Additive manufacturing (AM) is one of the fastest-growing manufacturing technologies in modern times. One of the major challenges in the application of 3D-printed polymeric objects is expanding the applications to structural components, as they are often limited by their mechanical and thermal properties. To enhance the mechanical properties of 3D-printed thermoset polymer objects, reinforcing the polymer with continuous carbon fiber (CF) tow is an expanding direction of research and development. A 3D printer was constructed capable of printing with a continuous CF-reinforced dual curable thermoset resin system. Mechanical performance of the 3D-printed composites varied with the utilization of different resin chemistries. Three different commercially available violet light curable resins were mixed with a thermal initiator to improve curing by overcoming the shadowing effect of violet light by the CF. The resulting specimens’ compositions were analyzed, and then the specimens were mechanically characterized for comparison in tensile and flexural performance. The 3D-printed composites’ compositions were correlated to the printing parameters and resin characteristics. Slight enhancements in tensile and flexural properties from some commercially available resins over others appeared to be the result of better wet-out and adhesion.

Reinforcing thermoset polymers with continuous carbon fiber (CF) tow has emerged as a promising avenue to overcome the thermal and mechanical performance limitations of 3D printed polymeric structures for load-bearing applications. Unlike traditional methods, manufacturing continuous fiber-reinforced composites by 3D printing has the unique capability of locally varying the mechanical properties of the composites. In this study, continuous CF thermoset composite specimens were printed with varying line spacing, resin flow rate, and nozzle sizes. The resin flow rates for different line spacings and nozzle sizes were optimized by topographic analysis. Printed composite mechanical properties were evaluated, and their trends were correlated with the trend of print parameter changes. Results showed that tensile strength and modulus could be altered and improved by ~50% by adjusting the printing process parameters. Higher composite strength and modulus were obtained by shortening the line spacing and nozzle diameter.

Continuous carbon fiber-reinforced (CCFR) thermoset composites have received significant attention due to their excellent mechanical and thermal properties. The implementation of 3D printing introduces cost-effectiveness and design flexibility into their manufacturing processes. The light-assisted 3D printing process shows promise for manufacturing CCFR composites using low-viscosity thermoset resin, which would otherwise be unprintable. Because of the lack of shape-retaining capability, 3D printing of various shapes is challenging with low-viscosity thermoset resin. This study demonstrated an overshoot-associated algorithm for 3D printing various shapes using low-viscosity thermoset resin and continuous carbon fiber. Additionally, 3D-printed unidirectional composites were mechanically characterized. The printed specimen exhibited tensile strength of 390 ± 22 MPa and an interlaminar strength of 38 ± 1.7 MPa, with a fiber volume fraction of 15.7 ± 0.43%. Void analysis revealed that the printed specimen contained 5.5% overall voids. Moreover, the analysis showed the presence of numerous irregular cylindrical-shaped intra-tow voids, which governed the tensile properties. However, the inter-tow voids were small and spherical-shaped, governing the interlaminar shear strength. Therefore, the printed specimens showed exceptional interlaminar shear strength, and the tensile strength had the potential to increase further by improving the impregnation of polymer resin within the fiber.

In-space manufacturing (ISM) enables on-demand fabrication of large space structures that exceed current launch payload volume. While past research has focused on additive manufacturing of thermoplastics and their composites, fiber-reinforced thermoset composites (FRTSC) offer lower energy processing, superior thermomechanical properties, durability, and easy integration of multifunctional material systems through diverse chemistry, composite architecture, and novel processing. The challenges to using thermosets composites in space are containment of fluids, control of the chemical reaction with compact processing equipment, and maturation of processing methods. Recent studies suggest that in-space manufacturing of FRTSC can be advanced using encapsulated catalyzed poly(dicyclopentadiene) (pDCPD) carbon fiber preforms. Structural elements can be processed with modest equipment using frontal polymerization (FP) of pultruded composite tubes, bulk polymerization of solid beams by rapid out-of-oven lamination (ROL), and FP of panels with programmed curvature from flat additively manufactured preforms. Looking ahead, novel chemistry, integrated devices, and in-space manufacturing of FRTSC can be combined to achieve multifunctional space structures with self-healing, self-passivation, and self-sensing and extend the service life of space structures. This review examines the current state of ISM, current challenges, and the emerging role that ISM of multifunctional thermoset composites can have in enabling sustainable space infrastructure.

Despite having better processibility, durability, and thermomechanical performances, thermoset composites raise concerns of limited storage life, resin volatility, and property consistency when considered for in-space manufacturing. The large costs in time, energy, and equipment for processing are also important selection criteria. Here, we tackle such concerns by infusing carbon fibers with frontally polymerizable (FP) resin such as catalyzed dicyclopentadiene (DCPD) and enclose them between sealed, impermeable, and compliant polymer films to demonstrate significant improvement in storage life at −20 °C (>6 months) and in containment of resin volatility during cure (<1% in total mass loss) under vacuum environments. Due to the reactive nature of FP resins, we rapidly cure the sealed prepregs thermally (5 min at 155 °C) using low energy (~1.79 MJ/kg) and pressure (11 psi) to manufacture low void composites (<1% voids) with consistent \({T}_{g}\) (160 °C) and flexural properties (~180 GPa) after prolonged prepreg storage. The improved stability is attributed to the prevention of water ingress, which improves the effectiveness of the tributyl phosphite inhibitor. We further demonstrate scalability from flat laminates to tubular longerons along with the applicability of such containment strategy to other forms of reactive thermoset resins, including radical-induced cationic frontally polymerizable epoxies.