Effect of bedding direction on mode Ⅰ fracture characteristics of precrack shale

The mechanical properties of layered shales are usually anisotropic due to the influence of internal bedding azimuths. In order to explore the influence of bedding direction mode Ⅰ fracture characteristics, three point bending static compression tests and numerical simulation tests were carried out on half-disc specimens with precrack angles of 0° and different bedding dip angle β. The test results show that the mode Ⅰ standardized stress intensity factor of the specimen Y_Ⅰ varies significantly with the change of bedding angle, and presents a good cubic function relationship with bedding angle; only when the bedding angle β is 0° or 90°, the specimen shows a pure mode Ⅰ fracture mode, that is, the change of bedding angle will change the fracture mode of the specimen. At the same time, the mode Ⅰ fracture toughness of specimens decreases gradually with the increase of bedding angle, and presents a quadratic function relationship with bedding angle. When the bedding angle is perpendicular to the precrack angle, the mode Ⅰ fracture toughness of the specimen is the largest. When the bedding angle is parallel to the precrack angle, the mode Ⅰ fracture toughness of the specimen is the smallest. In addition, based on the extended finite element method(XFEM), the fracture mechanism of the half-disc layered shale specimen is studied, and the accuracy of the test and calculation results is verified.