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Message no. 1
From: David Buehrer <dbuehrer@******.CARL.ORG>
Subject: Explosives question
Date: Tue, 10 Nov 1998 11:36:27 -0700
How much energy from an explosion can be focused by shaping the
explosive? 50%? 75%? 90%?

-David B.
--
"Earn what you have been given."
--
email: dbuehrer@******.carl.org
http://www.geocities.com/TimesSquare/1068/homepage.htm
Message no. 2
From: Gurth <gurth@******.NL>
Subject: Re: Explosives question
Date: Wed, 11 Nov 1998 13:08:37 +0100
According to David Buehrer, at 11:36 on 10 Nov 98, the word on the street was...

> How much energy from an explosion can be focused by shaping the
> explosive? 50%? 75%? 90%?

Depends on how you're shaping it and what you're trying to penetrate or
cut with the charge. If you want to make a nice hole in something, your
best option is to shape the explosive over a cone-shaped liner. This liner
gets deformed by the explosion and pushed through the material; the
penetration depth depends on many factors, though -- material used for the
cone, material being cut, stand-of distance, cone diameter, and more. For
optimum penetration, I suggest salvaging a HEAT warhead from a missile or
gun :)

I'm not sure how effective it would be to just make a cone-shaped hole in
the bottom of an explosive charge (without using a liner), but my guess is
effectiveness would be a lot less than with even a rudimentary liner.

--
Gurth@******.nl - http://www.xs4all.nl/~gurth/index.html
He likes to sleep. Sometimes he has good dreams.
-> NERPS Project Leader * ShadowRN GridSec * Unofficial Shadowrun Guru <-
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Incubated into the First Church of the Sqooshy Ball, 21-05-1998
Message no. 3
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Re: Explosives question
Date: Thu, 12 Nov 1998 12:18:37 -0800
>How much energy from an explosion can be focused by shaping the
>explosive? 50%? 75%? 90%?

An explosion in the context of modern explosives occurs as a rapid
oxydation of oxygen-deficient and oxygen-rich (fuel) compounds which
deflagrate or detonate produce volumes of gas and a release of heat.

The shock front of an explosion will preferentially take the easiest path.

With proper cofferdamning and tamping, 100% of the explosive blast can be
focussed in the desired direction. Note that this may require a lot of
material, depending upon the energy and brisance of the explosives being
used.

If the tamping is not done correctly, a fractional portion (or whole
shebang, if things are really cocked) of the blast may vent out of the
weakened or incorrectly tamped area. This is why explosives experts are
very, very careful and reknowned for their attention to detail and
meticulousness.

The Munroe effect (named after the discoverer James Munroe), or shaped
charge effect, results in forming the explosives into an inverted cone and
lining it with a metal (typically copper). This results in a focussed
stream of plasma (though recent research suggests solid particles in a
colloidal suspension) with a velocity far higher than the detonation
velocity of the explosive.

Since the efficiency of an explosive is related to its diameter (for
various reasons too long to go into), shaped charges are usually classed by
how many diameters they penetrate. A decent shaped charge will penetrate 7
to 10 times its diameter in rolled homogenous steel.

Hope that answers the question.

>-David B.

--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
Message no. 4
From: The Bookworm <Thomas.M.Price@*******.EDU>
Subject: Re: Explosives question
Date: Thu, 12 Nov 1998 16:30:18 -0600
On Thu, 12 Nov 1998, Adam Getchell wrote:

> With proper cofferdamning and tamping, 100% of the explosive blast can be
> focussed in the desired direction. Note that this may require a lot of
> material, depending upon the energy and brisance of the explosives being
> used.

Think BIG METAL CASE. You need something STRONGER than the wall if you
want ALL of the explosive force from your breaching charge to go THROUGH
that wall. Usualy you just try to get the highest percentage that is
practical (IE you can carry the explosive charge and its tampering
material without a forklift:)).

> If the tamping is not done correctly, a fractional portion (or whole
> shebang, if things are really cocked) of the blast may vent out of the
> weakened or incorrectly tamped area. This is why explosives experts are
> very, very careful and reknowned for their attention to detail and
> meticulousness.

They are also know for using a *little* extra HE if they are not sure of
the effectiveness of their tamping and the job HAS to be done right the
first time. "When in doubt double the amount of Explosives" :)

> The Munroe effect (named after the discoverer James Munroe), or shaped
> charge effect, results in forming the explosives into an inverted cone and
> lining it with a metal (typically copper). This results in a focussed
> stream of plasma (though recent research suggests solid particles in a
> colloidal suspension) with a velocity far higher than the detonation
> velocity of the explosive.

IF i recall correctly Monroe discovered the effect when he was using some
explosives that came with the manufacturers name/logo impressed into the
explosive block. The mirror image was cut into his metal tamping material
that was facing the impression.

Also if you want to cut a line in your surface instead of a deep hole you
can make a slightly different charge. You mold your HE into a form that
sort of looks like an angle iron and add a liner as in the conical shaped
charge. The force is concentrated on a vector that bisects the acute angle
of the crosssection. Since you are only combining force vectors in 2
dimentions instead of 3 your efficiency is not as great but you get a nice
long cut instead of a small deep hole. Hmm this needs a diagram

ASCI Diagram of a Ribbon Shape Charge

^
/^\
//^\\
///^\\\ <--- Horrible ASCII drawing of HE cross section
////|\\\\
//// | \\\\
//// | \\\\
//// | \\\\
-------|-------------- <--surface to be cut
-------|--------------
|
| <-direction of force
V


I hope that helps anyone that got confused and that it didnt confuse
anyone else. :)


Thomas Price
aka The Bookworm
thomas.m.price@*******.edu
Message no. 5
From: Mike Bobroff <Airwasp@***.COM>
Subject: Re: Explosives question
Date: Fri, 13 Nov 1998 15:33:03 EST
In a message dated 11/12/98 3:16:09 PM US Eastern Standard Time,
acgetchell@*******.EDU writes:

> >How much energy from an explosion can be focused by shaping the
> >explosive? 50%? 75%? 90%?
>
> An explosion in the context of modern explosives occurs as a rapid
> oxydation of oxygen-deficient and oxygen-rich (fuel) compounds which
> deflagrate or detonate produce volumes of gas and a release of heat.
>
> The shock front of an explosion will preferentially take the easiest path.
>
Okay, I may be coming in right in the middle of this thread, but here goes
anyway ...

On a show called Spytech which I saw a few months ago, a terrorist group used
a shape charge to hurl a chunk of metal into a car using a laser as a
detonator trigger (the car passes through the laser beam which then activates
the bomb and *boom*).

According to the demolition expert they had, 60% (IIRC) of the force of the
explosion went in the direction of the plate (and blowing the car to kingdom
come.

As for being able to get 100% of the force of a blast in a certain direction,
I would have to say -NO-. And the only way to be able to pull off something
like that the explosive needs to be wrapped almost all of the way around
itself by something the calibre of naval armor (bulwark).

-Mike
Message no. 6
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Re: Explosives question
Date: Tue, 17 Nov 1998 12:39:02 -0800
>As for being able to get 100% of the force of a blast in a certain direction,
>I would have to say -NO-. And the only way to be able to pull off something
>like that the explosive needs to be wrapped almost all of the way around
>itself by something the calibre of naval armor (bulwark).

Some few years ago back in Berkeley a tanker truck got into an accident in
Highway 22 tunnel: the resulting explosion killed everyone in the tunnel.

And no, you don't have to tamp explosives with armor. Many experts use
factory dust. The hardness of the tamping isn't the issue, most
high-brisant explosives will shatter it anyways.

The issue is conservation of momentum: with enough mass, the rapidly
expanding volumes of gas generated by the deflagration/detonation will
automatically, thermodynamically seek the minimum energy state; that is,
the easiest path to travel. Detonations and shock wave front
formation/propagation occur on a very short timescale: deflagration to
detonation transfer itself occurs because of the inertia of an *air* column
pushes the pressure wave into a shock front.

The inertia of materials is much greater, and a detonation will avoid it
whenever an easier path exists. A properly tamped charge will provide that
pathway in an expected direction.

The issue is more complicated than this, of course. Physicists usually
solve these sorts of problems with hydrodynamics code: mass solution of
Poisson's equation and various numerical anaylsis predictor-corrector
algorithms, such as Runge-Kutta or Moultons-Bashforth.

>-Mike

--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu

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