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Highlights Polymer composites reinforced with carbon fiber (CF) are strong, light weight and corrosion‐resistant, and have a wide range of applications in automobile, sports, aerospace, wind energy etc. but are prone to fail at the interface of epoxy and fiber due to weak interfacial adhesion between the fiber and epoxy. Formation of an interphase region with a continuous gradation of properties between fiber and the epoxy can potentially delay failure. Development of a larger interphase can be facilitated by the inclusion of graphene platelets on carbon fiber surface through various deposition processes. The present investigation utilizes a unique combination of magnesium nitrate hexahydrate and carboxyl graphene (G‐COOH) to create a colloidal solution for the particulate type deposition of G‐COOH onto carbon fibers through electrophoretic deposition (EPD). Four layers of EPD deposited carbon fibers have been used to make the composite using vacuum assisted resin transfer molding technique. Tensile and flexural tests have been conducted on the pristine and 0.45 wt% of G‐COOH deposited carbon fiber (0.45G‐COOH CF) epoxy composite. G‐COOH addition leads to thickening of the interphase which has been confirmed through energy‐dispersive x‐ray spectroscopy line scanning. The tensile and flexural strength properties of the carboxyl graphene deposited composites exhibited an increase of 62% and 12% respectively. These improvements can be ascribed to the deposition of carboxyl graphene particles on the fiber and an enhancement in interphase thickness. Moreover, the addition of G‐COOH in composites resulted in a 38% increase in tensile strain. The interlaminar shear strength (ILSS) and void content measured in 0.45G‐COOH CF have been compared with pristine carbon fiber composite as well as 1.3 wt% of carboxyl graphene (1.3G‐COOH) deposited carbon fiber fabric composite that had a film type morphology of G‐COOH deposition. There is only a slight decrease in ILSS of 0.45G‐COOH carbon fiber composites occurred compared to pristine carbon fiber composites. The film type morphology of carbon fiber composite showed the highest void content and lowest ILSS compared to other composites. The fracture surfaces of the failed composites were thoroughly examined through scanning electron microscope and they showed that the failure mechanisms in both tension and flexural loading were severely affected by the presence of G‐COOH. Optimization of electrophoretic deposition process parameters for carboxyl graphene deposition on carbon fiber fabrics. Enhancement composite strength through the particle type deposition of carboxyl graphene over film type deposition. Evaluation of the tensile, flexural and interlaminar shear strength of particle type carboxyl graphene deposited composite. Identified the failure mechanisms of these tests. [ABSTRACT FROM AUTHOR]

Graphene nanoplatelets (GNPs) are extremely useful nanofillers in epoxy in carbon fiber‐reinforced polymer (CFRP) composites as they make CFPRs sustain higher loads before failure in different kinds of loading for example flexural, tensile and fatigue. The current study aims to investigate the effect of GNP coating on carbon fibers on the deformation modes of CFRPs under flexural loading. Laminates have been fabricated using vacuum‐assisted resin transfer molding (VARTM) after spray coating GNPs on unidirectional carbon fiber fabrics. One set of flexural tests were carried out where the strain was recorded using DIC and the other set had in‐situ deformation while recording optical images to monitor deformation. Since, the most probable causes of failure under flexural loading are local compression, shear or contact stresses due to a sharp ram, other mechanical tests like compression test and nano‐indentation were also carried out on the composites. Compressive stress–strain response was ascertained using combined loading compression (CLC) fixture and digital image corelation (DIC) while contact response was evaluated using nanoindentation. GNP‐coated CFRPs were shown to have an increase in compressive modulus of 16% and failure strain of 6%, respectively. Axial and transverse strains measured through DIC were more than two times higher in GNP‐coated CFRPs. Nano‐indentation tests across the entire composite showed some data with intermediate modulus (~10–45 GPa) and hardness (~1–5 GPa) between the epoxy and the fiber and this corresponded to an interphase region which was thicker in 0.4GNP laminate compared to pristine laminate. Flexural strength, flexural modulus and strain at maximum stress improved by 10%, 8%, and 9% respectively in GNP‐coated CFRPs compared to uncoated CFRPs. In addition, while pristine laminates showed non‐uniform distribution of strains during flexural loading, the distribution of strains was much more uniform in GNP‐coated laminate. However, in both kinds of laminates, the failure initiation was in the region of compressive bending stresses. Highlights: GNP‐added laminate showed an intermediate modulus and hardness interphase through a nanoindentation test.Digital image correlation analysis has been performed to obtain the strain maps during compressive and flexural loading.GNP‐added laminates showed higher failure strains compared to pristine laminates under the compressive loads.GNP‐added laminates performed well under flexural loading. [ABSTRACT FROM AUTHOR]