A Chaboche-based unified viscoplastic constitutive model, including features of strain range dependence, strain rate-dependence, static recovery, and mean stress evolution is developed and evaluated for simulating fatigue-creep and creep responses of Haynes 230. In other words, this constitutive model attempt to simulate not only strain-controlled fatigue and fatigue-creep responses of Haynes 230, but also stress-controlled creep responses. After investigating various flow rules and kinematic hardening rules, a unified viscoplastic constitutive model is developed for simulating both the fatigue-creep and creep responses. The parameter determination for this constitutive model, however, requires a robust optimization algorithm. The proposed unified constitutive model can adequately simulate fatigue-creep responses, and creep responses up to the secondary creep regimes. However, with the introduction of damage modeling features the constitutive model can simulate the tertiary creep regime responses, but with some limitations in simulating fatigue-creep responses. Nonetheless, the unified viscoplastic constitutive model with or without damage modeling features has shown to be able to capture the stress-controlled creep responses while still maintaining high fidelity in capturing the strain-controlled fatigue and fatigue-creep responses.

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