(267c) Multichannel Hollow Carbon Fiber Reinforcement in an Epoxy Resin Matrix for Direct Ink Writing of High-Performance Composites

Carbon-fiber-reinforced polymers have been widely used as additive manufacturing materials for high-performance composites. However, as applications within the aerospace and automotive industries evolve, demand for lighter weight materials with feasible processing methods has increased. Herein, we utilized novel hollow carbon fibers (HCFs) with a honeycomb cross-section as lightweight reinforcements for high-performance composites fabricated via direct ink writing. The printability, mechanical performance, and underlying microstructural features of an HCF-based matrix were investigated. According to rheological tests, the pre-printing characteristics of HCF-based inks are similar to those of traditional densified carbon fibers (DCFs). However, mechanical (flexure and tensile) testing found that traditional DCF composites outperform HCF composites. Possible failure mechanisms and variations in mechanical properties were investigated using scanning electron microscopy. Interestingly, this analysis revealed that epoxy infiltrated the entire channel length in the hollow fibers with easy pullout of long, uniform epoxy strands. Although interlocking between fibers and the matrix was expected to provide mechanical improvements, weak fiber–matrix bonding in the fiber interiors resulted in decreased tensile and flexural strengths. These findings demonstrate that appropriate sizing of the surfaces within the HCFs could provide opportunities for interlocking with various matrix systems, including high-temperature resins. Future work entails investigating and characterizing the influence of HCF channels on the resultant strength and exploring novel methods for improving interfacial bonding through modification of the channel surfaces.