Effect of Graphitic Nanofibers on Interfacial Adhesion and Fracture Toughness of Carbon Fibers-reinforced Epoxy Composites

The mechanical properties of carbon fiber-reinforced epoxy composites (CFRPs) are greatly dependent on the interfacial adhesion between the carbon fibers and the epoxy matrix. Introducing nanomaterial reinforcements into the interface is an effective approach to enhance the interfacial adhesion of CFRPs. The main purpose of this work was to introduce graphitic nanofiber (GNFs) between an epoxy matrix and carbon fibers to enhance interfacial properties. The composites were reinforced with various concentrations of GNFs. For all of the fabricated composites, the optimum GNF content was found to be 0.6 wt%, which enhanced the interlaminar shear strength (ILSS) and fracture toughness (KIC) by 101.9% and 33.2%, respectively, compared with those of neat composites. In particular, we observed a direct linear relationship between ILSS and KIC through surface free energy. The related reinforcing mechanisms were also analyzed and the enhancements in mechanical properties are mainly attributed to the interfacial interlocking effect. Such an effort could accelerate the conversion of composites into high performance materials and provide fundamental understanding toward realizing the theoretical limits of interfacial adhesion and mechanical properties.