The effect of three-dimensional grain morphology on the deformation at a free surface in polycrystalline aggregates is investigated by means of a large scale finite element and statistical approach. For a given 2D surface at z = 0 containing 39 grains with given crystal orientations, eight 3D random polycrystalline aggregates are constructed having different 3D grain shapes and orientations except at z = 0, based on an original 3D image analysis procedure. They are subjected to overall tensile loading conditions. The continuum crystal plasticity framework is adopted and the resulting plastic strain fields at the free surface z = 0 are analysed. Ensemble average and variance maps of the plastic strain field at the observed free surface are computed. In the case of elastoplastic copper grains, fluctuations ranging between 2% and 80% are found in the equivalent plastic slip level at a given material point of the observed surface from one realization of the microstructure to another. The obtained fields are compared to the prediction based on the associated columnar grain microstructure, often used in literature.
The effect of three-dimensional grain morphology on the deformation at a free surface in polycrystalline aggregates is investigated by means of a large scale finite element and statistical approach. For a given 2D surface at z = 0 containing 39 grains with given crystal orientations, 17 random 3D polycrystalline aggregates are constructed having different 3D grain shapes and orientations except at z = 0, based on an original 3D image analysis procedure. They are subjected to overall tensile loading conditions. The resulting stress-strain fields at the free surface z = 0 are analysed. Ensemble average and variance maps of the stress field at the observed surface are computed. In the case of an anisotropic elastic behaviour of the grains, fluctuations ranging between 5% and 60% are found in the equivalent stress level at a given material point of the observed surface from one realization of the microstructure to another. These results have important implications in the way of comparing finite element simulations and surface strain field measurements in metal polycrystals.
International audienceThe global response of polycrystalline aggregates is investigated, in order to simulate grain size effects in IF ferritic steels. The mechanics of generalized continua is used to describe the studied phenomena. The polycrystal is regarded as a heterogeneous Cosserat medium, and the overall properties are estimated using a specific homogenization technique. To illustrate the capabilities of the model, some simple bidimensionnal computations are presented for different grain sizes. Afterwards tridimensionnal computations are shown in order to extract the global effect on the mechanical behaviour for grain sizes ranging from 5 µm to 120 µm. The finite element response is harder for the smallest grain size, but the model still underestimate the grain size effect on the tensile respons
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