From: William Logan Lee <bill@extro.ucc.su.oz.au>
Subject: Re: Rivet popping
Organization: /etc/organization
Date: Sun, 22 Nov 1992 16:22:32 GMT


From William Logan Lee <bill@extro.ucc.su.oz.au>

In article <BxICpE.Kw0@law7.DaytonOH.NCR.COM> ecrjbruce@economics.adelaide.edu.au writes:
>Not exactly an answer but along the same lines.  One of the early ways to take
>out a tank was to fire a shell against it that hasn't got a snowballs chance in
>hell of killing it.  This would often cause molten globs of metal to spray
>around inside the tank killing or wounding the crew (would you perform at your
>best with molten metal over you?) and generally causing havoc.

Unfortunately, they are not molten globs of metal, but anything that is on
the inside of the armour plate (including chunks of the armour itself).
What happens is that after the explosion, a compression waves travels out
from the point of the explosion through the armour.  Then it reaches the
other side and anything on that side in contact with the armour receives
that compression wave.  Can you remember seeing a physics demonstration
called "Newton's Balls" with a row of suspended ball bearings being struck
on one end of the row.  The end ball flies off, with very little observed
movement of the intervening balls.  This is the principle of the HEP (HESH)
ammunition.  Paint, screws, fittings all come off the inside of the armour
and zip around the inside of the armoured compartment.  What's more, when
the compression wave reaches the inside of the armour, it rebounds as a
tension wave.  If the armour does not have required _tensile_ strength, it
can fail, and a scab of armour detatches itself from the rest of the armour.
This is travelling at a (relatively) low velocity (compared to the velocity
of the detonation wave) and bounces around the inside of the armour,
wreaking havok on anything in its path.
 
>Later model tanks certainly fixed this problem, although I can't give you a
>date on this.  As late as WW2 this was still a reasonably common occurence.

I had not heard of this problem being fixed, but the increased thickness,
and quality of armour would have contributed.  Eliminating bolt heads on
the inside of the armour, as well as other fittings would also have
contributed.  Wet ammunition storage as introduced into late model Sherman
tanks assisted in containing and cooling spall fragments from non-
penetrating hits.  A non-penetrating hit from an armour piercing round
can cause the same effects as a HESH round.
I did read of a tanker's recollections from WW2 where he described having
to sandpaper the inside of the turret to remove loose flakes  of paint,
then repainting the inside so as to reduce the danger from non-penetrating
hits.
After WW2, woven Kevlar lining has been used to reduce this still-present
danger, as well as to try to limit the effects of a penetrating hit.

>It also forms the basis of the theory behind HESH (high explosive squash head)
>where an amount of HE is pressed up against a tank by the force of the round
>then it explodes and sends metal fragments and molten globules throughout the
>interior to take out the crew.  From what I have been told the results are not
>a pretty sight.

Bill Lee

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