Vehicle armour

The U.S. Army's M1 Abrams MBT with TUSK upgrade uses composite, reactive and slat armour

Military vehicles are commonly armoured (or armored; see spelling differences) to withstand the impact of shrapnel, bullets, missiles or shells, protecting the personnel inside from enemy fire. Such vehicles include armoured fighting vehicles like tanks, aircraft and ships.

Civilian vehicles may also be armoured. These vehicles include cars used by reporters, officials and others in conflict zones or where violent crime is common, and presidential limousines. Civilian armoured cars are also routinely used by security firms to carry money or valuables to reduce the risk of highway robbery or the hijacking of the cargo.

Armour may also be used in vehicles to protect from threats other than a deliberate attack. Some spacecraft are equipped with specialised armour to protect them against impacts from micrometeoroids or fragments of space junk. Modern aircraft powered by jet engines usually have them fitted with a sort of armour in the form of an aramid composite kevlar bandage around the fan casing or debris containment walls built into the casing of their gas turbine engines to prevent injuries or airframe damage should the fan, compressor, or turbine blades break free.[1]

The design and purpose of the vehicle determines the amount of armour plating carried, as the plating is often very heavy and excessive amounts of armour restrict mobility. In order to decrease this problem, some new materials (nanomaterials) and material compositions are being researched which include buckypaper,[2] and aluminium foam armour plates.[3]

Materials

Metals

Steel

Rolled homogeneous armour is strong, hard, and tough (does not shatter when struck with a fast, hard blow). Steel with these characteristics is produced by processing cast steel billets of appropriate size and then rolling them into plates of required thickness. Rolling and forging (hammering the steel when it is red hot) irons out the grain structure in the steel, removing imperfections which would reduce the strength of the steel. Rolling also elongates the grain structure in the steel to form long lines, which enable the stress the steel is placed under when loaded to flow throughout the metal, and not be concentrated in one area.

Aluminium

The British Fox CVR(W) was built largely of aluminium.

Aluminium is used when light weight is a necessity. It is most commonly used on APCs and armoured cars.

Iron

Wrought iron was used on ironclad warships. Early European iron armour consisted of 10 to 13 cm of wrought iron backed by up to one meter of solid wood.

Titanium

Titanium has almost twice the density of aluminium, but is as strong as iron. So, despite being more expensive, it finds an application in areas where weight is a concern, such as personal armour and military aviation. Some notable examples of its use include the USAF A-10 Thunderbolt II and the Soviet/Russian-built Sukhoi Su-25 ground-attack aircraft, utilising a bathtub-shaped titanium enclosure for the pilot, as well as the Soviet/Russian Mil Mi-24 attack helicopter.

Uranium

Because of its high density, depleted uranium can also be used in tank armour, sandwiched between sheets of steel armour plate. For instance, some late-production M1A1HA and M1A2 Abrams tanks built after 1998 have DU reinforcement as part of the armour plating in the front of the hull and the front of the turret, and there is a program to upgrade the rest (see Chobham armour).

Plastic

Plastic metal was a type of vehicle armour originally developed for merchant ships by the British Admiralty in 1940. The original composition was described as 50% clean granite of half-inch size, 43% of limestone mineral, and 7% of bitumen. It was typically applied in a layer two inches thick and backed by half an inch of steel.

Plastic armour was highly effective at stopping armour piercing bullets because the hard granite particles would deflect the bullet, which would then lodge between plastic armour and the steel backing plate. Plastic armour could be applied by pouring it into a cavity formed by the steel backing plate and a temporary wooden form.

Glass

Ballistic test of a bullet-resistant glass panel

Bulletproof glass is a colloquial term for glass that is particularly resistant to being penetrated when struck by bullets. The industry generally refers to it as bullet-resistant glass or transparent armour.

Bullet-resistant glass is usually constructed using a strong but transparent material such as polycarbonate thermoplastic or by using layers of laminated glass. The desired result is a material with the appearance and light-transmitting behaviour of standard glass, which offers varying degrees of protection from small arms fire.

The polycarbonate layer, usually consisting of products such as Armormax, Makroclear, Cyrolon, Lexan or Tuffak, is often sandwiched between layers of regular glass. The use of plastic in the laminate provides impact-resistance, such as physical assault with a hammer, an axe, etc. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet and thereby prevents penetration. This type of bullet-resistant glass is usually 70–75 mm (2.8–3.0 in) thick.

Bullet-resistant glass constructed of laminated glass layers is built from glass sheets bonded together with polyvinyl butyral, polyurethane or ethylene-vinyl acetate. This type of bullet-resistant glass has been in regular use on combat vehicles since World War II; it is typically about 100–120 mm (3.9–4.7 in) thick and is usually extremely heavy.

Newer materials are being developed. One such, aluminium oxynitride, is much lighter but at US$10–15 per square inch is much more costly.

Ceramic

Ceramic's precise mechanism for defeating HEAT was uncovered in the 1980s. High speed photography showed that the ceramic material shatters as the HEAT round penetrates, the highly energetic fragments destroying the geometry of the metal jet generated by the hollow charge, greatly diminishing the penetration. Ceramic layers can also be used as part of composite armour solutions. The high hardness of some ceramic materials serves as a disruptor that shatters and spreads the kinetic energy of projectiles.

Composite

Plasan Sand Cat light (5t) military vehicle featuring integrated composite armoured body

Composite armour is armour consisting of layers of two or more materials with significantly different physical properties; steel and ceramics are the most common types of material in composite armour. Composite armour was initially developed in the 1940s, although it did not enter service until much later and the early examples are often ignored in the face of newer armour such as Chobham armour. Composite armour's effectiveness depends on its composition and may be effective against kinetic energy penetrators as well as shaped charge munitions; heavy metals are sometimes included specifically for protection from kinetic energy penetrators.

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