Damage of Carbon/Epoxy Composite Plates Subjected to Mechanical Impact and Simulated Lightning

Damage is inflicted on carbon-fiber/epoxy composite plates using both simulated lightning strike and mechanical impact in the effort to understand the relative effect of the two damage mechanisms. A methodology is proposed to characterize the damage resistance and tolerance of unconfigured composite plates subjected to lightning strike in a fashion that is consistent with the extensive work previously done on low-velocity impact. Using current and voltage diagnostics, it is possible to extrapolate the amount of electromechanical energy absorbed by the plate during the strike and compare it to that absorbed during a mechanical impact. Damage resistance is characterized by means of ultrasonic C-scans and microscopy, whereas residual strength is measured by means of compression after impact testing. Results show that the energy dissipated in a specimen during the lightning strike is much greater than the strain energy introduced by mechanical impact, and hence a comparison based on energy is not recommended. However, based on the relative threat levels associated with the impact and the lightning strike events, the comparison yields insightful observations on both damage state and residual performance. In general, for the configurations tested, lightning strike damage seems to be less detrimental than the mechanical impact in terms of both damage area and residual strength.