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 enables the stress the steel is placed under when loaded to flow throughout the metal, and not be concentrated in one area. It tends to be softer as heat treatment is difficult or impossible. Nevertheless, the flexibility in shape has made it popular as the structural hull in modern tanks.
Aluminium was built largely of aluminium.
Aluminium is used when light weight is a necessity. It is most commonly used on
APCs and
armoured cars. While certainly not the strongest metal, it is cheap, lightweight, and tough enough that it can serve as easy armour.
Iron Wrought
iron was used on
ironclad warships. Early European iron armour consisted of 10 to 12.5 cm of wrought iron backed by up to one metre of solid
wood. It has since been replaced by steel due to steel being significantly stronger.
Titanium Titanium has almost twice the density of aluminium, but can have a yield strength similar to high strength steels, giving it a high
specific strength. It also has a high specific resilience and specific toughness. 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 (DU) 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. Some main battle tank armour utilises polymers, for example polyurethane as used in the "BDD" appliqué armour applied to modernized
T-62 and
T-55.
Glass Bullet-resistant 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
bulletproof 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 light (5 ton) 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. Composite armour used on modern Western and Israeli main battle tanks largely consists of non-explosive reactive armour (NERA) elements - a type of
reactive armour. These elements are often a laminate consisting of two hard plates (usually high hardness steel) with some low density interlayer material between them. Upon impact, the interlayer swells and moves the plates, disrupting heat 'jets' and possibly degrading kinetic energy projectiles. Behind these elements will be some backing element designed to stop the degraded jet or projectile element, which may be of high hardness steel, or some composite of steel and ceramic or possibly uranium. Soviet main battle tanks from the
T-64 onward utilised composite armour which often consisted of some low density filler between relatively thick steel plates or castings, for example
Combination K. For example, the T-64 turret had a layer of ceramic balls and aluminium sandwiched between layers of cast steel armour, whilst some models of the
T-72 features a glass filler called "Kvartz". The tank
glacis was often a sandwich of steel and some low density filler, either textolite (a
fibreglass reinforced polymer) or ceramic plates. Later T-80 and T-72 turrets contained NERA elements, similar to those discussed above. ==Ships==