Inorganic polymer fibers with carbon content above 90%. The carbon content is higher than 99%% of the graphite fibers. The axial strength and modulus of carbon fibers are high, no creep, good fatigue resistance, heat and conductivity between nonmetal and metal, thermal expansion coefficient is small, corrosion resistance, fiber density is low, x-ray permeability is good. But the impact resistance is poor, easy to damage, oxidation under the effect of strong acid, and metal composite will occur when metal carbonization, carburizing and electrochemical corrosion phenomenon. Therefore, the surface treatment of carbon fibers is required before use. Carbon fiber can be separately used polyacrylonitrile fiber, asphalt fiber, viscose silk or phenolic fiber by carbonization, according to the state is divided into filament, short fiber and staple fiber; According to mechanical properties of general and high-performance type. The strength of the general-purpose carbon fiber is 1000 MPA, the modulus is about 100GPa. High-performance carbon fibers are also divided into high-strength type (strength 2000MPa, modulus 250GPa) and higher model (modulus 300GPa above). The strength is more than 4000MPa, also known as ultra high-strength type; The modulus is larger than 450GPa called the Hyper model. With the development of aerospace and aerospace industry, high-strength and elongation of carbon fibers have emerged, with the elongation of more than 2%. The maximum dosage is polyacrylonitrile-based carbon fibers. Carbon fibers can be processed into fabrics, mats, mats, belts, paper and other materials. Carbon fiber is used in addition to the insulation material, generally not alone, as a reinforcement material added to the resin, metal, ceramics, concrete and other materials, forming composites. Carbon fiber reinforced composites can be used as aircraft structural materials, electromagnetic shielding materials, artificial ligament and other physical substitution materials, as well as the manufacture of rocket shells, mobile boats, industrial robots, automotive leaf springs and drive shafts. Carbon fibers are mainly divided into polyacrylonitrile (PAN)-based carbon fibers and pitch-based carbon fibers according to the different materials and production methods. Carbon fibre products include pan-based carbon fibers (high-strength) and pitch-based carbon fibers (highly elastic). Different types of resins can also ensure that they have a good penetration effect on the concrete, such as substrate coating resins, and adhesion to carbon fiber sheets and concrete structures, such as epoxy bonding resins. Only relying on carbon fiber sheet itself can not fully exert its strong mechanical properties and superior durability, only through the epoxy resin coated carbon fiber sheet adhesion to the surface of reinforced concrete structure and closely combined with the formation of a whole work together to achieve the purpose of reinforcing. Therefore, the performance of epoxy resins is one of the most important keys. Epoxy resins have different properties because of different types, and adapt to different requirements of various parts. For example, the substrate coating resin has a good penetration effect of concrete, can penetrate into the concrete depth; the epoxy resin coated with CFRP is easy to "penetrate" the carbon fiber sheet and has strong adhesion. Depending on the temperature of the use, the resin is also divided into summer and winter class resins. Carbon fiber materials are compared with other reinforcing materials. (1) Tensile strength: The tensile strength of carbon fiber is about 10 times times the steel. (2) Elastic modulus: The tensile modulus of carbon fiber composites is higher than steel, but the tensile modulus of Aramid and fiberglass composites is only half and one-fourth of steel. (3) Fatigue strength: The fatigue strength of carbon fiber and aramid fibre composites is higher than that of high strength. Under the effect of alternating stress, the fatigue limit is only the 30%~40% of static load. Because the fiber and matrix composite can alleviate the crack propagation, as well as the possibility that the fiber internal force redistribution, the fatigue limit of composites is higher, the 70%~80% of static load strength is about, and there is a remarkable indication of deformation before the destruction. (4) Weight: about one-fifth of steel. (5) compared with CFRP sheets: carbon fiber sheets can be pasted on the structural surfaces of various shapes, whereas plates are more suitable for regular component surfaces. In addition, because the substrate resin paste is more than the amount of sheet, thickness, and the concrete interface adhesion strength of the sheet.
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