A novel filament design for improving fused filament fabrication of continuous fiber composites

Fused filament fabrication (FFF) of polymer composites with continuous fibers could enable the manufacture of complex structures with exceptionally high specific strength and stiffness. Although filaments with continuous fiber reinforcement are “printable”, the fibers undergo damage during printing, leading to reductions in strength and reliability. Of further concern, the printed material generally exhibits low interlaminar tensile strength. In this study, a novel prototype filament for FFF with continuous carbon fibers and polyphenylene sulfide matrix was evaluated for its potential to resist process-related fiber damage introduced during printing and to increase the interlaminar tensile strength. The filament design enrolls a circumferential matrix coating around a fiber reinforced core. According to the measures of strength, the new filament design improved the reliability in axial strength as well as increased the interlaminar tensile strength by over 80 %. While the new coated filament exhibited superior performance overall in the printed condition, it was more sensitive to temperature changes and underwent a substantial decrease in axial tensile strength at T > 330 °C due to the decrease in matrix viscosity and consequent reduction in fiber protection. The printability of the new filament design is reported as a function of nozzle temperature, and the mechanisms that cause void formation and fiber damage are discussed.