Self-consistent modelling of the plastic deformation of FCC polycrystals and its implications for diffraction measurements of internal stresses

Using a self consistent scheme we model the development of elastic lattice strains during uniaxial loading for selected families of grains with specific orientations. These lattice strains vary dramatically for the different grain orientations, and most families of grains show a high degree of non-linearity at the start of the plastic regime. The 311 reflection does, however, respond almost linearly to loading, and therefore it constitutes a suitable reflection for characterization of macroscopic stresses and strains by diffraction for the given conditions. As a consequence of the high degree of non-linearity in the lattice strain response during loading highly anisotropic intergranular residual lattice strains develop during unloading. The evaluation of the model predictions by neutron diffraction is exemplified by selected results from in-situ loading experiments performed on austenitic stainless steel specimens. As a necessary condition for the proper understanding of the results we have included a description of the slip pattern resulting from the model applied and its relation to the slip patterns derived from the upper-bound Taylor model and the lower-bound Sachs model. (C) 1998 Acta Metallurgica Inc.