The direct boundary element method based on the quadratic discontinuous element is used to simulate surface crack propagation under various loading conditions. Based on the quasi-static assumption, an algorithm is proposed to investigate the crack propagation process. The load is assumed to be moving away from, moving toward, and passing through, the crack. The effects of friction, load magnitude, and slant angle of the crack are studied. The results show that there exist three propagation types for a load moving away from the crack. In the case of a load moving toward to the crack, a wear flake can be formed easily for a negative or large positive slant angle crack. The results of crack propagation for a load passing through the crack show that a large load may or may not cause serious crack propagation. This depends on the slant angle and the friction force.
