Mechanical properties of additively printed, UV cured, continuous fiber unidirectional composites for multifunctional applications

This paper investigates the mechanical properties and microstructure of additively manufactured, continuous fiber reinforced composites made by the Continuous Fiber 3D Printing (CF3D®) process. We specifically investigate composites of GF-2, a high temperature thermosetting acrylic polymer, and T-1100, a high strength carbon fiber, with a 41.5% fiber volume fraction. The resulting composites have a longitudinal tensile modulus of 122 GPa and a strength of 1599 MPa, which is 89% and 55% of the theoretical value by rule of mixtures, respectively. This appears to be the highest strength additively manufactured composites to date, largely due to the high mechanical properties of the T-1100 fiber, low defects, and substantial fiber volume fraction. Comparable results are obtained for a cationic cure resin, CATPRO14. We optically measured the fiber–fiber contact surface area fraction of GF-2 and employing the unidirectional strength model of Karam to predict a strength efficiency of 0.6, which is in good agreement with mechanical estimate of 0.55. Comparing results with the efficiency factors of high fiber volume prepreg laminates, we determine the printing process yields composites with 88%–95% of the anticipated longitudinal modulus and 65%–70% of the anticipated longitudinal tensile strength of those processed by traditional methods. To extend the printing to multifunctional microvascular composites, we consider the mechanical implications of including sacrificial filaments of 100–300 μm within each tow. A modest decrease in longitudinal strength in proportion to the microchannel volume fraction is predicted, where the decrease is mainly attributed to the increased fiber-to-fiber interactions in more tightly packed tows.