Implications of equilibrium on principal macrostresses measured by neutron diffraction

The application of the elastic equilibrium condition σij,j=0 to stress measurements by neutron diffraction is discussed. In particular, implications of the variation of σii with xi are considered. This has relevance to evaluation of sub-surface triaxial stress measurements, especially assumptions about principal stress directions. The relations are also given for cylindrical and spherical coordinate systems. Examples of the use of the condition are presented in the context of neutron stress measurements.