Friction Stir Lap Welding of AA 7075-T6 Stringers on AA 2024-T3 Skin

Friction stir welding (FSW) is an emerging manufacturing technology that is being increasingly used in the fabrication of aerospace structures. The Institute for Aerospace Research of the National Research Council Canada began an extensive study to establish design process guidelines and to facilitate the development and use of FSW in a large-scale representative structural element from an aircraft, such as a fuselage panel. This paper mainly focuses on the results of mechanical tests and subsequent analysis that was used to ascertain the feasibility of using FSW to join AA 7075 stringers to AA 2024 skin. The weld configurations studied were: discontinuous (with plunge-in entry and exit holes), continuous welds, single pass welds, double pass welds, and plugged (rivet) discontinuous welds. S-N curves, bending behaviour, failure locations, defect characterization and joint distortion are discussed. The results were also compared with riveted lap joints of identical geometry mainly in terms of cyclic strength performance of FSW panels. This research provided some valuable insight into both the fabrication and the application of FSW on stringer/skin lap joints.