Silver-based conductive materials for lightning strike protection of aircraft composite structures

Lightning strike protection of composite structures, is an increasingly studied subject in the aerospace industry. The important weight savings offered by composite structures are hindered by their lower electrical conductivity, as much as four orders of magnitude, compared to their aluminium alloy coun-terparts. Commercially available metallic expanded foils such as expanded copper foils (ECF) offer good protection at the cost of difficult reparability and significant weight penalty, thus negating the weight benefits that composites can bring. Here we study a wet-metallization process with Tollen's reagent to plate milled carbon fibres with silver. The silver coated carbon fibres (SCCF) are integrated to a carbon fibre reinforced polymer (CFRP) panel with different adhesives under three configurations, then the panels are sealed with aerospace grade paint for realistic finition and are subjected to high impulse strikes. The aim of the SCCF sacrificial coating, layered upon the CFRP panel, is to effectively mitigate damage due to lightning strike and to offer a scalable and viable LSP solution. Configuration DPE-SCCF (Painted Double stacked PEDOT:PSS and SCCF) had 54% retention of flexural strength in bending and an area of damage of 314 squared millimeters. Moreover, configuration PE-SCCF (Painted PEDOT:PSS and SCCF) being two times less areally dense than the former, had 42% retention of flexural strength in bending with an area of damage of 1550 squared millimeters, 5 times more than the DPE-SCCF configuration. Finally, configuration PR-SCCF (Painted Primer and SCCF) had an area of damage of 777 squared millimeters. All three configurations displayed delamination in the first two plies. Both configurations PE-SCCF and DPE-SCCF performed better than P-CFRP (Painted unprotected CFRP panels) in retained mechanical properties but displayed inferior retention of mechanical properties compared to P-ECF (Painted Expanded Copper Foil).