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Author: Subject: Unconventional Shaped Charges
Axt
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[*] posted on 24-6-2004 at 19:49
Unconventional Shaped Charges


Cylindrical Lined Charges


I'd like a topic on unconventional shaped charges, obviously a practical use but it has a lot of science behind it, so hopefully it isnt locked.

Starting off, I found a reference to cylindrical lined charges in fundamentals of shaped charges (walters, Zukas) only a single sentence in 400 pages is devoted to this, and states:

"Cylindrical liners are capable of generating high velocity (and low mass) jets."


I decided to try this, as according to the Birkhoff theory, theoretically cylindrical liners will produce a jet 2x the VOD of the explosive! of course this wont happen in an improvised device but thats the highest theoretical velocity possible. Close to zero standoff should provide the best performance since the jet should be fully formed within the cavity.

The design of the charges was incredibly simple, two liners were chosen, both being 1mm thick aluminium but varying in diametre, 20mm and 16mm, both were 65mm in length, tape was used over the hole to keep explosive out of the cavity. The charge casing was light DWV PVC, 50mm wide, 110mm high. Charge was ANNMSA 140:100:70. Initiation was a commercial #8 detonator. Target was 1 inch thick steel plate. Below shows the finished liners, casing and charge performance.


MOVIE AVAILABLE



On detonation the charges performed exceptionally, both completely penetrated the 1" target. Its also testament to the effectiveness of the ANNMSA composition, note the large dent in the steel where the charges were placed. The penetration dimensions are shown below.

16mm liner: Entry = 14mm, Exit = 14mm
20mm liner: Entry = 23mm, Exit = 11mm

Therefore the 20mm liner started off wider but taped back to less then the 16mm liner, while the 16mm provided a constant diametre hole. This suggests that the small diametre liner would provide a deeper penetration if used on a thicker target. Spalling was present on the exit and might suggest that plugging also contributed in producing the large holes. Though no "plugs" were found.



[Edited on 7-6-2005 by chemoleo]
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[*] posted on 24-6-2004 at 21:35


Wow, thats pretty impressive. How much ANNMSA was used in the charges? What does the SA stand for, Silver Azide or Silver Acetylide?

[Edited on 25-6-2004 by rogue chemist]
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[*] posted on 24-6-2004 at 21:48


SA = Sulphuric acid

The ratio given was the charge weight in grams, 140g AN, 100g NM and 70g SA. So 310g all up.

I'll rephrase to make sense of the spalling (the large exit wound), it was mostly created by the zero standoff and power of the impact on the surface of the metal, but the 20mm in particular had a rough exit which may have been blown out in a plug rather then by plastic displacement. The 50:16 charge diametre to liner diametre wins.

[Edited on 25-6-2004 by Axt]
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[*] posted on 25-6-2004 at 01:05


Great references Myuo!

ANNMSA takes the form of large wet crystals, which may seem strange considering the amount of liquid in the mix. However after the AN is dissolved into the H2SO4 and the NM is added it crystalises out of the acid trapping all the liquid in its structure. I wont test with another explosive, due to the amount of effort it takes to make it. ANNMSA is easy and is a high VOD explosive. The only comparisons I can provide is the the commercial emulsion in the MEKP comparisons movie against the ANNMSA movie on the same page, as they are the same volume against the same target, there is no comparison!

I wont scan FOSC, as its being re-printed in a softcover version. Not that I care about lining the authors pockets but I think if people are genuinely interested they will just buy the book. Unavailable texts are something different and I fully appreciate some of the rare scans people provide. FOSC is still available through isee.org and a few other places. Definately one for the bookshelf if you are interested in this. Though it tends to go straight from the basics to the advanced leaving out the middle ground, for example there hardly a mention of LSC's.

My interest primary lies in things I can test for myself, theres enough of those that I'll be occupied for a looooong time :D
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[*] posted on 25-6-2004 at 07:01


Yes, Myuo deleted his post again. I remember him doing this in several other threads too - I wonder why?
It's very strange. And annoying if he provides several useful references :(


Axt, do you have references on ANNMSA?
I don't quite understand the principle of this explosive, particualry the presence of sulphuric acid?!? It is basically a mixture of ammonium sulphate, nitromethane and conc. HNO3?

PS Vulture, are you saying the average thread is crap? Or that the average forbidden practical discussion is crap? :o:o
Aren't we nice and positive :P;)

[Edited on 25-6-2004 by chemoleo]




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[*] posted on 25-6-2004 at 17:28


No references, just something I made up with to increase the sensitivity of O balanced ANNM.

NM/HNO3 Is a very brisant explosive in its own right, and the intimate contact between these liquids is better then NM/AN for example. Ammonium sulphate will happily explode as well, and acts to hold it into a solid structure.

Though im not sure about the safety of this mix, pure NM mixed with pure HNO3 is very sensitive. Theres many dilutants in this mix however NH4NO3/NH4HSO4/H2SO4/HNO3/NH4CH2NO2 probably more... I'll try shooting it to get some measure of its safety.

A better visual on the holes:



Im more impressed by the spalling from the shock transmission through the steel. Never seen it first hand before.


[Edited on 7-6-2005 by chemoleo]
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[*] posted on 26-6-2004 at 13:34


Combined spall wave and shaped charge warhead. ;)

It would be very interesting to see how deep your charges could cut as according to theory your shaped charge should form incoherent jets as I understand it. It would also be interesting to see the penetration effect of long cavity charges of this type as they could be made very long with little effort and limited amounts of explosives.
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[*] posted on 27-6-2004 at 03:10


I can see where your incoherent jet theory is arising from, but most theorys seem to go to shit once you get the the extremes such as a cylinder, I wont speculate as to whats happening. Myuo posted some nice references regarding acceleration of jets through a cylinder, seemingly the effective VOD can be increased by using a hollow cylindrical cavity in its length since the accelerated jet initiates the explosive as it passes through it.

I will probably try greater standoff to define the jet effect. For all I know it may well be accelerated shock waves acting as a hole punch!, which should diminish quickly as standoff is increased.


[Edited on 28-6-2004 by Axt]
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[*] posted on 28-6-2004 at 00:15


Tulip Lined Charges


Literature refers to this shape as the "tulip" which is in fact an ogive, for which I have posted on before where bullet jackets were used as the liner material. I havnt seen this shape used in anything but experimental designs so its unlikely to do anything that cant be done better by the conical, hemispherical or trumpet shapes. The picture below shows the jet shape from tulip liner, note the large head of the jet followed by the thin tail.



In addition to the bullet jackets I've attempted to use a chrome plated steel motorcycle part as a liner, as can be seen below it was a complete failure, I'll blame the liner material. Around 600g of ANNMSA was used with 2LD standoff. It simply splattered the liner over a 3" circle into the steel with the fragments penetrating at most 3/4".


MOVIE AVAILABLE


A better and easier source for tulip shaped liners would be aluminium nose cones for model aeroplanes, most will have a hole on the apex for attaching it to the plane but the liners should still work. The Japanese used a hole through the apex of their liners during WWII.

80g of the ANNMSA composition was shot today with a .25-06, no detonation occured, which is good.

NOTE - There may be a temporary geocities preoblem with the movie ..

[Edited on 7-6-2005 by chemoleo]
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[*] posted on 28-6-2004 at 13:15


I´ve never tried any tulip lined charges. I have only some experiences with hemispherical liners. I´ve made liners from Cu plate (0,55mm thickness) and they can penetrate steel about 1,5 LD.
For example 20g of RDX plastick with Cu liner (15mm in diameter) completely pierced 2cm of steel and resulting hole is close to be constant in diameter (8-9mm).

Now I´m also interested in your cylindrical liners (thanx for this idea), because I´ve some Al and Cu pipes so I want to use them with my plastick:)
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[*] posted on 1-7-2004 at 01:22


Linear Shaped Charges with Standoff


ExplosiveNM/70%HNO3 70:30
Charge weight285g/m
Liner20 x 1.4mm Al
Liner angle90°
Standoff10mm
Target6mm steel


I wasn't going to post this as its not exactly "unconventional" but it does provide an easy way of intigrating the correct standoff into the charge with common materials. The linear shaped charge (LSC) is made by simply hot gluing a section of 25mm aluminium angle into a length of 20x20mm channel. By using these materials you have a LSC that with a capacity of 235ml per metre. The liner is 20mm wide with a standoff of 10mm, which is about right considering it is an improvised device therefore a slightly lower standoff is likely to provide the best performance.

A liquid explosive is the most practical for a long linear charge, therefore a charge of 70ml nitromethane and 30ml 70% nitric acid was used in the 420mm length of LSC. Initiation was a commercial #8 detonator.On detonation the charge cut the steel very cleanly, no other marks were on the plate, but it was bent back as expected. The picture below shows the detonation and the cleanliness of the cut over the full length of the LSC.





[Edited on 7-6-2005 by chemoleo]
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[*] posted on 23-7-2004 at 18:26


Same setup as above, but fired into a 1" steel plate to see the depth achieved. Managed 8mm deep cut though it skewed a bit as it was glued together.


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[Edited on 7-6-2005 by chemoleo]
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[*] posted on 15-2-2005 at 05:59


Glass Lined Charges

Liner1mm Glass
Shape60° Conical
Diametre50mm
Confinement2.5mm PVC
Charge200g NM/70% HNO3 70:30
Head height68mm
Initiator0.5g PETN
Standoff70mm
Penetration>50mm steel


Glass liners have been the topic of some debate, so I ran a test using a 50mm (2";) glass funnel, the spout was broken off and sealed by gluing on a piece of Al foil. The casing was made with 50mm DWV PVC fittings, with a 50mm slab adaptor used to hold the liner in position and provide the standoff.

NOTE: I used an extra fitting to provide greater head height (height of explosive between apex of cone & detonator) as it was too small once I glued it together. For best performance the head height, especially in an improvised charge should be at least 1.5X the liner diametre. This extra fitting isn't in the pictures, though can be seen in the movie.


MOVIE AVAILABLE


The charge was fired into the same 2" slab of steel in the tulip charge above, but this time with better results. The jet
completely penetrated the steel with a clean even hole, opening at 23mm, exiting with 12mm.



I found a comparison table for different demolition charges, which compare one glass to two steel lined charges. The glass compares favourably with the larger diametre steel lined charge which gives half the penetration of the glass. Check the attachment for the specifics of each charge which vary in charge weight, confinement etc. It seems glass will function equally well, or greater then steel. While copper is still better, a good glass cone will be far better then a shoddy copper one, and cheaper. The glass funnel used above was only $1.50.

[Edited on 16-2-2005 by Axt]

[Edited on 7-6-2005 by chemoleo]

steel-glass-charges.jpg - 42kB
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[*] posted on 15-2-2005 at 19:33


Very impressive. 5 cm - that is VERY thick. It must have been a pain carrying this plate onto that hill of yours :P.

I wondered - are there computer simulations/programs that simulate/calculate the optimal standoff to achieve maximum penetration? Surely this can be calculated, a bit of fluid/gas (?) dynamics here should help?
I mean, a given liner shape (i.e. V/parabolic- shaped) with a given standoff should produce a calculable VoD of the gas jet at the point where it hits the target plate (providing the VoD of the explosive itself is known). I imagine the theory is similar to water sprays (i.e. in the case of a parabolic liner) all centering on one spot, where they repel each other and are sped up in due course (or in the case of gasses, compressed to enormous densities which are many hundreds/thousands of K hot) - which then hits the target plate. Hmm. Guess I have to look up the theory.

Anyway, rather than zooming in onto the optimal standoff by experimentation, couldn't a bit of theory/calculation be used?

[Edited on 16-2-2005 by chemoleo]




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[*] posted on 16-2-2005 at 00:28


Actually the "precision" of the charge has more to do with the optimum standoff then anything else, especially when improvised which are far from perfect. An "ideal" charge with a cohearent jet will function well at very long standoff distances as, when compared to parting steel, air resistance is minimal. Though the less "ideal" or "precise" the charge the breakup of the jet governs the optimum standoff, for which the calculations are incredibly complex, the book reference in first post has some of the mathematical theory on jet breakup. While its likely possible to come up with a formula to get standoff from liner material, cone angle etc. it would have to be taken from experimental results. And I have no idea how "cohearent" a glass liner would be, high pressures do funny things!
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[*] posted on 17-2-2005 at 11:04


To Axt: Excellent work Master! Wow, the Explosion are quite impressive;) Especially the Nitromethane-Nitric Acid mix look's very cool!

I hope that I have time to test it at the weekend. These Cylindrical shaped charges are extremely easy IMO. Why not trying a Blast with Peroxide Watergel?

I didn't need very long and my Distillation setup is ready to produce LITERS of pure 60-85% H2O2. I think that H2O2 Explosives are stronger than ordinary mixes....back on topic:

Do you think that copper is again the best liner material for cylindrical shaped charges? I mean...even glass tubes wouldn't be that hard to get....:)
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[*] posted on 17-2-2005 at 12:01


Axt, so when comparing cylinder to cone liners, for the same mass of charge, which one would you expect to achieve higher penetration? Also, it's not clear to me how the best cylinder height and diameter is determined given the mass of charge to be used.

[Edited on 17-2-2005 by Quince]




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[*] posted on 17-2-2005 at 12:07


Maybe someone can now test DPPP's cutting power? I can't at the moment 'cause I haven't got the chemicals where I am now.
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[*] posted on 17-2-2005 at 14:43


I thought the DPPP thread concluded that the proposed synthesis did not actually produce anything but some form of AP.

Also, my previous question in this thread still stands :)

[Edited on 17-2-2005 by Quince]




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[*] posted on 17-2-2005 at 14:51


Quote:

Why not trying a Blast with Peroxide Watergel?


I don't think it would work well at all. Not only if it very hard to pack with consistancy, as it tends to hold large air voids that are really hard to get out if packed into a casing. It's VOD is also likely quite low. Keep it for general blasting where energy rather then VOD is needed.

Quote:
Do you think that copper is again the best liner material for cylindrical shaped charges?


Copper is undoubtedly one of the best, that why its used commercially/militarily. But that factors in cost and workability, actually platinum should make for a considerably better liner for those that dont mind spending thousands of dollars per charge :o

Quote:
Axt, so when comparing cylinder to cone liners, for the same mass of charge, which one would you expect to achieve higher penetration?


Conical. I dont know by which method the cylindrical liners are working, the 14mm ID of the liner creating a 14mm hole makes it seem like its acting like a hole punch, in which case it will either punch right through or not far at all. Using a bit of standoff would help show if it's the effect of a metal jet or the blast itself.

Quote:
Also, it's not clear to me how the best cylinder height and diameter is determined given the mass of charge to be used.


I dont know, I had a guess. Though it should scale well, so take the 16mm liner as the example and scale off it.

[Edited on 17-2-2005 by Axt]
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[*] posted on 17-2-2005 at 14:59


Would blasting gelatin work well for a shaped charge? It's the easiest for me to make with my current resources.

Regarding liner materials, I'm curious as to what properties of the material determine its effectiveness. Why is copper better than many of the other materials?




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[*] posted on 23-2-2005 at 23:05


"Why is copper better than many of the other materials?" i think current is produced through the copper make a magntic field protecting the copper from the plasma, just a guess. MHD theory.

[Edited on 24-2-2005 by searat]
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[*] posted on 24-2-2005 at 01:20


I think that would only work if the copper was a coil, as in a well known e-bomb design.



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[*] posted on 24-2-2005 at 02:11


Plasma? .. theres no plasma.

Anyway, I wasn't replying to this as I really don't know the full answer. The "desirable" properties are stated in a number of references but there are always contradictions. For example why is lead so much worse then glass, even though lead is more dense and ductile? Where one would think glass will be low density and non-cohesive. Though lead will vaporise if too thin.

Anyway, heres the favourable characteristics of shaped charge jet materials, (extract from Walters, Zukas):

- High melting temperature (rules out lead, but why liquid jets are worse, I dont know).
- High density (enhance penetration)
- High bulk speed of sound (effects cohesiveness of jet, tip velocity).
- Grain texture/orientation (for good elongation of jet).
- High dynamic strength (when under severe pressure/strain, not necessarily high static strength).

The reference that will be of most interest is :

S. Buc. "Shaped Charge Liner Materials: Resources, Processes, Properties, Costs and Applications", SPC 91, pp. 282-2, (1993). (anyone know what "SPC" refers to?

And a table from:

Doig, A. "Some Metallurgical Aspects of Shaped Charge Liners". Journal Of Battlefield Technology, vol 1, No. 1. March 1998.




[Edited on 24-2-2005 by Axt]

[Edited on 7-6-2005 by chemoleo]
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[*] posted on 24-2-2005 at 18:58


Thanks for the table. I've been thinking of trying this, but the only copper I have is about 2 mm thick, which is too much and can't be worked into a cone.

I'm curious as to how proper thickness is estimated.




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