Numerical assessment of the rate-dependent cracking behaviours of single-flawed rocks in split Hopkinson pressure bar tests

Abstract

This paper numerically investigated the rate-dependent progressive cracking behaviours of single-flawed rock specimens in split Hopkinson pressure bar (SHPB) tests. First, a 3D numerical SHPB system is established based on the discrete element method (DEM). By comparing with our laboratory experiments, micro-parameters of the DEM model are calibrated, which guarantees the reliability of the numerical simulations results. Via slice-cutting view, the inner and surface progressive cracking processes are explicitly revealed and compared, which compensates some defects in laboratory tests. Our numerical simulation results show that the progressive cracking behaviours of the single-flawed rock specimens exhibit evident rate dependence. Under low strain rates, tensile wing cracks dominate the entire cracking process, and only a few shear cracks appear during the post-peak stage. In contrast, under high strain rates, tensile wing racks are significantly suppressed, while anti-wing cracks and shear cracks are fully developed, leading to the final X-shaped failure modes. In addition, progressive cracking behaviours of the single-flawed rock specimens with different flaw inclination angles are assessed. Via stress field visualization and theoretical analysis, the different initiation locations of tensile wing cracks are explained. Furthermore, based on the generalized maximal tangential stress (GMTS) criteria, the fracture initiation angles of tensile wing cracks are predicted. The results show that the fracture initiation angles and the fracture process zone (FPZ) are significantly affected by the strain rate. The length of FPZ under dynamic loads is evidently longer than that under static loads, and the length of FPZ generally increases with an increasing strain rate, exhibiting evident rate dependence.