Contact electric conductivity of carbon fibers tows and anisotropic conductivity of 3D braided carbon fiber / epoxy composite materials

Carbon fiber composites have been widely used for aircraft and vehicle design, while the carbon fiber composites are electric conductive, and the conductivity depends on carbon fibers themselves and contacts among fibers. Among the conductive mechanisms, contact-based electrical conduction plays a pivotal role in determining the overall conductivity of carbon fiber composites. Understanding how to isolate contact conduction from the overall electrical behavior of composite is essential for optimizing composite design for electrical applications. Here we developed a micro-contact model to investigate the longitudinal and transverse electrical conductivity of 3D braided carbon fiber/epoxy resin composites. An analytical model based on the electrical tunneling effect was proposed to calculate the contact resistance between carbon fiber tows. Statistical methods were employed to determine the fiber contact ratio and the effective contact area between carbon fiber tows. Additionally, the electrical resistances of various contact configurations among carbon fiber tows were calculated based on the braided preform structure. To further analyze the conductivity, finite element analysis (FEA) models were constructed, both with and without yarn contacts, to evaluate longitudinal and transverse electrical conductivity. The results revealed that longitudinal conductivity is predominantly governed by continuous carbon fiber tows, whereas transverse conductivity is influenced by through-transverse carbon fiber tows and fiber-to-fiber contacts.