A MICROMECHANICAL APPROACH TO INELASTIC BEHAVIOR OF METALS

This paper describes micromechanical constitutive equations for polycrystals and shows their modeling capabilities. The field of interest of the model concerns monotonic and cyclic multiaxial loadings, with the assumption of small perturbation. First we discuss the type of physical variables that have to be introduced on a microscale. The case of FCC metals is especially investigated, so that the localization process includes the evaluation of stresses and strains for each grain and each octahedral slip system. The stress-strain relations are written on a microscale for each slip system. All the elementary contributions are then summed up to obtain the macroscopic strain rate. Two types of applications are shown. One deals with the representation of yield surfaces for a 2024 aluminium alloy tested at room temperature. A good agreement is found between numerical simulations and experiments for the initial and the subsequent surfaces after tension-torsion loading paths. The second identification is made on a 316L stainless steel, also tested in tension-torsion at room temperature. For this last case, the model is able to account for the memory effect and the supplementary hardening related with the non-proportionality of the loading path.