Characterization of thermoplastic composite joints fabricated by the combined refill friction stir spot welding and riveting process

Carbon fiber-reinforced thermoplastics have been extensively studied to reduce the weight of transportation equipment. In this study, to enhance the interlocking effect of Ti-6Al-4V rivets, the new riveting process combined with refill friction stir spot welding (FSSW) was attempted. Consequently, the successful combination of refill FSSW and riveting resulted in a flared trumpet-shaped rivet, expanding the diameter of its tip significantly. Tensile shear tests exhibited both the stirred zone induced by refill FSSW and the flared rivet affected the fracture behavior. The cross-sectional observations revealed the existence of cracks at the boundary between the stirred zone and base material during tensile shear tests. Furthermore, a unique arrangement of the fiber caused by the stirring action was identified by observing the fracture surface using scanning electron microscopy. The study findings clarify the advantages of combining refill FSSW with riveting, providing insights into the potential implementation of this combined process in thermoplastic composites.