Experimental study on the crack propagation and acoustic emission characteristics of notched rock beams under post-peak cyclic loading

Rocks in nature are often subjected to cyclic loads caused by earthquakes, which still exist after the rock reaches its maximum bearing capacity. To obtain the crack propagation characteristics of rocks under post-peak cyclic loading, notched granite beams were tested by means of three-point bending test method combined with digital image correlation (DIC) and acoustic emission (AE) technology. The horizontal strain, horizontal displacement and crack development characteristics of rock surface were obtained by DIC. Correspondingly, the acoustic emission characteristics, such as ring count and b value, were also used to monitor and analyze the development of micro cracks and macro cracks. Our results show that the strain concentration area accumulates and propagates along both sides of the crack. In the initial post-peak cycle stage, the effective crack length first appears the characteristics of reciprocating increase, then increases rapidly until it is stable. While the crack opening displacement increases reciprocally with each cyclic loading and unloading. From the AE characteristics, the ringing counts increases gradually with the loading and a significant counts rise occurs at unloading stage. For the b value, it also shows a cyclic change with the post-peak cyclic loading. The amplitude of b value gradually increases to the maximum and then decreases to a stable level with the increase of the number of post-peak cycles. This indicates that rock fracture crack propagation undergoes a reciprocating, rapid and gradual stabilization process with the increase of cycle times under post-peak cycling.