Composite materials are materials designed and manufactured according to people's needs. They are composed of two or more materials with different properties through physical or chemical methods, forming materials with new properties at the macroscopic (microscopic) level. They not only retain the advantages of the properties of each component material, but also achieve comprehensive properties that cannot be achieved by a single component material through the complementarity and correlation of the properties of each component. This makes the comprehensive performance of composite materials superior to the original component materials to meet various different requirements.

The matrix materials of composite materials are divided into two categories: metallic and non-metallic. Commonly used metallic matrices include aluminum, magnesium, copper, titanium, and their alloys. Non-metallic matrices mainly include synthetic resins, rubber, ceramics, graphite, and carbon. Reinforcing materials mainly include glass fibers, carbon fibers, boron fibers, aramid fibers, silicon carbide fibers, asbestos fibers, whiskers, metal wires, and hard fine particles.

Composite materials mainly include the following categories: metal matrix composites, ceramic matrix composites, polymer matrix composites, fiber-reinforced composites, particulate-reinforced composites, platelet-reinforced composites, layered composites, particulate composites, and fiber composites.

History

The history of composite material use can be traced back to ancient times. From ancient times to the present, straw or wheat straw reinforced clay and reinforced concrete, which has been used for hundreds of years, are both composed of two composite materials. In the 1940s, due to the needs of the aviation industry, glass fiber reinforced plastics (commonly known as fiberglass) were developed, and the term "composite materials" emerged. After the 1950s, high-strength and high-modulus fibers such as carbon fiber, graphite fiber, and boron fiber were successively developed. In the 1970s, aramid fiber and silicon carbide fiber appeared. These high-strength, high-modulus fibers can be combined with synthetic resins, carbon, graphite, ceramics, rubber and other non-metallic matrices or aluminum, magnesium, titanium and other metallic matrices to form composite materials with unique characteristics.

The development of modern high technology is inseparable from composite materials, which play a very important role in the development of modern science and technology. The depth and breadth of research and application of composite materials, as well as the speed and scale of their production development, have become one of the important indicators to measure the advanced level of a country's science and technology. Since the beginning of the 21st century, the global composite materials market has grown rapidly.

In the 1960s, to meet the needs of materials used in aerospace and other technologies, composite materials with high-performance fibers (such as carbon fiber, boron fiber, aramid fiber, silicon carbide fiber, etc.) as reinforcing materials were developed and produced. Their specific strength is greater than 4 × 10 cm, and specific modulus is greater than 4 × 10 cm. To distinguish it from the first generation of glass fiber reinforced resin composite materials, this type of composite material is called advanced composite material. According to different matrix materials, advanced composite materials are divided into resin matrix, metal matrix, and ceramic matrix composite materials. Their operating temperatures reach 250-350℃, 350-1200℃, and above 1200℃ respectively. In addition to being used as structural materials, advanced composite materials can also be used as functional materials, such as gradient composite materials (functional composite materials whose chemical and crystallographic composition, structure, and voids vary continuously in space), smart composite materials (functional composite materials with sensing, processing, and execution functions that can adapt to environmental changes), biomimetic composite materials, stealth composite materials, etc.

At present, the global composite materials industry is showing a trend of sustained growth. With the increasing application of composite materials in various fields, especially in aerospace, automobiles, construction, and electronics, the market size of the composite materials industry is continuously expanding. China's composite materials industry is also showing a trend of sustained growth. With the advancement of technology, new composite materials with better performance and wider application fields are constantly emerging, and the market size is also continuously expanding.

Basic Classification

Composite materials are a type of mixture. They play a significant role in many fields and have replaced many traditional materials. Composite materials are classified according to their composition into metal-metal composites, non-metal-metal composites, and non-metal-non-metal composites. According to their structural characteristics, they are further divided into:

① Fiber-reinforced composite materials. Various fiber reinforcements are placed in the matrix material to form a composite. For example, fiber-reinforced plastics and fiber-reinforced metals.

② Laminated composite materials. Composed of surface materials and core materials with different properties. Typically, the surface materials are high-strength and thin; the core materials are lightweight and low-strength, but have a certain stiffness and thickness. They are divided into solid laminates and honeycomb laminates.

③ Fine-grained composite materials. Hard fine grains are uniformly distributed in the matrix, such as dispersion-strengthened alloys and metal ceramics.

④ Hybrid composite materials. Composed of two or more reinforcing phase materials mixed in a matrix phase material. Compared with ordinary single-reinforcing phase composite materials, their impact strength, fatigue strength, and fracture toughness are significantly improved, and they also have special thermal expansion properties. They are divided into in-layer hybrid, inter-layer hybrid, sandwich hybrid, in-layer/inter-layer hybrid, and ultra-hybrid composite materials.

Basic Properties

Among composite materials, fiber-reinforced materials are widely used and have a large volume. Their characteristics are low specific gravity, high specific strength, and high specific modulus. For example, the material composed of carbon fiber and epoxy resin has a specific strength and specific modulus several times larger than steel and aluminum alloys, and also has excellent chemical stability, friction resistance, wear resistance, self-lubrication, heat resistance, fatigue resistance, creep resistance, noise reduction, electrical insulation, and other properties. Graphite fiber and resin composites can produce materials with a coefficient of expansion of almost zero. Another characteristic of fiber-reinforced materials is anisotropy, so the arrangement of fibers can be designed according to the strength requirements of different parts of the component. Aluminum-based composite materials reinforced with carbon fiber and silicon carbide fiber can still maintain sufficient strength and modulus at 500℃. Silicon carbide fiber and titanium composites not only improve the heat resistance of titanium but also increase wear resistance, and can be used as engine fan blades. Silicon carbide fiber and ceramic composites can be used at temperatures up to 1500℃, which is much higher than the operating temperature (1100℃) of superalloy turbine blades. Carbon fiber reinforced carbon, graphite fiber reinforced carbon, or graphite fiber reinforced graphite form ablation-resistant materials that have been used in spacecraft, rockets, missiles, and nuclear reactors. Because of their low density, non-metallic matrix composites can reduce weight, improve speed, and save energy when used in automobiles and airplanes. The composite leaf spring made of carbon fiber and glass fiber has a stiffness and load-carrying capacity comparable to a steel leaf spring that is 5 times heavier.

Molding Methods

The molding methods for composite materials vary depending on the matrix material. There are many molding methods for resin matrix composites, including hand lay-up, spray molding, fiber winding, molding, pultrusion, RTM molding, autoclave molding, diaphragm molding, transfer molding, reaction injection molding, soft film expansion molding, stamping, etc. Metal matrix composite molding methods are divided into solid-state molding and liquid-state molding. The former is achieved by applying pressure below the melting point of the matrix, including diffusion welding, powder metallurgy, hot rolling, hot drawing, hot isostatic pressing, and explosion welding. The latter involves melting the matrix and filling it into the reinforcement material, including traditional casting, vacuum suction casting, vacuum back pressure casting, squeeze casting, and spray casting. The molding methods for ceramic matrix composites mainly include solid-state sintering, chemical vapor infiltration molding, and chemical vapor deposition molding.

Related Materials

Nanocomposites

Due to their excellent comprehensive properties, especially their designable properties, composite materials are widely used in aerospace, national defense, transportation, sports and other fields. Nanocomposites are a particularly attractive part of this, and have developed rapidly in recent years. The new materials development strategies of developed countries around the world place great importance on the development of nanocomposites. This research direction mainly includes nano-polymer-based composites, nano-carbon-tube functional composites, and nano-tungsten-copper composites.

In the field of nano-polymer-based composites, the co-rotating twin-screw extrusion method is mainly used to disperse nano-powders, and the dispersion level reaches the nanometer level, resulting in nanocomposites with properties that meet design requirements. In the nano-montmorillonite/PA6 composite material we prepared, the interlayer spacing of nano-montmorillonite is 1.96 nm, which is at the level of similar materials in China (Chinese Academy of Sciences is 1.5-1.7 nm). After the montmorillonite is compounded into the nylon matrix, it is completely exfoliated into nano-particles with a thickness of 1-1.5 nm. The composite material has excellent temperature resistance, barrier properties, and water absorption resistance. This material has been industrialized; the nano-TiO2/polypropylene composite material under development has excellent antibacterial effects, and the nano-TiO2 powder is dispersed in polypropylene to less than 60 nm. This technology is currently applying for an invention patent. Because the molding process of nano-polymer composites is different from that of ordinary polymers, this direction is also actively carrying out research on new molding methods to promote the industrialization of nanocomposites.

Functional Composites

Functional composite materials refer to composite materials that provide physical properties other than mechanical properties. For example: conductive, superconducting, semiconductive, magnetic, piezoelectric, damping, wave absorption, wave transmission, friction, shielding, flame retardant, heat-resistant, sound absorption, heat insulation, etc., highlighting a certain function. They are collectively called functional composite materials. Functional composite materials are mainly composed of functional bodies, reinforcements, and matrices. The functional body can be composed of one or more functional materials. Multi-functional composite materials can have multiple functions. At the same time, new functions may be produced due to the composite effect. Multi-functional composite materials are the development direction of functional composite materials.

Wood-Plastic Composites

Wood-plastic composites are composite materials synthesized from plastics and low-value biomass fibers such as sawdust, wood chips, bamboo chips, rice husks, wheat straw, soybean skins, peanut shells, sugarcane bagasse, and cotton stalks as main raw materials.

It simultaneously possesses the advantages of plant fibers and plastics, has a wide range of applications, and can almost cover all the application areas of original wood, plastics, plastic steel, aluminum alloys and other similar composite materials. It also solves the problem of resource recycling of waste materials in the plastics and wood industries.

Its main characteristics are: resource utilization of raw materials, product plasticity, environmentally friendly use, economical cost, and recyclable recovery.

Application Fields

The main application areas of composite materials are:

① Aerospace field. Due to the good thermal stability, high specific strength, and high specific stiffness of composite materials, they can be used to manufacture aircraft wings and front fuselages, satellite antennas and their supporting structures, solar cell wings and shells, large carrier rocket casings, engine casings, and space shuttle structural components.

② Automobile industry. Due to their special vibration damping characteristics, composite materials can reduce vibration and noise, have good fatigue resistance, are easy to repair after damage, and are easy to form integrally. Therefore, they can be used to manufacture car bodies, load-bearing components, drive shafts, engine mounts and their internal components.

③ Chemical, textile, and machinery manufacturing fields. Materials composed of carbon fibers with good corrosion resistance and resin matrix can be used to manufacture chemical equipment, textile machinery, paper machines, copiers, high-speed machine tools, instruments, etc.

④ Medical field. Carbon fiber composite materials have excellent mechanical properties and do not absorb X-rays, and can be used to manufacture medical X-ray machines and orthopedic braces. Carbon fiber composite materials also have biocompatibility and blood compatibility, good stability in biological environments, and are also used as biomedical materials.

In addition, composite materials are also used to manufacture sports equipment and as building materials, which we have also introduced in detail in our previously published industry news.