Thermomechanical couplings in crystalline plasticity under fatigue loading

Polycrystalline metallic materials are made of an aggregate of grains more or less well-oriented, with respect to the loading axis, for plastic gliding. Under mechanical loading, this leads to a heterogeneous deformation at the microstructure scale. This local plasticity, linked to fatigue damage, triggers a heterogeneous thermal dissipation linked to mechanical irreversibilities. Some original experimental works enabling the simultaneous determination of thermal and strain fields, in the same area, at the microstructure scale have already been realized in the laboratory on a A316L steel [1]. Two complementary ways have now to be followed: some additional numerical treatments in order to access experimental sources of dissipation and the development of the corresponding constitutive modeling at the grain scale. This second aspect is presented in this communication and concerns the implementation in the ABAQUS FE code of a constitutive model in large deformations and in coupled crystalline thermoplasticity. Using a fictive microstructure, based on a random distribution of, crystallographic orientations, and grain sizes, it enables to compare the kinematic and thermal distributions during monotonic tests, study the heterogeneity of stored energy at grain scale and test the consistent of behavior law under cycle numerical loading. Experimental analysis and simulation of thermomechanical coupling at the grain scale, seen as the sign of local damage, could lead to the definition of new thermodynamically based fatigue criteria.