Modelling the distribution of lattice strains following plastic deformation of a polycrystal. Application to aluminum AA 7075 T6

A modelling approach is described for computing the contribution to neutron diffraction peaks from variations in lattice strains in a polycrystalline material which has been subjected to plastic deformation. A grain-by-grain finite element formulation combined with crystal elastoplasticity was used to calculate the evolution of elastic lattice strains under loading conditions consistent with experiments performed on aluminum AA 7075 T6 samples. Eleven groups of crystals were associated with eleven measured neutron diffraction peaks. The full distribution of lattice strains was obtained for each of the crystal groups, thereby giving equivalent "digital" diffraction peaks. The model was able to incorporate various microstructural and material parameters. The impact of those parameters on the calculated diffraction peak profiles was studied, focusing on the Probability Distribution Functions best representing those profiles. It was found that Weibull and Gaussian distributions compete, with an advantage given to the former, due to its ability to account for skewness.