Strain determination from digital image correlation of Laue diffraction spots

Accurate strain/stress characterization has important implications in practice, where it is typically connected with safe operation of engineering components. Improving the accuracy and spatial resolution of the measurement techniques can be therefore very beneficial for materials science by helping the understanding of complex material behaviour and the development of novel materials with improved properties [Borbély, A. (2015). J. Appl. Cryst. 48, doi:10.1107/S1600576715018981]

Strain measurement by diffraction methods is based on Bragg’s law, which in the case of a strained crystal predicts a shift of the diffraction peaks compared to their position measured on a reference state. Classically this shift is determined as the difference between the corresponding absolute peak positions. In view of the large number of parameters needed to measure these absolute readings it is interesting to ask what the accuracy of today’s X-ray diffraction (XRD) methods are and how these might be improved.

Two recently published articles by [Petit et al. (2015). J. Synchrotron Rad. 22, 980-994; doi:10.1107/ S1600577515005780] and [Zhang et al. (2015). J. Appl. Cryst. 48, doi:10.1107/S1600576715018397] introduce evaluation schemes based on the shift of diffraction peaks determined by digital image correlation (DIC). This new approach eliminates the uncertainties related to the choice of an adequate mathematical model describing the experimental intensity distribution. The papers explain in a clear and intuitive way why the innovative idea of applying DIC to diffraction peaks works so well for Laue spots.

The authors go on to discuss additional implications of the DIC technique for strain determination by diffraction methods.