Dynamic properties and fracture characteristics of rocks subject to impact loading

Split Hopkinson pressure bar(SHPB) apparatus was used to study the factor of dynamic strength increasing, the density of dissipation energy and the fragment size of limestone, dolomite and sandstone subject to impact loading. SHPB has some difficulties to measure the higher strain rate and dynamic damage process for rock materials. The grain-based model was thus built by using the high resolution scanning and image processing technique combined with the discrete element method. The accuracy of numerical simulation was verified with the experimental SHPB results. The results indicated that the dynamic failure strength of rock material was rate dependent strongly, but the elastic modulus did not increase significantly with the increasing strain rate. The semi-empirical formula for evaluating the factor of dynamic strength increasing is consistent with the Ханукаев equation. The failure pattern of the rock transforms from the intact→splitting damage→pulverized damage with the increasing strain rate. This phenomenon is determined by the number of the micro cracks activated and the interaction between the cracks. The increase of the crack density and the change of the crack propagation path are the mechanism of the dynamic fracture of the rock, and the macrosopic responses are the rate effect and fragmentation of the material.