Damage response of composites coated with conducting materials subjected to emulated lightning strikes

Highlights: • Eight different coating materials were subjected to emulated lightning tests to study the damage protection offered to polymer composite substrates • Lightning impulse currents of about 40 kA, and continuous currents of 200 A for 1 s were employed for testing • Metallic coatings performed better at lightning protection compared to hybrid coatings composed of different materials • There is lack of correlation between measured 4-probe electrical resistivity/resistance and the degree of protection offered against lightning Lightning strike protection (LSP) offered by two different classes of conductive coatings deposited on carbon fiber-reinforced polymer (CFRP) panels was studied in three stages: (i) emulated lightning impulse strikes, (ii) conducted continuous currents, and (iii) physical aspects of lightning-coating interaction. Two types of coatings, hybrid and metallic were studied. Hybrid (multi-material) coatings consisted of silver nanoparticles dispersed in conducting polymer PEDOT:PSS, and silver-coated carbon-nanofiber transferred onto an epoxy surfacing film. For metallic coatings, continuous coatings of silver, and a composite of 10% copper in tin were considered. We evaluate the material design schemes of these two classes of materials based on the degree of protection offered to the composite substrates from emulated lightning strikes. Two additional cases, CFRP with an epoxy surfacing film and a continuous coating of tin were also studied, while expanded copper foil (ECF)-protected and unprotected CFRP formed the reference materials. Continuous metallic coatings outperformed their hybrid counterparts, although none of the materials was comparable to ECF in terms of LSP performance. This work demonstrates the limitations of electrical resistivity and/or sheet resistance measurements to provide a reliable estimate about the performance of conductive coatings and that emulated lightning strikes are crucial for assessment of lightning protection.