Issue 48

H.S. Bedi et alii, Frattura ed Integrità Strutturale, 48 (2019) 571-576; DOI: 10.3221/IGF-ESIS.48.55 575 analysis is performed on the failed fiber surfaces. Fig. 4 presents the analysis of the surface of debonded fibers using SEM, throwing some more light on the failure mechanism of different fiber/epoxy composites. The presence of matrix debris adhering the surface of CNT grafted CF debonded from epoxy (Fig. 4b) implies that failure occurs at the interface of nanotubes and matrix away from the CF/epoxy interface [13]. Whereas, the clean surface of debonded fiber in HCF/epoxy composites (Fig. 4a) suggests failure taking place at the fiber/epoxy interface. This implies poor interfacial bond in HCF/epoxy composites and lower IFSS as compared to CNTCF/epoxy composites. C ONCLUSION he effect of loading rate and grafted CNTs on the interfacial shear strength (IFSS) of carbon fiber reinforced epoxy composites is studied. Single fiber micro-droplet debond tests are carried out on unsized and CNT grafted carbon fiber epoxy composites at two displacement rates of 0.05 and 5 mm/min. An increase in IFSS is observed by increasing the test speed for both unsized and CNT grafted carbon fiber reinforced epoxy composites. The benefit of incorporating grafted CNTs in the composite system is clear from the high values of IFSS for CNTCF/epoxy composites than HCF/epoxy composites. IFSS of CNT based hybrid composites are approximately 30% higher than their non-CNT counterparts. At higher speeds of loading, matrix is found to play a more significant role in the failure process by yielding more to increase the energy of fracture and hence the IFSS of the composite. A CKNOWLEDGEMENT uthors would like to thank the financial support and lab facilities provided by Indian Institute of Technology Ropar to carry out this research work. R EFERENCES [1] Jacob, G.C., Starbuck, J.M., Fellers, J.F., Simunovic, S. and Boeman, R.G. (2004). Strain rate effects on the mechanical properties of polymer composite materials, J. Appl. Polym. Sci., 94(1), pp. 296-301. [2] Sockalingam, S. and Nilakantan, G. (2012). Fiber-matrix interface characterization through the microbond test, International Journal of Aeronautical and Space Sciences, 13(3), pp. 282-295. [3] Qian, H., Bismarck, A., Greenhalgh, E.S., Kalinka, G. and Shaffer, M.S. (2008). Hierarchical composites reinforced with carbon nanotube grafted fibers: the potential assessed at the single fiber level, Chem. Mater., 20(5), pp. 1862- 1869. [4] Gao, X., Jensen, R., Li, W., Deitzel, J., McKnight, S. and Gillespie Jr, J. (2008). Effect of fiber surface texture created from silane blends on the strength and energy absorption of the glass fiber/epoxy interphase, Journal of Composite Materials, 42(5), pp. 513-534. [5] Chandrasekaran, V., Advani, S. and Santare, M. (2011). Influence of resin properties on interlaminar shear strength of glass/epoxy/MWNT hybrid composites, Composites, Part A, 42(8), pp. 1007-1016. [6] Breuer, O. and Sundararaj, U. (2004). Big returns from small fibers: a review of polymer/carbon nanotube composites, Polym. Compos., 25(6), pp. 630-645. [7] Winey, K.I. and Vaia, R.A. (2007). Polymer nanocomposites, MRS Bull., 32(04), pp. 314-322. [8] Qian, H., Greenhalgh, E.S., Shaffer, M.S. and Bismarck, A. (2010). Carbon nanotube-based hierarchical composites: a review, J. Mater. Chem., 20(23), pp. 4751-4762. [9] Li, M., Gu, Y.Z., Liu, Y.N., Li, Y.X. and Zhang, Z.G. (2013). Interfacial improvement of carbon fiber/epoxy composites using a simple process for depositing commercially functionalized carbon nanotubes on the fibers, Carbon, 52, pp. 109-121. [10] Li, Q., Church, J.S., Naebe, M. and Fox, B.L. (2016). Interfacial characterization and reinforcing mechanism of novel carbon nanotube–Carbon fibre hybrid composites, Carbon, 109, pp. 74-86. [11] Jiang, D., Liu, L., Long, J., Xing, L., Huang, Y., Wu, Z., Yan, X. and Guo, Z. (2014). Reinforced unsaturated polyester composites by chemically grafting amino-POSS onto carbon fibers with active double spiral structural spiralphosphodicholor, Compos. Sci. Technol., 100, pp. 158-165. T A