Research on the fabrication of continuous carbon fiber reinforced polyamide 6 composites by means of ultrasonic vibration

Because of the high viscosity and poor fluidity of thermoplastic resin, it is easy to form voids in thermoplastic composites fabricated by traditional methods. The introduction of ultrasonic vibration into the fabrication of thermoplastic composites promotes the flow of thermoplastic resin and improve the quality of thermoplastic composites. In this study, continuous carbon fiber-reinforced polyamide 6 (CF/PA 6) composites were fabricated by ultrasonic vibration. The effects of ultrasonic amplitude and welding time on the temperature variations of the CF/PA 6 stack during the fabrication process were studied. Experimental results show that increasing the ultrasonic amplitude and welding time can increase the fiber volume fraction and decrease the void content of CF/PA 6 composites. The maximum fiber volume fraction is around 49.6%, and the minimum void content is around 0.09%. Meanwhile, the average diameter of single carbon fiber in CF/PA composites decreases from 7 μm of as-received carbon fiber to 6.03 ± 0.04 μm of composites fabricated at the welding time of 15 s and the ultrasonic amplitude of 90 μm. Additionally, the flexural strength of composites is improved within a limited window, while the flexural modulus increases with the increase of ultrasonic amplitude and welding time due to more compact CF fabrics in the composite laminates. The obtained maximum flexural modulus of CF/PA 6 composite laminates can reach up to 31.8 ± 3.9 GPa. The failure mode of composites is sensitive to the ultrasonic vibration parameters.