In Situ Observation via Active Infrared Thermography for Fatigue Damage of Dissimilar Heat‐Welded Joints by Friction Stir Spot Welding

ABSTRACT This study, which focused on overlapping heat‐welded joints comprising aluminum alloy and carbon fiber reinforced polymer (CFRP) prepared by friction stir spot welding (FSSW), clarifies the fatigue properties of such joints under various loading types to apply this joining technology. The fatigue strength of the joint under peel loading was substantially lower than that under shear loading. Fatigue cracks in dissimilar joints initiate and propagate from the joint interface or within the joint, making them difficult to observe. This study proposes an in situ observational approach using active infrared thermography to clarify the mechanism of fatigue fracture within the peel joint and nondestructively assess the fatigue damage behavior from outside the joint. The shape of the FSSW region and peeling area due to the fatigue damage of joints can be detected via active infrared thermography by extracting the components that capture the temperature fluctuations and thermal diffusion caused by cyclic heating.