Investigation of Large Grained Samples — Principles

In order to analyse the residual stresses in large grained materials, the single crystal anisotropy has to be considered in calculating the stresses from the experimental strain data. Therefore an evaluation of the crystallite under study is necessary. The procedure for establishing the orientation matrix from two observed reflections is described. Using a four-circle-diffractometer the knowledge of the orientation matrix then allows the calculation of the diffractometer setting for every given reflection (hkl). So this method is well suited for an automized measuring routine which gives the strain tensor based on the experimentally determined diffraction angles 2θ for several reflections of an individual grain. For the refinement of the strain tensor components the least-squares method is used. The stress tensor referred to the crystal axes system is then calculated using the single crystal elastic constants. To compare the stress states in different crystallites, their stress tensors have to be transformed into a common reference system.