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International audience; In the present study, the effects of both the microstructure and defects on the high cycle fatigue behavior of the 316L austenitic stainless steel are investigated thanks to finite element simulations of polycrystalline aggregates. The numerical analysis relies on a metallurgical and mechanical characterization. To complete the experimental study, load-controlled fatigue tests are also carried out to determine the fatigue limits at 2.106 cycles under uniaxial and multiaxial loading conditions using both smooth specimens and specimens containing an artificial hemispherical surface defect. In the finite element models, where the grain morphologies are explicitly modeled, the anisotropic behavior of each crystal is described by the generalized Hooke's law and by a single crystal visco-plastic model. From the simulations carried out with different defect sizes and orientation sets, statistical informations regarding mesoscopic mechanical fields are analyzed. Then, using the FE results, the ability of a probabilistic fatigue criterion to predict the influence of defects and biaxiality on the average fatigue limits is evaluated thanks to a comparison with the experimental data.

Une analyse du comportement en fatigue à grand nombre de cycles est conduite à travers la simulation numérique d'agrégats polycristallins. Plusieurs matériaux métalliques à structure cristalline cubique à face centrée mais de coefficients d'anisotropie élastique différents sont choisis. Plusieurs volumes élémentaires statistiques (VES), constitués d'un ensemble de 300 grains de texture isotrope et de géométrie équiaxe, sont sollicités au niveau de la limite de fatigue médiane macroscopique à 10(7) cycles. Trois modélisations sont étudiées : 2D avec déformation plane généralisée, 3D périodique et 3D avec surface libre. Plusieurs variables mésoscopiques (moyenne dans les grains) issues des simulations sont analysées en utilisant la statistique des valeurs extrêmes. Les résultats montrent un effet néfaste sur la tenue en fatigue des agrégats modélisés avec une surface libre si l'anisotropie élastique cristalline est suffisante., An analysis of high cycle fatigue behavior is done via the numerical simulation of polycrystalline aggregates. Different metallic materials with a FCC crystalline structure, but different cubic elastic coefficients, are investigated. Several statistical elementary volumes (SEV), consisting of 300 grains with isotropic texture and equiaxed geometries, are loaded at the median macroscopic fatigue limit for 10(7) cycles. Three different models are studied: 2D generalized plane strain, 3D periodic and 3D periodic with a free surface. Different mesoscopic variables are analyzed using extreme value statistics. The results show a detrimental effect on the fatigue strength of the modeled aggregates with a free surface, if the crystalline elastic anisotropy is sufficient.