Effect of multi-axial stress state on creep behavior and stress rupture life of a Ni-based DS superalloy

Effect of multi-axial stress state on creep behavior and stress rupture life of a Ni-based directionally solidified (DS) superalloy has been systematically investigated. Emphasis is placed on the roles of the applied net section stress level, initial theoretical stress concentration factor (Kt), notch shape, plate thickness and sample shape. The results show that creep behavior is obviously affected by all the mentioned factors, which are concretely embodied in the redistribution of stresses, accumulation of creep strains and evolution of creep damage. The indicators for describing the constraint degree are further quantitatively discussed and the tri-axiality factor I1/σMises is exhibited as a good indicator. Based on the Monkman-Grant relationship, the stress rupture lives of notched specimens are predicted, which are related to the constraint degree and agree well with the existing experimental laws.