Damage Mechanism of Resistance Welded Thermoplastic Composite Joint Based on Acoustic Emission Monitoring and Heat Transfer Modeling

Resistance welding (RW) is a promising joining technique for thermoplastic composites (TPCs), where comprehensive characterization of the joint's damage mechanism serves as a foundation for performance assessment and process optimization. To identify the damage mechanism beyond fractographic observations, the damage evolution of the RW CF/PPS joint was explored via acoustic emission (AE) in this study. Moreover, a transient heat transfer model was built to illustrate the temperature distribution in the weld region, considering its governing influence on damage modes. Effects of electrical inputs, model dimensionality, and temperature dependences of material parameters were considered to improve the model's fidelity, with component experiments conducted to support this effort. Results demonstrated that AE analyses could indicate the cohesive-dominant damage mechanism beyond the mixed failure recognized from fractographies, as characterized by the persistent matrix cracking and heating element (HE) deformation. Moreover, the detrimental adhesive failure in terms of debonding between PPS film and CF/PPS adherend was found to influence only the initial loading stage, and its location agreed well with the low-temperature region from heat transfer modeling. This highlighted the importance of temperature distribution in elucidating the damage mechanism, but careful considerations should be devoted to its modeling approach. Here, the 3D model was more reliable than its 2D counterparts. Furthermore, temperature dependences of HE's resistance and electrical input calculations were identified as critical modeling factors. This study is anticipated to gain deep insight into the damage mechanism of resistance welded thermoplastic composite joints and provide suggestions for reasonable heat transfer modeling.