Mechanism of fracture in macro- and micro-scales in hollow centre cracked disc specimen

The hollow centre cracked disc (HCCD) specimen is one of the suggested alternative methods for determining the fracture toughness of rock. This work aims to investigate the fracture mechanism in HCCD in macro- and micro-scales using numerical methods, extended finite element method (X-FEM) and particle flow code (PFC) modeling, respectively. In the X-FEM, heaviside and near-tip enrichment functions are employed to consider the presence of the crack in the model. In PFC modeling the movement and interaction of stressed assemblies of rigid spherical particles are modeled using the distinct element method (DEM). A numerical code called MEX-FEM based on XFEM has been developed to simulate the problems involving crack. The models of pure modes I and II in macro-scale are simulated in micro-scale. The results show that dimensionless stress intensity factors (Y (I), Y (II)) for pure modes I and II increase by increasing the crack length ratio. The angle at which the pure mode II occurs decreases by increasing the crack length ratio. In mixed mode I-II, The value of Y (I) decreases by increasing the crack angle, while the value of Y (II) increases to a given crack angle and then it decreases. Moreover, the fracture in micro-scale, unlike the macro-scale, includes a combination of different modes of fracturing.