stress generalization is concisely presented for future use. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i2/p185_s1?isAuthorized=no

Simple model for directional distortional hardening in metal plasticity within thermodynamics / Feigenbaum, Heidi P. in Journal of engineering mechanics, Vol. 134 n°9 (Septembre 2008) 

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Simple Plasticity Sand Model Accounting for Fabric Change Effects / Dafalias, Yannis F. in Journal of engineering mechanics, Vol. 130 N°6 (Juin 2004) 

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