Fatigue life prediction based on equivalent initial flaw size for Al-Li alloy 2297 under spectrum loading

•Fatigue tests of Al-Li alloy 2297 under spectrum loading were conducted.•A fatigue life prediction approach based on the Equivalent Initial Flaw Size (EIFS) concept was followed.•EIFS extrapolated from constant amplitude fatigue test data was used to predict the fatigue life under spectrum loading.•Different ways to determine the EIFS were compared.•The load-interaction effects were considered. Fatigue life prediction methods based on the Equivalent Initial Flaw Size (EIFS) concept under variable amplitude (VA) spectrum loading conditions were studied in this paper. Fatigue tests of Al-Li alloy 2297 under constant amplitude (CA) and VA loading cases were carried out. Based on the comparison of predictions and test results, different ways to determine the EIFSs and whether the load-interaction effects should be considered in VA fatigue life prediction were discussed to recommend their applicable cases. A good agreement is observed between EIFS model predictions and experimental data, especially in case of high maximum stresses in VA loading.