Numerical approach for strain rate dependency on the dynamic tensile strength of rock

From previous research, it was revealed that the inhomogeneity of rock is a factor causing the difference of the dynamic and static strength in tension. It is, however, insufficient to verify the reason why the dynamic tensile strength increases with increasing rate of strain. In this study, to investigate the strain rate dependency of dynamic tensile strength, the fracture processes for varying strain rate with changing the length of specimen and loading conditions were conducted. From these analyses, it can be concluded that the dynamic tensile strengths increase in increasing local strain rate at fracture plane and the strength increase causes apparent strain rate dependency of the strength. The coefficient increase of uniformity stimulates the reduction of strain rate dependency, i.e., the strain rate dependency of dynamic tensile strength is caused by inhomogeneity of rock. To discuss the fracture formation for various strain rates, fracture process and principal stress field in the specimen at a high and low strain rate were analyzed. The higher strain rate generated a large number of microcracks, but the formation of fracture plane is interfered by the interaction of microcracks. In conclusion, the dynamic tensile strength increase at a high strain rate is caused by the crack arrest due to the generation of a large number of short microcracks.