Commonly known as composite material, it is composed of two or more materials with different properties, such as fiber reinforcement and substrate (matrix), through various technological means. It is equivalent to fiber reinforced plastics (FRP), fiber reinforced metal (FRM), metal-plastic laminated materials, etc. It has the characteristics of light weight, high strength and good stiffness. These composite materials are widely used in automobile parts.
Composite materials are anisotropic and heterogeneous materials with the following outstanding characteristics compared with other materials:
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, the smaller the dead weight of the part; The higher the specific modulus, the greater the rigidity of the part. Therefore, it is of great significance to high-speed running structural parts or transportation tools that need to reduce their own weight.
2) The interface between fiber and matrix in fiber reinforced composites can effectively prevent the propagation of fatigue crack, and the external load is borne by the reinforced fiber. The fatigue strength limit of most metal materials is 30% - 50% of their tensile strength, while that of composite materials can reach 60% - 80%.
3) Adding a small amount of chopped carbon fiber into thermoplastic can greatly improve its wear resistance, which can be increased by several times. For example, PVC reinforced with carbon fiber is 3.8 times of its own, and PTFE is 3 times of its own; Polypropylene is 2.5 times of its own; Polyamide is 1.2 times of its own; Polyester is twice as much as itself. Suitable plastic and steel plate composite can be used as wear-resistant objects, such as bearing materials. A three-layer composite material with polytetrafluoroethylene (or polyformaldehyde) as the surface layer and porous bronze and steel plate as the inner layer can be made into a good material for sliding bearings.
4) Good chemical stability. Fiber-reinforced phenolic plastics can be used in acidic media containing chloride ions for a long time. Glass fiber reinforced plastics can be used to manufacture chemical pipelines, pumps, valves and containers that are resistant to strong acids, salts, esters and some solvents. If alkali-resistant fiber is used to composite with plastic, it can also be used in strong alkali medium. Alkali-resistant fiber can be used to replace reinforcement and cement composite.
5) High temperature ablation resistance. In fiber reinforced composites, the melting point (or softening point) of other fibers is generally above 2000 ℃, except for the glass fiber with a low softening point (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 basically maintain the level at room temperature at 400 ℃. Similarly, carbon fiber reinforced metal nickel not only reduces density, but also improves high-temperature performance. Due to its extremely low thermal conductivity and instantaneous resistance to ultra-high temperature, GRP can be used as ablative material.
6) Good processability and designability. Adjusting the shape, layout and content of reinforcing materials can meet the performance requirements of component strength and rigidity, and the materials and components can be formed at one time, reducing the number of parts, fasteners and joints, and greatly improving the material utilization rate.