Armour Piercing 201 (Advanced Ceramics)

From: "Katie Lauren Lucas" <katie@fysh.org>

> Quoting Edward Lipsett <translation@intercomltd.com>:

Not as such, I'm afraid.

See http://yarchive.net/explosives/shaped_charge.html
for some good books on the subject.

The situation is rather more complex: I'll simplify it as much as I can, at
the
risk of innacuracy and omission of important stuff ( such as HEP/HESH).

There are 2 good ways of penetrating thick armour: fire a pencil-like
projectile
at insanely high speeds ( about 2km/sec )
( see http://www.army-technology.com/contractors/ammunition/apfsds.htm )
or detonate a shaped charge of explosive very close to the armour that
explosively forms a slug of metal (usually copper) and projects this slug at
even more insane
velocities, (5 km/sec +). That is, "Armour Piercing (Fin Stabilised)
Discarding Sabot" and "High Explosive Anti=Tank", APFSDS and HEAT
respectively.

No, a HEAT round doesn't "burn through" the armour. And it's not molten. It's
solid. BUT at the speeds involved, for penetration, both situations are best
modelled as bursts of compressible fluid hitting another compressible fluid.
See http://www.logwell.com/tech/shot/perforator_life_cycle.html for a
nice animation of how a hollow charge forms a rodlike projectile.

When a cylinder of stuff hits a chunk of armour at these high speeds, the
cylinder is compressed, and ablates away at the point of impact. The armour
also ablates away,
it "sprays". But the cylinder, be it long-rod-penetrator or molten
copper slug, has backup, which gets fed into the point of impact, moving it
through the armour till
finally a much-diminished remnant gets through the last bit of armour.
The pressure is then off, and the cylinder explosively dissasembles due to
pressure release.
To a bystander without a superfast X-ray camera, there's a flash outside
the tank, a lot of hot gas and splinters jetting away from the point of
impact, and simultaneously an explosion inside the target.

OK, now on to ceramics:

Ceramic/Layered/Composite armour is composed of materials with different
densities. A cylinder penetrating them has shockwaves set up in it as it hits
the different densities, so some of the cylinder is lightly compressed, the
next bit heavily compressed, the next bit lightly and so on. This causes the
long cylinder to break apart
(actually explosively disassemble - it explodes) before it goes very
far, the point of penetration no longer has backup, and instead of a neat
hole, you get a shallow divot.

For projectiles at lower velocities, completely different mechanisms are
involved,

Quoting Alan and Carmel Brain <aebrain@webone.com.au>:
> but that's another matter. Your "ceramic fragments and steel absorbs"

It's more for the pure penetrator cases - as soon as you start playing
with any of the more advanced rounds, things do get complicated...

{In the realm we were looking at armour types for, we're looking to defend
against sharp, high-impact objects - axes, notably. Splash isn't so much
of a problem as complete penetration. The other advantage to ceramics is that
the surfaces are easier to curve in multiple directions to help deflect
cutting tools and pincers. Which don't tend to be an issue with proper
armoured vehicles... oh, and ceramics don't melt. But then neither do many
metals at the
temperatures the flame-throwers are limited to...}

From: "Katie Lauren Lucas" <katie@fysh.org>

> Quoting Alan and Carmel Brain <aebrain@webone.com.au>:

Your "cermaic fragments and steel absorbs" reminds me of the "Plastic Armour"
of the dark days in 1940.

From: http://www.angelfire.com/art/enchanter/concrete.html

Ed Sackett writes:-
An interesting type of armor was developed to replace concrete. It was
code-named Plastic Armour (see? I'm not afraid to use a British
spelling) and consisted of several inches of asphalt poured hot into forms
built
around the vulnerable deck structures. It was backed with 3/16" mild
steel -
hardly what you'd call armor plate. The ingenuity lay in what was mixed into
the asphalt: clean, sharp, ¾" granite gravel, about 1 part to 2 parts of
asphalt. Once the mixture had set the forms were taken away, and this very
unlikely stuff proved quite effective at stopping machine gun bullets and even
20 mm shells.

It worked because the gravel tilted on impact, pivoting inside the asphalt
matrix and inducing keyholing by the bullet, which spent its kinetic energy
going sideways instead of straight in. The mild steel backing flexed inward,
spreading the shock over a wide area and thus preventing penetration. When we
recall that some German aircraft MGs fired ammo the equivalent of proof loads,
that's an impressive level of protection. 20 mm shells were similarly
defeated. Strafing attacks suddenly became less lethal, and Plastic Armour was
in great demand by bridge and deck crews.

http://webhome.idirect.com/~jproc/radiostor/000818b.jpg shows plastic
armour around the gun positions of the Liberty Ship SS John Brown.

Funnily enough, although it would stop high velocity rounds, you could put a
nail through it.

Quoting Alan and Carmel Brain <aebrain@webone.com.au>:
> Your "cermaic fragments and steel absorbs" reminds me of the "Plastic

> It worked because the gravel tilted on impact, pivoting inside the

Cool. I'd not come across that before.

Learn new something every day...