Creep Crack Propagation under Decreasing Load Condition

Abstract

Crack propagation under sustaining or increasing load conditions in monotonic creep and time-dependent fatigue has been described successfully by the creep J-integral. This paper extends the creep J-integral concept to the crack propagation in decreasing load conditions. Because the J-integral can be originally defined for a linear or nonlinear elastic body even in an unloading condition although it can not for a plastic body, and because the creep J-integral in a creep body is analogous to the J-integral in an elastic one, the creep J-integral can be expected to be valid in the decreasing load (stress relaxation) condition when a unique stress-strain rate relation exists. Crack propagation tests of 0.16% carbon steel were carried out in creep and time-dependent fatigue conditions with the stress relaxation. As the result, the crack propagation rate had a good correlation with the creep J-integral for the stress relaxation period. In time-dependent fatigue, moreover, the crack propagation rate was correlated well with the creep J-integral (or creep J-integral range) independently of the stress waveform. These show the applicability of the creep J-integral concept for crack propagation during the stress relaxation.