Carbon fiber (carbon fiber), as a high-performance composite material, is widely used in aerospace, automobile manufacturing, sports equipment and construction engineering because of its excellent properties such as light weight, high strength, corrosion resistance and high temperature resistance. However, in order to further improve its mechanical properties, especially tensile, bending and impact strength, researchers continue to explore and improve the preparation process and structural design of Carbon fiber materials.
　　First of all, the strength of Carbon fiber is closely related to the quality of its precursor. Generally, Carbon fiber is made from polyacrylonitrile (PAN) precursor through several high-temperature treatment processes, such as pre-oxidation, carbonization and graphitization. The more uniform the molecular structure of precursor and the fewer defects, the more complete the crystal structure of Carbon fiber formed in the subsequent treatment, thus having higher strength. Therefore, optimizing the spinning process and chemical composition of precursor is the basis of improving the strength of Carbon fiber.

Secondly, by improving the physical and chemical structure of fiber surface, the bonding force between fiber and matrix resin can be significantly enhanced. In composite materials, the interfacial bonding between Carbon fiber and resin determines whether the load can be effectively transferred to the fiber, thus affecting the strength performance of the whole material. By surface oxidation, plasma etching or coating treatment, the number and roughness of active functional groups on the fiber surface can be increased, and the interfacial bonding performance can be improved, thus improving the overall strength of composites.
　　In addition, the arrangement of fibers also has an important influence on the strength. Carbon fibers arranged in one direction show extremely high strength in the direction of stress; However, by adopting braided structure or multi-axial ply design, high strength requirements in isotropic or specific directions can be realized. For example, in aircraft wings or racing car bodies, reasonable design of fiber ply angle and thickness can effectively resist multi-directional complex stress.
　　Finally, the introduction of nano-reinforced phase is also a new way to improve the strength of Carbon fiber materials. For example, by adding carbon nanotubes (CNT) or graphene into the matrix, a three-dimensional reinforced network can be formed, which not only improves the modulus of the material, but also effectively prevents crack propagation, thus enhancing its impact resistance and fatigue resistance.

To sum up, the strength of Carbon fiber can be effectively improved by optimizing the quality of precursor, improving surface treatment technology, rationally designing fiber arrangement and introducing nano additives. With the development of materials science, Carbon fiber will show its outstanding performance potential in more high-end fields.