3D Printing and Characterization of Carbon Fiber Epoxy Composites

The conventional composite fabrication processes, such as hand lay-up, autoclave, vacuum-assisted resin transfer molding (VaRTM), and filament winding, hinder the prospect of future development and application due to expensive mold fabrication, limited part geometries, and lack of repeatability. An extrusion-based additive manufacturing technique, such as direct-ink-writing (DIW), undermines the limitation of conventional manufacturing processes, which opens the horizon of multi-material parts fabrication cost-effectively. This research investigates the design of a printable ink followed by 3D printing and characterization of single and multi-filament dog-bone specimens under tensile loading. The ink comprises milled carbon fibers, epoxy resin, silica fillers, and polymer additives. In 3D printing, a single filament forms a representative volume element (RVE), which upon stacking a series of RVE layer-by-layer in sequence, forms a 3D object. Thus, understanding the deformation behavior and mechanics of load transfer in a single filament to its adjacent neighboring filament through the interface plays a critical role. An adequate understanding of single and multi-filament failure mechanisms and the contribution of interfaces in a 3D printed multi-filament object is yet to be understood. This research extensively focuses on the fundamental understanding of the microstructure development and mechanical behavior of 3D printed single filament and multi-filament samples under tensile loading. The rheology of the ink exhibits strong shear thinning characteristics during extrusion while ability to retain shape. The single filament sample shows the highest tensile strength and modulus compared to multi-filament samples. It is believed that the presence of void at the filament-filament interface leads to premature failure of the multi-filament samples.