Improving the fatigue life of 2297-T87 aluminum-lithium alloy lugs by cold expansion, interference fitting, and their combination

Cold expansion and interference fitting are two efficient methods for improving the fatigue life of open-hole structures. However, their combined effect on the fatigue behavior of aluminum-lithium lugs has barely been investigated. Therefore, this study aims to improve the fatigue life of 2297-T87 aluminum-lithium alloy lugs by utilizing cold expansion, interference fitting, and their combination, using experimental and numerical methods to determine the effects of these techniques. Scanning electron microscopy was employed for fracture analysis, three-dimensional finite element models were used to characterize cyclic loading-related stress histories and stress distributions around holes, and the Smith-Watson-Topper method was used to predict fatigue life. The combination of cold expansion with interference fitting achieved a 14.4-fold improvement of fatigue life, as determined by fatigue tests. Numerical modeling showed that the above combination decreases the mean stress and stress amplitude, outperforming other methods in terms of fatigue resistance, in agreement with experimental results.