Analysis of creep–fatigue life prediction models for nickel-based super alloys

Creep fatigue is the main damage form of engine parts operating under both cyclic mechanical and thermal loading conditions. In the present work time-dependent creep and cycle-dependent fatigue of nickel-based super alloys is discussed. Three different kinds of creep–fatigue life models are investigated for the nickel-based super alloys. Effects of temperature, loading ratio and loading hold time to material failure are considered. Comparison with experiments reveals that the linear accumulation concept based on Forman model provides reasonable results on the creep–fatigue interaction if the life is dominated by mechanical fatigue damage. For higher loading ratios, however, deviations become significant. In the lower frequency region the modified FCE models and Saxena models give more reasonable predictions, but show large discrepancy to tests with hold time. The modified Saxena model suggested in the present work contains a separate term for hold time effects and agrees with the experimental observations more accurately.