Investigation of welding repair methods for thermoplastic composite joints

Abstract

Repair is a common process to extend the service life of composite structures, and there is a need for techniques compatible with thermoplastic composites (TPCs). As the assembly of TPC joints through welding is gaining importance, evaluating their potential for repairability is essential. This work aims to develop novel techniques to repair welded TPC joints: 1) Successive repair (three cycles) of broken joints by ultrasonic-assisted method with neat and nanocomposite films, and 2) one-step repair using ultrasonic welding (USW) and resistance heating. It was found from tensile testing that multi-walled carbon nanotube/polypropylene (MWCNT/PP) films partially restored the lap shear strength (LSS), but pure PP films enabled significant recovery of the LSS as 94.5%, 89.4%, and 86.7% after the first, second, and third repair cycle, respectively. Nanocomposite films were however promising for monitoring the initiation and propagation of the damage occurring within the repaired joints, even after three repair cycles. Moreover, results from one-step repair using USW revealed that a stronger and more uniform repair interface was obtained, compared to resistance heating. Overall, the repair methods developed in this study exhibited promise for TPC joint repair, with strength recovery between 63.8% and 94.5%.