Substance of Creep-Fatigue Interaction Examined From the Point of View of a Crack Propagation Mechanics

Abstract

The crack propagation rate under creep-fatigue interaction condition could not be predicted by the rule of a linear summation of crack propagation rates of pure creep and fatigue. The acceleration of the crack propagation rate was found to be due mostly to the increase in the accumulation of creep strain and plastic strain in the vicinity of the crack tip. In consideration of the interaction between creep deformation and elastic-plastic deformation, non-steady state creep J-integral range and fatigue J-integral range were evaluated as true driving forces of the time-dependent and the cycle-dependent crack propagation rates, respectively. The interacted creep-fatigue crack propagation was then devided into either the time-dependent creep type correlated with the creep J-integral range or the cycle-dependent fatigue type correlated with the fatigue J-integral range. Same results were obtained for small crack propagation, though it was suggested that another kind of interaction between cracking and grain boundary cavitation may possibly bring the acceleration of early crack growth.