Molecular dynamics study on the effect of salt environment on interfacial structure, stress, and adhesion of carbon fiber/epoxy interface

Epoxy resins are widely used as matrices for bonding carbon fiber tightly together in fabricating carbon fiber reinforced polymer (CFRP), which has been increasingly used in marine and offshore applications. To analyze CFRP performance in salt environment, it requires a fundamental understanding of the behavior of carbon fiber/epoxy interface under saltwater exposure. Here the molecular interface model of carbon fiber/epoxy bonded system is constructed to analyze the interfacial integrity in salt environment. The simulation results show that salt solution leads to largest loss of interfacial adhesion, which correlates with structural and mechanical degradation of bonded interface, as indicated by the decreased epoxy density close to interface and reduced interfacial stress as compared to dry and wet case. Through examining interfacial structure and stress during pulling process, it is observed that epoxy detaches in a sequential manner and the final debonding occurs more easily under saltwater ingress. By simultaneously capturing mechanical degradation and interfacial deterioration, it is clear that strong mechanical properties of carbon fiber/epoxy bonded interface are critical for long-term interfacial integrity and performance of CFRP in salt environment. This study provides microscopic information of interfacial deterioration in CFRP composite, which forms basis for predicting performance degradation of macroscopic CFRP in consideration of environmental exposure.