| dc.description.abstract | Since its conception in 1991, friction stir welding (FSW) proved useful and advantageous for joining metallic materials in structures used in aerospace, automotive, rail, maritime, and technology. As engineers improve efficiency and capability by incorporating lighter and stronger materials, there is a need to improve processes to join polymers and polymer composites. Though there are several established processes to weld thermoplastic materials, FSW of polymeric materials has yet to be adopted in industry. This dissertation discusses advances in polymer FSW technology with a focus on improving process quality and efficiency while exploring applications that may benefit from FSW adoption. Many factors affect joint quality during FSW including processing parameters and tool design. The first research uses statistical approaches in design of experiments to study the influence of the thread pitch in threaded FSW tool pins when welding high density polyethylene (HDPE). The thread pitch contributes to joint strength and tool temperature, though the welding speed has the greatest contribution to polymer diffusion across the joint. The second project explores a novel FSW application for joining PVC pipes and couplings. Friction stir welded joints exceed ASTM burst pressure standards, reduce processing times compared to currently employed solvent welding techniques, and require low processing forces that harness potential for small, portable FSW machines. The remaining work in this dissertation considers composite materials. In a derivative process called top plate friction stir processing (FSP), metal-polymer composites are formed in existing thermoplastic structures to improve properties such as electrical and thermal conductivity. Top plate FSP demonstrates the ability to for composites in wide areas and reduces overall processing time compared to formally studies FSP methods. The final two studies use FSW to join woven carbon fiber reinforced thermoplastic (CFRTP) laminates that have increasing prevalence in aerospace applications. FSW disrupts the fibers in the weld zone, refines their size, and distributes them with preferred orientation throughout the weld zone. Despite the added complexity of integrated fibers, FSW demonstrates the ability to join CFRTP with little surface preparation necessary in other welding techniques and shows good potential for high-strength joints. Further consideration of post-weld annealing indicates improved joint strength from increased polymer crystallinity. | |
