Effects of Rock Texture on Digital Image Correlation

Digital image correlation (DIC) is a non-contact optical method that can provide high-resolution strain and displacement measurements, but its effectiveness depends on surface texture contrast. This study investigates the effects of surface characteristics on the quality of DIC results in tonalite and marble samples under Brazilian tests. Tonalite samples have a coarse texture with a heterogeneous mineral composition; therefore, DIC analysis was conducted without artificial speckle patterns. Marble, instead, poses a challenge due to its uniform fine texture and composition. Thus, using point and line grids to enhance surface contrast, artificial speckle patterns were applied to marble samples. A total of 39 disk samples (12 tonalite and 27 marble) were tested with video frames recorded during loading and analyzed using Ncorr software. The results confirmed that tonalite’s natural texture allows accurate strain mapping without artificial speckle patterns. In contrast, marbles without speckles are not effective in strain evolution mapping due to a lack of surface contrast. Marble with both point- and line-speckled patterns effectively mapped the strain evolution except for some distortion and directionality along speckles in displacement fields. This result suggests that the preparation of speckled surfaces need special attention for effective deformation evolution mapping in homogeneous materials.