Residual stress and material flow prediction in Friction Stir Welding of Gr2 Titanium T-joints

Friction Stir Welding is nowadays an established technique successfully used by many industries. However, most of the research and, consequently, most of the applications regard aluminum alloys and butt joints. T-joints are of high interest for different industrial sectors as aeronautical, aerospace, naval and ground transportation, for which joint integrity and low residual stress are extremely important. In this study, an experimental and numerical approach is proposed with the aim to study the peculiarities of the residual stress distribution and material flow occurring in FSW of CP-Ti T-joints. Experiments were carried out to assess the feasibility of the process and to acquire the temperature data needed for the validation of a specifically set-up numerical model. Peculiar numerical strategies have been defined in order to calculate the residual stress with affordable CPU time and to highlight the bonding surface between the skin and the stringer. Main findings include a longitudinal residual stress profile different from the one usually found for butt joints. The reasons for this behavior were explained through a deep investigation on the temperature distribution in space and evolution in time. Finally, the bonding surface between skin and stringer was highlighted together with the possibility of flow defects in the fillet area.