Volume 5, Issue 4 (April 2008)
Fatigue Crack Growth in Integrally Stiffened Panels Joined Using Friction Stir Welding and Swept Friction Stir Spot Welding
Fatigue crack growth rates in AA2024-T3 sheet joined to AA7075-T6 stiffeners by friction stir welding have been compared with rates measured in panels joined with rivets and in unstiffened parent material panels. Friction stir panels were prepared with both continuous friction stir welding (FSW) and swept friction stir spot welding (FSSW). Fatigue cracks in edge crack panels with continuous FSW joints tended to grow into the parent material away from the stiffeners. This behavior was attributed to the reduced stress levels corresponding to the increased thickness of continuous FSW joints and the support of the attached stiffener. Fatigue cracks in edge crack panels were found to follow the joint line in panels made with discrete fasteners (both rivets and swept FSSW joints). The measured crack growth rates in riveted panels increased at an increasing rate as the crack approached the riveted joints. In contrast, crack growth rates in panels joined with FSSW decreased at a decreasing rate as the crack approached the swept spot joints. Test results indicate that the swept FSSW process produced favorable residual stresses that inhibited fatigue crack growth along the joint line.