Characterization crack growth behavior in creep-fatigue loading conditions through different specimen geometries

Creep-fatigue interaction would accelerate crack growth behavior and change crack growth mode, which is different from that presenting in pure creep or fatigue regimes. In addition, the constraint ahead of crack tip affects the relationship between crack growth rate and fracture mechanics parameter and thus influences the accuracy of the life prediction for defected high-temperature components. For the aim of revealing the role of various specimen geometries in the creep-fatigue regimes, crack growth behaviors were investigated using five different types of cracked specimens (including C-ring in tension CST, compact tension CT, single notch tension SENT, single notch bend SENB, middle tension MT). The crack growth and damage evolution were simulated using finite element method coupled with a non-linear creep-fatigue interaction damage model. Moreover, the solutions of (C-t)(avg) for different specimen geometries were given to expand the range of testing specimens. By analysing crack growth behavior with various specimen geometries under creep-fatigue conditions, CT and CST showed the highest crack growth rates, which were eight times as the lowest crack growth rates in MT. This revealed that distinctions in specimen geometry influenced the in-plane constraint level ahead of crack tip. Furthermore, a load-independent constraint parameter Q* was introduced to correlate the crack growth rate. The sequence of crack growth rate at a given value of (C-t)(avg) was same to the reduction of Q*. A normalized constraint level was employed to correlate with the normalized crack growth rate for the aim of transferring lab results into engineering issues.