Chobham armour

Chobham armour is the informal name of a composite armour developed in the 1960s at the British tank research centre on Chobham Common, Surrey. The name has since become the common generic term for composite ceramic vehicle armour. Other names informally given to Chobham Armour include "Burlington" and "Dorchester."

Although the construction details of the Chobham armour remain a secret, it has been described as being composed of ceramic tiles encased within a metal framework and bonded to a backing plate and several elastic layers. Due to the extreme hardness of the ceramics used, they offer superior resistance against shaped charges such as high explosive anti-tank (HEAT) rounds and they shatter kinetic energy penetrators.

The armour was first tested in the context of the development of a British prototype vehicle, the FV4211, and first applied on the preseries of the American M1. Only the M1 Abrams, Challenger 1, and Challenger 2 tanks have been disclosed as being thus armoured. The framework holding the ceramics is usually produced in large blocks, giving these tanks, and especially their turrets, a distinctive angled appearance.

Due to the extreme hardness of the ceramics used, they offer superior resistance against a shaped charge jet and they shatter kinetic energy penetrators (KE-penetrators). The (pulverised) ceramic also strongly abrades any penetrator. Against lighter projectiles the hardness of the tiles causes a "shatter gap" effect: a higher velocity will, within a certain velocity range (the "gap"), not lead to a deeper penetration but destroy the projectile itself instead. Because the ceramic is so brittle the entrance channel of a shaped charge jet is not smooth—as it would be when penetrating a metal—but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed jet causes still greater irregularities in the ceramic, until in the end it is defeated. The newer composites, though tougher, optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection". This mechanism—using the jet's own energy against it—has caused the effects of Chobham to be compared to those of reactive armour. This should not be confused with the effect used in many laminate armours of any kind: that of sandwiching an inert but soft elastic material such as rubber, between two of the armour plates. The impact of either a shaped charge jet or long-rod penetrator after the first layer has been perforated and while the rubber layer is being penetrated will cause the rubber to deform and expand, so deforming both the back and front plates. Both attack methods will suffer from obstruction to their expected paths, so experiencing a greater thickness of armour than there is nominally, thus lowering penetration. Also for rod penetrations, the transverse force experienced due to the deformation may cause the rod to shatter, bend, or just change its path, again lowering penetration.

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