Stress Relaxation Curves Modelling for Creep-Fatigue Damage Estimation of Nickel-based Alloy 617

Abstract This paper focuses on the model assessment for characterizing the stress relaxation behavior for creep-fatigue damage estimation of Alloy 617, this is to generate an overall model for verification of relaxed stress at long-term prediction. The creep-fatigue tests were initially conducted under tension hold only, with a variety of hold times and total strain ranges. In this study, the predictive performance of the models is selected and fitted to the short-term stress relaxation data sets, then extrapolated to some extent. The models include classical relaxation models, long-term creep models, and model integration. Peleg’s model shows the most superior results in comparison to the other leading models according to the R² value. The creep-fatigue damage calculation is performed once again according to the ideal model. The results show that the damage estimations are more accurate, meaning that the data points are closer to the draft Alloy 617 code case. The fractured surface shows a brittle crack initiation at the oxide surface followed by a transgranular crack.