Understanding Dynamic Wicking and Curing of Epoxy Resin in Carbon Fiber Tows for 3D Printing Application

Abstract

In recent years, additive manufacturing (AM), also known as 3D printing, has been developed as one of the major fabrication technologies for advanced composite materials. 3D printing offers a great way of producing composites with costefficiency, scalability, high productivity, and design flexibility. Among the numerous materials used in 3D printing, thermoplastic polymers with discontinuous reinforcement (i.e. powder, nanoparticles, short fibers) have been used successfully thanks to high processability. However, the thermoplastic/discontinuous fiber composites are often limited to extreme circumstances requiring high service temperature or mechanical properties due to the low glass transition temperature of the polymers or discontinuous reinforcement. Thermosetting polymer/continuous carbon fiber composites can be an alternative, but there has been no reported AM technique addressing the process of thermosetting polymers and continuous carbon fibers for direct 3D printing. A fundamental challenge of fabricating such composites is in controlling the irreversible viscosity change of thermosets. If a drastic increase of the polymer viscosity occurs before infusion, it is hard to infiltrate the polymers into the fiber bundle, whereas under-cured polymer cannot sustain a designed pattern during the process. Herein, we analyze dynamic capillary-driven flow generated by thermal gradient along carbon fibers based on the understanding of dynamic wicking and curing of epoxy resin in carbon fibers. It gives a significant breakthrough in overcoming these obstacles by controlling the viscosity and degree of cure of the thermosetting polymers. With numerical analysis, we prove that different liquid absorption capability along the fibers induces dynamic wicking of the resin. And in computational simulation, in-composite heating system (heating along carbon fibers) exhibits the abilities to heat the resin uniformly acting like internal heating and cure the composites with a high degree of curing. And we apply the dynamic capillarydriven flow to the 3D printing for manufacturing thermosetting/continuous carbon fiber composites. The great mechanical properties of the printed composites show that dynamic capillary-driven flow is applicable in fabrication of the composite.