In order to predict crack propagation-rate within a quasi-brittle material,the expansion mechanism of a Ⅰ-Ⅱ mixed mode crack in quasi-brittle materials was investigated based on coupling the damage model with fracture mechanics.Due to complexity of calculation and the crack distribution in quasi-brittle materials,the mixed crack was simplified as a 2-D plane problem.Area around the crack tip was divided into four zones according to their deforming characters and the crack propagation was considered equivale...