Composite materials are heterogeneous and anisotropic materials. Compared with other materials, composite materials have the following outstanding characteristics:
1) High specific strength and specific modulus. Specific strength and specific modulus refer to the ratio of material strength and modulus to density. The higher the specific strength is, the lower the dead weight of the part will be. The higher the specific modulus is, the more rigid the part is. Therefore, it is of great significance to the high speed running structural parts or the transportation means which need to reduce the dead weight.
2) The interface between fiber and matrix in fiber reinforced composites can effectively prevent fatigue crack propagation, and the additional load is borne by the reinforcement fiber. The fatigue strength limit of most metal materials is 30% ~ 50% of their tensile strength, while composite materials can reach 60% ~ 80%.
3) Adding a small amount of chopped carbon fiber to the thermoplastic can greatly improve its wear resistance, which can be increased by several times. For example, after reinforced with carbon fiber, polyvinyl chloride is 3.8 times that of itself, and polytetrafluoroethylene is 3 times that of itself. Polypropylene is 2.5 times its own size; Polyamide is 1.2 times as large as itself; The polyester is twice as big as itself. Appropriate choice of plastic and steel composite can be made wear - resistant objects, such as bearing materials. With polytetrafluoroethylene (or polyformaldehyde) as the surface layer, porous bronze and steel plate as the inner layer of the three-layer composite material, can be made into a good material for sliding bearing.
4) Excellent chemical stability. Fiber-reinforced phenolic plastics can be used for a long time in acidic media containing chlorine ions, and can be used to manufacture chemical pipes, pumps, valves and containers resistant to strong acids, salts, esters and some solvents. If use alkali resistant fiber and plastic compound, still can use in medium of strong alkali. Alkali - resistant fibers can be used instead of reinforcing steel and cement.
5) Good ablative resistance at high temperature. In fiber-reinforced composites, the melting point (or softening point) of other fibers is generally above 2000℃ except that the softening point of glass fibers is lower (700~900℃). The strength and modulus of composites composed of these fibers and metal matrix are improved at high temperature. For example, after reinforced with carbon fiber or boron fiber, the strength and modulus can be basically kept at room temperature at 400℃. The density and high temperature properties of nickel reinforced by carbon fiber are also improved. Due to the extremely low thermal conductivity of FRP, it can be used as an ablative material for ultra-high temperature resistance.
6) Good manufacturability and designability. By adjusting the shape, arrangement and content of the reinforced material, the strength and stiffness of the component can be satisfied, and the material and the component can be molded once, which reduces the number of parts, fasteners and joints, and greatly improves the material utilization rate.
