Man is born without powerful claws and long tusks, so his main weapon is the brain. The stick lengthens the arm, and the stone cuts the beast. But the universe has no purpose to help man - a boat made of rotten wood, a thatched hut fit only for summer, and weapons made from improvised materials cause limited damage. Then the man came up with the idea to combine the available materials with each other. Long before the industrial revolution and the age of science, the first composite materials were created. How did they develop, and at the current level of development, do they have a future?

Composite materials differ in that they use two or more components that do not combine into one substance. For example, you won't find iron and charcoal in a cast iron cauldron unless you get to the atomic level. But you can, with the help of simple tools at hand, separate the plywood into layers and follow the glue on them. Typically, composite materials consist of a matrix and reinforcing elements, fillers. Using different substances with these two properties, it is possible to obtain composite materials with completely different properties depending on the substances used and the design of the matrix and materials.

The first composite material is easy to make, but fundamentally changes people's lives. So that the tree does not rot in the water, the man came up with the idea of ​​impregnating it with resin. The quality of the boat has been greatly improved. Another ancient composite material is raw bricks, rods made of clay and chopped plant fibers. Buildings built from this material are reliable. Dry clay provides strength, and straw holds it together and helps the clay not crack. The first mud brick houses appeared in Mesopotamia and Egypt, where there were no dense forests for thatched huts. But five thousand years before our time, people found a great alternative to them - thanks to one of the first composite materials.

Build a house from Adobe

The bow was invented in both Europe and the Americas. However, to increase their damaging effect, it was necessary to increase the traditional (curved) bows to enormous sizes. It is unrealistic to use it for hunting or riding. Here, the Mongolian nomads found a solution - the compound bow, or compound bow, in which several layers of wood could be glued together, connecting them with a flexible and durable stone, and also adding bone inserts, turned out to be effective. At the same time, the shoulder of the bow is designed to bend forward - in this case, the bowstring maintains a longer tension when fired, transferring energy to the arrow. The limb of the bow acts as a lever, and this design allows for a relatively small bow with great lethality. With them, it is convenient for the rider to mount a horse - to shoot enemy troops or hunt at a distance.

Archer, 1920s

Composite materials also include concrete, which has the above structure: pebbles and sand are used as a reinforcing base, which are filled with a filler - cement. From the resulting complex substances, it is possible to build strong and practically non-combustible structures. Concrete has been known for at least two thousand years, back in ancient Rome.

Composite materials offer a dizzying array of effective solutions, but they are not a panacea. There are always limits, and in fact these limits determine whether composite materials should be preferred over other solutions. In addition to high cost, the first composite materials have a number of specific disadvantages. For example, the first compound bows were held together with waterproof animal-based adhesives. Samarny brick is hygroscopic, therefore it does not collapse and must be covered with plaster. This was acceptable for the region where it was invented, but adobe houses were rare in the northern regions, where there was a lot of rain and plaster did not help. For a long time, the limited range of natural materials narrowed the range of possibilities for composites, until scientific breakthroughs in chemistry fundamentally changed the picture.

In the 19th century, the development of chemistry allowed industry to obtain new materials. The discovery of polymerization enabled the invention of rubber and plastics, giving rise to a new type of composite material. Without them, the 20th century would not have been an era of industrialization at all: if new composite materials had not been developed, natural materials would not have been enough for all construction sites. For example, in Russia they learned how to get calcium phenol carbonate (analogous to Bakelite). It belongs to thermoplastics: it conducts heat and electricity poorly, does not burn. Using various fillers, carborite can be used both as an insulator and as a material for housings of various equipment. Its greatest use was as an insulating material in the GOELRO project, which electrified the entire Soviet Union.

Old Bakelite telephone, mid 20th century

The second important factor in the mass introduction of composite materials is the reduction in cost and improvement of materials known to man. For example, the first reinforced concrete houses were built in the middle of the 19th century. But only the industrial production of ferroalloys and the improvement of their properties made it possible at the beginning of the 20th century to start creating the material on a large scale.

One discovery leads to another. Looking for an artificial alternative to fabric, rayon, derived from cellulose, was discovered. In the production of viscose, they learned how to get cellophane, which at first was almost a by-product, but turned out to be an excellent packaging material. Almost all newly discovered materials can be used as fillers in composite materials, which, in turn, have properties almost unimaginable for previous materials.

Modern composite materials

Although composite materials are needed to create new industries, their use is not always more expensive than existing ones. Scaling up the technology reduces costs and makes it possible to replace scarce materials. For example, the victory of the USSR in the Great Patriotic War is difficult to imagine without the mass construction of aircraft. The best material for aircraft equipment is aluminum alloy - lightweight and durable. But the output of this non-ferrous metal is completely insufficient. And save... plywood. Of course, this is not just plywood, it is also high-tech. Impregnation of birch veneer with phenolic resin - to obtain triangular wood. According to some parameters, it is twice as strong as wood, although one and a half times weaker than aluminum of the same weight. Although a triangular wooden plane is heavier than a metal one,

Corning is best known for its scratch-resistant coating for smartphone screens, Gorilla Glass. But back in the 1800s, she worked with glass, and in the 1930s, her experts discovered fiberglass, another popular ingredient for composites. It turns out that glass that is clean and devoid of impurities and stains is very durable, and thin wires made from it are also very elastic. By weaving them together, you get fiberglass - a strong, relatively light material that also does not oxidize. Back in the 1950s, materials for boat hulls and aircraft skins were produced on its basis. Another important property of fiberglass is radio transparency, so it is used in fairings. Thanks to this set of “opportunities”, fiberglass is widely used in our time.

Composite shipbuilding technology used to build 12,700 minesweepers

The new century has become ideal for composites: new substances are being synthesized all the time, and industry needs fundamentally new materials. The reader "by eye" will no longer be sure whether he sees a "pure" material or a composite. What areas of application of composite materials are currently the most relevant?
One of the most extreme working conditions in nuclear reactors. In their design, a composite material of the SiC-SiC type was used: a silicon carbide matrix reinforced with silicon carbide fibers, capable of long-term operation under radiation and high temperatures.

Advanced hydrogen energy sources are also inseparable from composite materials: carbon fiber materials are considered as an integral part of gas diffusion layers and bipolar plates of fuel cells with polymeric proton-conducting membranes.

The main body of the rocket is made of carbon fiber, Research Institute of Special Machine Building

On the basis of carbon compounds, an extremely diverse composite material is obtained. In addition, various forms of carbon are used both in the matrix and as a binder filler. Carbon-carbon composite materials can be used at temperatures up to two thousand degrees! Many metals melt when heated in this way. In the Soviet Union, for example, the Gravimol carbon material was made for the Buran spacecraft - fairings and leading edges of the wings were made from it, which became very hot during landing. Can we produce this material in Russia?

"Currently, active work is underway to switch to domestic PAN precursors - an important raw material for the production of carbon fibers, the basis of many composite materials." Artur Radikovich, Deputy Director for Science and Innovation at JSC NIIgrafit (part of the state corporation Rosatom) This is important for both the civilian and military industries, Gareev told Naked Science, adding that Yumatex produces a number of UMT fibers , which are the most high-tech carbon fibers in Russia - they are several times stronger than steel. In general, NIIGrafit is engaged in the development of composite materials based on carbon fibers, structural graphite, etc. for components of rockets, aerospace and aviation equipment and other devices operating at high temperatures.

“Depending on the reinforced structure, the same carbon-carbon composites can work in friction conditions and withstand long-term loads of aircraft brake pads, for example, in the Russian MS-21. Due to their electrical conductivity, carbon-carbon composites are used to make heaters for high-temperature furnaces, and they can work reliably for a long time. However, such CMs (composites) are very brittle, which limits their use in engineering,” PoyaArtur Gareev removes applicability restrictions.

When flexibility is required, layers of woven carbon fiber are bonded with epoxy or polymer to form carbon fibers. The best of them have strength comparable to metal, but with a much greater mass. They don't run as hot as carbon-carbon composites, but can last for many years. One of the most famous examples of the use of carbon fiber in Russia is the wing of the promising MS-21 aircraft. The unpainted carbon fiber color is called "black wing", but in addition to color, in addition to saving weight, they also allow for a more efficient and economical wing shape. In general, composites make up 40% of aviation materials, which is one of the best indicators in the world. 2018, Aerocomposite for creating elements of aircraft (part of PJSC "UAC"),

Polymers can be not only a matrix, but also fillers. Aramid threads can be used as a base for clothing and body armor. Composite materials based on them "win" metals, since they are lighter and comparable in strength. One of the promising areas is ultra-high molecular weight polyethylene (UHMWPE) fibers. In terms of strength, it surpasses aramid fibers, and the best bulletproof vests based on it have a density comparable to that of water: 1 g/cm 3 .

Composites in general are not opposed to metals, which will obviously be the basis for creating the technology of modern civilization for a long time to come. The design and development of composites based on metal matrices, as well as composites in which non-metallic phases are placed or formed in a special way, can combine many of the advantages of metals with new properties of composite systems. Manufacturing requires high precision in the process. JSC "NPO CNIITMASH" has developed a technology for the production of products from metal matrix composites reinforced with oxide, carbide and nitride nanoparticles:

“One of the methods for obtaining products from composite materials based on a metal matrix is ​​the method of selective laser melting, which makes it possible to obtain products of complex geometry that require minimal mechanical processing,” explains Ivan Ivanov, Ph.D. physical and mathematical road. Director of the Institute of Metallurgy and Mechanical Engineering of the Faculty of Natural Sciences. An example is the possibility of using DUO (dispersion-strengthened oxide) steels. The structure of this composite material is a metal matrix in which the nanosized oxide phase is uniformly distributed. They are used in aggressive environments with increased thermal, corrosion and radiation loads.

Why hasn't the aggressive creation of new alloys and materials reduced the need for composites? “Copper, for example, has a density close to nine, while composite materials have a density less than two, but have comparable thermal conductivity. Therefore, they are in great demand in the aerospace industry.oh industry, ”Artur Gareev cites as an example. The lower the density, the lower the mass of a substance of the same volume. At the same time, the total length of the wires in the aircraft exceeds 200 kilometers (!), so reducing their weight will significantly reduce fuel consumption.

Gareev added that new fibers based on mesophase pitch are currently being developed in Russia — they have a thermal conductivity of about 600 W/(m*K) compared to 394 W/(m*K) for copper. They will become a good substitute for metals when it becomes possible to establish production in Russia. In terms of structure, the composite can compete with titanium and aluminum: at half density (about 1.4 g/cm3 versus 3 g/cm3), they have similar strength and modulus of elasticity. At the same time, carbon plastic works well.

Why haven't composite materials replaced all other materials? Almost all of them have some drawbacks. For example, fiberglass can be used as a hull, but only when hitting obstacles. The metal is more ductile, beats better and is easier to repair. Carbon-carbon composites are often brittle. CFRPs are flexible, but generally anisotropic: that is, they exhibit their properties (thermal conductivity, strength) only in a certain direction relative to the material.

It might even be useful in some cases, but designers want the same strength when applied at any angle. Scientists have a job. At the same time, we do not have a "golden bullet" for choosing materials in new projects. Every time an engineer has to calculate which material is better: metal, polymer, composite. Or maybe it's great - there is a place for creativity.

How are new composite materials produced? First, in fact, what indicators are facing scientists and researchers. It is known which combination of binder and filler should be used to achieve a given property. Boron nitride, for example, provides good neutron shielding and imparts high thermal conductivity to the composite. We need conductivity - then we use graphite as a filler. But the main work still remains in the laboratory - in what proportion and how they can be combined in order to best meet the given requirements.

How to improve composite materials? Maybe everything can be calculated on a supercomputer? Or, on the contrary, have they reached their limit? “You can't make a complete composite on a supercomputer,” Artur Gareev explains. “Because there are some physical and chemical effects that you cannot model. Usually you need to work on technologies that combine matrix and filler in the laboratory. But you can certainly improve them. New fibers, new materials appear.

As a simple example, Gareev mentioned the level of progress made by the Japanese in the production of carbon fibers based on mesophase resin. If we talk about Russia, now it is important to master the production and use of fibern UHMWPE. A recent perspective is smart composite materials that actively respond to changing environmental conditions. For example, they give the signal to bend, harden on impact, and even recover. Here Gareev calls polymer piezoelectric composites an interesting direction. In fact, it is a material, each part of which works as a sensor.

Self-healing can be achieved by "flashing" the aluminum matrix with wires made of nitinol (a compound of nickel and titanium) and other materials with a memory effect. When cooled below the critical temperature, it forms an internal energized when heated, it returns to the form in which it was before heating. Nitinol itself has a memory effect, but in the composition of the composite this effect is enhanced.

There are many other practical things. From the functional side, radio-transparent, radiation-resistant composite materials are being studied. Radiation-strengthened composites can be used to fabricate large structures for low-power nuclear power plants. Of course, even with the material for these courses, there is now room for improvement.

Finally, a Naked Science correspondent asked Artur Radikovich to be a futurist for a moment and ask what kind of composites would he like to see in the future?

- Biocomposites combining living tissue with synthetic materials. Enabling people to significantly increase the efficiency and endurance of their body!

This material was developed in collaboration with the Homo Science educational project. On this online platform, scientists, experts and popularizers in an accessible and entertaining way talk about "atoms" in the context of physics, chemistry, information technology, medicine, mathematics and biology. We recommend that you follow the news there.