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Friction Stir Welding (FSW) of skin stiffened structures is being developed as a rivet replacement technology in the aerospace industry. Preliminary research was done on compressive strength and deformation characteristics of FSW aluminum skin stiffened panels. 7075-T6 aluminum sheets were bent to form stiffeners and friction stir welded to 7075-T6 aluminum sheets to fabricate two FSW panels. Another stiffened panel of similar dimensions was made by using traditional riveting. The compression test results and the failure modes of the panels are presented in this paper. The tests revealed that the FSW panels failed at approximately 17% higher load than the riveted panel. The failure loads of the FSW test panels were within 3 to 10% of the predicted load obtained by using two existing theoretical methods, and the failure load of the rivet panel was within 11 to 20% of the predicted load.

The Friction Spot Welding (FSSW) process as invented by GKSS in Germany has shown potential for application in several industrial fields as a solid state joining technology. This study evaluates this “refill” method of friction spot welding in aluminum sheet. Efforts to date have concentrated on simple flat lap joints. Process and tool development studies have been performed and have focused on understanding and managing material flow in order to minimize flash, ensure full consolidation and produce a nearly flush surface. The metallurgical and mechanical properties as a function of tool geometry and processing parameters are discussed and the lap shear strength is shown in this preliminary work to compare favorably to riveting and resistance spot welding.

Friction Stir Welding (FSW) is a new and innovative solid state joining process that now allows the welding of previously unweldable aluminum alloys. Traditionally, these alloys have found use only in mechanically joined structures. Discussed is an overview of the FSW process for both full penetration butt welds and partial penetration lap welds, as well as the specific metallurgical and mechanical properties of friction stir welded lap shear joints in 2090-T83 aluminum lithium alloy. Flat sheet shear testing of friction stir welded and riveted specimens are compared, as are compression buckling tests of stringer stiffened panels. The results of these studies indicate that friction stir welding is a viable and potentially cost reducing alternative to aluminum riveted structures.