Enhanced Mechanical Properties of <scp>3D</scp> Printed Fiber Composites via Simultaneously Printing Short‐Continuous Fibers in a Bi‐Matrix Co‐Extrusion Process

ABSTRACT Continuous fiber‐reinforced composites are widely used in aerospace, rail transportation, automotive, and sports equipment, and are highly favored in lightweight and structural design. The use of fused deposition modeling (FDM) 3D printing technology to manufacture these composites can compensate for the shortcomings of traditional manufacturing processes, meeting the needs of green manufacturing, personalized customization, and complex component processing. Resin‐rich areas, which are inevitable in 3D printed continuous fiber‐reinforced composites, lead to a reduction in fiber content and weaken the mechanical properties. The focus of this research is to improve the mechanical properties of 3D printed fiber composites by simultaneously printing short and continuous fibers in a bi‐matrix co‐extrusion process. A thermosetting pre‐impregnated continuous fiber filament and a short fiber reinforced thermoplastic filament are co‐extruded, enabling the distribution of short fibers in the resin‐rich areas. Numerical models that can characterize the novel printed structure are proposed to explore the reinforcing mechanism. Moreover, annealing is applied to further enhance the mechanical properties. The results show that the tensile and flexural properties are improved after employing the short carbon fibers in the resin‐enriched areas. The flexural modulus and strength increase by 27.4% and 28.3%, respectively. The annealing treatment addresses the performance issue associated with the short fibers and further enhances the flexural modulus and strength by 15% and 13.8%, respectively. This research provides a new method to enhance the mechanical properties of 3D printed fiber composites.