Subject: Re: Shaped charges?
From: glhurst@onr.com (Gerald L. Hurst)
Date: Oct 30 1996
Newsgroups: alt.engr.explosives

In article <556g4t$ge7@news1.t1.usa.pipeline.com>,
hummas@usa.pipeline.com(Bill M) says:

>I might also add, for those home experimenters out there, that, 
>along with the forward jet of material, there is also a backward 
>moving mass of material (how much depends on the configuration 
>of your explosive and container). Considerations which make 
>shaped charges difficult for kitchen chemists are the uniformity 
>(both in density and quality) of the explosive and of the  
>detonation. 
 
If you are referring to the slug or "carrot" which is formed along with
the particulate jet, the former also moves forward but only at a fraction
of the velocity of the jet.  The slug, which is often shaped like a 
carrot, can sometimes be found nestling in the (steel) target hole left 
by the jet.

The only part of the assembly that actually moves backward is a portion
of the gas cloud.  Momentum conservation dictates that the gas blast
to the rear must be greater than forward.

The velocity of the jet increases and its mass decreases as the cone
angle is decreased until it approaches twice the velocity of the 
explosive and zero mass(in theory).  In practice, the optimal cone 
angle for good penetration depth is usually about 60 degrees with a 
stand-off of about 2.5-3.5 diameters.  These values are a compromise 
for penetration because greater stand-off would give even better 
penetration if the charge and cone were perfect. With most real 
charges the jet is imperfectly focused and threfore spreads and 
becomes less effective over large distances.

A pound of C-4 in even a field packed shaped charge will pierce 7" of
steel.  This would be considered poor performance per unit size  
compared to the penetration the oilfield casing perforation guys get 
with their precision pressed RDX and HMX  charges combined with equally 
precise special metal linings.

Jerry (Ico)

From: Jim Calpin <calpinj@mitre.org>
Subject: Re: Solid gold shaped charges (was Re: shaped charges)
Newsgroups: sci.military
Organization: The MITRE Corporation
Date: Tue, 28 Mar 1995 23:34:38 GMT

> 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.