Multimodal experimental and numerical evaluation of Residual Stress in AA6082-T6 Friction Stir Welding pipe girths

Although Residual Stress (RS) induced by Friction Stir Welding (FSW) has been widely investigated for planar weldments, the same attention has not been paid as far as the curved variant is concerned. To comprehensively address this gap, the present paper studies the RS in three AA6082-T6 FSW pipes (37.5 mm outer diameter $\times$ 3 mm thickness) manufactured with varying feed speeds, i.e. 50, 75, 100 mm/min. RS evaluations were cross-validated by two independent experimental methods, i.e. Neutron Diffraction and Contour Method. A novel multi-physics Finite Element (FE) model was implemented and calibrated using the previously obtained experimental outcomes to shed light on the key physical mechanism responsible for the arising of RS. The analysis unveiled M-like hoop RS patterns akin to flat FSW butt-welds but having lower magnitudes ranging from −20 MPa to 65 MPa, most likely due to the different thermal histories. The axial RS oscillates between -20 MPa and 20 MPa, whereas the radial component turned out to negligible. The FE model also demonstrated how feed speed, plunge force, and external clamping conditions alter RS magnitude while identifying 75 mm/min as the optimal speed that minimises the peak hoop RS to 40 MPa.