Structural evolution of carbon fibers in interfacial reinforced CFRP under cyclic tensile loading

The microstructure of carbon fiber—including its crystal structure and defect characteristics—is a critical factor governing its mechanical properties and ensuring the long-term stability of carbon fiber-reinforced composites. However, advancements in carbon fiber–resin matrix interface reinforcement technology have altered the stress distribution in CFRP, leaving the evolution mechanisms of carbon fiber microstructure still largely unexplored. These knowledge gaps pose significant challenges to the development of high-performance carbon fiber-reinforced composites. Therefore, this study explored the evolution of the carbon fiber microstructure in the interface-reinforced CFRP under cyclic tensile loading based on polydopamine coating interface-reinforced CFRP (PDA-CFRP). Mechanical experimental evaluation found that the mechanical properties and fatigue properties of PDA-CFRP were significantly improved due to the polydopamine coating-reinforced interface between carbon fiber and epoxy resin. In addition, after tensile fatigue testing, it can be clearly observed that the defect level in PDA-CFRP is lower than that in CFRP, as well as the reduction of (002) crystal plane spacing. These results suggest that cyclic tensile loading leads to an increase in carbon fiber defects and a decrease in the (002) interplanar spacing in CFRP, and that interface modification can reduce these evolutions by uniformly distributing stress. This study not only reveals theoretical insights into the damage and fracture of carbon fibers in CFRP under cyclic tensile loading but also provides theoretical guidance for the design of high-performance CFRP.