Imaging strain localization by X-ray radiography and digital image correlation: Deformation bands in Rothbach sandstone

Three samples of Rothbach sandstone cored perpendicular, obliquely (45°) and parallel to the bedding were triaxially compacted at 140 MPa effective pressure. X-ray radiographs were acquired before and after the experiment, and two-dimensional digital image correlation (DIC) was used to map out the spatial distribution of compactive strain in these samples and investigate the effect of the bedding on the development of strain localization. Our technique could resolve the spatial distribution of strains on the order of 10−3, and DIC of X-ray radiographs of the three samples underscores different modes of localization. While diffuse compaction bands and compactive shear bands developed in the samples perpendicular and oblique to bedding, relatively homogenous compaction was observed in the sample cored parallel to bedding. The strain patterns inferred from 2D DIC were confirmed by complementary microstructural study including quantitative characterization of crack density. This feasibility study demonstrates the potential of extending this technique to higher resolutions using 3D X-ray CT data of triaxially compressed rock samples.