Contour Method Evaluation of Residual Stress in AA6082-T6 Friction Stir Welded Pipe Joints, Validation by Neutron Diffraction and Finite Element Modelling

Over the last two decades, the Contour Method (CM) has been proven to be an ideal candidate for reconstructing macro-scale Residual Stress (RS) in welded joints, encompassing fusion and solid-state welding. Regarding the latter class of joining methods, the CM has primarily been exploited to characterise RS in Friction Stir Welded (FSW) planar geometries, while its application to thin-walled circular FSW products has gained little interest, mainly due to numerous challenges involved. To address these outstanding issues, full-field RS distributions in 3 mm thick AA6082-T6 FSW pipe joints, produced with three distinct processing parameters, are investigated using a multimodal experimental and numerical approach. The CM-retrieved RS is validated through independent Neutron Diffraction measurements, and the uncertainty derived from the evaluation processes is thoroughly quantified. These analyses are complemented with a Finite Element (FE) model of the circular FSW process calibrated on a single welding condition while holding out the others for validation. The experimental activity showed RS with similar distributions compared to the planar FSW counterpart but yielding lower magnitudes. Additionally, the FE led to RS matching those experimentally probed under all the analysed welding conditions, providing insights into the mechanisms governing the formation of RS in circular FSW.