Multiscale Damage Analyses of Red Sandstone in Uniaxial Compression Based on Advanced Digital Volume Correlation

X-ray computed tomography (XCT) combined with digital volume correlation (DVC) has proven to be a powerful tool for bulk deformation measurements of rocks subjected to in-situ experiments. Traditional DVC (i.e., local/global approaches) is generally applied to roughly characterize damage growth by mapping strain localization. However, due to the brittleness of sandstone, damage detection and quantification are very challenging for small spatial resolutions, especially at the microscale (i.e., voxel levels). In this paper, an advanced global approach (i.e., multimesh DVC) was developed, in which mechanical regularization, brittle damage law, and mesh refinement were considered. Such DVC scheme provides an adapted mesh based on damage activity to measure crack opening displacements at the mesoscale and eventually at the voxel scale. An in-situ uniaxial compression test applied to red sandstone was carried out. Kinematic fields and damage development were analyzed at different scales via multimesh DVC. Macroscale (i.e., specimen-scale) analyses showed the overall deformation characteristics of the specimen by mean strain curves. Mesoscale (i.e., element-scale) results displayed the crack opening displacement fields at sub-voxel resolution. Microscale (i.e., voxel-scale) studies focused on local damage growth using extremely small spatial resolutions (i.e., one voxel). All these investigations quantitatively revealed microcrack initiation, propagation, and coalescence to form the final macrocrack, providing a powerful proof for understanding damage mechanisms in rocks.