Micro-debond Experiment and Analytical Model for Interfacial Fracture Toughness between Single Carbon Fiber and TiO₂ Micro-droplet

To improve mechanical behaviors of the carbon fiber-reinforced metal matrix composites, TiO₂-coated carbon fibers are usually used in the composites to protect the fiber from degradation. Thus, it is crucial to maintain both strong interfacial bonding at carbon fiber–TiO₂ interlayer interface and high interfacial fracture toughness, which influence the damage tolerance of the composites as well as their energy absorption capacity. In this study, different single carbon fiber/TiO₂ systems with and without modified carbon fiber were prepared at heat treatment temperatures of 80 and 700 °C, respectively, and an analytical modeling for evaluating interfacial fracture toughness from the micro-debond tests by using the tests that record only the debond and friction force as a function of the TiO₂ micro-droplet length was implemented first, and then, the interfacial adhesion forces, interfacial fracture toughness and the influence of friction force and thermal residual stress on the fracture toughness of the systems were discussed in detail. From the experimental and theoretical results, heat treatment temperature and local strong bonding sites have a significant effect on the interfacial fracture toughness, while the interfacial morphology and functional groups are dominant in determining the interfacial adhesion forces. Meanwhile, the dominant factor of the interfacial fracture toughness will change as the heat treatment temperature increases. The friction force is a major contributor to the interfacial fracture toughness of the systems treated under lower temperature (80 °C), while the residual thermal stress is responsible for the toughness of the systems treated under higher temperature (700 °C). The results in this study can serve as reliable input data in multi-scale simulation of the carbon fiber-reinforced light metal matrix composites and offer exciting opportunities for further investigation of the microscopic deformation mechanisms in the composites.