Influence of high-temperature dwell time on creep-fatigue behavior in a 1000Â MW steam turbine rotor

Creep-fatigue behavior at different dwell times was numerically investigated for a 1000 MW steam turbine rotor. Fixed iterations of the startup-running-shutdown process were chosen, and the dwell time of the running phase was changed to study the effect of dwell time on creep-fatigue behavior. Toward this end, a viscoplastic constitutive model with damage was presented to describe creep-fatigue deformation behavior. Multiaxial creep-fatigue tests and thermo-mechanical fatigue tests were conducted to validate the material model. Good agreement was achieved between the simulated and measured results. Analysis of the temperature field disclosed three phases: a warming phase, a transition phase, and an elevated temperature phase. The damage evolution at five locations was compared, and the results showed that the creep damage at the blade groove (thermo-mechanical-load dominated structure) and fatigue damage at the inlet notch zone (thermal-stress dominated structure) were more significant than those at other locations. Specific investigation of the dwell time on the creep-fatigue damage was performed in terms of creep damage, fatigue damage, and accumulated plastic strains. The results revealed that the dwell time significantly accelerated the creep damage at the blade groove and the fatigue damage at the inlet notch zone.