Fatigue performance on 7050 aluminum alloy by twice hole expansion strengthening of split mandrel

To investigate the impact of various forms of hole expansion strengthening of split mandrel (HESSM) process on the fatigue performance of 7050 aluminum alloy, a 3D finite element simulation analysis model is established for once hole expansion strengthening (OHES) and twice hole expansion strengthening. HESSM experiment is conducted to explore its influence on hole wall stress, microstructure, and fatigue life. The results show that the depth of the plastic deformation layer in the middle area of the hole wall is 1.69 times for specimens by twice hole expansion strengthening than that of OHES. Additionally, residual stress on the hole wall is higher and uniform for compared with OHES, when by twice hole expansion strengthening in opposite directions (THESOD) using split mandrel. The median fatigue life of the specimen by OHES is 1.52 times that of without expansion strengthening (WES). The median fatigue life of the specimen by twice hole expansion strengthening in the same direction using split mandrel is 1.73 times that of WES, and the median fatigue life of the specimen by THESOD using split mandrel is 1.80 times that of WES.