Enhancing Electrical and Mechanical Stabilities of Carbon Fiber-Reinforced Composite Holes via Nanocomposite Sealing under Fatigue Loadings

Abstract Galvanic corrosion and electrical coupling at carbon fiber-reinforced composite (CFRC)–metal interfaces remain critical challenges in aerospace, defense, energy, marine, and automotive structures, particularly around mechanically fastened holes where exposed carbon fibers may contact metallic fasteners. This study investigates nanoclay- and nanotalc-modified epoxy sealants as insulating barrier layers for improving the electrical and mechanical stability of CFRC holes under cyclic tensile loading. Nanoclay and nanotalc were incorporated into epoxy at 0, 2, 4, and 8 wt.% and applied to the inner surfaces of drilled CFRC holes before assembly with threaded and shafted steel bolts. Electrical resistance was monitored as a function of applied load and loading time to evaluate the stability of the sealed CFRC–metal interface. FTIR analysis confirmed characteristic functional groups associated with the epoxy matrix and nanoparticle-modified sealants. The resistance results showed that nanoparticle-modified sealants generally increased interfacial electrical resistance compared with epoxy-only specimens, indicating improved electrical isolation between the conductive carbon fibers and steel bolts. Shafted bolt configurations produced more stable resistance behavior and less hole damage than threaded bolts, which was attributed to smoother contact geometry and reduced localized stress concentration. Among the tested sealants, nanoclay-modified epoxy showed particularly promising performance, reaching a peak resistance of 43.9 Ω at 8 wt.% under the tested conditions. However, high nanoparticle loading may increase the possibility of nonuniform dispersion, local stiffness changes, and damage sensitivity; therefore, nanoparticle concentration must be optimized. These results demonstrate that layered nanoparticle-modified epoxy sealants can improve the electrical stability of CFRC–metal joints under cyclic tensile loading. Overall, the findings indicate that nanoclay- and nanotalc-modified epoxy sealants provide a promising approach for improving the durability and reliability of composite–metal assemblies by enhancing electrical isolation at mechanically fastened CFRC holes.