circular shape charges

[pyromaniac_guy]

I have seen linear shape charges that have been 'bent' into a circle for cutting pipe, cable ect. Obviously in cases such as this the jet forms a ring or decresing diameter as it propagates. Is it logical to assume that this decreasing diameter of the jet interfears with the production and propagation of the jet? Does anyone have any data on the efficency of such devices? If one wanted to cut a large cable or pipe with the lowest mass (ie easiest to emplace) charge, would it possibly be more logical to use a series of normal LSC's that are displaced from each other down the length of the cable slightly? (ie forming a 'spiral' if you will of short segments of LSC)

[mr.evil]

Maybe not what you are looking for, but take a look at this:http://www.geocities.com/mail2xtreme/ShapedCharges/ page.

Also, i suggest you read some shaped charge files, like improvised shaped charges(what a logical name :rolleyes: )

[pyromaniac_guy]

Mr evil,
Thanks for your response, but I'm not looking for anything improvised, I'm looking for maximum theoretical performace, ie assume i dont mind using osmium as a liner and HNIW as a explosive filler. I am simply interested in the theoretical best efficency for severing either a hollow tube and or a thick cable (ie cable made up of many strands of wire) seperatly or in conjunction...

I did a quick search through the archives and google, didnt find anything relavent

[Chris Shiherlis]

There is no interference of the jet when the diameter decreases. That would the case when the jet would be produced instantaniously over all the length of LSC. But a jet is produced by the shockwave progessing through the LSC: so it is first produced at the beginning and the jet forming is moving towards to the end with the speed of the shockwave. So clearly the jet doesn't collide/interfere at any point.
A jet just starts cutting the pipe at one point and gradually ( :) )moving/cutting to the other end.

<small>[ August 11, 2002, 10:31 AM: Message edited by: Chris Shiherlis ]</small>

[kingspaz]

nice to see you back chris. i like the new attitude <img border="0" title="" alt="[Wink]" src="wink.gif" />

[Chris Shiherlis]

Yeah, resurrected from the dead, new and improved.
I hoped the highly regarded and very much underestimated :) mister Wantsomfet would rehabilitate me, which would not only make my return possible with a clean reputation and the respect I deserve :) , but more importantly it would also get me Pamela willing to fulfill my every wish.

But sadly Mr. Wantsomfet never replied so I had to take the matters into my own hands :) .
So here I am. I will just treat you sensitive guys with a little more respect. And I will never bring that topic back up. And "that topic" is, of course, the foolish idea that flashpowder... :rolleyes:

Note the fact that I use a lot of irony, so it's not my old attitude surfacing, it's....humour...bordering dangerously close to bitchy sarcasm.

+++++++++

<img border="0" title="" alt="[Wink]" src="wink.gif" />

NBK

<small>[ August 18, 2002, 10:15 AM: Message edited by: nbk2000 ]</small>

[pyromaniac_guy]

chris, that takes for granted that the velocity of the jet is equal to or greater than that of the Vdet of the explosive... while that may be true for the leading edge (if you will), it isnt going to be the case for the whole thing....

BTW, how come we cant use parenthasis in the forum any more???

+++++++++++++++++++++++++++++++++++++++++++++++++
They work just fine. NBK.

<small>[ August 15, 2002, 09:59 PM: Message edited by: nbk2000 ]</small>

[Chris Shiherlis]

Well pyromaniac, that's not an assumption, that is just a fact. And that's basically the principal of a shaped charge: to concentrate the explosive energy by the V-shape and subsequently "liquifying" the liner and squirting it forward in the shape of a sharp needle with great speed which is always much greater than the VoD of the explosive charge. I believe the tip of the jet can reach a velocity that's more than twice the velocity of the explosive used. I don't have my papers at hand but I believe in some cases the velocity of the tip reaches up to 20 km/s.

[kingspaz]

hey, about the velocity of the jet tip, look at the shape of the cone before detonation and at the jets maximum duration (just before it desintergrates). the tip is MUCH further away from the base of the cone formed than before detonation. for this to happen the tip must have accelerated and achieved a higher velocity than the base of the cone otherwise the shape would be the sam as before detonation only opposite. does anybody else know what i'm trying to put forward as proof of the tip having higher velocity?

[Microtek]

Yes Kingspaz I get what you're saying but even if this wasn't the case ( that the jet tip is faster than the VOD ), the segments of the LSC still wouldn't interfere with each other ( except if the jet shot through the cable and hit the LSC on the other side ). If you divide the LSC into small segments ( only conceptual division ) and consider the propagation of the initiation from the detonator, then segment A will be initiated before segment B if A lies closer to the detonator. As the two segments are identical, the jet formation and speed will be identical ( in the ideal case ). Therefore the etire jet will be delayed by a period equal to dS/V where dS is the characteristic distance for the segments and V is the actual detonation velocity.

[pyromaniac_guy]

Chris,
the tip of the jet does have a speed higher than the Vdet of the explosive [although i have never hurd of jet tips on the order of what you are talking about... for example, the first book i pick up, urbanski's introduction to the technology of explosives quotes a tip speed of 6 to 10km/s so i doubt tip speed is &gt;2x Vdet, unless you propose urbanski was refering to a shape charge that used 2000 m/sec explosives], and although the tip carries a good part of the kinetic energy of the jet, it does not contain ALL of the energy, nor even most of it. If the slower portions of the jet start to interfear with each other then the efficency of the shape charge to cut pipe will be reduced...

[xoo1246]

Two images:
<a href="http://w1.478.telia.com/~u47802930/JetConfiguration01.jpg" target="_blank">http://w1.478.telia.com/~u47802930/JetConfiguration01.jpg</a>
<a href="http://w1.478.telia.com/~u47802930/JetConfiguration02.jpg" target="_blank">http://w1.478.telia.com/~u47802930/JetConfiguration02.jpg</a>

[nbk2000]

In a patent issued to General Dynamics for the Javelin Missile warhead, it states that the maximum velocity for a shaped charge liner is determined by the velocity of sound in the material which the liner is made of.

Thus, if the speed of sound for copper is 8,000 m/s (I don't have the exact number in front of me so I'm just going to use an arbitrary number instead) than the tip of the jet CANNOT be faster than 8,000 m/s

It also states that the the lighter the liner, the more efficient penetration you get for a given amount of explosive. With proper ratios, over 85% of the liner weight will be over the 2,000 m/s minimum velocity required for penetration. Whereas, typical SC efficiency is 15%.

[pyromaniac_guy]

the speed of sound in copper is only 3353m/s and for aluminum 5150 m/s
common speeds listed for shaped charges are on the order of 8 to 10km/s, so either there must be something wrong with the patent NBK is refering to, or something more exotic is being used as a liner

[nbk2000]

The speed of sound increases as the temperature of the material is increased.

For instance, Air, at 22*C, has a mach speed of 344.4 m/s. But, increase the temp to 2527*C, and the mach speed increases to 983 m/s.

Now, when a liner is inverted in a few microseconds and liquifies under the intense heat and pressure, how hot is it? And what's the mach speed of that material at that temperature?

If we assumed a tripling of velocity at the same temp as the air example, than 3353 m/s becomes more than 9,000 m/s, within the established values.

Aaahhhhh...now do you see? There's nothing wrong with the patent after all. They just left out some of the infamous "known to those skilled in the arts" details. :)

[Chris Shiherlis]

Pyromaniac, I don't know where I got that 20 km/s for the jet tip velocity. Seems my memory isn't that reliable anymore (too many beers?). I better get my papers.
And NBK, like the edit, thanks for being so tolerant and open minded. It looks like I am just pushing it to the edge of bitching sarcasm, but I ain't, it's just my clumsy way of communicating.

---------
"Pamela come on, a deal is a deal, I prooved them it detonated so bend over and start......."

<small>[ August 23, 2002, 05:51 PM: Message edited by: Chris Shiherlis ]</small>

[Chris Shiherlis]

Tried to find some sites that could back me up and proove I didn't make a mistake by saying the jet tip moves at twice the speed of the VoD and around 20 km/s but I couldn't find them. The lamest excuse would be saying I meant feet per second not km/s :) .
But looking for 'shaped charge jet velocity' I found some nice sites anyway:
<a href="http://www.logwell.com/tech/shot/perforator_life_cycle.html" target="_blank">www.logwell.com/tech/shot/perforator_life_cycle.html</a>

<a href="http://thor.prohosting.com/~normkay/noframes/no_reactive.html" target="_blank">http://thor.prohosting.com/~normkay/noframes/no_reactive.html</a>

<a href="http://catalogue.pwallen.co.uk/Catalogue/EO/495/11148.html" target="_blank">http://catalogue.pwallen.co.uk/Catalogue/EO/495/11148.html</a>

And sorry for the other post, stupid mistake.

<small>[ August 24, 2002, 11:09 AM: Message edited by: Chris Shiherlis ]</small>

[darkdontay]

<a href="http://www.security.pwallen.co.uk/Catalogue/EO/495/11148.html" target="_blank">http://www.security.pwallen.co.uk/Catalogue/EO/495/11148.html</a>

Here you go I belive this is what you where wanting in your last link.