The surface of stainless-steel (SS) mesh was modified by growing carbon nanotubes (CNTs) from ethanol flame. The CNT-modified SS mesh was then used as a heating element for the resistance welding of glass-fibre-reinforced polyetherimide (GF/PEI) laminates to improve the interfacial bond strength of SS wire and PEI resin. Interfacial microstructure, the mechanical properties of the welded joint and the effects of CNT growth time (t_g ) on the wettability of PEI resin solution to SS wire were investigated. The results indicate that the addition of CNTs increased wettability due to the capillary action of high-porosity CNT coating. The microstructure of the welded joints changed with t_g , and the thickness of the welding implant layer decreased below t_g = 10 min, and the maximum single lap shear strength (SLSS) value of the welded joint was 39.2 MPa when t_g = 10 min. The strengthening mechanism of CNTs and the failure modes of the welded joints were also elucidated in detail by the interfacial shear strength (IFSS) between SS wire, PEI resin and the fractography analysis.

A hole in the center of the aluminum (Al) alloy was processed to compensate for the mechanical properties of resistance welded joints of the carbon fiber reinforced epoxy resin matrix (CF/Epoxy) laminate and Al alloy for solving the problem of poor bonding quality in the center of the joint due to uneven temperature distribution in the resistance welding process. The resistance welded lap configuration of the upper Al and the lower laminate was employed, and through holes with a different diameter (d_h) were prefabricated on the upper Al alloy plates. The molten polyetherimide (PEI) resin was bonded to the surfaces of the samples on both sides under the action of Joule heat, and the excess PEI resin filled the prefabricated through-hole of the Al alloy plate under pressure and realized the jointing of the 6063Al alloy plate and the CF/Epoxy laminate. The micro-morphology of the welded interface was characterized by scanning electron microscopy (SEM), and the heat distribution of the sample was simulated using COMSOL. The tensile shear force of the joint was tested, which rises with an increase of d_h. The failure interface was analyzed in detail, which showed a strong correlation with d_h.

The approach for joining carbon fiber reinforced epoxy (CF/Epoxy) composites proposed in this study is based on the use of a plasticizing chip (PC), one side with rich resin and the other side with bare fiber, prepared by 1, 2, 3 or 4 pieces of glass fiber reinforced polyetherimide (GF/PEI) prepregs and a piece of glass fiber cloth (GFC), added as a last ply in the stacking sequence of CF/Epoxy composites. During curing, the epoxy partially penetrates in the side with a bare fiber of PC, leading to micro-mechanical interlocking as the main connection mechanism between the PC and the CF/Epoxy composites. To verify the effects of PC on the thermal and mechanical properties of CF/Epoxy composites, TGA, DMA, DCB, bending, interlaminar shear and drop-weight tests were carried out. The results showed that PC can effectively alleviate the impact of thermal degradation without weakening the properties of CF/Epoxy composites.