Investigation on fatigue performance of open-hole plates treated by dynamic cold expansion under large expansion size based on electromagnetic loading

This study aims to explore the upper limit of expansion size in dynamic cold expansion (DCE) and discuss the fatigue life enhancement mechanisms of this process. To achieve this, fatigue tests were conducted and the fractured surfaces were analyzed. Residual stress was measured both experimentally and numerically, and micromorphology was investigated. The stress distributions were also used to predict the fatigue life, with corresponding investigations of static cold expansion (SCE) conducted for comparison. The results indicate that the DCE process can achieve a larger upper limit expansion size than the SCE, leading to an extension of higher fatigue life. Additionally, the DCE induces larger compressive residual stress, especially at the mandrel entrance layer, and more significant grain refinement than the SCE. These factors are considered as the main mechanisms responsible for the fatigue life enhancement in the DCE process. The predicted results were in good agreement with the experimental data.