Continuum damage mechanism-based life prediction for Ni-based superalloy under complex loadings

A continuum damage mechanism (CDM) based life model for directionally solidified Ni-based superalloy under complex cyclic loadings is presented. Complex loadings including pure fatigue, pure creep and fatigue–creep interaction with different hold time and hold types are considered at 850°C and 980°C. Linear combination of fatigue damage developed by Chaboche and creep damage proposed by Kachanov is used to model the CDM method. The damage analyses reveal that there is a critical hold time of 120s. When the hold time is less than this point, there exists a critical stress under which the creep and fatigue damage are the same at 50% each. When the hold time is more than 120s, the creep damage is more than 50% which means that the creep always dominates the failures. However, when the hold times are less than 120s, fatigue damage dominates under most of the stress levels. About 97 fatigue test data under different loading conditions were used to verify the feasible of the method. The results indicate that a good prediction fell within a factor of 2 scatter band is obtained.