CREEP CRACK-GROWTH IN HIGH-TEMPERATURE DUCTILE MATERIALS

In the past 15 years, considerable advancements have occurred in the area of time-dependent fracture mechanics (TDFM) for predicting crack growth in the presence of creep strains. These concepts and the supporting experimental data are reviewed in this paper with particular emphasis on ductile high temperature steels such as Cr-Mo and Cr-Mo-V ferritic steels and the stainless steels. Three crack tip parameters, C*(t), C(t) and C(t), are identified and discussed in detail for characterizing the creep crack growth rate at elevated temperatures in ductile materials. In the extensive creep regime all three parameters are identical. In the small-scale and the transition creep region, C* is not valid and C(t) not-equal C(t). In this paper, these parameters, their mechanics basis and their abilities to correlate creep crack growth rates in high temperature steels are discussed in detail. The areas which need further work are also outlined.