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a b s t r a c tVoid growth and coalescence in single crystals are investigated using crystal plasticity based 3D finite element calculations. A unit cell involving a single spherical void and fully periodic boundary conditions is deformed under constant macroscopic stress triaxiality. Simulations are performed for different values of the stress triaxiality, for different crystal orientations, and for low and high work-hardening capacity. Under low stress triaxiality, the void shape evolution, void growth, and strain at the onset of coalescence are strongly dependent on the crystal orientation, while under high stress triaxiality, only the void growth rate is affected by the crystal orientation. These effects lead to significant variations in the ductility defined as the strain at the onset of coalescence. An attempt is made to predict the onset of coalescence using two different versions of the Thomason void coalescence criterion, initially developed in the framework of isotropic perfect plasticity. The first version is based on a mean effective yield stress of the matrix and involves a fitting parameter to properly take into account material strain hardening. The second version of the Thomason criterion is based on a local value of the effective yield stress in the ligament between the voids, with no fitting parameter. The first version is accurate to within 20% relative error for most cases, and often more accurate. The second version provides the same level of accuracy except for one crystal orientation. Such a predictive coalescence criterion constitutes an important ingredient towards the development of a full constitutive model for porous single crystals.

Rolling textures of low-carbon steel predicted by full constraints and relaxed constraints Taylor models, as well by a self-consistent model, are quantitatively compared to experimental results. It appears that none of these models really performs well, the best results being obtained by the Pancake model. A new model ("Lamel model") is then proposed as a further development of the Pancake model. It treats a stack of two lamella-shaped grains at a time. The new model is described in detail, after which the results obtained for rolling of low-carbon steel are discussed. The prediction of the overall texture now is quantitatively correct. However, the "),-fibre components are better predicted than the a-fibre ones. Finally it is concluded that further work is necessary, as the same kind of success is not guaranteed for other cases, such as rolling of f.c.c, materials.

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International audienceAn original approach is proposed in order to compute the homogenized response of composite materials with elasto-(visco) plastic constituents. The formulation is based on an incremental variational principle according to which the local stress-strain relation derives from a single incremental potential constructed from a free energy and a dissipation function. Both rate-dependent and rate-independent plasticity are handled within the same framework through the choice of the dissipation function. The key feature of the model is the explicit use of the elastic trial strain in order to define a Linear Comparison Composite whose mechanical response coincides with the response of the actual composite at a given time step. The hereditary character of the behavior is accounted for through internal variables. The method was successfully applied to several two-phase elasto-plastic and elasto-viscoplastic composites made of a continuous matrix reinforced by ellipsoidal inclusions. General loading conditions, including cyclic ones, were considered. The proposed method provides accurate predictions of the macroscopic response in many cases, and competes with previously proposed schemes in elasto-(visco) plasticity

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