On the Failure Mechanism of Brittle Granite in 2-D Rock Indentation

Abstract

Abstract Rock indentation is one of the main mechanical rock breaking approaches, in which the indenter moves perpendicular to the rock surface. A detailed understanding of the failure mechanism of brittle granite is of great importance to achieve high efficiency in rock breaking and to optimize the cutting parameters during deep hard formation drilling. In the present study, a rock indentation simulation model of Ya’an granite is carried out, using the grain-based model (GBM), which is based on the discrete element method of Particle Flow Code (PFC2D), to reproduce the crack initiation, propagation, and coalescence processes in intact rock. This study also includes an experimental program to examine the crack initiation, propagation, and the acoustic emissions in rock specimens. The results show that the microcracks generate gradually in intact rock with respect to penetration depth, and some of the microcracks coalesce with the crack number increasing, eventually resulting in the macrofracture formation. Four types of microcracks will generate during the indentation: intragrain tensile crack, intragrain shear crack, intergrain tensile crack, and intergrain shear crack. Among these four types of cracks, the intergrain tensile crack and intragrain shear crack are the two main crack types generated in indentation, especially the intergrain tensile crack. The rock failure mechanisms are different with the variation of grain size, and the lateral fragmentation of rock is restricted because of the chip hold-down effect of hydrostatic pressure. This study leads to an enhanced understanding of rock breaking mechanisms of Ya’an granite and provides the basis for improving the rock excavation machine design.