Spatial-Temporal Heterogeneity of Rock Samples’ Deformation and Damage: Experimental Study and Digital Image Correlation Analysis

In-situ observations and laboratory experiments showed that slow deformation waves widely exist in geomedia under loading conditions. Slow deformation waves’ behavior exhibits some similarities in media ranging from the scale as large as the Earth's crust to the scale as small as the laboratory test samples. However, the mechanism underlying their generation has not been clarified yet. In this research an experimental study was performed on small-scale red sandstone samples subjected to uniaxial compression at the displacement rates of 0.1, 0.5, and 1 mm/min. Slow deformation waves under different loading rates were analyzed by speckle photography for microscopic characterization combined with the digital image correlation (DIC) technique. The Luders deformation bands were predominantly observed in the flow channels formed at the stage of macro-elastic deformation. The spatial-temporal heterogeneity of the rock sample surface was quantified, and the deformation waves' propagation velocities under different loading rates were obtained. The linear relationship between the propagation velocities of slow deformation waves and the loading rates was determined. The research findings shed some new lights on the evolutionary characteristics of the slow deformation waves.