Development and strategic position of carbon fiber composites
The emergence of carbon fiber is a revolution in the history of materials. Carbon fiber is the first choice of high performance materials in the world. It has many excellent properties, such as high strength, high modulus, high temperature resistance, fatigue resistance, electrical conductivity, light quality and easy processing. It is gradually conquering and replacing traditional materials. It has been widely used in aerospace, aviation and military fields. All over the world, the development of high performance carbon fiber industry is playing an extremely important role. In addition to its important application in the military field, carbon fiber has a wider space in the development of civil goods, and has begun to penetrate into the various fields of the national economy and the people’s livelihood. In terms of mechanical and electrical, building materials, style, chemical, medical and other fields, carbon fiber has an unparalleled application advantage.
Carbon fiber was born in the early 50s in response to the needs of advanced science and technology such as rocket, aerospace and aviation. In the 80s, high performance and super high performance carbon fibers appeared one after another. This was another leap in technology, and it also marked a advanced stage in the research and production of carbon fiber. After more than 20 years of development, carbon fiber and its composite materials have been transferred from the initial stage to the growth stage, and their industrial status has been basically established.
Carbon fiber composites
Two. Properties and uses of carbon fiber composites
Carbon fiber is a special kind of fiber composed of carbon elements, which is made of hot stable oxidation, carbonization and graphitization process, which contains high carbon content and is not fused during heat treatment. The carbon content varies with different species, generally more than 90. Carbon fiber has the characteristics of general carbon materials, such as high temperature resistance, abrasion resistance, conduction, heat conduction and corrosion resistance. But different from ordinary carbon materials, the carbon fiber has remarkable anisotropy, softness, good machinability, high degree of strength along the direction of fiber axis and small proportion of carbon fiber.
1, the chemical properties of carbon fiber
Carbon fiber is a fibrous carbon material. We know that carbon material is one of the excellent chemical properties. This is one of the earliest characteristics of carbon materials recognized by human beings. Except for strong oxidizing acids and other special substances, it is almost chemically inert near normal atmospheric temperature and pressure. It can be considered that the chemical changes of carbon fibers can hardly be observed under the normal working temperature of less than 250 degrees. According to the relevant data, from the chemical properties of carbon materials, the carbon materials have neither obvious oxidation nor formation of carbides and interlaminar compounds at less than 250 degrees centigrade. As carbon materials have pore structure, the porosity is about 25%, which is easy to produce gas degassing in the process of heating. This process is more conducive to the stability of electrical properties and the application in the field of electric heating.
2. Physical properties of carbon fiber
(a) thermal properties: carbon materials are highly anisotropic due to the high anisotropy of graphite crystals, which are different from the dependence of the general solid material and temperature. From the industrial application point of view, the specific heat of carbon materials is generally constant. Almost not with the degree of graphitization and the type of carbon materials.
(b) thermal conductivity: the heat conduction mechanism of carbon materials does not depend on electrons, but depends on the vibration and heat conduction of the lattice. Therefore, Wiedemann Franz’s law is not conformed to the metal. According to the relevant information, the thermal conductivity of ordinary carbon materials is very high, and the thermal conductivity parallel to the grain direction is comparable to brass.
(c) electrical properties: the electrical properties of carbon materials are mainly related to the electronic behavior of graphite crystals and different processing temperatures. The electronic band structure of graphite and the types of carriers and their diffusion mechanisms determine the above properties. The electrical properties of carbon materials possess the characteristics of intrinsic semiconductors. The variation of resistivity is mainly related to the number of carriers.
3, the main use of carbon fiber
It is made of resin, metal, ceramic and other matrix to make structural materials. Carbon fiber reinforced epoxy resin composite material has the highest comprehensive strength and specific modulus, which is the highest in existing structural materials. In areas where stiffness, weight and fatigue properties are strictly required, CFRP has advantages in situations requiring high temperature and high chemical stability.
Composite materials made of carbon fiber and epoxy resin have become an advanced aerospace material due to their small specific gravity, high rigidity and high strength.
The most amazing application is that the “nano rope” made of long carbon fibers can change the space elevator from ideal to reality. The space elevator will be able to transport passengers and various goods to the space rail station, and can also use this “nanoscale” to fix the space launch platform with the ground, on such a launching platform. The launch of satellites and space probes can greatly reduce the cost of launching. The practical applications of carbon fiber composites are summarized as follows:
(1) the aerospace industry is used as a missile anti heat and structural material such as rocket nozzle, nose cone, large area of heat proof layer; satellite frame, antenna, solar wing plate floor, satellite rocket combined parts; space aircraft head, wing front and hatch and other parts; Harbert Space Telescope measurement frame, solar panel and radio antenna.
(2) the aviation industry uses the main bearing structural materials, such as the main wing, the tail wing and the body; the sub bearing components, such as the rudder, the landing gear, the aileron, the spoiler, the engine room, the fairing and the seat plate, and the c/c brake disc.
(3) transportation is used as automobile transmission shaft, leaf spring, frame and brake block; shipbuilding and marine engineering are used to make fishing boats and fish.