抄録
Based on the satisfactory results of the recent studies on a J-integral approach to the creep crack propagation at elevated temperatures and the fatigue crack propagation at room temperature, the applicability was studied of the creep J-integral to the time dependent fatigue crack and of the cyclic J-integral to the cycle dependent fatigue crack under combined creep-fatigue conditions. A simple method for experimental estimation of the creep J-integral range and the cyclic J-integral was proposed for a center cracked plate (CCP) specimen with a rather shallow crack. Using a 0.16% carbon steel (S15C), the crack propagation test was carried out at 400°C under various frequencies. The correlation between time dependent fatigue crack propagation rate and creep J-integral was found at relatively low frequencies, and that between cycle dependent fatigue crack propagation rate and cyclic J-integral was exhibited at comparatively high frequencies. The creep-fatigue interaction between the two characteristic crack propagations was scarcely recognized, which led to the conclusion that the crack propagation under combined creep and fatigue condition was regarded as being controlled by more dominant one. Also found was the fact that the transition of the crack propagation rate from cycle dependent fatigue to time dependent creep or vice versa did not take place due to the increase in J-integral value during crack propagation.
