Experimental characterization of strain localization in rock

In this study, damage evolution and strain localization in sandstone have been experimentally investigated in uniaxial compression tests. A digital image correlation technique has been applied to obtain apparent strain fields which can visually display the deformation and damage evolution of rock. The experimental results show that regions with apparent strain concentration (RASC) develop at the initial loading stage and distribute diffusely on the sample surface which may correspond to the damaged areas. With incremental load, the RASCs localize spatially, probably via coalescence into a line-shaped area that behaves like a macroscopic crack leading to the eventual failure of the specimen. A factor DRASC representing the deviation of the average apparent strain in RASCs from the average on the whole sample surface and a localization factor Lf, are proposed to characterize the evolution of damage and localization. DRASC increases slowly in the initial phase of loading and rises rapidly after the onset of localization. Lf decreases during loading which indicate the localization of spatial distribution of damage. The two factors can be used to well reflect the damage evolution and strain localization of rock specimens under compression.