Digital image correlation analysis (crack wetting test)

In order to evaluate the effect of moisture on the deformation of an individual macroscopic fracture within an unsaturated granite, we used the digital image correlation (DIC) method to measure strains across an induced tensile fracture in a Herrnholz granite prism (63 × 90 × 33 mm, width: height: thickness) undergoing unidirectional capillary-driven water imbibition in two orientations (from the crack tip, and the crack mouth). The DIC analysis was undertaken using the open-source 2D digital image correlation software Ncorr. It tracks surface deformation by correlating the best fit between pixel values within a defined search window in images taken during progressive wetting of the sample to those in the reference image acquired immediately prior to the water introduction.