Dynamic Mechanical Properties and Fracturing Behavior of Marble Specimens Containing Single and Double Flaws in SHPB Tests

Dynamic impact tests were conducted on rectangular marble specimens with flaws to investigate the effect of the flaw angles and ligament angles on the rock dynamic mechanical properties, fracturing behavior, and energy evolution characteristics. A 75-mm diameter split Hopkinson pressure bar (SHPB) device was used in the tests. The experimental results show that the flaw geometries have a strong effect on the dynamic mechanical properties and fracturing behavior of rocks. In general, the effects of the flaw angle and flaw number on the dynamic strength are more significant than the effect of the ligament angle. A high-speed camera was used to monitor and record the crack initiation and coalescence and the failure processes of the marble specimens in real-time. The crack propagation can be divided into two major stages, i.e., the formation of white patches and the generation of macrocracks. The white patches usually appear prior to the peak stress of the specimen. The shear cracks usually initiate at or near the flaw tips and propagate to form X or half-X shear belts that dominate the macroscopic failure under impact loading. Nine types of crack coalescence behaviors are identified for the marble specimens with double flaws, and the macro failure modes of the specimens is usually combined by some of them. The energy absorption properties of the marble specimen are also significantly affected by the pre-existing flaws. The energy absorption ratio can be maximized by setting a certain number of pre-existing flaws with an appropriate inclination angle and a proper ligament angle to effectively improve the fragmentation efficiency of rocks.