Experimental Analysis on Deformation Evolution and Crack Propagation of Rock Under Cyclic Indentation

Indentation-induced cracking may have many implications in rock drilling and cutting processes. In the present work, cyclic indentation tests have been conducted on Yunnan sandstones to investigate the deformation and failure process. Deformation fields on the sample surface have been obtained via the digital image correlation (DIC) technique. It has been found that the macroscopic force–indentation curve exhibits hysteresis and the residual displacements increase during the loading–unloading cycles. Furthermore, a median crack has been observed to nucleate, running almost parallel to the loading axis when the indentation force amounts to a critical value. Such a crack always results in the final failure of the sandstone samples. Experimental analysis reveals the deformation and failure mechanism of sandstone during cyclic indentation. By the DIC technique, the displacement distribution along the crack surface can be easily calculated and, hence, the fracture parameters, such as crack opening displacement and fracture toughness.