Abstract: It is great crucial for shale gas exploration and reservoir evaluation to investigate the rupture time and spatial position during the loading process of shale. Brazilian tests on shale were carried out under different angles between the loading direction and bedding planes to examine failure process. The digital image correlation (DIC) technique is adopted to track shale real-time deformation field evolution of crack initiation, propagation and coalescence during entire process, meanwhile, the force-displacement curve is recorded. Scanning electron microscopy (SEM) is applied to obtain fracture surface characteristics and microstructure of carbonaceous shale. Based on experimental data, the relationships between the loading direction and the micro fracture initiation time, spatial location, propagation rules and fracture mechanism of shale are explored. The results show that shale Brazilian disc split strength gradually increases with the increase of the angle between the loading direction and bedding plane. With the increase of the angle, the crack initiation time gradually increases, but the consumed time from crack initiation, propagation to damage decreases. The cracks basically produce from the ends of the specimen and propagate along the bedding plane. The cracks gradually develop from the middle of the specimen to the outside along with loading angle from 0° to 90° except the vertical main fracture of 90° sample. There exists a certain difference between main damage types of different shale specimen with loading directions. The fracture mode gradually transits from tension shear failure to shear sliding failure except the vertical main fracture of 90°sample with the increase of the angle between the loading direction and bedding plane.

Key words: carbonaceous shale, Brazilian split test, digital image correlation (DIC), temporospatial, anisotropy