Composite materials are new materials that people use advanced material preparation technology to optimize the combination of material components with different properties. Generally defined composite materials need to meet the following conditions:
(i) Composite materials must be man-made, materials designed and manufactured by people according to their needs;
(ii) The composite material must be composed of two or more material components with different chemical and physical properties, combined in the designed form, ratio, and distribution, with obvious interfaces between the components;
(iii) It is structurally designable and can be designed for composite structures;
(iv) The composite material not only maintains the advantages of the material properties of each component, but also can obtain comprehensive performance that cannot be achieved by a single component material through the complementation and correlation of the properties of each component.
The matrix materials of composite materials are divided into two categories: metal and non-metal. Commonly used metal substrates are aluminum, magnesium, copper, titanium and their alloys. Non-metallic substrates mainly include synthetic resin, rubber, ceramics, graphite, carbon and so on. Reinforcing materials mainly include glass fiber, carbon fiber, boron fiber, aramid fiber, silicon carbide fiber, asbestos fiber, whisker, and metal.
Composite material is a mixture. It has played a big role in many fields, replacing many traditional materials. Composite materials are divided into metal and metal composite materials, non-metal and metal composite materials, and non-metal and non-metal composite materials according to their composition. According to its structural characteristics, it is divided into: ①Fiber reinforced composite materials. Various fiber reinforcements are placed in the matrix material to compound. Such as fiber reinforced plastics, fiber reinforced metals, etc. ② Sandwich composite materials. It is composed of different surface materials and core materials. Generally, the face material is high and thin; the core material is light and low in strength, but has a certain rigidity and thickness. There are two types: solid sandwich and honeycomb sandwich. ③Fine-grained composite materials. Distribute hard fine particles evenly in the matrix, such as dispersion strengthened alloys, cermets, etc. ④ Hybrid composite materials. It is composed of two or more reinforcing phase materials mixed in one matrix phase material. Compared with ordinary single-reinforced phase composite materials, its impact strength, fatigue strength and fracture toughness are significantly improved, and it has special thermal expansion properties. It is divided into intra-layer hybrid, inter-layer hybrid, sandwich hybrid, intra-layer/inter-layer hybrid and super hybrid composite materials. Composite materials can be divided into two categories: structural composite materials and functional composite materials.
Structural composite material is a material used as a load-bearing structure. It is basically composed of a reinforcement component that can withstand a load and a matrix component that can connect the reinforcement to form a whole material and at the same time act as a force transmission. Reinforcements include various glass, ceramics, carbon, polymers, metals, and natural fibers, fabrics, whiskers, sheets and particles, etc. The matrix includes polymers (resins), metals, ceramics, glass, carbon and Cement etc. A wide variety of structural composite materials can be composed of different reinforcements and different matrices, and are named after the matrix used, such as polymer (resin)-based composite materials. The feature of structural composite materials is that they can be designed according to the force requirements of the materials in use, and more importantly, they can also be designed for composite structures, that is, the reinforcement layout design, which can reasonably meet the needs and save materials.
Functional composite materials are generally composed of functional body components and matrix components. The matrix not only plays the role of forming a whole, but also can produce synergy or strengthen the function. Functional composite materials refer to composite materials that provide other physical properties in addition to mechanical properties. Such as: conductivity, superconductivity, semiconductivity, magnetism, piezoelectricity, damping, wave absorption, wave transmission, friction, shielding, flame retardant, heat protection, sound absorption, heat insulation, etc. highlight a certain function. Collectively referred to as functional composite materials. The functional composite material is mainly composed of a functional body, a reinforcement body and a matrix. The functional body can be composed of one or more functional materials. The multifunctional composite material can have multiple functions. At the same time, there may be new functions due to compound effects. Multifunctional composite materials are the development direction of functional composite materials.
Composite materials can also be divided into common and advanced categories.
Commonly used composite materials such as glass fiber reinforced plastics are made of glass fiber and other lower-performance reinforcements and common high polymers (resins). Because of its low price, it has been developed in large quantities and has been widely used in ships, vehicles, chemical pipelines and storage tanks, building structures, sports goods, etc.
Advanced composite materials refer to composite materials composed of high-performance reinforcements such as carbon fiber and aramid equal to high-performance heat-resistant polymers. Later, metal-based, ceramic-based, carbon (graphite)-based and functional composite materials were included. Although their performance is excellent, the price is relatively high. They are mainly used in the defense industry, aerospace, precision machinery, deep submersibles, robotic structural parts and high-end sports goods.
The molding methods of composite materials vary according to the base material. There are many molding methods for resin-based composite materials, including hand lay-up molding, injection molding, filament winding molding, compression molding, pultrusion molding, RTM molding, autoclave molding, diaphragm molding, migration molding, reaction injection molding, and soft film expansion Forming, stamping, etc. The metal matrix composite material forming method is divided into solid phase forming method and liquid phase forming method. The former is formed by applying pressure at a temperature lower than the melting point of the matrix, including diffusion welding, powder metallurgy, hot rolling, hot drawing, hot isostatic pressing and explosive welding.
The latter is to melt the matrix and fill it into the reinforcement material, including traditional casting, vacuum suction casting, vacuum back pressure casting, squeeze casting and injection casting, etc. The molding methods of ceramic matrix composite materials mainly include solid phase sintering, chemical Vapor infiltration molding, chemical vapor deposition molding, etc. The main application areas are:
①Aerospace industry. Because the composite material has good thermal stability, high specific strength and specific rigidity, it can be used to manufacture aircraft wings and front fuselage, satellite antennas and their supporting structures, solar battery wings and shells, large carrier rocket shells, engine shells, Space shuttle structural parts, etc.
②The automobile industry. Because composite materials have special vibration damping characteristics, they can reduce vibration and noise, have good fatigue resistance, are easy to repair after damage, and are easy to form as a whole, so they can be used to manufacture automobile bodies, stressed components, transmission shafts, engine mounts and their interiors member.
③Chemical, textile and machinery manufacturing fields. The composite material of carbon fiber with good corrosion resistance and resin matrix can be used to manufacture chemical equipment, textile machine, paper machine, copier, high-speed machine tool, precision instrument, etc.
④Medical field. Carbon fiber composite materials have excellent mechanical properties and non-X-ray absorption characteristics, and can be used to manufacture medical X-ray machines and orthopedic stents. Carbon fiber composite materials also have biological tissue compatibility and blood compatibility, and have good stability in biological environments. They are also used as biomedical materials. In addition, composite materials are also used in the manufacture of sports equipment and as building materials.