The concept of composite material means that one kind of material can not meet the requirements of use, and two or more materials need to be compounded together to form another material that can meet people's requirements, that is, composite material. For example, although a single type of glass fiber has high strength, the fibers are loose and can only withstand tension, not bending, shearing and compressive stress. It is also difficult to make a fixed geometry and is a loose soft. If they are bonded together with synthetic resin, they can be made into a variety of hard products with a fixed shape, which can withstand both tensile stress, bending, compression and shear stress. This constitutes a glass fiber reinforced plastic matrix composite material. Because its strength is equivalent to steel, and it contains glass components, it also has the color, shape, corrosion resistance, electrical insulation, heat insulation and other properties of glass. Like glass, this popular name "FRP" has been formed in history. This term was proposed by the former Minister of the Ministry of Building Materials Industry, Comrade Lai Jifa in 1958, and was expanded from the building materials system to the whole country. The meaning of glass fiber reinforced plastic refers to the reinforced plastic with glass fiber as the reinforcing material and synthetic resin as the binder. It is called glass fiber reinforced plastic abroad. With the development of the FRP industry in China, as a plastic-based reinforcement material, glass fiber has been expanded to carbon fiber, boron fiber, aramid fiber, alumina fiber and silicon carbide fiber. Undoubtedly, these new fibers reinforced plastic , Is some high-performance fiber-reinforced composite materials, and then the common name glass fiber reinforced plastics can not be summarized. Considering the origin and development of history, glass fiber reinforced plastic composite materials are usually used, such a name is more comprehensive.
Lightweight and high strength The relative density is between 1.5 and 2.0, which is only 1/4 to 1/5 of carbon steel, but the tensile strength is close to or even higher than that of carbon steel, and the specific strength can be compared with high-grade alloy steel. Therefore, it has excellent results in aviation, rockets, space vehicles, high-pressure containers and other products that need to reduce their weight. The tensile, bending and compressive strength of some epoxy FRP can reach more than 400Mpa.
FRP is a good corrosion-resistant material, which has good resistance to the atmosphere, water and general concentrations of acids, alkalis, salts, and a variety of oils and solvents. It has been applied to all aspects of chemical corrosion protection and is replacing carbon steel, stainless steel, wood, non-ferrous metals, etc. Good electrical performance is an excellent insulating material used to make insulators. Good dielectric properties can be protected at high frequencies. Microwave penetration is good, and it has been widely used in radomes.
Good thermal performance
FRP has low thermal conductivity, at room temperature is 1.25 ~ 1.67kJ / (m · h · K), only 1/100 ~ 1/1000 of metal, is an excellent thermal insulation material. In the case of instantaneous ultra-high temperature, it is an ideal thermal protection and ablation-resistant material, which can protect the spacecraft from high-speed air flow above 2000 ℃.
(1) Various structural products can be flexibly designed according to needs to meet the requirements of use, which can make the product have a good integrity.
(2) The materials can be fully selected to meet the performance of the product, such as: corrosion-resistant, transient high-temperature resistant, particularly high-strength in a certain direction of the product, good dielectric, etc. can be designed.
(1) The molding process can be flexibly selected according to the shape, technical requirements, uses and quantity of the product.
(2) The process is simple and can be formed at one time, and the economic effect is outstanding. Especially for the products with complex shapes and small quantities that are not easy to form, the process superiority is more prominent.
Low modulus of elasticity The modulus of elasticity of FRP is twice that of wood, but 10 times smaller than that of steel (E = 2.1 × 105). Therefore, it is often felt that the rigidity of the product structure is insufficient and it is easy to deform. It can be made into a thin shell structure, a sandwich structure, or can be compensated by high modulus fibers or reinforced ribs. Long-term temperature resistance is poor. Generally FRP can not be used for a long time at high temperature. The strength of general polyester FRP above 50 ℃ obviously decreases, generally only used below 100 ℃; general-purpose epoxy FRP above 60 ℃, the strength decreases significantly. However, high temperature resistant resin can be selected to make long-term working temperature between 200 and 300 ℃ possible.
Aging phenomenon Aging phenomenon is a common defect of plastics, and FRP is no exception. It is easy to cause performance degradation under the action of ultraviolet rays, wind, sand, rain, snow, chemical media, and mechanical stress. Low shear strength The interlayer shear strength is borne by the resin, so it is very low. The adhesion between the layers can be improved by selecting processes, using coupling agents, etc. The most important thing is to avoid shearing the layers as much as possible during product design.