Study of Fracture Criterion under Mixed Mode Conditions

Fracture tests under mixed mode I+II, I+III and I+II+III conditions were carried out by using a cylindrical specimen with circular crack. In the case of the mixed mode I+II, it is found that the fracture direction can be well predicted by the maximum tangential stress direction, and the fracture occurs when the K_<θmax> reaches the plane-strain fracture toughness, K_. The results are similar to those obtained by the other mixed mode testing method. Under the mixed mode I+III, it is found that the fracture toughness can be well predicted by the maximum tangential stress criterion, and the fracture direction θ_0=0°. In the case of the mixed mode I+II+III, the maximum strain energy release rate, G_<θmax> was obtained at 180° on the circular crack.