Fatigue Life and Fatigue Crack Growth Behavior of Nonthrough Cracks in Friction Stir-Welded 2024-T3 Aluminum Alloy

Friction stir-welded (FSW) joints are evaluated under two welding conditions to investigate their properties for application to aircraft structures. It is found that the welding condition affects the hardness profile, static strength, and fracture location. The tool mark near the burr, the kissing bond, the burr, and the edge of the specimen within the base material are found to be the origins of fatigue fractures in FSW joints, and the welding condition affects these origins and fatigue life. The kissing bond is not the origin of a fracture when low stress is applied. The fatigue life of a FSW joint is longer than that of a riveted joint. An evaluation of fatigue crack growth for each case via observation of the fracture surface indicates that the crack growth rate when the kissing bond is the origin of the fracture is close to that of the base material. The crack growth rate when the tool mark near the burr is the origin of the fracture is different from that of the base material: Overestimating the stress intensity factor range based on assuming the crack geometry contributes to the difference.