Mechanical Characterization of Aircraft Panels Stiffened by Friction Stir Welded Extruded Parts

Friction Stir Welding (FSW) appears to be one of the most attractive joining techniques for aircraft industry because, being a solid state welding process, allows overcoming all the well-known problems related to phase transformation of fusion welding process. In addiction, welding is very attractive in view of the fact that it allow saving weight in aerostructures if compared to the riveting technology. In the present paper, the experimental mechanical characterization of a subcomponent manufactured using the FSW lap joint technique is presented. The coupons simulate a bulkhead panel, i.e. a panel which separates a pressurized ambient of aircraft (i.e. the cabin) by another non-pressurized (i.e. the hold). Such a panel is usually stiffened by extruded parts that are riveted to the panel itself. In this case the extruded parts, with a T shape section, are friction stir welded to the panel by means of two different beads in single lap configuration. Loading conditions have been chosen to simulate two real operative conditions: hoop stress and T-pull. Results allow appreciating the good performances attained by coupons. Some specific features of FSW w.r.t. lap joint, such as “hook defect”, play a significant role in both the failure occurrences observed during the static tests and in the crack initiation phenomenon observed during the cyclic tests. Care should be put in both process parameters setting and tool design in order to minimize the hook defect occurrence.