UNIAXIAL FATIGUE, CREEP AND RATCHETING RESPONSE SIMULATIONS OF ALLOY 617 USING DAMAGE COUPLED VISCOPLASTIC MODEL

A damage coupled unified constitutive model (UCM-CDM) is developed in this study to predict uniaxial fatigue, fatigue-creep, ratcheting and creep responses of Alloy 617. The experimental data used for validating the UCM-CDM included these responses for different strain rates and strain ranges for temperatures 760-1000 degrees C. Rate dependent modeling features like Norton's power law, static recovery, and isotropic damage evolution law are incorporated in an existing UCM for improving simulations of short-term stress relaxation and long-term creep responses. A backstress threshold modeling feature is incorporated in the UCM-CDM for improving ratcheting prediction for a wide range of mean and amplitude stresses. Simulations of the creep responses, including the primary, secondary and tertiary creep responses, in addition to the fatigue, fatigue-creep and ratcheting responses using the UCM with one set of model parameter are examined.