Analysis of energy dissipation and crack evolution law of sandstone under impact load

Abstract

Based on the split Hopkinson pressure bar (SHPB) laboratory tests, the dynamic mechanical properties and failure mode of sandstone are analyzed, and a SHPB numerical model is established by particle flow code (PFC). The dynamic stress equilibrium, stress wave propagation, stress-strain characteristics and failure mode are analyzed, respectively, which verifies the effectiveness of the model. Then we studied the impact failure process form both mesoscopic cracks and energy point of views. The results show that microcracks are activated in large quantities with the increasing of strain rate. When the crack density reaches a certain degree, the interaction between the cracks can not be ignored. The failure mode gradually changes from local tension–shear damage mode to axial splitting failure mode and then to crushing failure mode. During the impact failure process, the energy is mainly consumed by the generation of the cracks and the friction caused by the slip of the particles, namely, broken dissipation energy. As the impact load increases, the broken dissipation energy density shows the high–speed growth and the low–speed growth stage successively with a double exponential growth pattern. The friction energy increases continually by a certain percentage, which indicates it should be considered during the analysis of fracturing process. Moreover, the dynamic strength and fragmentation degrees are closely related to energy dissipation density.