SckizoBoy said:
OK... despite being a chemist and having a good grounding in physics, this problem still bothers me...
How do High-Explosive Anti-Tank shells do what they do? I mean, any better than APC, APCBC or APHE rounds...? And how does spaced armour reduce its effectiveness?
Better yet, can anyone explain the Monroe effect? I've looked it up, I've had people explain it to me, but I'm just not getting something there...
/the random
I'd point out that HEAT rockets aren't infallible - shells relying on normal kientics are actually better in many utilities.
With a normal penetrator, whether a bullet, a crossbow bolt, or an APDS round, the penetrative power is generated from the propelling force at the point of firing. This accelerates the projectile, which then mashes through stuff, generally to newton's depth approximation.
With a normal explosive shell, the aim is to either use enough explosive to distort to destroy the armour (inefficient) or to reinforce the front of the shell enough that it mostly penetrates the armour before fully exploding on the other side.
HEAT and HESH rounds don't rely on this, and are able to give
similar but not necessarily better anti-tank capability against steel armour. It's more flexible because it can be mounted on delivery systems which don't go fast enough to penetrate by pure kinetic energy or explosive payload alone (rockets, low velocity guns, recoiless rifles, RPGs).
All the delivery system has to do is get the warhead to the armour, rather than actually getting through it as well, because the warhead does that.
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With HEAT rounds, the charge is supposed to detonate on the surface, then rely on the aforementioned Munroe effect to
create a jet of metal as a penetrator. It's kind of 'a bullet firing a bullet'.
It's important to mention that the jet of metal doesn't get hot enough to melt through the armour, it's pure kinetics.
Looking at this image, it's surprisingly intuitive why that jet forms as it does. The liner is accelerated most in the middle, and less as you move towards the edges. I guess this can be justified by imagining the explosive at the edge of the liner as volume expansion from series of point objects.
Momentum is conserved because what's left of the case in that diagram, the majority of the explosive, and whatever else is left of the rocket will be dispersing, mostly to the left in that frame of reference.
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HESH rounds kind of use the armour it's trying to defeat as the penetrator, though usually with a less refined end result in mind! Instead of getting a pellet as in the picture, you get shards of armour spalling from the other side.
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Spaced armour helps with both of these types because it stops the shaped charge from deploying properly. It forms away from the face of the armour, and then (hopefully) doesn't penetrate as far or at all.
With HEAT this is because the jet will disperse before penetrating both layers, with HESH it's because only the top layer of armour will be spalled, and the fragments don't have enough energy to penetrate the second layer of armour.
Has that clarified things, or made them worse?!
