Creep-fatigue deformation characteristics and life prediction model of Inconel 718 superalloy under hybrid stress–strain-controlled mode

In this paper, the creep-fatigue responses of the nickel-based superalloy Inconel 718 have been investigated by conducting hybrid stress–strain-controlled creep-fatigue interaction (HCFI) loading experiments at 650°C with different dwell stresses and dwell periods. Deformation responses demonstrate that stress dwell leads to complex cyclic responses, such as an increase in softening rate and changes in inelastic strain rate. Then, a novel creep equivalent stress determination method is proposed based on stress relaxed characteristics. After modifying the continuum damage mechanics (CDM) model with this method, accurate prediction results of the creep-fatigue cyclic life under strain-controlled creep-fatigue loading and HCFI loading can be obtained. Finally, the damage evolutions of Inconel 718 under HCFI loading are analyzed by CDM model. The results of damage evolution indicate that the trend of damage accumulation under different test conditions is consistent with the trend of inelastic strain in the material.