Abstract
Prediction of failure life under creep-fatigue condition is of practical importance for sound design and operation of high-temperature plants. Stress-based time-fraction approach often overpredicts failure life because of difference of deformation under monotonic creep and creep-fatigue loading. Strain-based life prediction procedure called ductility exhaustion method has been developed to overcome shortcoming of simpler stress-based approach. However, overly conservative prediction is obtained for some materials by the conventional way of creep damage counting in the ductility exhaustion method. A new method which includes alternative ways of creep damage calculation and modeling creep-fatigue interaction, was developed in this study. This method was applied to a number of creep-fatigue tests conducted for modified 9Cr-1Mo steel (P91) and HCM12A (P122). Excellent agreement was obtained between predicted and experimental lives.
