“When the sand is kneaded, the light color is different from the ordinary.”
This is a poem chanting exquisite porcelain. Ceramics, with its unique shape, color and texture, has not only become a common appliance in people’s life for thousands of years, but also a pleasing art.
In everyone’s impression, ceramics are fragile.
With a slight fall, a valuable ancient porcelain can be “broken to pieces” in an instant. But do you know that ceramics have been “transformed” by modern science and technology, and can be used as bulletproof materials because of its physical properties. It can be called a “new star” rising in the bulletproof field.
Imagine that a small bullet on the battlefield can bring fatal damage to soldiers, while fragile ceramics can block bullets flying at high speed.
Where does it come from? Next, let’s go into the world of bulletproof ceramics and find out.
High strength, hard, composite armor
Bulletproof ceramics belong to a family of inorganic non-metallic materials. Strictly speaking, they are not the same kind of materials as the porcelain used in our daily life.
As a special ceramic, different from the ceramic utensils made from local soil, the preparation of bulletproof ceramics needs to go through a series of complex processes such as powder preparation, molding and high-temperature sintering. It is the product of the rapid development of modern technologies such as chemistry, metallurgy and materials.
As early as 1918, it was recorded that coating a layer of enamel on the surface of steel armor can significantly improve its bulletproof performance. However, bulletproof ceramics in the real sense only appeared after the 1960s.
The reason why bulletproof ceramics can be bulletproof is that they have extremely high hardness and strength.
After the bullet hits the high-strength and hard ceramic, it will break and cause the ceramic to break. The whole process will consume most of the energy of the bullet and form an “inverted pyramid” failure cone at the impact point. This is also the typical damaged morphology of ceramics after being shot.
Of course, due to the brittleness of ceramics, only relying on ceramics itself can not be “foolproof”. Bulletproof ceramics are generally placed on the bullet facing surface and should be bonded with other backing materials to form composite armor for common use.
The backing material is generally fiber-reinforced composites such as para aramid or ultra-high molecular weight polyethylene, whose main function is to absorb the residual ballistic impact energy.
In order to improve the resistance of ceramics to multiple blows, it is often necessary to coat the ceramic panel with high-strength fiber fabric to prevent the crack propagation caused by elastic blow.
The combination of high-strength hard ceramics and rigid backing constitutes the basic structure of modern ceramic composite armor.
Baptism of war, shield of life
In the 1960s, U.S. helicopters and crew members in the jungles of Vietnam were often killed by ground light weapons. In order to reduce the battle damage of equipment and casualties of passengers, in 1962, an American aerospace company first developed a composite armor with hard ceramics on the front.
The alumina ceramic block was adhered to the tough aluminum back plate with a thickness of about 6mm to resist the shooting of 7.62mm armor piercing projectile.
That is, during this period, the US military opened the precedent of large-scale military application of bulletproof ceramics.
Under the same conditions, the weight of ceramic is much lower than that of metal. On military aircraft with very strict weight requirements, ceramic armor is widely used for the protection of belly, cockpit, engine and other key parts.
The Russian mi-28 helicopter is strengthened with ceramic armor around the cockpit, which can resist several machine gun shots. Its excellent protection ability has won the reputation of “Flying Fortress”. For armored vehicles, ceramic composite armor is a “secret weapon” to improve the protection ability.
British “Challenger 2”, French “Le Clair”, Russian “Amata” and other main battle tanks are heavily equipped with this armor. It is reported that a “Challenger 2” tank of the British army was hit by 14 RPG rockets and an anti tank missile, but no casualties were found among the internal crew, which shows the “shield” ability of modern ceramic composite armor.
When heavy equipment was covered with light and high-strength ceramic “armor”, people turned their attention to the soldiers shuttling through the hail of bullets. In fact, steel bulletproof chest armor appeared as early as World War II.
It was not popular with the soldiers because it was too bulky. In the 1970s, the US military launched a soft and lightweight Kevlar bulletproof vest. Although it has good performance in protecting low-speed bullets and explosive fragments, it is often “weak” in protection when encountering high-speed bullets fired by rifles. In fact, the so-called “bulletproof” is not “invulnerable”, but graded protection according to the protection ability.
Equipment with a certain protection level can only meet the requirements of protecting bullets of this level and lower levels. The “King Kong is not bad” bulletproof vests in film and television dramas do not exist.
In order to improve the protection ability, scientists thought of making bulletproof ceramics into insert plates, which can be used together with soft bulletproof clothing, just like the “goggles” on ancient armor.
In this way, it can not only greatly improve the protection ability of the core part of the human body, but also take into account the mobility of the wearer.
At first, small pieces of ceramics were spliced into a plug-in board. With the progress of technology, people use more whole ceramics to eliminate the weak points of small ceramic pieces due to splicing gaps, and some are made into curved surfaces to fit the human body.
This is also the basic style of the current bulletproof plug-in board. At present, the preparation technology of bulletproof ceramics has become more and more mature and has become the “life shield” to protect soldiers.
With the help of science and technology, it will be upgraded again.
After decades of development, there are many kinds of bulletproof ceramics widely used at present, including alumina, silicon carbide, boron carbide, silicon nitride, titanium boride and so on. Among them, the most common are alumina, silicon carbide and boron carbide ceramics.
With the upgrading of weapon system, the traditional single-phase ceramics can not meet the actual military needs, especially the requirements for bulletproof equipment are higher and higher. Therefore, bulletproof ceramics began to develop towards diversification, compounding and functionalization——
Functionally graded ceramics.
Through the micro component design, the ceramic properties change regularly and continuously. For example, titanium boride and metal titanium, as well as metal / ceramic composite systems such as alumina, silicon carbide, boron carbide, silicon nitride and metal aluminum, form a structural change in the thickness direction to ensure the transition of bulletproof ceramics from high hardness on the attack surface to high toughness on the back surface.
In this way, it can not only meet the requirements of armor bullet resistance, but also enhance its ability to resist multiple bullets. It has great advantages in protecting medium and small caliber armor piercing bullets.
Nano multiphase ceramics. On the basis of single-phase ceramics, sub micron or nano dispersed particles are added to form multiphase ceramics. For example, silicon carbide silicon nitride aluminum oxide, boron carbide silicon carbide can improve the hardness, toughness and strength of ceramics in a certain range.
It is reported that foreign countries are exploring the sintering process of bonding nano scale powders together, which can reduce the grain size of ceramics to tens of nanometers, so as to improve the hardness and strength of materials.
This is a major development direction of advanced ceramic armor in the future.
Transparent ceramics. Transparent ceramics represented by single crystal alumina (sapphire), nitrogen alumina and magnesia alumina spinel can replace bulletproof glass and be used in military equipment such as single soldier bulletproof mask, missile detection window, vehicle observation window and submarine periscope because of their high strength and hardness and good optical properties. Because it can manufacture transparent parts with large size and complex shape at low cost, such ceramics have been listed as one of the key optical functional transparent materials in the 21st century by many military powers.
At present, ceramics are widely used both in military and civil technology. It can be predicted that the ancient story of spear and shield will still play a wonderful duel in the future battlefield.
