An investigation on the effect of GNP addition on the mechanism of deformation in unidirectional carbon-fiber epoxy composites using mechanical testing and in-situ SEM

A few recent studies on carbon fiber epoxy composites have shown that there is a region in the epoxy near the fibers that is enriched in carbon and can be called as an interphase due to its distinct properties. However, the effect of nature and thickness of this interphase on deformation during mechanical loading has not been shown explicitly. Multiple studies have shown that addition of graphene nano-platelets can significantly influence the size and properties of the interphase and thereby improve the tensile and flexural response of carbon-fiber matrix composites. However, the effect of GNPs on the transverse loading of the composites is not known and the same has been found out in the current study. No differences have been found in the transverse tensile properties of the pristine and GNP-added laminates as the failure is controlled by the weakest epoxy region. Moreover, tensile, shear and transverse strains have been recorded in-situ during longitudinal tensile loading of notched composites with and without GNPs. This has shown that composites made from GNP-coated fibers are able to bear higher localized strains before failure. A similar longitudinal tensile test has also been performed inside an SEM and that has provided clinching evidence that addition of GNPs leads to much fewer fibre breaks and much greater adhesion of fibers to epoxies under shear.

Automated summary

Recent studies have shown that the carbon-rich region in carbon fiber epoxy composites can be called an interphase, and that the addition of graphene nano-platelets can significantly influence the properties of the interphase. The effects of graphene nano-platelets on transverse loading and in-situ strains during longitudinal tensile loading have been investigated, demonstrating improved performance of composites with GNP-coated fibers. The SEM analysis further confirms that GNP addition leads to fewer fiber breaks and enhanced fiber-epoxy adhesion under shear loading.