Enhanced resistance-welding hybrid joints of titanium alloy/thermoplastic composites using a carbon-nanotube lamina

The joining of titanium (Ti) alloy and composite parts with weight reduction and cost saving is being developed to improve aircraft performance. The high-efficiency resistance welding technology was explored for joining Ti alloy plate and glass fabric reinforced polyetherimide (GF/PEI) laminate in this work and a carbon nanotube (CNT) reinforced laminae was embedded into the interface of the welding region to enhance the strength of the hybrid joints of Ti -GF/PEI. The CNTs were in-situ grown on the surface of the Ti alloy plate, and their structures and morphologies were characterized by Raman spectrum, scanning electron microscope (SEM) and transmission electron microscope (TEM). The single lap shear strength (LSS) of the hybrid joints was evaluated with tensile tests. The LSS values first increased and then decreased with welding time (t(w)) due to the combined effects of the improving molten state of PEI resin and its local thermal degradation induced by excessive heat accumulation. The optimum LSS of the hybrid joint with CNT reinforced lamina is increased by 146% to 17.28 MPa in comparison with that of the hybrid joint without CNTs. The failure modes shift from interlayer debonding of the Ti alloy plate and the implant to the cohesive fracture of the implant and the delamination of the GF/PEI laminate with increasing t(w). The ultrasonic C-scan images also show an increase of the number of internal defects of GF/PEI laminates with t(w).