Development and testing of spray-coated lightning strike protection systems for fiber-reinforced thermoplastic composites

Abstract

This project investigated a conductive nanomaterial spray-coated lightning strike protection (LSP) for thermoplastic composites (TPCs) for use on aircraft exterior surfaces. The aerospace industry has expressed increasing interest in TPCs for future aircraft due to processing and material advantages over thermoset composites (TSCs). TPC components can be joined by induction welding, allowing a significant weight savings in comparison to joining by fasteners. However, current metallic LSP systems interfere with the induction welding process. A post-processed, economically viable, spray-coated LSP would solve the induction welding interference problem. In Phase One of this study, four nano and sub-micro conductive LSP coatings were formulated and tested for surface conductivity. The two best candidates were further developed and prepared for spray-coating tests. Phase Two entailed spray-coating six TPC panels with selected LSP and performing Zone 2A lightning strike testing. Two variations of silver coated copper (Ag/Cu) were selected as the conductive filler with 15% and 30% silver content, respectively. Two loading levels of 55 wt% and 70 wt% were tested in an epoxy carrier. Challenges in spray-coating with the 70 wt% loading caused the resistance to be higher than 55 wt% panels. Despite the lower conductive coating weight and higher resistance, the 70 wt% panels performed better than 55 wt% panels. The higher silver content Ag/Cu30 also produced marginally better LSP results. With further development, spray-coated Ag/Cu sub-micro flakes could be a viable, economical post-processed LSP system.