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Topic Last Updated on 16-07-2024
What Is a Composite?
At its core, the word “composite” means a “mixture” or “compound.” Today, engineers use this word to refer to a material consisting of two or more parts. The properties of a composite differ quantitatively and qualitatively from the properties of each of its constituent materials. Despite the variety of compositions, most of the composite materials have two fundamental parts: the reinforced filler, which is responsible for the desired mechanical properties, and the matrix, which binds the reinforcing elements.
The principle of the composite device
- Metal-ceramic
- Ceramic-polymer
- Metal-polymer
Can a metal alloy, for example, be a composite? The answer is no, as the composite materials do not mix and remain physically separated from each other.
A good example of a composite is reinforced concrete, in which metal bars are used with a concrete matrix. The reinforced filler they form differs in properties both from metal rebar and pure concrete: metal rods create the “skeleton” of the product, giving the necessary strength, and concrete connects and fills the space between the rebar, providing heat and sound insulation.
The principle of the composite device
Composites are not new to humanity. They were used by the Mesopotamians in 3,400 BCE to glue wood at different angles, producing a material with properties far superior to natural wood. The ancient Egyptians, meanwhile, mixed clay and straw to produce bricks.
Bakelite was the first plastic made from synthetic components
The first modern polymer composite material was patented in 1909 by the American chemist Leo Baekeland. He combined phenol-formaldehyde resin (formed by the reaction of phenol and formaldehyde) with various fillers: asbestos powder, wood flour, cellulose. The resulting material was called “Bakelite,” and in the first half of the 20th century, it was actively used in the production of various parts of the external housing of household appliances, like telephones, lamps, radios, and even women’s jewelry.
An Amazing Property
There are plenty of composites in the modern world, but there are also just as many tasks they can solve! Take polymer composite water pipes as an example. They are made of fiberglass; that is, the reinforcing filler is glass filaments, and the matrix is a thermoplastic polymer (plastic).
Traditionally, metals like steel and copper were used for manufacturing of pipes. Metal pipes have well-known drawbacks — they are heavy and prone to corrosion. Composite pipes are significantly lighter, stronger, and more durable (lasting 50–100 years). There is yet another advantage that is of the utmost importance: composite pipes are much cheaper.
Composite materials do have their drawbacks, however. Let’s look again at the same pipes:
Repair
Unfortunately, fiberglass pipes may burst on impact, and repairing such a pipe section is next to impossible.
Disposal
Metal pipes can be melted down, while composites need to be crushed and disposed of.
Production
The composite industry is young: technological processes are not firmly established, and there aren’t enough specialists in the field.
VERY DIFFERENT COMPOSITES
COMPOSITES CAN BE CLASSIFIED BY THE TYPE OF REINFORCED FILLER OR BY THE MATRIX USED
TYPES OF REINFORCED FILLER
Fibrous
Fibers are used as a filler. Even a small number of them leads to the appearance of new mechanical properties.
Fiberglass, carbon fiber, fiberboard, MDF
Layered
The matrix and filler are arranged in layers.
Bulletproof glass, textolites — laminated plastics reinforced with fabrics from various fibers
Powdered
Used to reduce the cost of the material or to give it increased strength.
Concrete, Bakelite
BY MATRIX TYPE
Ceramic
Ceramic base with carbon or ceramic fibers.
Borosilicate glass, gas turbine installations, jet engine exhaust nozzles, brakes, bearings, heat exchangers, nuclear reactors
Metal
Matrix of light metal-aluminum or magnesium alloy, reinforced with ceramic or carbon fibers. For example, aluminum reinforced with silicon carbide.
Used in the aerospace industry and the automotive industry (diesel engine pistons).
Polymeric
The most popular type of matrix. The matrix of polymer composites is thermoplastics (which retain their properties under repeated heating and cooling) and thermosetting resins (which irreversibly set into a structure when cured).
Fiberglass containing up to 80% silicate glass fibers. They are characterized by optical and radio permeability, low thermal conductivity, high strength, good electrical insulation, and low cost. Used in the manufacture of sports cars, boats, fishing rods, and sports equipment.
Carbon plastics with artificial or natural carbon fibers based on cellulose. Carbon fiber plastics are lighter and stronger than fiberglass, are opaque, do not change linear dimensions with temperature changes, and conduct current well. They are able to withstand high temperatures even under extreme conditions. They are used in aviation, rocket engineering, and in the production of light sports equipment.
Boroplastic with boron fibers, yarns, and bundles. Very hard, wear-resistant, and resistant to corrosive substances. They are expensive and do not tolerate high operating temperatures. They are used in aviation and space technology, where it is required to withstand long-term loads in a high-pressure environment.
