Reactive extrusion additive manufacturing of a short carbon fiber thermosetting composite via active mixing

Reactive extrusion additive manufacturing (REAM) is a recently developed process that utilizes reactive thermoset resin-hardener systems that are mixed inside a shearing element, deposited layer by layer to form a structure, and cured in-situ without external energy. An externally powered active mixing element was developed and used to demonstrate REAM with a highly viscous resin that was filled with 10 wt% chopped carbon fibers. This was achieved by adding fumed silica and increasing the temperature of the fiber-resin mixture to enable effective in-situ mixing while maintaining shape retention upon deposition. Tensile properties of fiberreinforced and reference REAM parts were measured and explained using their fiber alignment and length distribution. Finally, a mechanics model was utilized to determine the optimal fiber content for strength and stiffness, considering the degradation of fiber length at higher volume fractions due to the mixing.