Effect of complex stress states on creep rupture life of nickel-based superalloys: Mechanisms and modeling

This study investigates the effects of complex stress states on creep rupture life of nickel-based superalloys. Creep experiments were conducted at 900 degrees C on both smooth and single-hole plate specimens. A viscoplastic constitutive model was developed to simulate the creep behavior of single-hole plates and V-notched bars. The analysis offered a detailed mechanical explanation for the significant differences in creep rupture life observed among these differently structured specimens. This investigation incorporated the effects of complex stress states into the MonkmanGrant relationship, resulting in a new creep life model that accounts for stress triaxiality. The results indicate that the increased stress triaxiality significantly extends the creep life of Vnotched bars. In contrast, the single-hole plates, which approach a uniaxial stress state, exhibit a creep rupture life closely aligning with that of the standard smooth plates. The proposed model accurately predicts the creep rupture life of both single-hole plates and V-notched bars, with all predictions falling within a threefold scatter band.