On low cycle fatigue life of nickel-based superalloy valve membranes under non-proportional cyclic loading

A numerical model for low cycle fatigue damage analysis of valve membranes is presented in this paper. The isotropic and non-linear kinematic hardening laws of Lemaître–Chaboche, which define both the cyclic hardening and the ratchetting phenomenon, are adopted. The model for prediction of the number of cycles to crack initiation is based on a combination between Manson–Coffin relationship and Jiang–Sehitoglu fatigue parameter. The applied cyclic loading consists in a load pressure imposed to the internal face of the membrane and a vertical displacement of its hub section. The experimental results and numerical simulation predictions in terms of number of cycles to failure turned out to be in good concordance. Thus, numerical predictions are confirmed by microscopic observations made on membranes failed during testing.