PSI - Issue 41

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

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sides alternatively and eight fabrics were sprayed for each set of laminates. Vacuum-assisted resin transfer molding (VARTM) technique was used to manufacture the laminate. Eight fabrics of dimension 300 x 300 mm 2 for each condition laminate were stacked together on a flat granite table. Vacuum bagging was prepared with the help of double-sided sealant adhesive tape and a transparent bagging film. Before infusion of epoxy-hardener mixture (100:35 part by weight), it was kept under vacuum chamber to remove the trapped bubbles during mixing. The vacuum assisted infusion was done after degassing of epoxy-hardener mixture and to maintain the steady flow of epoxy in all directions, a flow mesh was placed over the carbon fibers. The curing of laminate was done at ambient temperature for 24 hours and subsequently at 70 o C for 16 hours. 4. Testing and characterization According to ASTM D3039M-17 standard (ASTM Committee D30, 2017), the static tensile test was carried out by Instron 8800 250 kN servo-hydraulic UTM (Universal Testing Machine). The specimen size was 150 mm x 25 mm x 1.7 mm (overall length x width x thickness) and schematically shown in Fig. 1. The tabbing was done to the grip section of the specimen at both ends. Bi-directional woven carbon fiber epoxy laminate was used as tabbing material. Minimum four specimens per condition were tested at room temperature at a crosshead speed of 1 mm/minute. Further, fracture surfaces of the failed specimens were observed using scanning electron microscopy (SEM).

Fig. 1. Geometry of static tensile test specimen

The morphology of the fractured surfaces has been investigated using scanning electron microscopy (SEM) Hitachi S-3400 N model. JEOL JSM-7600F Field Emission Gun-Scanning Electron Microscopes (FEG-SEM) was used to characterize the interphase through elemental mapping of the laminates by energy dispersive X-ray spectroscopy (EDS) equipped on SEM. EDS linear elemental mapping was recorded at least eight different sights for each condition of laminates. 5. Results and discussion 6. Interfacial region characteristics The interphase between the fiber and the matrix of all specimens was observed under SEM and the linear carbon elemental mapping was carried out using EDS by scanning the cross-section of the laminates. All linear EDS maps start from the carbon fiber and end at the epoxy (Fig. 2). Also, among all scans, one representative micrograph and the plot of each condition shown in Fig. 2. The gradual decrease of carbon element towards epoxy evidences the formation of interphase between the epoxy and fiber. Therefore, this gradual change in carbon element with respect to position has been measured for eight different scans for each condition and the average length of the interphase for each laminate is plotted in Fig. 3. The average thickness of the interphase of pristine, 0.2GNP and 0.4GNP is 1.38, 1.64 and 2.44 µm respectively. This increment of the interphase thickness is due to the presence of GNPs which can be attributed due to their carbonaceous nature. (Chen et al. , 2015) reported the improvement of 28% and 31% in interlaminar shear strength and flexural strength of 1 wt.% graphene sheets added unidirectional CF/epoxy composites respectively which was caused by the formation of gradient interface layer. Also, an improvement of 13% and 20% in interlaminar shear strength and flexural strength of CNT/quintuple sized-CF composites was reported due the larger gradient interphase compared to virgin carbon fiber composites (Yao et al. , 2015). Thus, the larger interphase signifies