Experimental and Simulation Study on Fracture Characteristics of Randstone under Cyclic Loading

The WHY-200/10 microcomputer-controlled universal testing machine was used to perform static and cyclic loading and unloading tests on cracked chevron notched Brazilian disc (CCNBD) of red sandstone, and the type I fracture mechanical characteristics and deformation feature of red sandstone under cyclic loading and unloading were studied. Based on the macro-mechanical parameters of red sandstone, PFC3D numerical simulation experiment was conducted to explore the law of microcrack propagation. The experimental results show as follows. Cyclic loading reduces the type Ι fracture toughness(KΙC) of sandstone, and with the increase of cycling times, the type Ι fracture toughness of sandstone decreases gradually until it reaches a certain threshold. The cyclic loading curve of CCNBD is strictly controlled by the static loading curve. The deformation at the failure point of the cyclic loading curve is similar to the post-peak deformation at the same load level as the static load curve. The process of radial displacement and deformation of the specimens under cyclic loading is related to the upper limit load ratio. There are mainly three stages: initial loading stage, middle stabilization stage and late acceleration stage. When the upper limit ratio is 0.95, the radial displacement deformation process and microcrack propagation of the sample occurred only in the initial and acceleration stages. When the upper limit ratio is 0.75, the displacement deformation process and microcrack propagation happen only in the initial and stable stages, and there is not fracture failure occurring. Under cyclic loading, the micro-cracks in the fracture process zone (FPZ) at both ends of the ligament of the sample were fully derived and expanded, and the number of final micro-cracks is significantly more than that under static loading. © 2021, Editorial Department of Journal of Hunan University. All right reserved.