Creep Life Prediction and Analysis of Stress- and Strain-Based Damage Indices for a Nickel-Based Superalloy

Creep-life prediction and assessment of creep-strain accumulation are important for the safe operation of gas-turbine hot-section components. This study investigates a nickel-based superalloy using finite element (FE) creep analysis and the Larson–Miller parameter (LMP) method to compare stress- and strain-based damage indices. Stress-controlled cylindrical models provided FE lives for comparison with reference creep-rupture times and fitting of a stress–LMP relationship. Corresponding displacement-controlled models with matched initial stresses were used to evaluate the two indices from stress histories and accumulated equivalent creep strain (CEEQ), respectively. A stress-controlled baseline at a matched CEEQ level quantified loading-path effects on the index ratio. The approach was then applied to the first-stage rotor blade of an F-class gas turbine. Of the FE life estimates, 87.5% were within a factor of two of the reference lives; all 32 cross-validated LMP predictions were within a factor of two of the FE lives. Compared with stress control, displacement control produced stress relaxation and markedly reduced CEEQ accumulation. The relative magnitudes of the two indices varied with loading path, temperature, and stress level. The critical blade location also exhibited stress relaxation and distinct evolution of the two indices.