Mixed-Mode Fracture Behaviour of Semicircular Bend Shale with Bedding Layer

The intersection of fractures, particularly the intersection of discontinuities, occurs frequently in practical engineering, mainly manifesting as a mixed-mode failure. In the present study, the three-point bend test was conducted on the semicircular bend (SCB) of pre-cracked shale samples with a bedding layer. A numerical model for simulating mixed-mode fracture propagation was constructed using the extended finite element method. The minimum strain energy density criterion was applied for crack initiation and propagation. According to the experimental results, the minimum strain energy density criterion better indicates the fracture path. When the approach angle was set at 30°, the mode I fracture toughness was 0.85 MPa m1/2 and the mode II fracture toughness was 0.38 MPa  m1/2. Furthermore, the mixed-mode fracture path and the crack initiation angle of the SCB with a bedding layer were discussed. As the approach angle became smaller and more prone to crack propagation, a tendency for the fracture propagation path to transfer to the fracture diversion was observed. If the Young's modulus of the layer is greater than the Young's modulus of the shale, the propagation path of the fracture would be far away from the layer. With the decrease in the tensile strength of the bedding layer, the fracture was more likely to propagate along the bedding layer orientation. The present study aimed to better understand the crack initiation and expansion in the mixed-mode fracture process with a bedding layer.