Numerical study of hard rock breakage under indenter impact by the hybrid FDEM

Abstract

Achieving efficient crushing of hard rocks has always been an urgent problem in mining and tunneling. A novel numerical model of rock fragmentation was developed by the hybrid FDEM (finite and discrete element method) to investigate the mechanism of hard rock breakage produced by indenter impact. Zero-thickness discrete elements embedded into the finite model were used to describe the micromechanics of the rock microscopic cementation via the mixed-mode cohesive traction response. The breakage patterns could be well reproduced by the developed numerical model, which was consistent with the experimental results. The rock breakage features, such as impact crater, crushing zone, small debris, large fragments, symmetrical cracks and lateral cracks, were closely related to the variation in the contact force. The element deletion rate at the crushing stage was larger than that of the relatively stable stage and unloading stage, with the lowest rate of element deletion. The formation mechanisms of the crushing zone, small debris, large fragments, and symmetrical cracks were different. The crushing zone formation related to the cohesive element failure in shear action; the cohesive element failure for small debris formation was caused by the combination of tensile and shear action; the symmetrical and lateral crack formations were both caused by the tensile action on the failed cohesive element, but the tensile stress that produced the cohesive element failure in the lateral crack path was from the compression stress reflected in the boundary.