A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
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Penetration <strong>and</strong> fragmentation<br />
<strong>of</strong> energy <strong>and</strong> momentum. The piercing power is proportional to the length <strong>of</strong><br />
the jet <strong>and</strong> the square root <strong>of</strong> its density.<br />
A shape charge performs at its best when the distance from the face <strong>of</strong> a<br />
target to the point <strong>of</strong> detonation is precisely calculated (the st<strong>and</strong>-<strong>of</strong>f). For this<br />
reason many shaped charge missile warheads have an extended st<strong>and</strong>-<strong>of</strong>f probe<br />
to initiate detonation. Manufacturers <strong>of</strong> shaped charge warheads are now seeking<br />
penetrative powers equal to six times the warhead diameter. However, there is<br />
a problem because warheads with long probes tend to become unstable in flight.<br />
The shaped charge liner is normally made <strong>of</strong> copper, <strong>and</strong> technology advances<br />
have usually been improvements in the precision <strong>of</strong> the liner shaping <strong>and</strong><br />
centring. Efforts have also been made to produce detonation wave fronts<br />
normal to the cone surface, so that the liner remains solid but changes shape<br />
like a fluid. The high-velocity jet formed by the transformation <strong>of</strong> the metal<br />
liner tends to break into separate particles, but the development <strong>of</strong> the<br />
explosively formed projectile, or self-forming fragment, has meant the retention<br />
<strong>of</strong> full effectiveness over long distances.<br />
If the liner is made parabolic in shape, rather than conical, the slug, instead<br />
<strong>of</strong> being needle shaped, becomes a chunky, U-shaped projectile. This type <strong>of</strong><br />
projectile does not burst into fragments or flatten against the target, but the<br />
penetrating power is naturally reduced.<br />
In a shaped charge, the initial velocity <strong>of</strong> the jet depends on the ratio ( )<br />
between the mass <strong>of</strong> the liner <strong>and</strong> the mass <strong>of</strong> explosive located behind the<br />
liner element. This velocity, V 1, is given by V 1=A( +k) –1/2 , where A is a constant<br />
defining the specific energy <strong>of</strong> the explosive, <strong>and</strong> k is a charge configuration<br />
constant. This formula was due to Gurney [7.70]. A less approximate analysis<br />
<strong>of</strong> the relationship between V 1 <strong>and</strong> the charge configuration has been given<br />
more recently by Chou et al. [7.71].<br />
The defeat <strong>of</strong> shaped charge jets by armour material was a problem that<br />
absorbed much military research <strong>and</strong> development in the years following the<br />
Second World War. Eventually these studies turned towards the idea <strong>of</strong> ‘active’<br />
or energetic armour elements, which would release energy when attacked that<br />
would counteract the effect <strong>of</strong> the charge. The principle <strong>of</strong> operation was taken<br />
an important step forward in the 1970s, by the invention <strong>of</strong> the ‘drive-plate’<br />
explosive s<strong>and</strong>wich concertina <strong>of</strong> two metal plates with an explosive layer<br />
between. When initiated by a high-speed jet, the explosive drives the metal<br />
plates to one side, <strong>and</strong> the moving plates absorb the mass <strong>of</strong> the jet. Work began<br />
in Israel in 1974 on prototype ‘add-on’ kits for tanks, which would cover the<br />
turret <strong>and</strong> the forward part <strong>of</strong> the hull. It was important to show that the explosive<br />
layer in the s<strong>and</strong>wich would not be initiated by any weapon other than the<br />
high-velocity jet <strong>of</strong> a shaped charge. The kits finally took the form <strong>of</strong> ‘blocks’ or<br />
‘tiles’ that could be fixed to the external surfaces, <strong>and</strong> which, in total, did not<br />
add more than 100 kg to the weight <strong>of</strong> the tank. Reactive armour first appeared<br />
on the battlefield in 1982, <strong>and</strong> one <strong>of</strong> the first unclassified accounts <strong>of</strong> its<br />
development history was given by Vered [7.72] in 1987.