Rock dynamic fracture of a novel semi-circular-disk specimen

The relationship between velocity, acceleration, and dynamic fracture toughness during rapid crack propagation is difficult to effectively capture. In this study, a novel semi-circular holed disc bend is proposed to achieve a long fracture path. Hopkinson pressure rods with crack growth and strain gauges are used to impact the semi-circular holed disc bend specimens and to monitor the cracking process of a mode-I fracture. The experiments show that the crack growth speed increases to a critical value after crack initiation and then oscillates as a result of the reflected stress wave. The dynamic propagation fracture toughness (K-IC(d)) increases with increasing crack velocity for steady crack propagation; however, this does not apply for unsteady propagation. An experimental-numerical-analytical method is developed to determine the dynamic stress intensity factor, which initially increases with time, then decreases, and ultimately increases again. The acceleration (v) can be used to investigate the unsteady crack propagation process. K-IC(d) values for v < 0 are greater than those for v > 0. An energy release rate formula related to v and the crack propagation velocity (v) is proposed and verified by the experiments. A thorough understanding of v, v, and K-IC(d) is important to analyze high-speed fault rupture processes.