Carbon fiber sandwich foam is a new type of fiber material with high strength and high modulus fiber with a carbon content of more than 95%. It is a microcrystalline graphite material obtained by carbonization and graphitization by stacking organic fibers such as flake graphite microcrystals along the fiber axial direction. Carbon fiber is soft on the outside and rigid on the inside, lighter than metal aluminum, but stronger than steel, and has the characteristics of corrosion resistance and high modulus. It is an important material in national defense, military industry and civilian use.

It not only has the inherent intrinsic properties of carbon materials, but also has the soft processability of textile fibers. It is a new generation of reinforcing fibers. Carbon fiber has many excellent properties. Carbon fiber has high axial strength and modulus, low density, high specific performance, no creep, ultra-high temperature resistance in non-oxidizing environment, good fatigue resistance, specific heat and electrical conductivity between non-metal and non-metallic. Between metals, the thermal expansion coefficient is small and anisotropic, the corrosion resistance is good, and the X-ray transmittance is good. Good electrical and thermal conductivity, good electromagnetic shielding, etc.

The Young's modulus of carbon fiber is more than 3 times that of traditional glass fiber. Compared with Kevlar fiber, its Young's modulus is about 2 times that of it, it does not swell or swell in organic solvents, acids and alkalis, and its corrosion resistance is outstanding. Carbon fiber is an inorganic polymer fiber with a carbon content higher than 90%. Among them, graphite fibers with a carbon content higher than 99% are called graphite fibers. The microstructure of carbon fiber is similar to artificial graphite, which is a turbostratic graphite structure.

The spacing between the layers of carbon fiber is about 3.39 to 3.42A. The carbon atoms between the parallel layers are not as regular as graphite, and the layers are connected by van der Waals force. The structure of carbon fiber is usually regarded as composed of two-dimensional ordered crystals and holes, and the content, size and distribution of holes have a great influence on the performance of carbon fiber.

When the porosity is lower than a certain critical value, the porosity has no obvious effect on the interlaminar shear strength, flexural strength and tensile strength of carbon fiber composites. Some studies have pointed out that the critical porosity that causes the decline of the mechanical properties of the material is 1%-4%. When the pore volume content is in the range of 0-4%, the interlaminar shear strength decreases by about 7% for every 1% increase in the pore volume content. Through the study of carbon fiber epoxy resin and carbon fiber bismaleimide resin laminates, it is found that when the porosity exceeds 0.9%, the interlaminar shear strength begins to decrease.