Modeling and effect analysis on crack growth behavior of Hastelloy X under high temperature creep-fatigue interaction

The crack growth behavior of Hastelloy X under creep-fatigue interaction at high temperature is investigated by a nonlinear creep-fatigue interaction damage model. Multiaxial stress is considered both in the fatigue and creep damage models. The effect of the variance of fatigue damage parameters is analyzed in a quantitative method and some linear effects were observed. The influence of hold time, crack depth ratio and load level on the crack growth behavior are studied and results under different hold time indicate that the increase of hold time, crack depth ratio and load level enhances the creep damage and accelerates the time-dependent crack growth rate. When the hold time varies from 1 to 60 min, the creep damage always dominates the damage accumulation, which can explain the overlap of the curves between da/dt and (C-t)(avg) observed in the experiment very well. The damage contributions of creep, fatigue, and their interaction are quantized thanks to the independent damage model for each part (1) when the hold time increases from 1 min to 60 min, the creep damage ratio rises from 70% to 99% and the interaction damage ratio decreases from 25% to 1%. (2) when the crack depth ratio increases from 0.35 to 0.5, the creep damage ratio rises from 80% to 90% and the interaction damage ratio decreases from 15% to 10%; (3) when the load level increases from 4200 N to 5000 N, the creep damage ratio rises from 75% to 90% and the interaction damage ratio decreases from 25% to 10%. It is also shown the increase of load level and crack depth ratio lead to the increase of equivalent stress and therefore enhances the creep damage and accelerates the crack growth rate.