Abstract: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, to study on the type I fracture mechanical characteristics and deformation of red sandstone under cyclic loading and unloading feature.Based on the macro-mechanical parameters of red sandstone, PFC3D numerical simulation experiment was conducted to investigate the law of microcrack propagation.The experimental results are as follows. The effect of cyclic loading will make the type Ι fracture toughness(KΙC) decreased,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 its static loading curve.The deformation at the cyclic loading failure point is similar to the post-peak deformation at the same load level in the static load curve.The process of radial displacement and deformation of the specimen 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 and microcrack propagation of the sample are only in the initial and acceleration stages.When the upper limit ratio is 0.75, the displacement deformation and microcrack propagation are only in the initial and stable stages, and no fracture failure occurs.Under cyclic loading, the micro-cracks in the fracture process zone (PFZ) at both ends of the ligament of the sample were fully derived and expanded, and the number of final micro-cracks was significantly more than that under static loading.