Comparison of welding techniques for carbon fibre-reinforced PEKK composite

Welding techniques such as ultrasonic, induction, and laser welding have attracted significant interest for joining thermoplastic composite aerostructures. In this study, single-lap joints (SLJs) employing carbon fibre-reinforced poly-ether-ketone-ketone (CF/PEKK) adherends are manufactured using ultrasonic (USW), induction (IW) and laser conduction (LCW) welding techniques and tested under quasi-static tension. The deformation mechanisms are compared against “reference” co-consolidated joints and fractography analysis is performed. Co-consolidated SLJs recorded the highest LSS of 33 MPa, while both IW, USW and LCW joints achieved mean LSS values of 23.6 MPa, 22.8 MPa and 17 MPa, respectively. Test video post-processing and digital image correlation studies indicate a strong correlation between LSS, overlap rotation, and evolution of peel and shear strains. In addition, the digital scanning calorimetry (DSC) assessment of the post-welding interface crystallinity indicates that IW, USW and LCW weld regions achieved 24%, 20% and 14% crystallinity, respectively, which correlates strongly with their LSS performance. These findings provide new insights into the performance and potential of these welding techniques, while also indicating that the welding processes can be further optimised to achieve greater LSS performance.