Creep-fatigue damage model considering transition strain rate of stress relaxation stage and its application on life prediction of Inconel625 diffusion bonded joint

Abstract

In present paper, creep-fatigue fracture behavior of Inconel625 diffusion bonded joint is investigated. Subsequently, the creep-fatigue damage model based on strain energy exhaustion theory is modified by taking transition strain rate of stress relaxation stage into account. Finally, creep-fatigue life of the joint is predicted. The results indicate that the crack fracture mode is transgranular dominated, all creep-fatigue lives predicted by the modified model fall within an error margin of 1.5 times. The creep damage is comparable to the fatigue damage when holding time is less than 60 s. However, when holding time exceeds 120 s, the creep damage is significantly greater than the fatigue damage. The cycle by cycle concept provides more accurate life prediction compared to that predicted by constitutive model. When the strain range is within ± 0.3 % and the holding time does not exceed 60 s, the joint exhibits a lifespan of exceeding 1000 cycles. Conversely, all predicted lifetimes are less than 260 cycles when the strain range exceeds ± 0.3 % or the holding time surpasses 60 s. Therefore, further improvement of the creep-fatigue strength for Inconel 625 diffusion bonded joint is necessary.