Dynamic damage and fracture characteristics of granite under cyclic impact simulated with coupled finite-difference and discrete element methods

Dynamic impact experiments were conducted on granite using a split Hopkinson pressure bar (SHPB) to determine the strengths and fracture morphologies of granite at different strain rates. A three-dimensional (3D) SHPB numerical model was established based on the finite-difference method (FDM)–discrete element method (DEM) coupling method. The model was validated by the experimental results. The dynamic fracture characteristics and energy evolution of the granite were further investigated under cyclic impact at medium and high strain rates. The results showed that the FDM-DEM coupling method can simulate the dynamic behavior of the granite. The peak strength and failure mode of the rock exhibit strong rate dependence: with the increase of strain rate, the failure mode of the rock specimen changes from mode I to mixed mode I-II, and the failure mode changes from tensile failure to tension-shear failure. The incident energy and reflected energy are linearly correlated, whereas the transmitted energy first increases, then decreases, and finally settles at a stable value, with the increase in the strain rate; the rate of change of energy dissipation is slow at first and then increases rapidly (exponentially). Under cyclic impact loading, the strain rate increases with the number of impacts, and the peak strength decreases. Before the rock specimens completely lose their load-bearing capacity, the damage increases slowly in a quasi-linear manner, whereas it changes abruptly upon complete failure.