Enhancing the thermal distribution homogenization and interfacial adhesion at induction welded composite interface by SCF reinforced thermoplastic layer

Induction welding of carbon fiber reinforced thermoplastic (CFRTP) often faces edge effect issue, which negatively affects the joint quality. This study explored the induction welding of carbon fiber reinforced polyamide 66 (CF/PA66) using a composite PA66 film reinforced with short carbon fiber (SCF) at interface to reduce edge effect and improve joint strength. Results indicated that the incorporation of SCF increased the number of polar functional groups on the resin film and increased surface roughness, promoting adhesion force between heating element (HE) and matrix. Additionally, the randomly dispersed SCFs formed interconnected heat-conduction pathways within the PA66 matrix, which enhanced the thermal conductivity of the interface by providing additional heat transfer routes alongside the HE. Finite element analysis (FEA) confirmed that the improved heat transfer capability at interface contributed to a more uniform temperature distribution. Furthermore, the PA66 films prepared with SCF exhibited a lower thermal expansion coefficient, which enhanced thermal shrinkage resistance and minimized stress concentration. Finally, the integration of SCF markedly enhanced lap shear strength (LSS) of joints, achieving an increase of 1.37 times compared to the strength of joints without SCF under optimal heat input conditions. This improvement presented a novel strategy for attaining high-quality induction-welded joints.