Composite armour is a type of
vehicle armour consisting of layers of different material such as
metals,
plastics,
ceramics or
air. Most composite armour are lighter than their all-metal equivalent, but instead occupy a larger volume for the same resistance to penetration. It is possible to design composite armour stronger, lighter and less voluminous than traditional armour, but the cost is often prohibitively high, restricting its use to especially vulnerable parts of a vehicle. Its primary purpose is to help defeat
high explosive anti-tank (HEAT) rounds.
HEAT had posed a serious threat to armoured vehicles since its introduction in World War II. Lightweight and small, HEAT rounds could nevertheless penetrate hundreds of millimeters of the hardest steel armours. The capability of most materials for defeating HEAT follows the "density law", which states that the penetration of shaped charge jets is proportional to the square root of the shaped charge liner density (typically copper) divided by the square root of the target density. On a weight basis, lighter targets are more advantageous than heavier targets, but using large quantities of lightweight materials has obvious disadvantages in terms of mechanical layout. Certain materials have a sweet spot in terms of density that makes them particularly useful in this role.[1]
The earliest known composite armour for armoured vehicles was developed as part of the US Army's T95 experimental series from the mid-1950s. The T95 featured "siliceous-cored armor" which contained a plate of fused silica glass between rolled steel plates. The stopping power of glass exceeds that of armour steel on a thickness basis and in many cases glass is more than twice as good as steel on a thickness basis. Although the T95 never entered production, a number of its concepts were used on the M60 Patton, and during the development stage (as the XM60) the siliceous-cored armour was at least considered for use, although it was not a feature of the production vehicles.[1]
The first widespread use of a composite armour appears to have been on the Soviet T-64. It used an armour known as Combination K, which apparently is glass-reinforced plastic sandwiched between inner and outer steel layers. Through a mechanism called thixotropy, the resin changes to a fluid under constant pressure, allowing the armour to be moulded into curved shapes. Later models of the T-64, along with newer designs, used a boron carbide-filled resin aggregate for greatly improved protection. However the quality of the tanks produced during this era varied widely; if the boron carbide was not available in time to meet production quotas, the tank would be shipped with any filler that could be found, and sometimes nothing at all. In order to deal with these problems, the Soviets invested heavily in reactive armour, which allowed them some ability to control quality, even after production.
