A split Hopkinson pressure bar for experimental investigation of dynamic pulverization under very high strain rates.

Off-fault damage or pulverized rocks found in large-scale strike-slip faults are of great interest in earthquake research. In order to experimentally investigate rock pulverization, we developed a split Hopkinson pressure bar with compact dimensions and high-speed imaging. The developed experimental setup is capable of generating very high strain rates up to 1320 s-1 with the satisfaction of stress equilibrium, which are essential to reproduce the dynamic pulverization observed in nature and obtain dynamic stress-strain responses accurately. High-speed imaging revealed that cracks initiate and propagate along the grain boundaries at very high speeds, while the dynamic stress-strain response suggested that energy dissipated into the fracture increases with stronger impacts. In addition, we show that the apparatus is capable of producing particle size distributions partly similar to those in naturally pulverized rocks of large-scale strike-slip faults. Thus, our developed system with compact dimensions opens new ways to understand the dynamics of the rock pulverization in off-fault regions of large-scale strike-slip faults.