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Author: Subject: Unconventional Shaped Charges
enhzflep
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[*] posted on 24-5-2006 at 20:45


Joeychemist,
I realise this isn't exactly what you asked for, but if given the time and inclination should allow you to calculate this for yourself...

If my memeory serves me corectly, you are doing pretty well to get 15% of the total energy expended in the explosion into doing any work on the target. (This may just be 15% of the energy goes into deforming the liner - I don't recall)

By knowing the size and volume of hole produced by a known quantity of a known explosive, you may begin to calculate some rather rough figures.

This however, will be filled with both precision errors (i.e is it 14%/15%/16% energy is usefull), in addition to the unknown quantity that represents the kinetic energy the jet still posseses at the point the plastic deformation (and hence penetration) stop.

As I say, would only be very rough, back-of-the-envelope type figures obtained here. However, depending on your use for such figures, this may be enough.

[Edited on 25-5-2006 by enhzflep]
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nitro-genes
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[*] posted on 26-5-2006 at 07:21


Quote:
Originally posted by Joeychemist
I'm looking for literature pertaining to kinetic energy of jet impact vs. work of plastic deformation of various target materials.

Any refs would be appreciated:)


Interesting :)

First, work has the same dimension as energy (joule), so what would be limiting in the tranfer of the energy from the jet to the target material?! Because of the huge pressures involved, both target and jet behave as a perfect liquid. So there is no frictional (heat) loss. Unfortunately this can't be true... If you would apply only this hydrodynamic approximation, the radial expansion at the tip region of the jet nears infinity! So there must be a lot of other factors involved here, which is obvious since target hardness does have an influence on the amount of deformation in the target caused by the jet...

This presentation describes some of the mathematics behind the energy rate change upon impact on the target which would be a good indication of the total work done on the target. Be prepared for some serious mathematics... :D

--> http://www.smithinst.ac.uk/Projects/PD/RA-QinetiQFortHalstead/FurtherReading/Presentation(AT2004)

Unfortunately, the kind of experimental data like you request may be very difficult to find, if even available at all...

I also wonder whether the kinetic energy of the jet is a good parameter to start with... Kinetic energy consists of mass and velocity. For example, there is a known optimum for the jet velocity and mass ratio in which the deepest penetration occurs. Although the question is if penetration equals work...
From my own experiments I have seen that the less penetration, the wider the diameter of the penetration hole becomes and visa versa. Because when the jet particulates in an early stage, which is the reason a home made SC does not penetrate very deep, the particles are no longer focused like in a continuous jet, and collide with the side of the wall, widening it. This is also demonstrated by the use of liners with a known assymetry in mass distribution. Overal can be seen that the penetration decreases as the "radial velocity" of the particles increases...

--> http://www.ciar.org/ttk/mbt/papers/symp_19/WM26_741.pdf

Therefore, I wouldn't be surpised if the hole volume (equals work?) is relatively constant within the same target material for liners with the same mass, but different shapes or assymetries...

As for any possible refs, you might check the "International Journal of Impact Engineering" I found a couple of refs that you might find interesting...

"A survey of shaped-charge jet penetration models."
William P. Walters*, W. J. Flis and P. C. Chou

International Journal of Impact Engineering, Volume 7, Issue 3, 1988, Pages 307-325

"Verification of the equation for radial crater growth by shaped charge jet penetration."
Manfred Held

International Journal of Impact Engineering, Volume 17, Issues 1-3, 1995, Pages 387-398

"Target strength effect on penetration by shaped charge jets"
W. A. Goocha, M. S. Burkinsa, W. P. Waltersa, A. A. Kozhushkob and A. B. Sinanib

International Journal of Impact Engineering, Volume 26 (2001) 243-24

[Edited on 26-5-2006 by nitro-genes]
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[*] posted on 27-5-2006 at 06:20


Oh, brother, your weren't kidding! That is some seriously indepth material.
I found something that was so close to what I have always wanted to explore that the pages are bookmarked forever! Damn good job!

It seems that air itself is a major determinate and that a vacume or even an alteration in gases, such as an argon field has a direct bearing on penitration & performance. But that is in a lab environment and from a practicle standpoint almost meaningless. For how could a vacume be maintained in a field situation? Still there is so much material in that journal that this thread could be fed for many years to come. -- Excellent stuff!

http://www.sciencedirect.com/science?_ob=IssueURL&_tocke...




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[*] posted on 28-5-2006 at 14:17


Thanks for the info on PiB, it worked even better than I had thought. I ended up with 90% PETN, 6% PiB and 4% motor oil, and it's even better than the sample I have of military plastique.
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[*] posted on 29-5-2006 at 03:06


Sounds good! :) What are the properties of this plastique, is it pliable like semtex, C4 or P4? Or more like a rubbery PBX?
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[*] posted on 29-5-2006 at 03:19


Haven't seen semtex, C4 or PBX, the only comparison is some military plastique of unknown origin. But it's fairly pliable, if you pull it apart it becomes quite "spongy" but it can be kneaded back with ease. After sitting for a while it gets fairly hard, but it softens up as you work with it. Density is around 1.4 when hand pressed into a mold.

I used bluetack as the source of PiB, it dissolved quite well in warm xylene (20g/100ml). After everything was in solution I let the filler settle out, decanted and precipitated with acetone. Yield was appr 12-13%.
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[*] posted on 29-5-2006 at 03:55


The "spongy" thing seems very familiar indeed. :) It is the result of the density and shape/surface area of the PETN crystals. It needs about 18% to fill all of the voids between them.
I wonder if there is a way to recrystalize PETN to get more dense crystals with a lower surface area. (spheres instead of the needles you get when recrystalized from acetone) Like with C4 this could increase workable density and thus peakpressure considerably...
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[*] posted on 30-5-2006 at 00:08


Have you tried recrystalizing from slowly cooled ethanol or even an acetone/ethanol mix?

If you can get your crystals into a roughly spherical shape then for maximum bulk density of your PETN powder, I'd seperate two different crystal sizes, maybe one four to five times the diameter of the other.

If these are mixed in the right proportions you should find that the smaller fills alot of the voids between the larger crystals.

All the info we need is hidden withing the vastness of federoff as I've stumbled across it in the past... REALLY should have made a note of the page thouigh whether all the effort of screening and recrystalizing is worth it just to get that soft pliable 90/10 plastique is debatable :)
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[*] posted on 30-5-2006 at 03:48


IIRC the optimum size distribution for spheres are 7:1, meaning that a sphere 1/7 of the size can fit in between uniformly packed spheres. But I doubt it's worth the effort since the increase in mass is quite insignificant.
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[*] posted on 30-5-2006 at 03:55


I see your point that theres not alot of difference in mass... between uniform spheres and a mix of two different sizes but the norm ISNT uniform spheres is it. Its more a random distribution of shapes and sizes.

I may be well off the mark but two specific sized spheres in the correct ratios must be a vast improvement in terms of bulk density over complete randomness of grain sizes?
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[*] posted on 30-5-2006 at 04:36


I have a suspicion that the most important thing is shape. Even rough spheres should pack a helluva lot better than irregular needles, and probably make it more plastic as well. Using multiple sizes might give further improvements, but I have a feeling it will be fairly insignificant.

But hey, I'd love to see you prove me wrong :-)
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[*] posted on 30-5-2006 at 06:19


Nearly equi-dimensional PETN crystals rather than the usual needle-like crystals can be obtained by slow cooling of a 40% soln of PETN in boiling EtOAc. (J. Tranchant, Ibid 117 & CA Ibid) (Edit: Was this what you had found also Frank?)

hmmm, ethylacetate can't be that hard to find, too bad though it isn't possible with regular acetone...

I could not find any other to-the-point papers about the recrystallization of PETN unfortunately, not that I would have acces to them anyway...

[Edited on 30-5-2006 by nitro-genes]
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[*] posted on 30-5-2006 at 10:28


For those who dont have access to mail order chemicals from laboratory supply companies ethyl acetate(ethanoate) is the major active ingredient in "gentle" acetone-free nail polish removers... suitable for use with acrylic false nails.

I know this because a few weeks ago I was at the pharmacy with my girlfriend and was helping her select an appropriate brand :)

EDIT:

Nitro... the info that I found in federoff was relating to C4 manufacture and IIRC it gave details of two specific grain sizes that are mixed to give RDX with a higher bulk density. When I get a chance I'll have another good look through to find out the mesh sizes and proportions they use.

[Edited on 30-5-2006 by Deceitful_Frank]
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[*] posted on 30-5-2006 at 14:06


Dislocations in energetic materials : I. the crystal growth and perfection of pentaerythritol tetranitrate (PETN)
Journal of Crystal Growth, Volume 67, Issue 2, July 1984, Pages 202-212
P. J. Halfpenny, K. J. Roberts and J. N. Sherwood

Abstract

Crystals of the secondary explosive material pentaerythritol tetranitrate (PETN) were grown from ethyl acetate and from acetone solutions by temperature lowering and solvent evaporation techniques. The growth-induced defect structure revealed by X-ray topography was found to consist of growth bands, growth sector boundaries, dislocations and solvent inclusions. All of the crystals grown exhibited only the forms {110} and {101} with the former dominating. Additional growth sectors were revealed by topography and were found to correspond to {111} facets which had grown out in the early stages of growth. The crystal perfection was found to increase with more accurate control of growth conditions. In general the {110} growth sectors exhibited a higher defect density than the {101} sectors. This can be explained on the basis of the relative growth rates of the habit faces and the nature of the growth dislocations present.

This one seem could help as it seems to include some information about different recrystallization techniques for PETN. Not entirely significant, but it could help pointing out the direction to go...

I couldn't find the paper about the recrystallization from ethylacetate mentioned in PATR. It does seem very promising though, saying it yields cubic crystals of almost identical size, behaving as a free flowing powder which seems ideal for the manufacture of higher PETN percentage, higher density plastique...

[Edited on 30-5-2006 by nitro-genes]
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[*] posted on 1-6-2006 at 02:37


After reading about 'bimodal' crystal sizes used for this very reason, I did a test: My standard plastique was prepared, but using one part of fine RDX to two parts of less fine. It needed less binder for the same pliability.

Getting two sizes can be as easy as letting part of the acetone sln. evaporate, and crushing the rest into water. A microscope is a big help to verify size, as what looks like much bigger crystals are ofter just conglomerates of finer crystals, getting crushed later in the mixing process.
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[*] posted on 1-6-2006 at 03:11


I thought it might be a good idea to take an ETN yeild and divide it 80:20.

Recrystalise the larger portion from slowly cooling hot ethanol and mix these larger crystals with the smaller proportion of the ultra fine dust of the raw neutralised ETN.

Good plan?
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[*] posted on 1-6-2006 at 06:04


Quote:
Originally posted by Boomer
After reading about 'bimodal' crystal sizes used for this very reason, I did a test: My standard plastique was prepared, but using one part of fine RDX to two parts of less fine. It needed less binder for the same pliability.


Nice, it is definitely possible than... :) You seem to have a lot of experience with RDX. What is the amount of plasticizer needed with standard made RDX to yield voidless plastique, and what is the resulting density compared to the two-crystalsizes-made-plastique?

I am curious about this since it seems RDX is more prone to form cubic crystals than PETN does (attachment) or there is simply more information available on this, also crystal density is slightly higher. So RDX based plastique may need less plasticizer anyway compared to PETN. I'm more in favour of improving my plastique by crystal modifications than using HE plasticizers like NG in large quantities or to use obscure meltcastings with MHN or ETN...(TNT is a pain in the ass to make as well as that pentolite may not perform very well at very small diameters)
I've made RDX few times before with 60% plus yields, I know it can be done much better, but still it is nothing compared to the high yields of PETN with the same amount of 90%+ NA. If RDX plastique is much easier to be prepared with higher densities than PETN based, I might prepare some RDX myself soon. Although a blend of PETN/RDX in a certain ratio may prove to benefit from the two different crystal shapes also...

I've obtianed 1 liter of ethylacetate now, so I'm looking forward to experiment a little with different recrystallization techniques...:P
Slow cooling is said to be the trick, but how slow, would "slow" be?! Maybe it doesn't matter for crystal shape, only for crystal size...

Quote:
Good plan?


Why not? :) Wouldn't store it too long though, I've read that unrecrystallized ETN decomposes quite readily.

[Edited on 1-6-2006 by nitro-genes]

Attachment: Crystallization and Characterization of RDX HMX and CL-20.pdf (456kB)
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[*] posted on 8-6-2006 at 00:08


Getting back on topic, I was wondering if anyone has any performance data for different target materials. I'd like to make a linear charge for clearing trees, but I have no idea how it performs on such targets.
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[*] posted on 8-6-2006 at 07:25


For most copper lined linear shaped charges penetration is little more than the width of the liner. This is for mild steel, I have also been looking for penetration in other materials like concrete etc. but I coudn't find anything...
This makes sense though, since for controlled demolitions it is common to use cheap dynamites in drilled holes to defeat concrete and save the expensive linear shaped charges for steel beams etc...

That also explains why there isn't a lot to find about the penetration in wood. I guess you are the only one cutting down trees with a shaped charge instead of a chainsaw...:P

I agree it is much more fun though... :D
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[*] posted on 9-6-2006 at 00:06


You're right, it's much more fun :-)

But besides from that, there are always situations where explosives are usefull. I remember seeing a patent for clearing trees from power lines, wich is a pretty dangerous job. The equipment consisted of explosive charges fixed to a clamping device that could be put in placed with a long rod. One charge on the underside of the tree above the wire and one below the wire on the opposite side not only cut the tree in three parts but also threw the middle part away from the wire. Quite impressive.

As for SC's in different materials I guess I'll have to do some guesswork based on penetration of rifle bullets. I know it's not the same but it should give a rough idea.

Oh BTW, if you feel your PiB-based plastique is to dull in apperance you can color it by dissolving a little dye for coloring candles in acetone :P
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[*] posted on 10-6-2006 at 06:28


I assume that the penetration of a linear shaped charge is also mainly dependant on the density and hardness of the target material, like in a non-linear shaped charge. So, if you look at non-linear shaped charges, for example the M2A4 with cone diameter of 4.88 inch:

Penetration of about 16 inch mildsteel and 12 inch armoursteel, and penetration of 30 inch, 84 inch, 72 inch and 84 inch for reinf. concrete, freshwater ice, permafrost and soil respectively. So compared to mildsteel, penetration is about 2 times higher for reinf. concrete and about 5 times higher for soil and ice. Most wood is about as dense as ice, so I think this figure may be relatively accurate. Don't know if these figures can be extrapolated to predict penetration for linear shaped charges though. But this would mean that penetration in wood is about 5-6 liner widths for a linear copper shaped charge...

Quote:
Originally posted by Fulmen
Oh BTW, if you feel your PiB-based plastique is to dull in apperance you can color it by dissolving a little dye for coloring candles in acetone :P


Pink would be nice... :D

[Edited on 10-6-2006 by nitro-genes]
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[*] posted on 11-6-2006 at 00:30


Thanks, even if it's not 100% accurate it will give me a place to start. I'll try to get some penetration data for firearms as well to see if it looks similar.
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[*] posted on 14-6-2006 at 10:19


Welll..... crap. I found an alternate explanation for the failure of my cylindrical shaped charge (see page nine of the thread, http://www.sciencemadness.org/talk/viewthread.php?tid=2219&a... ) and it means that I might have shot tons of these without any luck no matter how nicely aligned I made the charges.

The attached article mentions that for a cylindrical shaped charge to form a jet capable of penetration, the speed of sound in the liner must be equal or greater to the velocity of the contact point where the jet is formed, which is equal to the VoD.
Copper has a speed of sound of 3570m/s. Methyl nitrate VoDs at 8000m/s. OPPS.

OTOH Axt used Al (speed of sound 5100m/s) with a charge of ANNMSA which IMO won't have a VoD that is through the roof and might not reach the critical diameter. Or something. Axt wasn't even sure he got true penetration. Whatever the VoD, he did use a linger with a substantially higher speed of sound and an explosive with a substantially lower VoD than I did, and did get penetration of the target.

Therefore, I will try an shaped charge (very similar to my last one) using an aluminum tube and urea nitrate as the explosive, with a 40g methyl nitrate gelatine booster charge. Another charge, with the same setup, will use methyl nitrate as the main explosive charge.
IF the article is correct, the urea nitrate will penetrate, while methyl nitrate will just warp the witness plate with none or very little penetration.

If someone could grab the references on the 90km/s jets and the journal which explains the speed of sound/VoD/ability to penetrate relationship that would be wonderful. I would be interested since it seems weird to me even though it seems to be an established fact now... It would also be great to have an explanation even if the math is pretty heavy stuff.

Attachment: Acceleration device based on high explosive charge which con.pdf (524kB)
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[*] posted on 14-6-2006 at 14:23


Without actually reading the article (late and tired) I don't belive it for a second. Why? Because military liners are usually made from copper and fired with TNT and/or RDX/HMX. If copper only works with explosives that has an VOD below 3,5km/s it would be worthless as a liner material, and in real life it's the most common material there is.
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[*] posted on 14-6-2006 at 18:40


i also tryed al clindrical shaped charge with a copper tube and failed
http://home.arcor.de/kinger3/grose%20hohlladung/
so i will give a alu tube a try
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