Investigation on mixed-mode II-III fracture of the sandstone by using eccentric cracked disk

Most of the fractures in deep rock mass are in compression condition. The deep rock failure is complex and different modes of failure play important roles. In this study, the central cracked circular disk specimen was improved by deviating from the distance between the crack on the circular surface and the center of the circle, and a new mixed-mode II-III fracture specimen called the eccentric crack disk (ECD) specimen was proposed. The ECD specimen was a simple structure and easy to machining with low cost. In addition, it could be tested in conventional loading machines without extra fixtures. The finite element was used to calculate mode I, mode II and mode III stress intensity factors for different loading angles and crack deviation distances. The critical loading angles of mixed-mode II-III fracture under different crack deviation distances were obtained. And the mixed-mode II-III fracture experiments were carried out with sandstone. The experimental results clearly revealed that the crack initiation started from the middle of the crack. The experimental data also conformed to the effective stress intensity factor criterion of mixed-mode II-III mode fracture from the literature.