Printable epoxy carbon fiber composites and their mechanical properties

Additive manufacturing (AM) of fiber reinforced thermosetting resins has not been well explored due to material and processing restrictions including high viscosity, poor reinforcement dispersion, dimensional tolerance, and porosity. Yet, such a process would enable tool-less and agile manufacturing of small and complex composite parts with temperature and environmental stability superior to traditional thermoplastics. Printed thermoset composites could also be combined with traditional epoxy prepregs to make complex co-cured structures. In this work, a direct write AM process for epoxy / chopped carbon fiber composites is used which has been shown to provide cured composites tensile modulus and strength values 90% and 66% of the fully aligned composite, respectively. The fibers are largely oriented in the print direction, but have sufficient localized material flow to achieve acceptable transverse properties and low porosity. Sandwich structures created with additively printed cores and co-cured prepreg face sheets were fabricated and evaluated. Rather than creating a sandwich structure by adhesively bonding standard sizes of honeycomb core to cured composite face sheets, this work examined co-curing customized additively printed core structures with prepreg face sheets. This process can be used to design and optimize properties for complex geometries while reducing the number of manufacturing steps.