1997 年 46 巻 3Appendix 号 p. 49-55
The outline of the creep-fatigue life prediction model proposed by the authors and its applicability to the life prediction under variable strainings were summarized. In the model, crack growth curves in smooth specimens were predicted by the strain range partitioned crack growth rate equations, and these crack growth curves were used as damage accumulation curves. The sequential loading effect on creep-fatigue properties was evaluated considering the strain history dependency of cumulative damage curves. Results of two-step sequential straining tests such as High-Low and Low-High tests on Mod. 9Cr-1Mo, SUS304 and 316LC steel were presented and it was shown that the proposed model can be more successfully applied to the creep-fatigue life prediction under variable strainings than the conventional linear damage rule. Furthermore, in order to certify the validity of the model, the correspondence between predicted crack growth behaviors and experimentally obtained behaviors was examined. Surface crack growth behaviors in smooth bar specimens were observed for Mod. 9Cr-1Mo and 316LC steel and compared with those predicted. It was found that the predicted crack growth curves corresponded well with the relationships between the maximum crack length and the life ratio. Consequently, it was concluded that the proposed model can evaluate the material damage and the residual life under variable creep-fatigue strainings.
