Study on the fiber selection method and the microscopic mechanism of interfacial compatibility in crack-resistant epoxy/fiber composites based on interfacial properties

Interfacial properties between epoxy resin (EP) and reinforcing fibers play a critical role in determining the crack resistance of epoxy/fiber composites, but the optimal selection of reinforcing fibers remains a significant challenge. In this study, a multiscale interfacial compatibility evaluation framework is established by combining molecular dynamics simulations with experimental methods. This framework integrates microscopic indicators, such as the solubility parameter, with macroscopic indicators, such as the coefficient of thermal expansion, to guide the selection of reinforcing fibers. Among the four reinforcing fibers investigated, namely, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polyimide, and polyethylene terephthalate (PET), PET showed the best interfacial compatibility with EP. The EP/PET system had the lowest cohesive energy density, the smallest difference in solubility parameter, and the strongest intermolecular interactions. In addition, PET showed the best wettability with EP, and the corresponding composite also demonstrated relatively favorable thermophysical properties, including thermal conductivity. Thermal cycling aging results further revealed that the EP/PET composite possessed higher interfacial bonding strength and interfacial shear strength, together with a slower rate of interfacial degradation. Moreover, analysis of molecular simulation parameters, including interaction energy, revealed that the interfacial compatibility was predominantly governed by intermolecular van der Waals interactions. These results demonstrate the rationality of the proposed reinforcing fiber selection method and provide a theoretical basis for the constitutive design of crack-resistant epoxy composites.