An experimental methodology to relate local strain to microstructural texture

Abstract

This paper introduces an experimental methodology for obtaining high resolution full-field strain measurements in polycrystalline metals. The (sub)grain level resolution of these measurements was indispensable for relating measured strain fields to observed microstructure in the material. Microstructural information was obtained through electron backscatter diffraction and the optical technique of digital image correlation (DIC) was used to acquire full-field deformation measurements. By spatially overlaying both sets of results, the effects of different microstructural features such as orientation, grain boundary character, misorientation between grains, and twin boundaries on material response can be quantitatively studied. To obtain the necessary resolution for such measurements, the images used in DIC had to be captured at high magnifications. This necessity reduces the field of view and constrains the area of interest that can be monitored. To address this issue, results from adjacent measurement areas are combined together to create a data set with high spatial strain resolution over a larger region than can otherwise be observed. The procedure for performing this technique is outlined here, along with benefits, drawbacks, possible modifications, and example applications of the technique to cyclic plasticity and fatigue crack growth.