Numerical Simulation Investigation on Split Sleeve Cold Expansion of Ti-Al Stacked Structure

Split sleeve cold expansion (SSCX) can effectively enhance fatigue life of holes by improving the field of residual stress. Numerical simulations were conducted to investigate the parameter influence mechanism and obtain higher compressive residual stress (CRS). Expansion method, degree of cold expansion (DCE), friction coefficient between laminations and depth-diameter ratio were analyzed. For Ti-Al stacked joint holes, two expansion methods are proposed, namely aluminum alloy first followed titanium alloy (Al first) and titanium alloy first followed aluminum alloy (Ti first). The results show that expansion method and DCE have significant effects on the field of circumferential residual stress, and the friction has a negligible influence. A higher value of CRS and a wider layer of plastic deformation are induced with Ti first. Optimal DCE of Ti-Al stacked structure is 5.2%–5.6%. As the depth-diameter ratio is in the range of 0.5–1.25, a positive linear correlation between the maximum compressive residual stress (CRSmax) and depth-diameter ratio is shown.