Applicability of Fracture Mechanics Parameters to Crack Propagation Under Creep Condition

Abstract

A critical examination was made of the applicability of fracture mechanics parameters to crack propagation under creep condition with 304 stainless steels for a variety of specimen geometries at relatively high stress levels. The creep crack propagation rate could not be described in terms of elastic stress intensity factor but it could be in terms of net section stress for all dimensions of thin plate specimen. The net section stress, however, could not explain the difference between crack propagation rates of thin plate specimens and those of notched round bar specimens. This difference could be ascribed to the plastic constraint around the crack tip. Applicability of the modified J-integral to creep crack propagation was also examined and the results showed that this parameter was better for predicting the creep crack propagation rate at a high stress level. In the case of speicmens of similar geometries, the net section stress could be used in place of the modified J-integral provided that crack propagation rate was divided by the characteristic length of the specimen.