Effect of elastic anisotropy on strain relief and residual stress determination in cubic systems by FIB-DIC experiments

The focused ion beam milling assisted digital image correlation (FIB-DIC) method has recently proven to be effective to measure residual stresses of coatings and in bulk materials. In this work, the effect of elastic anisotropy on residual stress measurements is studied for single crystalline materials. 3D elastic anisotropic finite element models of the double slot milling geometry were developed, which consider the crystallographic orientation of the samples. In order to verify the finite element analysis, FIB-DIC measurements were performed on bent samples of nanocrystalline nickel and single crystalline CMSX-6 alloy. A well-defined stress state was generated by deforming the samples elastically in an in-situ four-point bending device. The FIB-DIC double slot analysis was performed along the sample section to measure the applied bending stresses. The classical bending beam theory provides reference stress values and thus a validation of the measured stress and strain values is possible. It was found, that the theoretically calculated strains agree well with the measured strains, and a discussion on the limitations of the assumptions at the basis of the model is presented.