Experimental investigation and modeling of the superalloy crack growth behavior under combined high and low cycle fatigue

The disk groove structure of aero engines is affected by combined high and low cycle fatigue (CCF) loads during service, and the crack growth rate model is a critical input condition for the damage tolerance analysis of the disk. In this study, the crack propagation behavior of the Inconel 718 superalloy, a commonly used material for disks, is investigated under the CCF loads. Firstly, crack propagation tests are conducted on the superalloy under three loading conditions: pure low cycle fatigue (LCF), pure high cycle fatigue (HCF), and CCF. The influence of different loads on the crack growth rate is analyzed. Then, considering the coupling effect of the HCF and LCF loads, a CCF equivalent stress intensity factor K _eq is proposed. A crack growth rate model is developed based on the K _eq. The predicted crack growth rates fall within the 1.7-fold dispersion band. Furthermore, the influence mechanism of the stress ratio and CCF loads on crack propagation is explored through fracture analysis, revealing that under CCF loads, the high cycle component significantly governs the crack propagation process. This study can provide valuable methods and data support for evaluating the crack propagation life of the groove structure.