Deformation heterogeneity in copper oligocrystals using high-resolution stereo DIC

We use high-resolution stereo DIC for the first time to study the evolution of strains in copper oligocrystals up to 20% applied tensile strain. Deformation heterogeneity is corroborated with grain-to-grain misorientation angles, Schmid factors, number of active slip systems, grain size and morphology, and geometric constraints from surrounding grains. None of these characteristics can be individually correlated to the resultant deformation, but together they dictate the strain evolution. We observe that the spatial distribution of strains changes substantially through the course of deformation. The steepness of the strain gradient across similar twin boundaries evolves differently through the course of deformation. Similarly, strain localization occurs in different grains at different stages of deformation. At the initial stages, some grains show the highest strains, but with lower strain rates than some neighbouring grains so that these latter grains show more severe strain localization than the former at the later stages of deformation.