Wet twisting treatment, process parameter optimisation and mechanical failure mechanisms of 3D printed carbon fibre reinforced composites

Advancing continuous carbon fibre-reinforced polymers (CFRP) is vital for efficient stress transfer, lightweight design and fabrication of complex structures. 3D printing technology promises to be able to form arbitrarily specified structures of continuous carbon fibre (CCF). However, the chemical inertness and high viscosity of carbon fibres and resins render them susceptible to severe interfacial bonding problems and printing defects. The optimisation of materials and processes represents an efficacious methodology for the pursuit of improvement. Therefore, this study aimed to improve the mechanical properties of CCF-reinforced thermoplastic polyurethane (CCF/TPU) material system by optimising printing process parameters, path planning and proposing a novel wet-twist treatment strategy. The failure behaviour was further investigated and the mechanisms to improve CCF impregnation, reduce defects and enhance interfacial bonding were analysed. The findings revealed that the failure behaviour at optimum printing parameters was fibre breakage. The wet twisting process effectively improves the impregnation of CCF by TPU and imparts a macroscopic helical morphology to CCF, eliminating weak fibre knots. The tensile strength and modulus of elasticity of the optimised printed parts were significantly increased by 62.18 % and 87.16 %. This provides a feasible way to improve the mechanical properties of CFRP and broaden the application scenarios.