Protecting planes from lightning strikes
Nickel-coated carbon fibres may outperform carbon mesh in composite aircraft?
Driven by the need to reduce weight and improve fuel efficiency, over the past two decades, aircraft manufacturers have increasingly turned to carbon fibre reinforced polymer (CFPRP) composites. The world’s largest passenger plane – the Airbus A380 – was largely made possible by the adoption of such composites, which comprise ~40% of its structure and components. While CFRP offers some structural advantages over aluminium, it is much less electrically-conductive, leaving it susceptible to damage by lightning strikes while in-flight.
As a result, manufacturers incorporate a range of different lightning strike protection solutions in each aircraft – the most common being thin metal meshes, foils, and embedded wires. But because such systems have been known to fall victim to corrosion, there are also ongoing research efforts to improve the conductivity of the composite itself, through the use of non-metals, namely graphene and buckypaper. However, a group of researchers, writing in Composites Science and Technology [DOI: 10.1016/j.compscitech.2018.11.011], have suggested a hybrid approach – one based on an existing commercial product, originally designed as a shield for electro-magnetic interference.
Commercial aircraft are struck by lightning, on average, once per year, but its impact depends on exactly where on the body of the aircraft it strikes. For this reason, lightning strike protection systems are optimised by zone. In this study, the authors looked only at Zone 2, which covers the vast majority of the airframe, and their material of choice was a nickel-coated carbon fibre nonwoven veil, available in two densities. From this, they produced a series of samples – standard CFRP, CFRP with a copper foil mesh, CFRP with a thin layer of veil (34g/m2), and CFRP with a thick layer of veil (70g/m2).
To characterise the lightning strike protection (LSP) potential of the samples, they subjected them to two specific waveforms of artificial lightning – one long-duration pulse at a relatively low current amplitude, and a shorter duration pulse with a much higher amplitude. Both of the veil-protected samples were found to offer better resistance to ablation from plasma, arcs, sparks and Joule heating than the copper mesh. They also at least matched copper in terms of minimising the spread of mechanical damage into the composite as a result of lighting. In fact, the thick-veil-protected sample outperformed the copper foil under both waveforms, leading the authors to conclude that it may be more effective than a commercial copper foil of the same density.
Yunli Guo, Yongzheng Xu, Qinglin Wang, Qi Dong, Xiaosu Yi, Yuxi Jia. “Eliminating lightning strike damage to carbon fiber composite structures in Zone 2 of aircraft by Ni-coated carbon fiber nonwoven veils” Composites Science and Technology 169 (2019) 95-102. DOI: 10.1016/j.compscitech.2018.11.011