PSI - Issue 14

Harpreet Singh Bedi et al. / Procedia Structural Integrity 14 (2019) 168–175 Harpreet S. Bedi, Prabhat K. Agnihotri/ Structural Integrity Procedia 00 (2018) 000–000

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of polymer chunks on the surface of CNT grafted CF debonded from epoxy (Fig. 7b) implies that failure occurs at the interface of nanotubes and matrix away from the CF/epoxy interface. Whereas, the clean surface of debonded HCF (Fig. 7a) suggests failure taking place at the fiber/polymer interface, the reason behind their lower IFSS as compared to CNTCF/epoxy. 4. Conclusion Interfacial interaction of unsized (HCF) and CNT grafted carbon fibers (CNTCF) with epoxy matrix is investigated. Contact angle measurements from polymer micro-droplets on single fiber filament helps in determining the wettability of different fiber/polymer combinations. CNT grafting on fiber surface decreases the contact angle of polymer droplet with fiber, thus improving the wettability. It is observed that the effective interfacial area (or interphase thickness) between the fiber and matrix increases by 150% to 300% by growing CNTs on fiber surface for 15 to 30 min. As a result of this increased interphase size and better wettability in CNT grafted CF/epoxy composites, improvements in interphase stiffness and interfacial shear strength (IFSS) are observed. CNTCF/epoxy composites possesses IFSS as much as 1.3 times that of HCF/epoxy composites. This ultimately enhances the overall performance of the CFRP composite. However, the length and density of the grafted nanotubes needs to be controlled and optimized to get positive changes in CFRP properties. Based on the findings of this study it can be concluded that the mechanical properties of CFRP composites can be controlled by synthesizing CNTs on the surface of carbon fiber. From the structural integrity view point, the presence of an interphase is important as it eliminates the unwanted stress concentration at the interface by gradually transforming the properties from highly stiff fiber to comparatively weaker matrix. This opens the pathway to design the interphase in hybrid composites as per the requirement of a specific application. Acknowledgements Authors would like to thank the financial support provided by Indian Institute of Technology Ropar to carry out the research work. References Agnihotri, P., Basu, S., Kar, K., 2011. Effect of carbon nanotube length and density on the properties of carbon nanotube-coated carbon fiber/polyester composites. Carbon 49, 3098-3106. Bedi, H.S., Padhee, S.S., Agnihotri, P.K., 2016. On the nature of interface of carbon nanotube coated carbon fibers with different polymers, 37th Risø International Symposium on Materials Science. Roskilde, Denmark, pp. 012014. Bedi, H.S., Tiwari, M., Agnihotri, P.K., 2018. Quantitative determination of size and properties of interphase in carbon nanotube based multiscale composites. Carbon 132, 181-190. Gao, S.L., Mäder, E., 2002. Characterisation of interphase nanoscale property variations in glass fibre reinforced polypropylene and epoxy resin composites. Composites Part A: Applied Science and Manufacturing 33, 559-576. Hernández-Pérez, A., Avilés, F., 2010. Modeling the influence of interphase on the elastic properties of carbon nanotube composites. Computational Materials Science 47, 926-933. Lee, C.J., Kim, D.W., Lee, T.J., Choi, Y.C., Park, Y.S., Lee, Y.H., Choi, W.B., Lee, N.S., Park, G.-S., Kim, J.M., 1999. Synthesis of aligned carbon nanotubes using thermal chemical vapor deposition. Chemical Physics Letters 312, 461-468. Li, M., Gu, Y.Z., Liu, Y.N., Li, Y.X., 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, 109-121. Li, Q., Church, J.S., Naebe, M., Fox, B.L., 2016. Interfacial characterization and reinforcing mechanism of novel carbon nanotube–Carbon fibre hybrid composites. Carbon 109, 74-86. Li, Y., Peng, Q., He, X., Hu, P., Wang, C., Shang, Y., Wang, R., Jiao, W., Lv, H., 2012. Synthesis and characterization of a new hierarchical reinforcement by chemically grafting graphene oxide onto carbon fibers. Journal of Materials Chemistry 22, 18748-18752. McHale, G., Newton, M.I., 2002. Global geometry and the equilibrium shapes of liquid drops on fibers. Colloids and Surfaces A: Physicochemical and Engineering Aspects 206, 79-86. Peng, Q., Li, Y., He, X., Lv, H., Hu, P., Shang, Y., Wang, C., Wang, R., Sritharan, T., Du, S., 2013. Interfacial enhancement of carbon fiber composites by poly (amido amine) functionalization. Composites Science and Technology 74, 37-42. Qian, H., Bismarck, A., Greenhalgh, E.S., Kalinka, G., Shaffer, M.S., 2008. Hierarchical composites reinforced with carbon nanotube grafted fibers: the potential assessed at the single fiber level. Chemistry of Materials 20, 1862-1869. Qian, H., Bismarck, A., Greenhalgh, E.S., Shaffer, M.S., 2010. Carbon nanotube grafted carbon fibres: a study of wetting and fibre fragmentation. Composites Part A: Applied Science and Manufacturing 41, 1107-1114.