PSI - Issue 28

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Anurag Singh/ Structural Integrity Procedia 00 (2019) 000 – 000

Anurag Singh et al. / Procedia Structural Integrity 28 (2020) 2206–2217

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1. Introduction Biomimicry has been a source of inspiration for the scientist in a quest for development. All natural materials are multifunctional to some extent. For example, the skin of human beings consists of many layers of cells and tissues. Each contains oil and perspiration glands, sensory receptors, hair follicles, blood vessels, and other components. These components serve functions other than providing the basic structure and protection for the internal organs (Parenteau 1999). Similarly, a multifunctional composite material which responds to the surroundings and serves more functions other than structural integrity is the need of the hour (Gandhi and Thompson 1992). These multifunctional materials improve efficiency by reducing the weight, fuel consumption, and at the same time providing the versatility to the system. These factors directly impact the economic growth by reducing the carbon emission; thus, inducing the sustainability to the aeronautic industry. Various industrial applications, including infrastructure, automotive and aerospace, use composite materials as the primary structure. In modern aeronautical industry, approximately 52 % of primary and secondary structures uses carbon fibre reinforced composite (CFRP) (Vipin Kumar et al. 2018; Wang et al. 2019). CFRP's are known for their specific characteristics which include high strength to weight ratio and high stiffness coupled with lightweight (Cristina et al. 2012; Shivakumar Gouda et al. 2013). Thus reducing the fuel consumptions and emissions on an aircraft and subsequently lowering the manufacturing and operational costs. These composites have excellent corrosion resistance, and they can withstand contact with moisture and chemicals. However, the introduction of these composites in aeronautical structure presents unique challenges and issues regarding their lack of multifunctionality; low electrical conductivity is one of the features. These advanced composites are often unsatisfactory compared to conventional conductive metals and are vulnerable to lightning strike damage. In the case of aircraft, a lightning strike is unconventional, yet it is something that at some point, is certain. The overall estimation that each transport aircraft is struck by lightning at least once every year. During the lightning strike, there is direct contact between the aircraft surface and the arc of the lightning (Karch and Metzner 2016). Increasing the electrical conductivity of CFRP's together with mechanical properties presents a real challenge because both efficient electron transfers in isolating bulk matrix and load transfer between fibres and matrix are required. Conductive carbon fibre composites that comprise this combination of properties can extend their usage in electromagnetic shielding, structure health monitoring, and lightning strike protection (Katunin 2016; Katunin et al. 2017). For improving the electrical conductivity in the polymer matrix composite, one of the methods is the use of nanoscale reinforcement like carbon-based nanoparticles, such as carbon nanotube, graphene nanoparticles, fullerenes, carbon nanofibers, carbon black, and carbon onions in the form of a randomly dispersed suspension and compacted fabrics with the polymer matrix composite system (Datsyuk et al. 2008; Jakubinek et al. 2015; Singh 2014; Singh et al. 2019; Špitalský et al. 2009) . Another popular method is the usage of the interleaf material treated with conducting metallic nanowires. Interleaf materials comprise of the thermoplastic films perforated and polymer veils coated with nanoparticles (Kumar et al. 2018). Recently, Kumar et al. employ the use of a conductive thermoplastic matrix to enhance the electrical conductivity of the composite system (Kumar et al. 2015, Kumar et al. 2017, Kumar et al. 2019). The metallic nanowires are deposited on the interleaf surface and across its thickness; they densely interconnect with each other to form a conductive network-like structure. Barjasteh et al. used graphene/graphite-based conductive polyamide veils as the interleaves to increase the electrical conductivity of the laminate composite (Barjasteh et al. 2017). Guo et al. developed a porous nylon veil loaded with AgNWs to increase the interlaminar fracture toughness and electrical conductivity simultaneously (Guo et al. 2014). Harman et al. prepared bismaleimide resin (BMI) based carbon fibre reinforced composite (CFRP), interleaved via conductive veils leading to increase in through-thickness conductivity of CFRP and consequently cutting edge LSP capabilities (Harman, Reid, and Thomas 2017). All the methodologies have shown advancement in the electrical conductivity, but for application of the composites in aircraft, the development is inadequate, typically the electrical conductivity in the through-thickness direction. In some cases, the surge in electrical conductivities adversely affects the mechanical properties, particularly the composite fracture toughness (Pozegic et al. 2016). Structural carbon-fibre composites with high electrical conductivity and high interlaminar toughness are essential for the next generation of aircraft. In summary, fabricating conductive CFRP could effectively improve the Lightning Strike Protection (LSP) effectiveness of CFRP, obtain high