shaped charges
John Johnson
From wolf...@expert.cc.purdue.edu (John Johnson)
[begin quote]
Are there any shaped charges that use depleated uranium cones instead of
steel or iron?
I would tend to think that this would be a better material for breaching
armour then just plain steel (ie SABOT ).
[end quote]
I was under the impression that SABOT rounds in the US used depleted
uranium penetrators, not steel. I have also heard of tungsten carbide
penetrators, but I don't know much about them. The depleted uranium
penetrators (incedentally, the most expensive ones around) are, as
far as I know, about as good a round as tanks get.
Disclaimer, this information is somewhat out of date, if there is newer,
better, shinier information on this subject, I would love to hear it.
Wolfling!!!
George Swan
From gs...@io.org (George Swan)
In article <D5to8...@ranger.daytonoh.attgis.com>,
John Johnson <wolf...@expert.cc.purdue.edu> wrote:
>I was under the impression that SABOT rounds in the US used depleted
>uranium penetrators, not steel. I have also heard of tungsten carbide
>penetrators, but I don't know much about them. The depleted uranium
>penetrators (incedentally, the most expensive ones around) are, as
>far as I know, about as good a round as tanks get.
>Disclaimer, this information is somewhat out of date, if there is newer,
>better, shinier information on this subject, I would love to hear it.
>Wolfling!!!
I think John missed something. The original poster was asking
about _shaped_charges_. The charge in the shaped charge turns
the metal into a high speed jet of molten metal. The shaped charge
does not explode all at once. The wave front of the explosion
sweeps through the charge, and basically focusses the molten
metal into a high speed jet capable of melting a hole in the
armour, and spraying the inside with molten metal.
>From wolf...@expert.cc.purdue.edu (John Johnson)
>[begin quote]
>Are there any shaped charges that use depleated uranium cones instead of
>steel or iron?
>I would tend to think that this would be a better material for breaching
>armour then just plain steel (ie SABOT ).
>[end quote]
Since it is important that the metal core of the shape charge
melt quickly they probably chose copper over steel and depleted
uranium because it is a much better conductor of heat. Gold
conducts heat even better than copper, so solid
gold would also have been a good choice 8-).
Jim Calpin
From Jim Calpin <cal...@mitre.org>
> I think John missed something. The original poster was asking
> about _shaped_charges_. The charge in the shaped charge turns
> the metal into a high speed jet of molten metal. The shaped charge
> does not explode all at once. The wave front of the explosion
> sweeps through the charge, and basically focusses the molten
> metal into a high speed jet capable of melting a hole in the
> armour, and spraying the inside with molten metal.
There is a great deal of confusion concerning the "Hows" and the "Whys"
of armor penetration, particularly with respect to shaped charges. The
reader is therefore referred to the two best works on the subject:
Giorgio Ferrari. "The Hows and Whys of Armor Penetration" Military
Technology, October 1988, p. 81-96. (Simply the best short summary
you'll ever find of how both shaped charges and KE penetrators work
their magic.)
Garret Birkhoff, et al. "Explosives With Lined Cavities". Journal of
Applied Physics. June 1948, p. 563-582. (The "original" treatise on
shaped charges. The first half qualitative and easily understood; the
second half gives you an outstanding theoretical basis for understanding
the math behind these damn things.)
Having said that, I will correct a basic misperception stated earlier and
endlessly propagated - the liner in a shaped charge does *not* melt! Ferrari
sums it up best:
"The kinetic energy imparted to the liner's metal (by the explosive wave-
front) is greater by several orders of magnitude than the level required to
to totally deform it. A body which has been charged with enough energy
as to disintegrate itself is virtually no longer coherent, and will
behave like an incoherent body, i.e. a fluid. This suggests to many that
the liner "melts". No, it does not melt, but it moves at such a high speed
that it can change it's shape like a fluid, if forced to do so."
Later, Ferrari closes the book on this controversey by stating "To the contrary
of what is unfortunately too often said and written, neither the jet nor
the slug are "pulverised", "melted", or "vaporised"; they are quite
solid, but can behave like liquids when attempts are made to interfere
with their motion. Birkhoff, et al have demonstrated that with quite a
conclusive experiment. Several shaped charge liners were sawn up into
pieces, and these were then carefully re-assembled and kept in place. When
the charges were detonated towards a deep water tank, it was regularly
possible to recover the slug - subdivided into as many pieces as the
liner had been cut into. This clearly shows that what is mistakenly
described as "melted" is actually not even melted enough to weld its
pieces back together."
> Since it is important that the metal core of the shape charge
> melt quickly they probably chose copper over steel and depleted
> uranium because it is a much better conductor of heat. Gold
> conducts heat even better than copper, so solid
> gold would also have been a good choice 8-).
Again, melting doesn't have anything to do with it. Please track down
the cited articles - they present a *wealth* of knowledge.
Daniel Hilliker
From ax...@freenet.carleton.ca (Daniel Hilliker)
Hi There...
In a previous posting, George Swan (gs...@io.org) writes:
> I think John missed something. The original poster was asking
> about _shaped_charges_. The charge in the shaped charge turns
> the metal into a high speed jet of molten metal. The shaped charge
> does not explode all at once. The wave front of the explosion
> sweeps through the charge, and basically focusses the molten
> metal into a high speed jet capable of melting a hole in the
> armour, and spraying the inside with molten metal.
True, except for a common mis-conception. The liner material in a
shaped charge (or an efp for that matter) is at no time molten. The whole
process is one of material flowing at extreme stress levels and extremely
high strain rates. The mechanism for defeating armour is this 'jet'
actually displacing and eroding material as it advances. Think of a jet
of high pressure water against a wall of plasticine. It makes a hole by
actually flowing the material aside. I saw some stuff during graduate
studies where the temperatures inside the jet were measured at about 450C,
well below the melting temperature of most metals.
> Since it is important that the metal core of the shape charge
> melt quickly they probably chose copper over steel and depleted
> uranium because it is a much better conductor of heat. Gold
> conducts heat even better than copper, so solid
> gold would also have been a good choice 8-).
About the melting, see above. About the gold, it's actually a very
good liner material. One of the main properties in a liner material is
ductility. Gold is about as ductile as it gets. One of our professors
discussed experiments where gold liners had been used with excellent
results. Mind you, would you want to be in charge of a unit where all
your weapons were in danger of being cannibalized?
--
Dan Hilliker - Engineers rule the World -
ax...@freenet.carleton.ca Per Ardua Ad Astra
<my opinions only, not my employer's>
Hank Meyer
From hcm...@uci.edu (Hank Meyer)
In article <D61xz...@ranger.daytonoh.attgis.com>, gs...@io.org (George
Swan) wrote:
> ...and basically focusses the molten metal into a high speed jet capable
of melting a hole in the armour...>
Common misconception...the molten stream does not "melt" thru the armor,
but acts as a kinetic penetrator and forces it way thru (just like a
long-rod penetrator).
--
Jim Calpin
From Jim Calpin <cal...@mitre.org>
> > ...and basically focusses the molten metal into a high speed jet capable
> of melting a hole in the armour...>
>
> Common misconception...the molten stream does not "melt" thru the armor,
> but acts as a kinetic penetrator and forces it way thru (just like a
> long-rod penetrator).
>
Actually, the mechanics of armor penetration are quite different for shaped
charges vs KE penetrators. The key variable in question is the velocity
of the penetrator - whether it is hypersonic or hyposonic with respect to
the material being penetrated (don't forget - the speed of sound in solids
is *much* higher than in air). Shaped charge - hypersonic. KE - hyposonic (the
important point being that the tip of the projectile transmits shock back from
the point of impact, deforming the projectile. No such transmission w/shaped
charges.)
The interaction between shaped charge jets
(the *real* penetrating power in a shaped charge) and armor can be treated
as a fluid-fluid interaction; KE penetration must be treated as a mechanical
interaction, thereby screwing up all the pretty equations one gets with
fluid-fluid interactions.
.and yes, for you nit-picky physicists out there, the ablation mode of
penetration for shaped charges is similar to the ablation mode for KE
penetrators (fluid-fluid), but the KE mode is no where near as mathematically
"pure" as the shaped charge mode.
Kelvin Chua
From bc73...@omega.ntu.ac.sg (Kelvin Chua)
In article <D66C5...@ranger.daytonoh.attgis.com>, hcm...@uci.edu (Hank Meyer) writes:
]> From hcm...@uci.edu (Hank Meyer)
>From this documentary I saw on shaped charges, I gathered that the molten
stream is at such high pressure and velocity, the armour behaves as if it were
a fluid even tho' it may still be solid; i.e the solid armour "flows" away from
the penetrating stream.
Bertil Jonell
From d9be...@dtek.chalmers.se (Bertil Jonell)
>From wolf...@expert.cc.purdue.edu (John Johnson)
>Are there any shaped charges that use depleated uranium cones instead of
>steel or iron?
Not to my knowledge (copper is the common metal btw, although Ogorkiewich
mentions tantalum as a superior choice in one of his books)
>I would tend to think that this would be a better material for breaching
>armour then just plain steel (ie SABOT ).
The high density of the DU would indeed give it an advantage (since the
quote of the densities of the jet material and the armour material appears
in the equation) and it's pyrophoric properties would create some spectacular
behind-armour effects.
I don't know why nobody's using it, perhaps it has other disadvantages
like brittleness?
-bertil-
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