Modeling of creep-fatigue interaction effects on crack growth at elevated temperatures

The well-known load frequency effect on creep-fatigue crack growth is explained by the interactions between fatigue and creep loading and is quantified using the concept of plasticity-induced crack closure. It is shown that the hold time during creep loading affects crack growth rates during subsequent fatigue cycles. Longer hold times lead to lower crack-tip opening stresses and faster crack growth rates during fatigue loading. To model the impact of hold time on crack opening stresses during fatigue loading, a strip-yield model was developed for creep-fatigue crack growth. The strip-yield model computes crack-tip opening stresses, which determine the effective stress intensity factor range and crack growth rate during the fatigue portion of each loading cycle. Maximum stress intensity factor is used to compute the crack growth rate during the creep portion of each cycle. The proposed strip-yield model is used to compute creep-fatigue crack growth rates for several structural materials, i.e., an Astroloy, aluminium alloy 2650 and 316 stainless steel. The model predictions of crack growth rates compare well with published experimental data for these alloys. This model achieves reliable predictions of crack growth rates and life prediction on components subjected to creep-fatigue loading at elevated temperatures by considering loading interaction effects.