Experimental and numerical studies on fracture characteristics of notched granite beams under cyclic loading and unloading

In underground engineering, such as mining engineering and deep tunnel engineering, the rock is often loaded and unloaded repeatedly. The strength of rock under cyclic load is lower than that under static load. To obtain the fracture response of the rock, the three-point bending tests of notched granite beams under cyclic loading and unloading were carried out with Electro-hydraulic Servo Material Test System. The acoustic emission technology was adopted to monitor the acoustic emission events of sample in the process of fracture. It is revealed that the fracture toughness of granite under cyclic loading and unloading is lower than that under static loading. Based on the acoustic emission energy obtained from monitoring, the damage evolution during cyclic loading and unloading was analyzed. The fracture mode of granite samples is analyzed by the RA value-average frequency correlation method. And the Felicity ratio during the loading and unloading cycle was calculated to evaluate the severity of initial damage of the material. It is revealed that Kaiser effect appears only in the elastic deformation stage of cyclic loading unloading bending. The Holmquist–Johnson–Cook damage constitutive model and Weibull distribution were used to establish the heterogeneous granite model. And the three-point bending of the model under cyclic loading and unloading was simulated to disclose the crack growth mechanism of rock. The study may provide some references for rock instability control in geotechnical engineering construction.