Lattice strain partitioning in a two-phase alloy and its redistribution upon yielding

Load sharing in two-phase alloys is investigated by means of finite element simulations of polycrystalline aggregates subjected to uni-axial compression. Attention is focused on the redistribution of stress as the overall load level increases and the material progresses from a purely elastic state to eventual yielding of both phases. Virtual specimens having two phases, one of iron and the other of copper, were created and subjected to compression. The lattice (elastic) strains, which are directly proportional to the stress, were examined over the course of the compression test for a system having equal volume fractions of each phase. Comparisons were made first with measurements by neutron diffraction to confirm that the simulated strains followed the observed behavior. The computed lattice strain tensors then were examined in terms of the changes in their principal directions as the overall load increased. The redirection of the stress signals a change in the relative stiffnesses of the phases, from which follows a repartitioning of stress between the phases.