Effect of Graphene Coating of Carbon Fibers on the Fracture of Uni-directional Laminates

Abstract

High specific strength and stiffness of carbon fiber reinforced polymer (CFRP) composites make them the preferred structural materials for a wide range of applications. The interfacial region between the matrix and reinforcing phases plays a critical role in determining the performance of CFRPs under mechanical loading. Hence, enhancing the interfacial bonding between the epoxy and the fibers is expected to improve the strength of the resulting composites. In the current study, a coating of graphene nano-platelets (GNPs) on unidirectional carbon-fibers has been made with the aim to strengthen the interface/interphase between the fiber and the matrix. Vacuum assisted resin transfer molding technique was used to manufacture the laminates after the solvent spray coating of the GNPs onto carbon fiber. The uncoated and GNPs coated CFRPs have been subjected to tensile tests followed by detailed fractographic analysis. Uniaxial tensile strength and Young’s modulus of the laminates have been found to improve with GNP addition. The fractographs reveal debonding gaps between fiber and epoxy in cross-sectional fracture surfaces and adherence of the epoxy with fibers in longitudinal fracture surfaces. Laminates made with fibers with a coating of GNPs showed smaller debonding gaps and larger epoxy adherence on the fibers than the pristine laminates. A larger interphase for the former laminate was found using carbon linear elemental mapping with the help of SEM equipped with energy dispersive X-ray spectroscopy.