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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7. Tensile Properties The tensile test of the tabbed specimens was performed and the average of four specimens is presented in Table 1. The 0.4GNP laminate shows 15% and 11% improvement in tensile strength compared to pristine and 0.2GNP laminate respectively. This can be attributed to the larger gradient interphase and adhesion between carbon fiber and the epoxy in 0.4GNP laminate. The formation of gradient interphase has shown appreciable benefits in interlaminar shear strength and flexural strength of the graphene/CNTs added CFRPs (Chen et al. , 2015; Yao et al. , 2015). Also, Young’s modulus of 0.4GNP laminate shows 10% improvement compared to pristine and 0.2GNP laminate. This can be ascribed to the stiffening effect of the rigid GNPs in the gradient interphase. The average tensile strength and modulus of the laminates increases with the increase in GNPs for wt.% (Fig. 4a). However, there is no substantial change in strain at maximum tensile strength i.e. failure strain of the laminates with increase in GNP wt.% (Fig. 4b). The strain of unidirectional laminate is mainly governed by the tensile strain of the fibers due to the major load acting on the fibers. Thus, there is no appreciable change in maximum tensile strain of all the laminates.

Table 1 Tensile properties of the GNP/CF/Epoxy laminates with different conditions

Strain at maximum tensile stress (%)

Sample Tensile modulus (GPa) Tensile strength (MPa)

Pristine

112 ± 2.8

1164 ± 96

2.5 ± 0.23

0.2GNP

112.1 ± 5.25

1209 ± 76

2.4 ± 0.02

0.4GNP

123.43 ± 9.75

1340 ± 24

2.6 ± 0.14

Fig. 4. Tensile test results of GNP/CF/epoxy composites with different conditions (a) flexural strength and modulus and (b) failure strain

8. Fractography of failed specimens The morphology of the fractured surfaces of tensile test specimens were examined under SEM and shown in Fig. 5. Debonding gaps between epoxy and carbon fiber were indicated by white arrows in the micrographs. Fig. 5(a) shows cross-sectional fracture surface of the pristine laminate which indicates the larger debonding gaps (0.7 – 1.73 µm) between the fibers and the epoxy. 0.2GNP laminate in Fig. 5 (b) also shows similar but smaller size debonds (0.53 – 1 µm) as compared to pristine laminate. However, 0.4GNP laminate in Fig. 5 (c) shows the closely packed fiber-epoxy fracture surface and the debonding gaps are fairly negligible compared to former laminates. In other words, the GNPs were coated onto the fibers to entangle with the epoxy and the observation made for 0.4GNP laminates in Fig. 5 (c) is