Assessing the Accuracy of Time‐Fraction and Ductility Exhaustion Approaches for Creep‐Fatigue Damage Prediction in Alloy 617 Through Feature Test Validation

ABSTRACT Determining creep‐fatigue damage formation is critical for elevated temperature components integrity. This study evaluates creep‐fatigue assessments with emphasis on differences between creep damage models. Evaluated are the time‐fraction model and the classical and stress‐modified ductility exhaustion creep damage models. This work extends the domain of stress‐modified ductility exhaustion models by introducing and validating such formalism to Ni‐based alloys. The fidelity of the assessments was benchmarked against uniaxial creep‐fatigue and multiaxial feature tests of Alloy 617. For uniaxial specimens, best estimate predictions rank ductility exhaustion as the most accurate and precise and time‐fraction as markedly conservative. For feature tests, ductility exhaustion predictions are within < 4.0 times difference, whereas time‐fraction underpredicts life by factors of 7–14. The observations suggest ductility exhaustion models as alternative to time‐fraction models in design codes for situations requiring characterization of the design margin. Further work in employing such models to assess other relevant phenomena (e.g., stress relaxation cracking) is discussed.