Abstract: There are a large number of cracks inside the rock mass. Due to the existence of fillers, the crack surface is closed in most cases, and friction will be generated when subjected to external forces, which will affect the crack initiation mode and propagation behavior of the rock mass cracks. Therefore, in order to study the crack initiation mode and propagation behavior of closed cracks, a rock-like material PMMA plexiglass plate was used to make pre-splitting specimens containing closed cracks, and uniaxial compression tests were performed on the specimens. Digital image correlation system (DIC) recorded the initiation and propagation characteristics of closed cracks. In addition, the extended finite element method (XFEM) was used to simulate the initiation and propagation of closed cracks, the failure process of the specimens with closed cracks was obtained through simulation, and the initiation and propagation characteristics of closed cracks were analyzed, which was in good agreement with the test results. The validity of the numerical simulation is verified. On this basis, the crack inclination angle and the friction coefficient of the crack surface are introduced as variables, and their influence on the crack initiation and propagation behavior of closed cracks is simulated. The research results show that the cracks generated under the condition of crack closure are airfoil tension cracks. Crack inclination and crack surface friction coefficient have a greater impact on the crack initiation mode and growth behavior of closed cracks. The larger the crack inclination angle is, the larger the crack initiation angle is. On the contrary, the larger the friction coefficient of the crack surface is, the smaller the crack initiation angle is. In addition, the friction coefficient of the crack surface has an inhibitory effect on the growth of closed cracks, and as the friction coefficient continues to increase, the inhibitory effect becomes more and more significant, and crack arrest occurs.

Key words: closed crack, friction coefficient, DIC, extended finite element, crack growth behavior