Predicting residual distortion of aluminum alloy stiffened sheet after friction stir welding by numerical simulation

Friction stir welding (FSW) has been widely applied in aluminum alloy manufacturing with its advantages of low residual stress and small deformation. But some FSW cases indicated that the residual distortion was still significant if a large size sheet be welded. In order to reduce the residual distortion of large aluminum alloy sheet after FSW, a general method adopted in this paper was that some stiffeners were designed on the sheet before it be welded. The process of FS-welded structure (sheet with stiffeners) was numerically simulated by finite element analysis (FEA) method. Based on the numerical simulation, the residual distortion of the structure was predicted and the effect of stiffeners was investigated. First, a three-dimensional FEA model was developed to analyze the welding process on a sheet, and the simulation results were verified by FSW experiments. Then, the verified model was applied on structure to compute residual distortion. The prediction displayed that the distortion pattern of structure was convex in longitudinal direction and concave in transversal direction after FSW. In simulation results, the distortion shape of structure was similar to that of sheet, but the distortion value of structure was much smaller. The comparison of simulation results showed that the residual plastic strain generated by FSW on the sheet and the structure was nearly the same, so the part of distortion which was reduced by stiffeners was the distortion induced by buckling.