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Goncalves Diogo - One of the best experts on this subject based on the ideXlab platform.
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PolyCrystalline modeling of the elastic-viscoPlastic behavior of 316L (N) austenitic stainless steels over a wide range of loadings : application to the study of high temperature cyclic behavior
2018Co-Authors: Goncalves DiogoAbstract:L’acier 316L(N) est le matériau de référence pour les structures du circuit primaire des réacteurs nucléaires de quatrième génération, en raison de leur résistance mécanique à la température de fonctionnement, de l’ordre de 550°C. La thèse a permis de développer un modèle polycristallin, capable de prédire le comportement de ces aciers, basé sur la description du glissement viscoplastique des dislocation à haute température, de mise en œuvre simple et avec l’identification d’un nombre de paramètres matériau limité. La démarche de modélisation a été progressive. Lors de la première étape, nous avons proposé et validé une loi d'homogénéisation élasto-viscoplastique à champs moyens, grâce à de nombreux calculs par éléments finis, en considérant des durcissements plastique et des viscosités cristallines. Ensuite, un modèle de viscoPlasticité cristalline, reposant sur les lois d’évolution des densités de différents types de dislocations, a été implémenté et les prédictions ont été validés en considérant un très grand nombre de résultats expérimentaux à faible. Le modèle a ensuite été enrichi afin de prendre en compte les mécanismes physiques supplémentaires observés à température élevée, comme la montée des dislocations, le vieillissement dynamique et l’apparition d’une structure de dislocation très hétérogène. Le modèle proposé nécessite uniquement l’ajustement de trois paramètres par identification inverse, utilisant seulement des essais de traction monotone avec saut de vitesse. Les prédictions du comportement mécanique en chargement uniaxial et cyclique sont également en bon accord avec les mesures expérimentales aux températures élevées.The 316L(N) stainless steels is the reference material for the primary circuit structures of fourth-generation nuclear reactors. This alloy present high mechanical resistance at the operation temperature range of these reactors, of the order of 550 °C. This PhD allowed to develop a polyCrystalline model based on the description of the viscoPlastic dislocation slip at high temperatures, with straightforward implementation and with identification of a limited number of material parameters. The modeling process was progressive. In a first step, we proposed and validated a mean-field elastic-viscoPlastic homogenization law, in comparison to numerous finite element calculations, considering Crystalline Plastic hardening and Crystalline viscosity. Then, a model of Crystalline viscoPlasticity, based on the evolution laws of the different dislocations densities was implemented and the predictions were validated considering a very large number of experimental results at low temperature. The model was then enhanced to take into account the additional physical mechanisms observed at high temperature, such as dislocation climb, dynamic strain aging and the appearance of a very heterogeneous dislocation structure. The proposed model requires the adjustment of only three parameters by inverse identification, using only monotonic tensile tests at different strain rates. The mechanical behavior predictions in uniaxial and cyclic loading are also in good agreement with experimental measurements at high temperature
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Modélisation polycristalline du comportement élasto-viscoplastique des aciers inoxydables austénitiques 316L(N) sur une large gamme de chargements : application à l'étude du comportement cyclique à température élevée
HAL CCSD, 2018Co-Authors: Goncalves DiogoAbstract:The 316L(N) stainless steels is the reference material for the primary circuit structures of fourth-generation nuclear reactors. This alloy present high mechanical resistance at the operation temperature range of these reactors, of the order of 550 °C. This PhD allowed to develop a polyCrystalline model based on the description of the viscoPlastic dislocation slip at high temperatures, with straightforward implementation and with identification of a limited number of material parameters. The modeling process was progressive. In a first step, we proposed and validated a mean-field elastic-viscoPlastic homogenization law, in comparison to numerous finite element calculations, considering Crystalline Plastic hardening and Crystalline viscosity. Then, a model of Crystalline viscoPlasticity, based on the evolution laws of the different dislocations densities was implemented and the predictions were validated considering a very large number of experimental results at low temperature. The model was then enhanced to take into account the additional physical mechanisms observed at high temperature, such as dislocation climb, dynamic strain aging and the appearance of a very heterogeneous dislocation structure. The proposed model requires the adjustment of only three parameters by inverse identification, using only monotonic tensile tests at different strain rates. The mechanical behavior predictions in uniaxial and cyclic loading are also in good agreement with experimental measurements at high temperature.L’acier 316L(N) est le matériau de référence pour les structures du circuit primaire des réacteurs nucléaires de quatrième génération, en raison de leur résistance mécanique à la température de fonctionnement, de l’ordre de 550°C. La thèse a permis de développer un modèle polycristallin, capable de prédire le comportement de ces aciers, basé sur la description du glissement viscoplastique des dislocation à haute température, de mise en œuvre simple et avec l’identification d’un nombre de paramètres matériau limité. La démarche de modélisation a été progressive. Lors de la première étape, nous avons proposé et validé une loi d'homogénéisation élasto-viscoplastique à champs moyens, grâce à de nombreux calculs par éléments finis, en considérant des durcissements plastique et des viscosités cristallines. Ensuite, un modèle de viscoPlasticité cristalline, reposant sur les lois d’évolution des densités de différents types de dislocations, a été implémenté et les prédictions ont été validés en considérant un très grand nombre de résultats expérimentaux à faible. Le modèle a ensuite été enrichi afin de prendre en compte les mécanismes physiques supplémentaires observés à température élevée, comme la montée des dislocations, le vieillissement dynamique et l’apparition d’une structure de dislocation très hétérogène. Le modèle proposé nécessite uniquement l’ajustement de trois paramètres par identification inverse, utilisant seulement des essais de traction monotone avec saut de vitesse. Les prédictions du comportement mécanique en chargement uniaxial et cyclique sont également en bon accord avec les mesures expérimentales aux températures élevées
Stephane Berbenni - One of the best experts on this subject based on the ideXlab platform.
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multi laminate Plastic strain organization for non uniform tfa modeling of poly crystal regularized Plastic flow
International Journal of Plasticity, 2008Co-Authors: P Franciosi, Stephane BerbenniAbstract:Abstract A recently presented single Plastic-potential, microstructure-based model of poly-crystal Plasticity by the authors considers a globally regularized Schmid law (RSL) as the slip flow criterion of a homogeneous equivalent super-crystal. The homogenization scheme that is taken of affine type is specialized to the transformation field analysis (TFA) framework. The relevancy of the TFA here results from a description of intra-Crystalline slip in terms of hierarchical multi-laminate (HML) structures that ensure the request of piece-wise homogeneous Plasticity. This RSL–TFA–HML modeling has been shown efficient for heterogeneous intra-Crystalline Plastic slip in terms of overall stiffness estimates when laminates are parallel to slip planes or normal to slip directions. It is also suitable for twinning modes of crystal Plasticity as stressed in this paper. The performed superposition of all possible HML Plastic strain modes makes the TFA of the non-uniform (NTFA) and coupled type proposed by Michel and Suquet [Michel, J.C., Suquet, P., 2003. Non-uniform transformation field analysis. International Journal of Solids and Structures 40, 6937–6955; Michel, J.C., Suquet, P., 2004. Computational analysis of nonlinear composite structures using the non-uniform transformation field analysis. Computer Methods in Applied Mechanics and Engineering 193, 5477–5502]. In this new contribution, we investigate further our extension of this modeling to poly-crystals. It is interpreted as based on a description of the aggregate morphology in terms of the distribution of the crystallographic orientations of the grain boundary and sub-boundary facets, rather than in terms of a mean grain or domain shape. In its initial form, our extension amounted to assuming all these facets oriented either parallel to slip planes or normal to slip directions, what is proved convenient for large enough grains. In order to extend the relevancy of the modeling down to ultra-fine grains, we introduce a graded form of the modeling that is made grain size dependent from specifying the conditions for which the TFA accommodation hardening is negligible according to the range of the physical one. Some numerical stiffness comparisons from this graded RSL–TFA–HML modeling are provided.
P Franciosi - One of the best experts on this subject based on the ideXlab platform.
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multi laminate Plastic strain organization for non uniform tfa modeling of poly crystal regularized Plastic flow
International Journal of Plasticity, 2008Co-Authors: P Franciosi, Stephane BerbenniAbstract:Abstract A recently presented single Plastic-potential, microstructure-based model of poly-crystal Plasticity by the authors considers a globally regularized Schmid law (RSL) as the slip flow criterion of a homogeneous equivalent super-crystal. The homogenization scheme that is taken of affine type is specialized to the transformation field analysis (TFA) framework. The relevancy of the TFA here results from a description of intra-Crystalline slip in terms of hierarchical multi-laminate (HML) structures that ensure the request of piece-wise homogeneous Plasticity. This RSL–TFA–HML modeling has been shown efficient for heterogeneous intra-Crystalline Plastic slip in terms of overall stiffness estimates when laminates are parallel to slip planes or normal to slip directions. It is also suitable for twinning modes of crystal Plasticity as stressed in this paper. The performed superposition of all possible HML Plastic strain modes makes the TFA of the non-uniform (NTFA) and coupled type proposed by Michel and Suquet [Michel, J.C., Suquet, P., 2003. Non-uniform transformation field analysis. International Journal of Solids and Structures 40, 6937–6955; Michel, J.C., Suquet, P., 2004. Computational analysis of nonlinear composite structures using the non-uniform transformation field analysis. Computer Methods in Applied Mechanics and Engineering 193, 5477–5502]. In this new contribution, we investigate further our extension of this modeling to poly-crystals. It is interpreted as based on a description of the aggregate morphology in terms of the distribution of the crystallographic orientations of the grain boundary and sub-boundary facets, rather than in terms of a mean grain or domain shape. In its initial form, our extension amounted to assuming all these facets oriented either parallel to slip planes or normal to slip directions, what is proved convenient for large enough grains. In order to extend the relevancy of the modeling down to ultra-fine grains, we introduce a graded form of the modeling that is made grain size dependent from specifying the conditions for which the TFA accommodation hardening is negligible according to the range of the physical one. Some numerical stiffness comparisons from this graded RSL–TFA–HML modeling are provided.