Investigating the effects of metallic submicron and nanofilms on fiber-reinforced composites for lightning strike protection and EMI shielding

Abstract

Lightning strike protection (LSP) and electromagnetic interference (EMI) shielding topics have been extensively investigated, since composite material was first introduced to an aircraft a few decades ago. Generally, electrically and thermally conductive materials, such as metallic foils, metal mesh, ply-integrated interwoven wires, a continuous conductive path of low-resistance materials, and highly conductive nanoparticles and nanoflakes are used to dissipate the high-density current, shockwaves, electromagnetic forces/charges, and heat generated during lightning strikes. This study deals with the fabrication of pre-impregnated (prepreg) composite structures of carbon and glass fibers incorporated with submicron and nanoscale gold (Ag), silver (Au), aluminum (Al), and copper (Cu) films on top of composite surfaces during the curing process, and determining the effectiveness of LSP and EMI shielding. Initially, electrical conductivity experiments were conducted on composite test coupons and the electrical properties investigated under tensile loadings within the elastic regions of the composites. Test results indicated that the surface resistivity did not change much under the tensile loads. EMI shielding tests confirmed that noise was not audible on an AM radio because of the metallic submicron and nanoscale film surfaces on the composites. During lightning strike tests, a high current of 200-k amps was applied on the surface of the composite structures. The LSP test indicated that after the lightning strike, the resulting damage on both sides of the fiber composite was considerably low due to the metallic films co-cured on the fiber-reinforced composites. An increase in current with the metallic films certainly helped to reduce damage to the composites and avionics systems after lightning strike tests.