PSI - Issue 41

Alok K. Srivastava et al. / Procedia Structural Integrity 41 (2022) 241–247 Alok K. Srivastava et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The interface between the matrix such as epoxy and reinforcing phases such as carbon fibers plays a decisive role in determination of mechanical properties of the composites (Hughes, 1991; Dassios, 2007). Incorporation of nano fillers e.g. carbon black, nano-silica particles, carbon nanotube and graphene oxides (B. R. K. Blackman, A. J. Kinloch, J. Sohn Lee, 2007; Han et al. , 2008; Kim et al. , 2011; Pathak et al. , 2016) in the epoxy matrix is a potent way of enhancing the strength and stiffness of CFRPs. The interface/interphase between the carbon fiber and the epoxy can be selectively strengthened by using different coating techniques e.g. layer by layer coating on the fiber, solvent spraying and electrophoretic deposition (Shan et al. , 2013; Wang et al. , 2016; Xiao et al. , 2018; Hung et al. , 2019; Srivastava et al. , 2019b). Also, interphase strengthening resulting from improved adhesion between the fiber and the matrix leads to improvement of interlaminar shear strength (Han et al. , 2017; Xiao et al. , 2018), tensile strength (Shan et al. , 2013; Wang et al. , 2016), flexural strength (Shan et al. , 2013; Hung et al. , 2019; Srivastava et al. , 2019a), and fracture toughness (Shan et al. , 2013; Mishra et al. , 2019) of the composites. Low weight percent (upto 0.3wt%) of the graphene based nanofillers mixed in epoxy before infusion has been recommended to maximize the tensile properties of the carbon fiber reinforced polymer composites. Furthermore, the fracture surfaces of the higher weight percent (0.5wt%) reveal the presence of agglomerates which might causes the reduced interfacial adhesion between fiber and matrix in comparison to 0.3wt% graphene based nanofiller (Ashori, Rahmani and Bahrami, 2015). In the same way, incorporation of 0.5wt% of graphene oxide through dip coating of carbon fibers in CFRP causes serious degradation in interfacial shear strength (IFSS), interlaminar shear strength (ILSS), flexural and tensile properties. Poor chemical adhesion and formation of agglomerates causes the degradation in former properties. However, the incorporation of 0.5wt%. graphene oxide functionalized with silane coupling agent results in improved IFSS, ILSS, flexural and tensile properties which is due to the enhanced interfacial properties of gradient interphase(Chen et al. , 2014). These studies communicate the merits of low the amount of graphene incorporation and the advantages of using functionalized graphene oxides in CFRPs. The fractographic examination of these multiscale composites has not been explored in detail yet. In this study, solvent spray coating of different weight percent of graphene nanoplatelets (GNPs) on carbon fibers was done prior to the laminate manufacturing through vacuum assisted resin transfer molding (VARTM) technique. These laminates were tested under uniaxial tensile loading conditions and the detailed fractographic examination was done. We also tried to characterize the interphase of CFRPs with and without GNP coatings with the help of SEM EDS and corelated it with the fracture and strength of the laminates. 2. Materials A unidirectional carbon fiber (UDCF tows consisting 3k filaments of 7µm diameter each) layered with the epoxy adaptable sizing was procured from Bhor Chemicals and Plastics Pvt. Ltd., Mumbai, India. The details of carbon fiber as per manufacturer’s data sheet are as follows: tensile strength (4000MPa), density (1.8 g/cm 3 ) and percentage elongation 1.7 %. Graphene nanoplatelets was procured in powder form from Ad-Nano Technologies Pvt. Ltd., Karnataka, India. GNPs have purity ~99%, surface area ~380 m 2 /g and comprised of 2-4 layers with average thickness of ~2-5 nm. A resin-hardener system Epofine-1564 and Finehard 3486-1 was purchased form Fine Finish Organics Private Ltd., Mumbai, India, which was composed of Bisphenol-A-diglycidyl ether-based resin and low viscosity polyetheramine hardener. The part by weight ratio of epoxy resin to hardener was mentioned to be 100:35 according to manufacturer’s data sheet. All materials were used as received unless otherwise stated. 3. GNP/UDCF/epoxy laminate fabrication An airbrush system Pilot Power AB-15 manufactured by Manik Radiators Pvt. Ltd. India has been used to spray coat the graphene nanoparticles (GNPs). To supply the compressed air, a dry single-piston Airbrush air compressor has been connected to the spray gun. 0.2 wt.% and 0.4 wt.% concentration of the GNPs with respect to the total fabric weight were used to spray for 0.2GNP and 0.4GNP laminates respectively. GNPs were ultrasonicated in ethanol with the help of probe-type sonicator (3 kHz, 250 Watts) for 30 minutes. To prevent the agglomeration of GNPs, bath sonication for 10 minutes was also done in intermediate steps of spray coating. The fabrics were coated from both