X-ray determination of strain differences between the sides of a twin boundary in polycrystalline nickel

On a polycrystalline nickel sample under isotropic loading in its plane, diffracting domains have been selected on both sides of a coherent twin boundary (grain and twin). For each of these domains, average strains in several crystal directions have been measured by X-ray diffraction. The strain tensors due to the applied stress have been determined. Assuming that the material response is elastic, in the grain, constant strain and stress tensors have been found, whereas in the twin, there is a strain gradient which may be considered as linear.