On the strain-free lattice constants in residual stress evaluation by diffraction

Any discussion of methodical problems in residual stress evaluation by diffraction (X-rays or neutrons) is based on the so-called ‘general transformation equation’. The problem of the unknown strain-free lattice constants has to be treated by an appropriate use of the transformation equation. We outline several solutions known from the literature for this problem. In the most general case, we include the lattice constants and the strain/stress tensor components as unkowns into the evaluation the general transformation equation. This results in a non-linear equation system for the unknowns which can be solved numerically.