Mode I fracture properties and energy partitioning of sandstone under coupled static-dynamic loading: Implications for rockburst

Abstract

A series of mode I fracture tests under coupled static-dynamic loading were performed on notched semi-circular bend (NSCB) sandstone specimens using the split Hopkinson pressure bar (SHPB) to investigate the dynamic fracture properties and energy partitioning, which can help further elucidate the rockburst mechanism and its kinetic energy source. The fracture processes were captured by the high-speed camera and the digital image correlation (DIC) technique was used. Effects of dynamic loading rates and static pre-load were then analyzed and highlighted. As the loading rate increases, the crack initiation toughness, crack propagation velocity, crack propagation toughness and energy dissipation (including fracture energy and kinetic energy) all increase, while the proportion of kinetic energy decreases. Low pre-load increases the above parameters compared to no pre-load, while high pre-load does the opposite. All the above behaviors are then explained from a perspective of micro-fracture. The mismatch between energy release and energy requirement for fracture is the cause of the kinetic energy of rockburst, and it can be characterized by the established realistic energy release rate (RERR) index.