The effects of plastic constraint and temperatures on fracture initiation from a notch were investigated by using various types of notched specimens, at the temperatures ranging from room temperature to liquid nitrogen temperature.
The results show that, when fracture initiates by fibrous crack, the COD at fibrous crack initiation is almost independent of plastic constraint of the specimens or of the test temperatures, while the COD at maximum load or at final fracture is largely dependent on them. When fracture initiates by cleavage crack, the critical COD also shows considerable dependence on those parameters above mentioned. These behaviors of critical COD are explained by the fracture mechanism in each mode of fracture.
