Residual Stresses in Friction Stir Welding

Friction stir welding is an innovative joining process being developed for use in aerospace manufacturing. Like most welding processes there exist problems with post-weld residual stresses and subsequent geometrical distortion. The residual stress-state of a welded component can be modified using suitably applied mechanical tensioning and thus distortion can be reduced or eliminated. In the present study, the finite element software, ABAQUS, has been used to model the friction stir welding process of aluminium alloy plates and to investigate the effects of process conditions on the residual stress. The finite element modelling has been carried out in two steps: thermal analysis and stress analysis. In the thermal analysis, the heat input from the friction stir welding operation was modelled using a surface heat flux. The calculated temperature field/history was then used for stress analysis. The main focus of the work was to examine the residual stresses generated from various welding conditions. The results suggested that the application of appropriate mechanical tensioning during welding would reduce the residual stress or even change the residual stresses from tensile state to compressive state. The calculated residual stresses were also compared with experimental measurements and good agreements were found between them.