<COMMENT>The ABI labs</COMMENT>
<P><B><JC>Chobham Armour
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<P>Chobham armour is a composite armour developed in the sixties at the British tank research centre on Chobham Common. Although the exact composition of Chobham armour remains a secret, it appears to be a composite armour of ceramic tiles within a matrix that is layered between steel armour plating, a combination that is excellent at defeating high explosive anti-tank (HEAT) rounds. Possible ceramics for such armours are: boron carbide, silicon carbide, aluminium oxide (sapphire or "alumina"), titanium boride or Syndie, a synthetic diamond composite. Of these boron carbide is the hardest and lightest, but also the most expensive and brittle.
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<P>The ceramics can be created by cold pressing or hot pressing. A high density is striven for in that air bubbles should be almost absent. Over the years newer and tougher fibre composites have been developed, giving about five times the protection value of the original pure ceramics, the best of which were again about five times as effective as a steel plate of equal weight. These are often a mixture of several ceramic materials. 
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<P>The latest developments involve the use of carbon nanotubes to improve toughness even further. The small hexagonal or square ceramic tiles are encased within a metal (today typically a titanium alloy) matrix, either by isostatically pressing them into the heated matrix, or by glueing them with an epoxy resin. A more general name is therefore: MMC or Metallic Matrix Composite. The word "composite" here refers to "composite armour", not to any composite materials, such as Ceramic Matrix Composites or MMCs in the wider sense, which optionally might be used in its construction.
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<P>A titanium matrix is extremely expensive to manufacture but the metal is favoured for its lightness, strength and resistance to corrosion, a constant problem with MMC's. The Rank company claims to have invented an alumina matrix for the insertion of boron carbide or silicon carbide tiles. Since the early nineties it is known that bringing the tiles under constant compression by their matrix greatly improves their resistance to kinetic penetrators, which is difficult to achieve when using glues.