Post lightning strike residual compressive strength prediction in unidirectional carbon reinforced polymer composites

Carbon fiber reinforced polymer composites (CFRPC) are being used as primary structures in many applications. However, unlike metallic materials, they are susceptible to damage by lightning strikes. When lightning strikes, due to its poor electrical conductivity, the composite material generates localized resistive heating near the strike area. This resistive heat causes elevated temperatures near the strike area, which leads to material property changes and the structural material's stiffness and strength reduction. As part of this study, a finite element (FE)-based coupled electro-thermo-mechanical modeling approach was adopted to simulate the effect of lightning strikes on a unidirectional (UD) carbon fiber reinforced polymer composite model to predict the residual compressive strength of the material. In the current study, a two-dimensional (2D), micromechanical finite element model of CFRPC was used to quantify its residual compressive response when subjected to simulated lightning strikes with different peak currents using the software ABAQUS. The normalized residual compressive strengths for various peak currents obtained from the proposed electro-thermo-mechanical model were compared with the available experimental data from the literature. The effectiveness of an electrically conductive protective coating in minimizing the compressive strength reduction was also evaluated. Further, the optimum electrical conductivity of the coating in terms of the matrix conductivity, for maintaining the desired compressive strength was also estimated. Furthermore, the effect of change in thickness of the conductive coating in compressive strength change was evaluated by considering two different coating thicknesses. The results show that for a given peak current, the thinner coating will not compromise the compressive strength as long as the conductance of the thin and thick coating is the same.