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

Abstract

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.

Future directions in ceramic additive manufacturing: Fiber reinforcements and artificial intelligence

“…245 In AFP, a gantry/robotic system with an attached fiber placement head deposits tows of pre-impregnated fibers. [245][246][247] The tows are placed on a tooling surface and built up into a composite component over a number of passes across the tool. The fabricated 247 component is then consolidated and cured, typically via autoclave.…”

“…[245][246][247] The tows are placed on a tooling surface and built up into a composite component over a number of passes across the tool. The fabricated 247 component is then consolidated and cured, typically via autoclave. Some manual process is still required in AFP for more complex geometries, such as hand layup of the impregnated fiber panels.…”

“…248 Additionally, the tows can easily wrinkly during sharp angle changes during deposition, resulting in defects. 247 As such, along with long processing time and limited fiber spacing, direct adaptation to CMCs has been limited. 237,248 Knowledge gained from AFP has been adapted to build more automated AM systems for continuous fiber PMCs that avoid the post-layup autoclave step.…”

“…Alternatively, In the case of the CF3D printer technology, a UV light source at the end of a robotic arm is used to cure an acrylic thermoset matrix impregnated into a C f tow to fix the shape. 247 While feedstock development, utilizing preceramic polymers and/or ceramic particle filled polymers, is of interest, easier adaptation of these methods could start with pyrolysis of printed PMC materials. In doing so, a porous C f -reinforced preform would be developed and could be densified through infiltration using preceramic polymers, chemical vapor infiltration (CVI), melt infiltration, or a hybrid process.…”

“…In the PMC community one of the foremost automated manufacturing methods is automated fiber placement (AFP), first appearing in a patent from 1974 245 . In AFP, a gantry/robotic system with an attached fiber placement head deposits tows of pre‐impregnated fibers 245–247 . The tows are placed on a tooling surface and built up into a composite component over a number of passes across the tool.…”