Feedforward-adjusted temperature field: A multiphysics protocol for process-structure co-optimization in GF/PPS ultrasonic welding

Ultrasonic welding is a promising joining technique for thermoplastic composites, but its application faces with non-uniform interfacial temperature distribution, resulting in poor joint mechanical performance. To overcome the limitation, this study evaluates the use of preheating in ultrasonic welding of glass fiber polyphenylene sulfide (GF/PPS) composites using both experimental and numerical methods. The cross-sectional morphologies, mechanical properties, fracture modes, and temperature distribution were systematically characterized. These results revealed that moderate preheating can significantly improve resin fusion at different interfacial locations, enhancing joint mechanical performance by homogenizing the interfacial temperature distribution. Numerical simulations were firstly used to confirm this improvement, of which mechanism was proved to be derived from transitioning localized frictional heating toward distributed viscoelastic heating at the welding interface, resulting in smaller interfacial temperature gradients. The maximum lap shear strength of the joints reached 23.1 MPa with 90 °C preheating, which is 10.5 % higher than the joints without preheating (22.6 MPa). These findings offer a comprehensive understanding of preheating effects in GF/PPS ultrasonic welding and suggest that optimization of stress distribution at the interface can further improve fusion uniformity and mechanical performance.