Modélisation du comportement des poudres métalliques à l'échelle du grain

The mechanical behaviour of granular materials, and, in particular, of metal powders, can be studied through discrete simulations, in which the material is modeled as an assembly of discrete particles. The method developped in this thesis consists in the modelling of a powder sample in the finite-element code ABAQUS, as an assembly of spherical meshed particles. The mechanical response of the sample to various loading paths is then simulated. The first part of the present work uses this method to extend the discrete-element method to the modelling of high relative density compaction. The finite-element-based discrete simulations method gives useful information about the non-linear behaviour of the grains at contacts. This information allows the formulation of a contact model which describes the complex interactions between dierent contacts at high relative densities. This model is then implemented in the discrete-element code YADE, so that the results of both methods can be compared. In the last part of this thesis, a numerical sample is submitted to loading paths in every direction of the stress space, to probe macroscopic yield surfaces. The focus is put on the evolution of yield surfaces with complex loading histories including changes in the loading direction, in order to obtain valuable indications on the materials' memory. Moreover, the micromechanical phenomena which cause the macroscopic evolution of yield surfaces can be understood through the observation of the microstructure.Le comportement mécanique des matériaux granulaires, et en particulier des poudres métalliques ductiles, peut être appréhendé par l'intermédiaire de simulations discrètes dans lesquelles les grains sont modélisés. Cette méthode a l'avantage de permettre l'exploration de chemins de chargement inaccessibles à une approche expérimentale. La méthode développée dans cette thèse consiste à modéliser des assemblages de sphères maillées dans le logiciel d'éléments finis ABAQUS pour effectuer des simulations en appliquant divers chemins de chargement. La première partie de ce travail consiste à utiliser cette méthode pour enrichir la méthode des éléments discrets en l'étendant au domaine de la compression à haute densité relative. La méthode de simulations discrètes par éléments finis donne des informations précieuses sur les déformations non-linéaires des grains aux contacts. Ces informations permettent de proposer un modèle de contact qui gère les interactions complexes entre les diérents contacts à haute densité relative. Par la suite, ce modèle est introduit dans le code d'éléments discrets YADE, et les résultats des deux méthodes peuvent être comparés. Dans la seconde partie de cette thèse, un échantillon numérique est soumis à des sollicitations dans toutes les directions de l'espace des contraintes, pour obtenir les surfaces de charge macroscopiques. L'accent est mis sur l'évolution des surfaces de charge lors de chargements complexes, avec des changements de direction, afin d'obtenir des indications sur la mémoire du matériau. Enfin, l'observation de la microstructure de l'échantillon permet de comprendre les phénomènes micromécaniques qui sont à l'origine de l'évolution macroscopique des surfaces de charge

The study of relations between loading history and yield surfaces in powder materials using discrete finite element simulations

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Strength characterization of rock masses, using a coupled DEM-DFN model

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Modelling polymeric deformable granular materials - from experimental data to numerical models at the grain scale

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A study on the uniqueness of the plastic flow direction for granular assemblies of ductile particles using discrete finite-element simulations

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Influence of particle deformation on the plastic flow of ductile granular materials

International audienceA multi-particle finite-element method was proposed to study the elastic-plastic behaviour of ductile powders composed of highly deformable elastic-plastic particles. The focus was put on the study of the uniqueness of the direction of plastic strain increment vectors for a given stress state on the plastic limit, which was assessed using a spherical stress-probing method. Results revealed a non-uniqueness of the direction of plastic flow in a small region of the stress space located in the vicinity of the loading point. The direction of plastic flow was almost unique elsewhere on the plastic limit. The non-uniqueness was explained using a combination of two distinct mechanisms for plastic deformation involving two very different plastic limits

Numerical analysis of granular bed behavior in thermocline storage tank and bed/wall interactions

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Thermal stress numerical study in granular packed bed storage tank

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Thermal stress numerical study in granular packed bed storage tank

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Rock-bed thermocline storage: A numerical analysis of granular bed behavior and interaction with storage tank

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