An improved method for calculation of creep damage during creep-fatigue cycling

Thermal mechanical cycling can result in creep-fatigue cycles in which the creep dwell has a wide variety of positions within the cycle. The effects of creep dwell position have been investigated using tests on three austenitic stainless steels: Type 316H, cast Type 304L and Type 347 weld metal. The analysis of these tests has resulted in the proposal of a new method to calculate creep damage. This method has been shown to give better predictions for the creep damage at failure than both the standard ductility exhaustion approach and the time fraction approach. In particular, the new method gives improved predictions of creep damage at failure for cycles with intermediate dwells and for cycles with low strain ranges. The present paper summarises the validation of this new method, the effects of multiaxial states of stress and the effects of compressive dwells.