A composite material is a mechanical engineering material that is a combination of two or more different materials. The various constituent materials can complement each other in performance, and produce synergistic effects, so that the comprehensive performance of the composite material is superior to the original constituent materials, thereby meeting various requirements.
The composition of the composite material includes two parts of a matrix and a reinforcing material. The non-metal matrix mainly includes synthetic resin, carbon, graphite, rubber and ceramics; the metal matrix mainly includes aluminum, magnesium, copper and their alloys; the reinforcing materials mainly include organic fibers such as glass fiber, carbon fiber, boron fiber, aramid fiber and carbonization. Silicon fiber, asbestos fiber, whisker, wire and hard fine particles.
The history of composite materials can be traced far, such as the straw-reinforced clays that have been used so far, and the reinforced concrete that has been used for hundreds of years, which is composed of two different materials.
Copper-tungsten and silver-tungsten electrical contact materials developed after the 1920s, tungsten carbide-cobalt-based cemented carbides, and other powder sintered materials are also composite materials. In the 1940s, due to the needs of the aviation industry, the radome of glass fiber reinforced plastic (commonly known as FRP) was developed, and the name of composite material appeared.
After the 1950s, high-strength, high-modulus fibers such as carbon fiber, graphite fiber and boron fiber were successively developed; in the 1970s, aramid fiber (abbreviated as aramid fiber), such as poly-parabenzamide fiber and silicon carbide fiber, appeared. . These high-strength, high-modulus fibers can be combined with non-metallic substrates such as synthetic resins, carbon, graphite, ceramics, rubber, or metal substrates such as aluminum, magnesium, and titanium to form different materials, in order to distinguish them from ordinary glass fibers. Material, this material is called advanced composite.
Composite materials can be divided into metal and metal composite materials according to their composition; metal and non-metal composite materials; non-metal and non-metal composite materials. According to the structural characteristics, it can be divided into fiber composite materials, laminated composite materials, fine particle composite materials and skeleton composite materials.
The fiber composite material is usually composed of a fibrous material in a matrix, such as a fiber reinforced plastic, a fiber reinforced metal, etc.; the laminated composite material is formed by laminating two or more different materials, such as using two different expansion coefficients. Metal, composite of thermal instrument materials that indicate temperature changes; fine-grained composites are uniformly distributed in the matrix, such as dispersion-strengthened alloys, cermets; skeleton composites are in continuous porous The structural material is filled with other materials, or a sandwich structural material composed of a panel and a core. Others, such as oriented eutectic composites, are obtained by forming a directional fibrous structure inside a specific smelting or liquid metal solidification condition, and are also referred to as self-reinforced fiber composite materials.
Among the composite materials, fiber reinforced materials are the most widely used and the largest amount. It is characterized by small specific gravity, specific strength and specific modulus. For example, carbon fiber and epoxy resin composite materials have higher specific strength and specific modulus than high strength steel and aluminum alloy, and also have excellent chemical stability, friction and wear resistance, self-lubrication, heat resistance and fatigue resistance. , resistance to creep, noise reduction, electrical insulation and other properties. For another example, the graphite fiber is composited with the resin to obtain a material having an expansion coefficient almost equal to zero.
Another feature of fiber reinforced composites is anisotropy, so the arrangement of the fibers can be tailored to the strength requirements of the different parts of the part. For example, aluminum-based composite materials reinforced with carbon fiber or silicon carbide fiber can maintain sufficient strength and modulus at 500 ° C, much better than unreinforced aluminum; silicon carbide fiber and titanium composite, not only the heat resistance of titanium Improved, and wear-resistant, can be used as engine fan blades; silicon carbide fiber and silicon nitride ceramic composite, the use temperature of up to 1500 ° C, much higher than the use temperature of super-alloy turbine blades.
Non-metallic matrix composites are used in automobiles to reduce weight, increase vehicle speed and save energy due to their low density. For example, the body and hood made of carbon fiber reinforced plastic can weigh more than half the weight of metal; the composite leaf spring made of carbon fiber and glass fiber has rigidity and load carrying capacity and steel with more than five times the weight. The leaf springs are equal.
The most widely used composite materials are glass fiber reinforced composites, followed by reinforced composites such as carbon fiber, graphite fiber, boron fiber, aramid fiber and silicon carbide. Because of its high price, advanced composite materials are mainly used in cutting-edge technologies such as military, aerospace and atomic energy. In addition to advanced sports equipment and key mechanical parts, civil composites are rarely used.
The composite material has a wide range, many varieties, excellent performance and great development prospects. The sheet molding compound in glass fiber reinforced thermosetting plastics has developed rapidly, and many branches have appeared. The products have been expanded from non-stressed parts to force-bearing parts such as transmission brackets. Glass fiber reinforced thermoplastics are becoming more widely used, and their rate of development has exceeded the rate of thermoset growth in some countries.
The development direction of advanced composite materials is to reduce costs and expand the scope of application. Using two or more different fibers as reinforcing materials not only reduces the cost, but also has a mixing effect that exceeds the general mixing rule. Basic structural components in aviation, industrial robots, structural materials for the development of the ocean, automotive leaf springs, and drive shafts will increasingly use hybrid fiber reinforced composite materials.
Directionally solidified cast composite materials such as cerium carbide and eutectic composites of nickel or cobalt, tantalum carbide and niobium, and inorganic fiber reinforced ceramic composites, which are used at temperatures exceeding those of existing heat resistant alloys, will also be developed. Carbon fiber and copper composite materials can be used as brush materials for special motors such as low voltage, high current motors and superconductors, wear-resistant antifriction and electronic materials.
In terms of molding process, enhanced reaction injection molding, reaction injection molding, elastic storage molding, and vacuum immersion molding have all been developed. Functional composites combine multiple functions, such as the combination of photovoltaic materials and electromagnetic materials into a magneto-optical composite. This material is very promising in functional conversion devices.
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