ENHANCED LIGHTNING STRIKE PROTECTION USING VERTICALLY ORIENTED CARBON FIBER MELDED WITH CONVENTIONAL CARBON FIBER-REINFORCED COMPOSITE AND ITS VALIDATION THROUGH DAMAGE ANALYSIS
Authors: SAHA SUBHABRATA , HMEIDAT NADIM S. , PARK CHANYEOP , YEOLE PRITESH , MILLEN SCOTT L.J. , MURPHY ADRIAN , KNOUFF BRIAN , THEODORE MERLIN , VAIDYA UDAY , HASSEN AHMED ARABI , KUNC VLASTIMIL , KUMAR VIPIN 
Published: November 2023

Lightning strike protection (LSP) is one of the prime factors in aerospace and wind industries concerning safety, enhanced service life, and reduced downtime. To ensure better LSP, high electrical conductivity is required to dissipate the current, which is always a challenge for polymer composites due to the inherent insulating nature of the polymer matrix. Conventional carbon fiber-reinforced composites (CFRP) offer electrical conductivity in the planar direction while the vertical i.e. through-thickness conductivity still remains a challenge. Having been motivated by this fact, we have fabricated CFRP interleaved with vertically oriented CF (Z-fiber) for the lightning strike test (100 kA). A paint was applied to mimic the actual service condition of the composite laminates. We have prepared two Z-fiber composites: (a) Z-1 containing one Z-fiber layer on the top along with conventional CF layers and (b) Z-5 containing five interleaved Z-fiber layers and compared the properties with conventional CFRP (Z-0). Interestingly, even a single Z-fiber layer (Z-1) showed lower damage (visual damage diameter 22 mm) than Z-0 (visual damage diameter 26 mm). Z-5 displayed the lowest damage (visual damage diameter 16.7 mm), which was further confirmed by cross-sectional optical microscopy. Improved LSP was attributed to the higher through-thickness electrical nano-platelets and silver nanoparticles/nanowires on the TT electrical conductivity of epoxy carbon fiber laminates [15]. Note that, the usage of nanofiller increases the overall cost and the dispersion of the nanofiller is challenging due to their high surface energy. On the other hand, the incorporation of vertically oriented CF (or Z fiber) could be a promising alternative route to reduce electrical anisotropy. Recently, a few research works have been published on the vertically oriented CF to improve the TT properties, e.g. thermal conductivity [16, 17]. Uteni et al. showed the vertical orientation of CF using electrostatic flocking in the fluorinated rubber and its effect on the TT thermal conductivity [16]. However, so far, no research article has been reported to the best of our knowledge on the lightning strike damage of vertically aligned CF-based CFRP composite. For the first time, our research group has shown the impact of interleaved vertically aligned short CF (Zfiber) on reducing the damage during the simulated lighting strike test by enhancing the TT electrical conductivity [18]. This is the continuation of the previous work. Herein, we have compared the effect of a single Z-fiber layer and five Z-fiber layers with conventional CFRP. An aerospace-grade paint was also applied to mimic the actual service condition of the composite laminates. A detailed study of the crosssectional morphology has been done after the lightning strike test to understand the depth of damage at varying CF configurations.