Performance evaluation of discontinuous friction stir welding
Friction stir welding has been shown by previous investigators to have many advantages over traditional metal joining practices. Friction stir lap welds and friction stir spot welds have been shown to be stronger than rivets when joining materials of the same thickness. Substructures containing continuous lap welded joints have demonstrated increased load carrying capabilities over their riveted counterparts. In full-scale structures, however, continuous welds are not always an option. Welds may be interrupted by fixturing limitations, tooling restrictions, or stiffening members that cross the weld path. In these situations, a discontinuous lap weld would be necessary. The principal problem with a discontinuous weld is that the tool plunge and exit locations cannot be eliminated with a run-off tab, as in continuous welded structures. These plunge and exit locations are then subjected to operational loads. In fatigue applications, it has been demonstrated that cracks will initiate in the exit hole of a discontinuous weld. The purpose of this study was to investigate techniques to terminate a lap weld without compromising the structure by leaving an unprotected exit hole.