Sciencemadness Discussion Board

Unconventional Shaped Charges

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Fulmen - 29-4-2006 at 10:59

PETN should be one of the best choices for this kind of work (together with RDX and HMX), so I doubt that could be the cause. Could be the standoff, a charge this well made could probably handle 3-4CD. If you look at radiographs you can se a "crown" of dispersed material that I assume is from the apex (or more correctly from when the main high-velocity jet catches up with the slower jet formed by the apex), with a short standoff this could possibly be dense enough to cause the entry hole you got.

Since you're so skilled in spinning metal, how about making a funnel or trumpet liner?

nitro-genes - 29-4-2006 at 14:14

Ahhh, the crown formation...I wouldn't have thought that with a relative slow plastique this would still leave such a dramatic impact. It wasn't exactly low-quality steel you know. ;) Althought the hardness of the steel has probably only a minor effect...

You would expect that this collision of the two "jet parts" would render the jet less effective than a trumpet shaped cone. Still, PATR mentions the ~ 60 deg. cone shape with a rounded apex to be one of the deepest penetrating shapes for the liner.
Everywhere, 60 degree cones, like in the M2A4 demolition charge, are said to be optimal. But in many missiles like the "Javelin", and other millitary penetrating devices, a much smaller angle is used. Something like 42 deg. IIRC.
Then again, many tank fired AP grenades (non sabot) use trumpet shaped liners. Probably it is a tradeoff between hole diameter and penetration depth...Or like I suspected before, the smaller angles may be less sensitive to errors in jet formation due to rotations etc.

So for a stationary liner, what would actually be the deepest penetrating liner design?
Any thoughts?

[Edited on 29-4-2006 by nitro-genes]

rot - 29-4-2006 at 23:55

I think this thread should be a sticky

Fulmen - 30-4-2006 at 00:53

60degrees might wery well be the most effective design, but since missiles and shells are more limited in diameter than length I assume they just use a smaller angle and more explosives to get the same result. I have the liner from an 84mm Carl Gustav RPG, and it's 77mm in diameter with a 50degree cone. The liner itself is in copper, but the most interesting part is the small brass "nipple" at the apex. It's simply a very small sylindrical tube, 5mm in diameter and 8mm long with a radius end. As for the trumpet liners I have only seen this in artillery shells, so you might be right in that they are less sensistive to spin-induced effects.

I guess the 60degree is the safest angle to use, since the litterature seem to favor it. A small funnel stem might be usefull, but it's probably more work than it's worth.

But what makes you think your PETN plastique is slow? PETN is almost as powerful as RDX, and should be just as good as the TNT-based explosives usually found in military devices.

Microtek - 30-4-2006 at 01:04

When making SCs, I have found air lenses to be a good way to reduce the necessary head height. The idea is that the wave front of the detonation expands like a roughly sphere, so a usually certaint amount of head height is included to allow the curvature of this wave front to decrease.
Another way to achieve this is to use lenses ( explosive or air lenses ). An explosive lense uses a pellet of low VOD explosive in the axis of the charge, a little below the detonator. This causes the center of the wave front to travel slower ( through the low VOD explosive ) than the edges ( through high VOD explosive ), so that the edges catch up to the center and the wave front becomes flat.
An air lense uses a non-explosive substance with a low sound velocity such as air, wood or foamed polymer to achieve the same thing.

By tinkering with the design, you can also get more complex wave front shapes, such as a slight funnel shape, which will give slightly better collapse of the liner.

Fulmen - 30-4-2006 at 01:39

Lenses are exiting, any more details on your experiments?

nitro-genes - 30-4-2006 at 07:02

Quote:
Originally posted by Fulmen
But what makes you think your PETN plastique is slow? PETN is almost as powerful as RDX, and should be just as good as the TNT-based explosives usually found in military devices.


Basically, the 82% PETN plastique is very similar, if not identical, in it's detonational properties as semtex 1A. Don't like to use the word though, since it makes me feel like a terrorist :). Density is about 1,4 g/cc with the same PETN percentage. VoD listed for semtex 1A is 7200 m/s with a detonation pressure of 167,5 Kbar.

-->http://www.explosia.cz/en/trhaviny/zvlastni.htm

If you compare this with some compositions used in military shaped charges:
Code:
Composition Density Pressure (Kbar) LX-14 1.833 370 Octol 77.6/22.4 1.821 342 Cyclotol 77/23 1.752 316 C4 1,630 265


So the detonation pressure is about half that of any modern military composition, I could't find any correlation equations for detonation pressure and jet lenght or jet velocity, but I don't think we are talking linear correlations here ;) With half as much pressure you would expect a serious decline in penetration though. I can't say anything about this from my last experiment since the 28mm liner completely went through the 5 cm plate.
I would like to make two identical liners and setups, and fire one with the remaining PETN/Pib and one with PETN/NG into multiple 1 cm thick plates.

What would be a good approximation of the detonation pressure of PETN/NG? Just the average of both at max. density? This would give about the same peakpressure as cyclotol...:P

About the shaped charge lenses, If been thinking about cutting them out of hard foam. Designing them properly is not so easy I think, you would need to have an approximation of the speed of the shockwave transmission through air at different distances from the explosive...

Quote:
Originally posted by Fulmen
I have the liner from an 84mm Carl Gustav RPG....


Ebay? :D

[Edited on 30-4-2006 by nitro-genes]

Fulmen - 30-4-2006 at 08:31

Quote:
Originally posted by nitro-genes
Quote:
Originally posted by Fulmen
I have the liner from an 84mm Carl Gustav RPG....


Ebay? :D



Sure, when hell freezes over :-)

Swany - 30-4-2006 at 09:00

Not looking too good, due to 'global warming'.

If I were to use ETN/HDN, perhaps with some NG to make it behave like a stiff cookie dough, would it be advisable to add some Al in order to even out the OB, or would it effect brisance in a negative way, even though total energy is higher? I would be adding about 10% to the mix.

Deceitful_Frank - 30-4-2006 at 09:36

Shaped charge performace is very much dependant on detonation pressure.

Detonation pressure is proportional to the density and heat output of the explosive but proportional to the SQUARE of the detonation velocity.

Aluminized explosives offer improved performance against relatively soft targets due to the enormous heat gain you get when you let Al reduce the products of the explosion AFTER detonation. It also has the effect of reducing the detonation velocity... maybe due to a reduction in homogenuity.

A 10% reduction in VoD gives a 21% reduction in detonation pressure (and likely a substantial reduction in shaped charge perfomance). the extra heat gained isnt enough to counteract this shortfall.

Aluminized explosives perform less well when the most shattering power is needed or high detonation pressures are required for an SC... compared to their pure CHNO counterparts.

EDIT:

Adding Al to explosives will reduce the brisance but obviously how effective the explosive is very much depends on the target... whether you want pure shattering power, pure heaving ability or which ratio of the two.

[Edited on 30-4-2006 by Deceitful_Frank]

[Edited on 30-4-2006 by Deceitful_Frank]

[Edited on 30-4-2006 by Deceitful_Frank]

My second shaped charge.

Deceitful_Frank - 30-4-2006 at 12:52

Well I fired my second baby last night and it proved to be much more successful than the first...

PENETRATION!

Not alot but some. As you can see the SC impact is a rather messy affair with what appears to be two main perforations. The one towards the middle of the steel wheel being deepest at around 6mm. Slightly below in the pic it steps up to 4mm though I suppose these are not actually two but one very deformed hole!

Below this you can also see a roughly circular area of deep pitting covering an area of about 4cm^2

Considering the perfection of the 40 degree prefabricated and subcalibrated Al cone, this is not exactly what I was expecting but compared to my last and first SC test, this is a vast improvement... better than a kick in the face!

This test wasnt without the usual fuckups despite much careful planning.

After piercing the bluack to provide entry for the EGDN and exit for the trapped air, I proceeded th fill using a plastic funnel pressed over one of the holes.
In my careless stupidity I didnt notice that the hole I had made for the EGDN with the nail had closed itself over on removal of said nail. The funnel filled with EGDN and on frantic manipulation to try to get the shit into the charge, some 10 grams flooded out of the funnel, over the experiment and splashed onto my bare hand (didnt think I'd need gloves for this bit!)

I'm sure you can guess what happened next... there is a very good reason why we dont like EGDN on our skin!



Anyway, I finally got what I had left of the EGDN, probably 75% of it into the charge and fire the bitch off...

WHAT A BLAST!

I had no idea how much difference a half decent cap could make with EGDN, it was beastly and after the first test last week... took me completely by surprize.

Last time I had to make do with 0.25 gram of damp shitty HMTD but this test used a full gram of fresh, dessicated and snappy peroxide! I'm also pretty sure that the cap was above the level of the EGDN inside the case so the initiation can still be improved upon. I think its time I thought about beefing up my caps to something abit more substantial and less kewl. Maybe 0.75 grams of cast ETN with 0.25 gram pressed ontop. Even if I retain the HMTD as the primary but in tiny amounts.

I'm not sure I can upload the video clip AND the pic in this same post so I'll have to double post...


[Edited on 30-4-2006 by Deceitful_Frank]

SC2 results.jpg - 607kB

Deceitful_Frank - 30-4-2006 at 13:12

...heres the clip.

Shit quality and just 10 seconds but you get the idea!

http://media.putfile.com/SC2b

[Edited on 30-4-2006 by Deceitful_Frank]

nitro-genes - 30-4-2006 at 14:49

Pretty amazing blastwave! That must have been quite a punch in the stomach...:)

Can't find the pictures of the penetration in the steel though...:(

[Edit: found them...My browser had some trouble displaying them properly]

Why don't you give the small lightbulb liners a shot, with a few millimeters of subcalibration I'm sure it would give a pretty good result with EGDN. You could use 1,5 times headheight without much decrease in performance, and this would need about 25 ml of EGDN for a 3 cm diameter liner.

Did you get the pictures of the hemispheres btw? :)

[Edited on 1-5-2006 by nitro-genes]

NBK - 30-4-2006 at 16:05

Quicksilver:

Would you have a direct link to that article/journal that references X-9094 as using gelled parrafin oil?

Searching here and on Google didn't pull it up, nor did searches at several Los Alamos portals.

I did find the manufacturers website though. :)

+++++++++

Yes, it's really me.

Go to http://www.roguesci.org/theforum/water-cooler/5199-polverone... if you don't believe me.

[Edited on 5-1-2006 by NBK]

Microtek - 30-4-2006 at 22:12

Regarding lenses, if you use an air lens the design is much easier.
You don't need exact VODs throughout the charge as long as the axial part of the propagation wave is retarded sufficiently. Then the wave front below the lens will be as if the charge was initiated from the circumference of the charge ( at the top ) by an infinite number of detonators. In other words, like an expanding donut.
This means that it will hit the liner more squarely.

PS. The transmission velocity of the shock wave in air is equal to the speed of sound in air; ca 330 m/s. It is likely that a simple air filled cavity would act like a shock tube ( much like the NONEL system ) to conduct a flamefront at ca 2000 m/s.
That i why I prefer to use some low density material to fill the void. Even though the flame front probably wouldn't transmit detonation...

quicksilver - 1-5-2006 at 06:36

Quote:
Originally posted by NBK
Quicksilver:

Would you have a direct link to that article/journal that references X-9094 as using gelled parrafin oil?

Searching here and on Google didn't pull it up, nor did searches at several Los Alamos portals.

I did find the manufacturers website though. :)

+++++++++

Yes, it's really me.

Go to http://www.roguesci.org/theforum/water-cooler/5199-polverone... if you don't believe me.

[Edited on 5-1-2006 by NBK]



Sorry...can't go there. You banned me; remember?

Deceitful_Frank - 1-5-2006 at 11:41

Quote:
Originally posted by nitro-genes
Pretty amazing blastwave! That must have been quite a punch in the stomach...:)

Can't find the pictures of the penetration in the steel though...:(

[Edit: found them...My browser had some trouble displaying them properly]

Why don't you give the small lightbulb liners a shot, with a few millimeters of subcalibration I'm sure it would give a pretty good result with EGDN. You could use 1,5 times headheight without much decrease in performance, and this would need about 25 ml of EGDN for a 3 cm diameter liner.

Did you get the pictures of the hemispheres btw? :)

[Edited on 1-5-2006 by nitro-genes]


LOL yes its was alot louder than I expected though I was a good 20-30 metres from it at detonation... felt it more in my feet and ears than in the gut region! :cool:
I suppose it was around 21-22ml or 32-ish grams that made it into the casing for firing and at density of 1.48 with strong initiation, I'm confident that close to its maximum 7300m/s and 197 kbar detonation pressure was acheived.

Been thinking today about possible causes for the messy entry. All I've come up with are possible Al spray from the 4mm wide subcalibration ring around the cone but more likely, the fact that the vinegar shaker lid wasnt seated perfectly level within the bottom of the HDPE tube... it was tilted over to one side by maybe 5-10 degrees. In effect I think that this meant that the central detonator wasnt actually directly above and in line with the axis of the top of the cone!
If I repeat this test I should use some slower drying epoxy to give me more than 1 minute to get the whole deal straight within the tube!

Think I'll give the lightbulb liners a miss for the time being as this setup seems to have good potential if I can iron out all the small creases. You mentioned about using 1.5 headheight as apposed to 1.7... whats the deal with this? As far as I'm aware once you get over 1.5 you enter the realm of diminishing returns. 2 would obviously be better but not worth the 33% increase in the amount of explosive required.
I've noticed members have been posting about wave shaping air lenses but this just seems like overcomplicating things to me... If I wanted to increase efficiency and save explosive I'd just incorporate inbuilt boat-tailing using plasticine inside the tube to save explosive where it isnt needed at the top-edges of the charge. Then just go with a headheight of 2! :D

As for other tests in the near future, I've discovered a handy source of mild steel foil for winding cones..... pepsi cans.
Some say 40 degrees and others reckon 60 gives the best balance of jet mass and velocity... 50 it is then!
This equates to an internal side ramp angle of 65 degrees.
360(cos65)=152 degrees so when I've cut my circle of foil this is how much of it I need to form the cone. Not sure how many layers to use till the thickness has been calculated.
IIRC steel falls somewhere between Cu and Al for SC performance.

I did indeed get those pictures of the hemispheres and was astouded by what 10 grams of your plastique could do... then I remembered from your U2U that the charges where fired under sand.

2g/cm^2 is some quite substantial tamping!

Astounded became... very very impressed ;)

[Edited on 1-5-2006 by Deceitful_Frank]

[Edited on 1-5-2006 by Deceitful_Frank]

NBK - 1-5-2006 at 20:00

Whatever happened to a simple "No."?

No.

I don't remember you. Were you that memorable of a K3wL that I should remember you? :P

Is this now the 'People NBK has banned from RS.org' thread? Did I miss the title change of this topic?

This board wouldn't even exist if I hadn't banned Madscientist, so what are you complaining about?

If you got a gripe with me, take it to e-mail at forumscan@yahoo.com , and don't clutter up the board with your whining.

Anyways...

I've read that making the lens as a mirror image of the liner, and placing them apex-to-apex, results in very high liner speeds in an explosives-efficient package.

Reason? Because, as the shock front wraps around the diameter of the lens to run parallel to the sides, it goes from radial to planular. When this wavefront hits, it's at a 90° angle to the liner, transfering maximum energy to the liner.

The liner collapses into an almost coherent mass which is launched at high velocity towards the target, almost like an EFP.

This is the basis of the X-charge warhead, which begat the Maverick missile warhead design.

Use of combustible metal liners results in a vaporific effect upon impact with the target.

If you make the charges large enough, you can use cast aluminum liners, with the liner thickness of 10% of CD. So a 100mm CD charge would have a 10mm thick cast aluminium liner.

Surely it's easier to cast such liners than spinning them at sub-mm thicknesses?

Yes, you need more explosives, but that's easier to make than precision liners.

BTW, having just measured it, the walls of a pepsi can are .0045" thick.

[Edited on 5-2-2006 by NBK]

12AX7 - 1-5-2006 at 22:21

Quote:
Originally posted by NBK
Is this now the 'People NBK has banned from RS.org' thread?


Third person here. I've heard rumors of your attitude. Seventeen lines in response to a mere one seems to bear it out. Just FYI.

Quote:
Surely it's easier to cast such liners than spinning them at sub-mm thicknesses?


I doubt it. It depends on what method, but you can only get out as much symmetry as you put in. A die cast part would be most stable, as cast, but you need to machine the dies and inject them with high pressure molten metal, too. I wouldn't count on sand or investment casting getting horrendously accurate results, though that depends on how accurate it needs to be at this thickness.

Accurate castings are made by casting as close as possible, then machining to tolerance. That just adds another step, and uses a machine that you could just as well use for spinning thinner liners.

Tim

nitro-genes - 2-5-2006 at 04:50

Quote:
...don't clutter up the board with your whining.


LOL, quicksilver's reply was was quite funny in my opinion. :D I think if one can't laugh about one's own mistakes it is a serious lack of character...:( Especially, when one laughs very hard about the mistakes of other people. "What the beast has fed upon today?!" .... WTF?!)

I don't think casting is that easy, casting bronze for example is an art in itself which can only be mastered after YEARS of practice. Not to mention that aluminium is much more susceptable to oxidation at these temperatures...

The X-charge principle is interesting though...

Did another 3 spins today, I tried to get as close to 60 deg. as I could. The middle one meets these requirements quite well...I dare to say that they do look pretty precise to me. :D



[Edited on 2-5-2006 by nitro-genes]

quicksilver - 2-5-2006 at 06:57

Quote:
Originally posted by Deceitful_Frank
LOL yes its was alot louder than I expected though I was a good 20-30 metres from it at detonation... felt it more in my feet and ears than in the gut region!


One of the amazing thing I noticed was the actual noise of the det itself. Did you hear a very slight but unique echoing "ping"? I had noticed a unique noise that was not present from simple industrial open air dets. I'm not talking about stemmed charges of rock blasting but simple stump, open air stuff. With a SC I occationally hear a very unique sound. This follows a "good shot".

Most of the written material I have seen thus far dealt with energetic material which had an oxygen def (black smoke, etc). But I have yet to see if a OB energetic material makes any difference or if it has been addressed as an issue in productive shots.
If the concept is one of: liner materials and hydrodynamic penetration then there may be a question as to the variences in the "propellant" of such a liner. Would an oxygen balenced explos make any difference in the SC? Although the liner behaves like a fluid reaserch has shown that it still is a solid.
We all have seen the folowing quote:
"Mathematical modellers, therefore, often fit their output to the results of firing trials (cross-calibration to reality) by adjusting some of the materials coefficients. ....(etc, ect)" Herein the author addresses the material used in liner production exclusivly.....but... Could one of the "materials coefficients" be the OB of the explosive?

[Edited on 2-5-2006 by quicksilver]

12AX7 - 2-5-2006 at 11:45

Quote:
Originally posted by nitro-genes
I don't think casting is that easy, casting bronze for example is an art in itself which can only be mastered after YEARS of practice.


It goes faster than that if you practice more often. Faster than say, chemistry, which takes a decade or more to master.

Once you get used to casting, say, zinc or aluminum, everything else is just hotter, which is up to your furnace to melt, not so much your skill. Melt process is a little different, flux for instance, but liquid metal is liquid metal, it flows about the same. Bronze is in fact easier because its higher density exerts more hydrostatic pressure, filling out details and thin sections. Really, the only significant skill you need in casting is molding.

Tim

nitro-genes - 2-5-2006 at 17:25

Quote:
Originally posted by NBK
Use of combustible metal liners results in a vaporific effect upon impact with the target.
[Edited on 5-2-2006 by NBK]


Maybe you mean "reactive liners", since aluminium in itself is not very usable for deeply penetrating SC's. Google revealed little information about this type of liner, but the basic idea is that the liner is composed of a combustible metal like aluminium together with a high temperature oxidiser of some kind. When the jet hits the target, the metal is combusted yielding a very high shattering effect on hard targets like concrete, but with only little penetration...

http://proceedings.ndia.org/3500/Daniels_Demo_NDIA.pdf

This is the same effect of the X-charge from the agm-65 maverick I think. The X-shape leads to an increase in mass of the slower slug fragment behind the jet, almost like an EFP, and is capable of causing more behind armour damage (BAD), like spalling for example. A lot of research has been done on increasing the shattering effect of a SC, since the damage from a simple shaped charge is focused entirely on one point and therefore not very effective in disabling an entire enemy structure at once...

I wonder if these explosive lenses really produce much longer jet lengths for that matter. Or that they, like microtek said, are mostly for reducing headheight, hence explosive needed...

Modern shaped charges can do over 8 CD's now, but from what I have read, this is mostly because of improvements in liner design, liner precision, liner material and faster explosive compositions...

[Edited on 3-5-2006 by nitro-genes]

Spinning Liners

enhzflep - 2-5-2006 at 21:53

Well, here's the extent of my failures thus far. They're all 0.3/0.4mm with the exception of the one on the right which, was 1mm. My feeling is that the failures are caused by incorrect technique and are excacerbated by insufficient friction, resulting in slipage between liner and mandrel(s). I could always chuck a piece of bussines card on either side of the liner for that extra grip.

Any thoughts nitro?

Pic_0078.jpg - 89kB

NBK - 2-5-2006 at 22:14

Since when does 6 lines = 17 lines? Please point out the error in this math. :)

I certainly don't expect people to trip over themselves to welcome me here, but I'd also expect people to acknowledge that I'm not some n00b idiot who's got nothing to add to the discussion, either.

You notice the reasons that the vast majority of people at RS.org get banned for?

A) Lack of literacy and grammer.

B) Asking for spoon-feeding, rather than helping themselves to learn by searching for the answers first.

C) K3wL'ness, defined by regurgiation of Anarchist crapbook recipes and lack of knowledge in the subject which they wish to participate in discussion about.

Do any of the three apply to me?

Like I said, if you got beef with me, take to e-mail or U2U.

+++++++++++++++

Nitro-genes:

No, I meant exactly what I said...Combustible liner.

Reactive liners are generally composed of two materials that, under the heat and pressure of explosive loading, undergo an exothermic reaction initiated at the point of detonation.

Examples would be thermite or intermetallic reactions.

By varying the particle sizes and ratios, as well as varying the jet through use of lenses and such, you vary the rate at which the energy of the reaction is released.

Fine particles in a dispersive jet results in near-instantanous energy release, suitable for cratering, but not for penetration.

More coherent jets, with courser particles or less reactive ratios, penetrate deeper into structures, suitable for fracturing of concrete and structural elements, and for killing enemies on the other side of cover through overpressure and fire.

Highly coherent jets, though, aren't very useful, for while the jet is as penetrative as a non-reactive liner, the energy release is so slow that it contributes nearly nothing, acting more like pyro glitter than an incendiary/explosive.

Now, this is in contrast with a combustible liner in an X-charge, which is projected at something like 10K/s towards a target where, upon impact, the white-hot metal mass is blown apart into a spray of particles as it penetrates, thereupon to ignite and combust in a thermobaric-type reaction ('Vaporific' back then) to create massive overpressure with blinding flash in the target.

NASA has been the most recent research into Vaporific effects, as part of micrometorite defense bumpers (Whipple Shields) for the International Space Station. The US Navy did plenty of research from the 40's till the 60's that's unclassified and (supposedly) publicly available, but China Lake isn't coming off it..."Security, Need to Know, 9/11" etc.

Copper liners, while more penetrative because of their mass and ductility, aren't going to have any BAE (Behind Armor Effects) like reactive or combustible liners would. Though this isn't the place to discuss practical applications.

Research by the Buerau of Mines showed that rough sand-cast iron liners, cleaned of sprue and other such gross remenants of casting by simple fileing, penetrated to near-similiar depths as machined liners.

The difference was in uniformity of the hole profile, with the rough liners creating 'pocked' holes, compared to the typically smooth holes made by highly symetrical liners.

So, while not pretty, cast liners are perfectly useable, especially in an improvised context. Especially since the materials to make them are SO cheap and available:

Heat to melt Aluminum Cans to pour into Sand molds made of Wood boards.

Compare to Lathe, Milling Machine, or even Drill Press.

One you can do in the forest, cave-man style. The other, not.

Since you've got a lathe, have you given any thought to spinning out an EFP platter? Hell, I'd bet there's people here and at RS.org that'd buy liners from you, if only to have one less variable in their designs to deal with. Something to think about. ;)

[Edited on 5-3-2006 by NBK]

Rosco Bodine - 2-5-2006 at 23:42

Here's a thought . Some of the bearing metal alloys
like Babbitt might be useful for casting liners . Some of the alloys could have the right combination of properties to give good performance and they are low melting and
easily cast to form precision parts directly from the mold .

nitro-genes - 3-5-2006 at 01:45

Quote:
Originally posted by enhzflep
Well, here's the extent of my failures thus far. They're all 0.3/0.4mm with the exception of the one on the right which, was 1mm. My feeling is that the failures are caused by incorrect technique and are excacerbated by insufficient friction, resulting in slipage between liner and mandrel(s). I could always chuck a piece of bussines card on either side of the liner for that extra grip.

Any thoughts nitro?


It surely is starting to look like a liner! :) I think you are almost there...The technique is mastered quick enough and is not really the cause of the failures. I also had a lot of trouble with "liner grip", which usually results in tearing of the metal...

Your biggest problem is the mandrel grip, and there is a very simple way to solve it. Just use smaller diameter circles in the beginning! Larger circles can be done, but you really have to start in the middle, and work carefully through to the sides. With a large circle, the work arm, and thus force, when pressed on the sides becomes larger than the grip of the mandrel can handle and it tends to slip or tear the metal...(been there ;)) There is a minimal, "grip surface" to "metal circle diameter" ratio so to say that allows good spinning...

Another very important thing is the mandrel-contramandrel fitting. When you firmly press your sheet metal between the mandrel and contramandrel, and then get it out, there should be no vissible rings of excessive pressure be vissible, especially at the sides. This is where the metal is pressed too thin, and eventually tears. The mandrel and contramandrel should fit together in a way that the pressure becomes evenly distributed over the entire surface area of the fitting...
You can use sanding paper or a vile to make a more smoothly curved mandrel and contramandrel fitting...

And last, the steeper the angle of what you want to spin, the more chance at tearing. This is no problem if you have mastered spinning better, but when I started, I did 60 deg. first with good results...
If you do want to make liners with 40 deg. then you just have to make sure that you don't thin the metal to a too great extend at the middle of the circle, as this causes tearing. This is very simply overcome by:
1 Once the middle of the circle becomes attached to the
mandrel, don't work on the middle of the circle anymore!
2 For every few strokes from the middle to the sides, make a rowing sweep from the sides to the middle. By doing this
you bring extra metal towards the point which is streched
most (the middle), and prevents tearing...

[Edited on 3-5-2006 by nitro-genes]

Boomer - 3-5-2006 at 06:41

Microtek wrote: "The transmission velocity of the shock wave in air is equal to the speed of sound in air; ca 330 m/s. It is likely that a simple air filled cavity would act like a shock tube ( much like the NONEL system ) to conduct a flamefront at ca 2000 m/s."

I don't think the shock will be limited to 330 m/s, since the air in front of the shock wave gets compressed (and therefore heated). My *guess* would be 1500 m/s like the 'air gap speed' used to calculate a mixtures VoD below TMD.

Air or styrofoam will make no difference. Other inert stuff gets up to 6 km/s (from memory - there's a table e.g. in Cooper), but this is not what we want (too thick lens needed).

Explosive lenses? This gets more and more professional me thinks.... :D

quicksilver - 3-5-2006 at 06:58

Quote:
Originally posted by Rosco Bodine
Here's a thought . Some of the bearing metal alloys
like Babbitt might be useful for casting liners . Some of the alloys could have the right combination of properties to give good performance and they are low melting and
easily cast to form precision parts directly from the mold .


US3255659 has some very interesting proposals in which the casting is made via powdered material - in an pressed mold format! Thus one could used most any material in which is available in powdered form. From the patent the use of nickel powder had been quite successful and the mold easy to produce in most any home workshop environment. The availablity of nickel, tin, copper and moly is easily found on the mil-surplus market (got about 40lbs mixed samples for a few dollars of >325 mesh)

One issue I had found with spinning is the shape-tool end; it needs to be very smooth and rounded. My attempts were via a wood lathe and I used a blunted chisel. The smoother I made it the better. I buffed the tip to a glass-like knob and found that spinning was much easier. But the adhestion of the material to the bearing surface / mandel as pointed out previously WAS a problem. The best method I found was posted here; the use of a nut/bolt arrangment central to the work. I may try some copper this weekend as I feel much more comfortable now after messing with it for a dozen time or so. The alternative of forming via sheet metal has been less than clean geometrically but it DOES work. The energetic material however becomes more and more a significant issue in what I have seen and that factor has promise the more varied attempts I see.

Microtek - 3-5-2006 at 07:09

I don't think there is much mass transport through the shock front, so I don't think there will be any noticeable compression of the air in front of the shock wave. At least, not by the shock wave in the air. Anyway, as long as the speed is significantly below that of the VOD of the explosive, that is all that matters.
I've seen a high speed xray video of such a charge going off, and it detonates as if there is no propagation through the cavity.

panoptic - 3-5-2006 at 09:06

And thus they stumbled upon the channel effect...



To be fair, the channel effect will have a run up distance and a critical diameter (may not happen in large diameter cavities).



If you wanted to further decrease the density of a plastic wave shaper, possibly microspheres could be used.

I hope someone will eventually be able to reproduce the Zukas book.


[Edited on 3-5-2006 by panoptic]

12AX7 - 3-5-2006 at 09:58

Quote:
Originally posted by NBK
Since when does 6 lines = 17 lines? Please point out the error in this math. :)


It counts as 17 in the quote box here. Even six you must admit is disproportionate and still makes the point.

The letter count is roughly 48 to 440, just as significant FYI.

Quote:
I certainly don't expect people to trip over themselves to welcome me here, but I'd also expect people to acknowledge that I'm not some n00b idiot who's got nothing to add to the discussion, either.


Heh, well, the very nature of this quoted statement suggests that you very much so do want us to roll out the red carpet and bow down for your entrance. Not good form for anyone, I'm afraid.

Also, I count 19 lines on the subject in your reply, consistent with your other reply. I would observe you have a definite fixation on this, hmm?

Quote:
Research by the Buerau of Mines showed that rough sand-cast iron liners, cleaned of sprue and other such gross remenants of casting by simple fileing, penetrated to near-similiar depths as machined liners.

The difference was in uniformity of the hole profile, with the rough liners creating 'pocked' holes, compared to the typically smooth holes made by highly symetrical liners.


Ah, good to know. Liners may be far cheaper and easier than thought, then :)

Tim

panoptic - 3-5-2006 at 10:27

Peripheral initation of SCs is as I understand it to reduce the required explosive mass (the shock is spherical initially in a 'normal' SC) as well as to cause a quicker collapse by having the wave front sweep over the liner during a shorter time span (not to mention the direction of the shock wave).



BTW, spun formed liners may supposedly generate rotating jets due to stress in the metal.



[Edited on 5-5-2006 by panoptic]

Polverone - 3-5-2006 at 10:31

TAKE FURTHER VERBAL SQUABBLING TO EMAIL OR U2U

This thread is about shaped charges.

nitro-genes - 3-5-2006 at 12:13

These are really incredible pictures! May I ask where you copied them from? :)

Quote:
Originally posted by panoptic
BTW, spunn formed liners may supposedly generate rotating jets due to stress in the metal.
[Edited on 3-5-2006 by panoptic]


I've read this before... Only axial rotations, no horizontal drift I believe. Do you also know what it exactly implicates for liner collaps and performance? Quite amazing that with these incredible pressures and stresses, the small amount of internal stress in the liner can still have such an effect on the jet...:o

[Edited on 3-5-2006 by nitro-genes]

a_bab - 3-5-2006 at 12:27

On the pictures subject, do you have the rest of them showing the full jet formed? :)

These are X-ray pictures obviously. You can see the progress of the detonation from the blasting cap to the charge. Nice indeed...

panoptic - 3-5-2006 at 13:43

Here.

There is a wealth of information on the subject around, on the net, via accademic databases, in governmental databases, in patents, you name it.

Find a few documents, learn the terminology, find others by it.

BTW, I don't think it is x-ray (you see the expanding gases), I think it is cross sections and a high speed camera (possibly a linear charge).

Somone mentioned large casted liners, this is a spun cast copper liner with 0.7 m charge diameter (think military industrial complex, earth penetrators).



(Sorry to clutter the thread with images)



[Edited on 5-5-2006 by panoptic]

Attachment: SC.pdf (750kB)
This file has been downloaded 3243 times


quicksilver - 4-5-2006 at 06:24

Quote:
Originally posted by nitro-genes
These are really incredible pictures! May I ask where you copied them from? :)


The reference to Zukas book is the Fundementals of Shaped Charges.... it was available through the author who is a member of the ISEE and a working professor at a university (in the mid-west I think). The thing is out of print now. Not even ISEE's Blaster's Library has it anymore (I think the original source). It wasn't cheap. From the author it was $75. If you can find a copy even for more it may be worth it as it was a seminal work on this issue.

nitro-genes - 4-5-2006 at 16:33

Yeah, would really like to have FoSC too... Axt is one of the proud owners of the book. Too bad about his strict policy concerning the scanning of books. I mean, it is out of print and only 407 pages to scan, come on... :D

In an attempt to save explosive material, I tried to make a beehive charge from some pvc tubing, a plastic coffeespoon and the remaining PETN/Pib (about 18 grams). I aligned every component as precise as I could, but it was still a failure... Only 3.8 cm penetration this time, and a very messy entrance hole. I didn't even bother to post the pictures of the result, if anyone would like to see them, I might reconsider. ;)

Anyways, this was the setup that was used:



The difficulty might not even be avoiding a miss-alignement of some sort, filling the charge correctly was just very diffcult as one might imagine. I decided to fill the conical part of the plastic spoon and the part with the liner seperately and then glue them together. This made it very likely that some airpockets remained where the two pieces were pressed together. Also, the conical coffeespoon part was very fexible, and thus not very precise...
It's is quite a job I would say too make a perfect beehive charge, not to mention a charge containing a well functioning waveshaper lens. I still have some NM left, so I might try a liquid type of HE (PLX) for this kind of experiments...

Ahh, well... At least the movieclip attached is somewhat entertaining. :)

If you look at the three frames that captured the actual detonation in the movieclip, I think you can see a assymetry in the upgoing sparks caused by the jet at the right side.

[Edited on 5-5-2006 by nitro-genes]

Attachment: 25mm Beehive shaped charge compressed.avi (934kB)
This file has been downloaded 1956 times


NBK - 4-5-2006 at 19:37

Go to this thread where you'll find a working Rapidshare download link and password for the PDF copy of FoSC that I scanned. :)

Thanks go to Axt for refusing to share, for otherwise I never would have bothered with it myself. :D

While the file has 'Excerpts' in the title, it's actually the entire useable contents of the book. The pages that I didn't scan were all computer code for modeling, using hardware and programs that is either obsolete, or classified.

Polverone, if you want to add it to the SM library, go ahead. Just credit the source like the others. ;)

Deceitful_Frank - 4-5-2006 at 22:25

Nice little clip there nitro... I grabbed a couple of frames myself though I resisted the urge to post them up on this thread. The brightly lit ones expecially impressive. That camcoder of yours must have some lens to close down quick enough to give such detail in the action AND the path, fence bushes etc.

I'm presently looking for a camcorder myself. May I ask what make and model you use?

Anyway back to the topic!

You say that you had difficuly aligning the boat-tailing cone and this might have caused the assynetry in the detonation. IMHO it would be no harder to align a central detonator than a central cone section. More likely the problem was in the filling of the charge.

Getting two sections perfectly full and gluing them together without air bubbles is nigh on impossble and with a device this small, all it would take would be a small void on one side to slow the detonation wave and cause the cone to collapse unevenly.

As you appear to state... precision is critical :P

Thinking of using a liquid explosive... totally biased but you know what my favourite! :cool:
If you are making SCs more than 3-4cm diameter you might consider a 38:62 by mass blend of EGDN and NM. thats a 1:4 molar ratio.

This is balanced for CO and H20, has excellent gas output, density 1.26, 6600 m/s and at 145 kbar, 3/4 the detonation pressure of pure EGDN... but you get 2.5 times as much!

Needs abit more of a kick in the ass to get it going than pure nitric ester but I believe the high amount of NM makes it bery resistant to LVD. Tested 100 grmas in 3.3cm diamter and when it goes... it REALLY goes!

Sure... lets see those damage pix.... and you gotta post that second lit frame too!

[Edited on 5-5-2006 by Deceitful_Frank]

[Edited on 5-5-2006 by Deceitful_Frank]

nitro-genes - 5-5-2006 at 08:25

Here are the results:



The first picture from the left to the right is the entryhole in the first block of steel, 2.5 cm thick. In the bottom left corner a very strange copper coloured spot can be seen, without any penetration.
The second picture is the exithole of the same block. Underneath I placed the 5 cm steel block that I used earlier, to get a total of 7.5 cm of steel thickness.

What appeared most odd to me was that the exithole in the first block is about 8 mm in diameter, but the entryhole of the second block is only 3,5 mm! :o The penetration hole through the 2,5 cm steel block had a very smooth appearance though...
The two blocks were seperated only by a small piece of some kind of ceramic, about 2 mm thick, to make the two blocks level. I can't believe this can be the cause of the sudden drop in hole diameter between the two blocks. Also note the strange copper stains surrounding the entry in the second block...What has happened here?!
The two steel types were very much alike...

The movie was made with a digital camera, the canon powershot 540a. It can make 640 * 480 movies @ 30 fps or 320 * 240 @ 60 fps with 4 times optical zoom. The images are great, but the sound is not very good, since it has a very small microphone. The deep lows are therefore enot very well recorded...

[Edited on 5-5-2006 by nitro-genes]

enhzflep - 5-5-2006 at 16:21

Nice pics, as always nitro.
The spot in the first image has the same appearance as many of my failed attempts. Given the fact that I was mostly using hmtd, I always had a much lower Vdet and pressure. I notice opposite this spot that there appears to be some 'ripples' for want of a better word. I speculate that it could in fact be the location of carrot imapact. Did you find it this time?

You don't mention if the hole was covered by the ceramic, or if it was used as a shim. In either case without clamping the whole assembly together, you are liable to suffer a huge preesure loss once the first block has been breeched.

In refference to the staining surrounding the 2nd entry hole - Notice that 'flaps' surrounding the exit hole have not just bent back to be perpendicular to the face. They have in fact, continued to bend somewhat due to their momentum. This effect may well be enough to create a vacuum stong enough to de-focus the jet, resulting in (a) the surrounding copper spray, (b)The pitted appearance of entry hole #2 and (c) the marked decrease from ~8 to ~2.5 mm in hole diam, as the outer 'sheath' of the jet was whisked away.

Deceitful_Frank - The JVC Everio MG-50 is a pretty good camera. 720x576 @ 25fps(Pal) 29.997fps(NTSC) (interlaced, so there's 1/2 a frame 50 or 60 times a sec), 15x optical zoom, f1.2 lens:o, 48khz dolby sound, shutter speed to 1/4000 sec, etc, etc. Looks and sounds just the like the real thing.:D
Depends on what (else)exactly you want the camera for.

quicksilver - 5-5-2006 at 18:29

Quote:
Originally posted by nitro-genes
Here are the results:
Also note the strange copper stains surrounding the entry in the second block...What has happened here?!
The two steel types were very much alike...

It's hard to tell via pictures even good ones.....could that be the plug smear?

Your pics of explos show a black smoke, etc. (OB -) Have you been consistent, using the same explos material?

Fundamentals of Shaped Charges

enhzflep - 7-5-2006 at 21:01

Quote:
Originally posted by NBK
Go to this thread where you'll find a working Rapidshare download link and password for the PDF copy of FoSC that I scanned. :)


For those of you unable to access the above link, here it is again

address: http://rapidshare.de/files/11491938/Excerpts_from_Fundamenta...
rar password: "http://www.roguesci.org"


Jerzy Urban;).....
-------------------------------------------------------------------------------------------------------------------------------------------
Who is Jerzy Urban?

Liner production

enhzflep - 10-5-2006 at 02:39

Was reading through some of the Los Alamos stuff today and came across what appears to be a magnificent description of the way to go about creating SC liners.

Had pondered the idea of using my old 5ton kick-press (hydraulic rocket press would be fine too) for punching out liners, but was somewhat unsure of how to go about designing the tools..... UNTIL I came across a declassified doc from the 70s that some of you may have seen before.

After wading through the copious refferences to cross-milling and micro-crystalline structure analysis, of the roughly 4mm thick tantalum:o liners, the 17page document seems to boil down to about 3 pages of what seems to be quite a good text.

It seems that once one has passed through the stage of tool development, that a liner may be produced in as little as 2-3mins, with no annealing and virtually none, if any machining.
Even then, the toughest part for me would be the calculations and finalization of tool dimesnsions, once they were determined, tool manufacture would be really quite quick and or cheap.

Having just dusted off my press and sourced some steel plate and bar, just thought I'd ask if anybody else has contemplated or utilized this method?

[Edited on 10-5-2006 by enhzflep]

Attachment: Punch Forming of Truncated cones.pdf (72kB)
This file has been downloaded 3968 times


Rosco Bodine - 10-5-2006 at 09:23

Drop forging would work nicely too , just heat the
disc shaped slug up to a plastic free forming
temperature and quickly transfer it to the forming die and
whack it with the drop hammer . Depending on
the number of forming strikes and the cooldown of
the part , the final blows can even work harden
the finished part .

enhzflep - 14-5-2006 at 17:16

The drop-forging method would also be very nice IMHO. With a potential of
reducing the number of job-specific tools needed for production. Not to mention
that pressing a button sure beats the hell out of swinging a fly-press, kicking a
kick-press, or smacking a tool (and trying to keep the bastard straight)with a hammer. This would be a much better way to go about producing liners.

That said, my aim is to do it as much as possible on a homework-shop scale.

In that case, removing the need to handle hot blanks would be nice, as would
doing without a drop-press. Sure, it's a few more tools to machine/pay to have
machined, but in my case - without free access to a drop-press, a greater number
of forming tools is the cheaper option for me. I.e couple a bucks for more steel,
+ $0 tool production, since I machine them all myself downstairs.

However, work hardening of the final part would be performed in either case,
with a corresponding increase in penetration... :D

Effects of Plasticizing

enhzflep - 15-5-2006 at 05:11

Did another test last nite, involving the effects of plasticizing a
relatively low density powder. Typically, it's hard to get my
flavour of the month to much more than about 0.8g/cc. With a
TMD of around 1.56g/cc, I just had to be losing some
oomph, albeit for the sake of safety.

Having extracted some Pib(?) from Blu-Tak, I went about
plasticizing some HMTD. Managed to make about 7gms the first
time around, just using the HMTD that had stuck to the paper
toweling used to dry it after production.

Dissolved the sticky stuff (Pib?) from blu-tak with Shellite,
allowed all solids to settle, before eyedropper-ing about 3gms
of the resultant clear liquid into the HMTD, allowing to dry until
it weighed around 7gms, and smelled more like blue-tak than
shellite.

Upon a rough calculation of the new density, I was pleased to
find it was somewhere around 1.3! Not quite TMD, but one hell
of a lot closer than is feasible/safe to press it to dry.

First round saw me placing 7gms into a SC (as illustrated
below) and once again firing into 10mm hard-steel. I almost got
right through. I did however notice that the hole didn't taper in
diameter towards the bottom, as has been the case in previous
trials. The ground shock was also distinctly sharper and of less
duration.

Second round saw me placing a 3-4gm lump onto concrete
with no container, and the absolute smallest detonator I could
make. Think chinese firecracker fuse, with 1.5cm hmtd at one
end, initiated by a speck of Double salts at the black-powder
/Hmtd junction. This was then dipped twice in NC
laquer to exclude air and twisted tightly while drying, to a
diameter of 60thou - 1.5mm. 4 of them will fit inside a standard
'BIC crystal' ballpoint pen with the inards removed.

Ha. removed a triangular piece of concrete 2inches on each side
about 1/2 inch deep...

Now the thing that especially amazed me was: HMTD has a
really bad OB. Yet the +ive effect on VDet far outweighed the
-ve effect on OB. Light output was also reduced. But noise was
definitely better. Weird stuff.

So, 7gms of this, with a worse OB than straight Hmtd, and only
6 "active" grams in it was able to do greater damage - and more safely
to my steel plate than 7-8g straight. Makes the idea of using
copper liners with it seem feasible.........(+dirt cheap) :D

Note in the pictures that the Stand-off/liner retaining ring has
been crushed by the force on the colapsing cone. Makes one
think twice about just gluing the cone in place.

PlasSC.jpg - 110kB

quicksilver - 15-5-2006 at 06:45

Quote:
Originally posted by enhzflep

Having just dusted off my press and sourced some steel plate and bar, just thought I'd ask if anybody else has contemplated or utilized this method?


YES. I have thought of utilizing the copper end caps of copper home-utility pipe. The issue is how to create a series of levels or other progressive stages in the hammer-forging process. We have all seen the stamping method of forming. It is used in cap production as well. The best of two worlds would be met if one could stamp / forge a basic cone and then utilize a lathe to smoothe the form; taking care to aniel or in some way alter the crystaline structure of the metal during this process. I was out of town on business and now that I am back I will attempt to play with this concept. It appears to be workable via a wooden cone templet w/ differing levels.

One of the best methods of Plasticizing I have seen was created via the solvent of the base-plasticizing material. Let's say it's etoh: that was used....the solvent was initially poured into a beaker along with a greater percentage of HE and -then- the plastic was added bit by bit to that solvent, utilizing a teflon spatual to gently disolve the plastic through a figure eight pattern of movement. The order of addition was important as it allowed the creation of a totally saturated plasticizing component which held more HE than simple addition of HE to plastic, etc. This then yielded a PBX which was like the commercial in most respects. The result from that effort fit within a mold of the SC that was extremely effective when compared to a simple press-fit of HE. In fact the PBX could be molded by hand to such a shape that it proformed a cutting action in and of itself on concrete which astounded the observer.

[Edited on 15-5-2006 by quicksilver]

Deceitful_Frank - 15-5-2006 at 12:25

It would appear that the exact composition of blu-tak is a trade secret as the manufacturers are tight-lipped as to what goes in to give the right balance of stickiness and moldability.

It does have a density of 1.9g/cm^3 though and I am pretty certain the main filler is chalk.

Assuming that the binders and plastisizers have a density of about 0.9g/cm^3, this leads me to believe that the binder/plastisizer system makes up around 50% by weight.... obviously alot less by volume due to the differences in densities of the ingredients... Hmmm, this may not be right as if chalk is used it would be hardly worth adding it to add bulk as by volume it would only make up a small proportion!

Anyway it doesnt really matter what the binder/plastisizer is... it works and helps you to acheive a good solid loading density and increased bulk strength of your HMTD!

Tomorrow I will be making ETN for the first time for some descent pressed caps and to plastisize this excellent nitric ester for use in my next shaped charge.

For compositions I'm thinking either an 80:17:3 blend of ETN/NM/PIB. To plastisize the 80+% ETN with PIB, caster oil and motor oil or to try to replace the inert filler in blu-tak with ETN.
The first blend would appear to be the most powerful due to the high percentage of active ingredients and as long as NM will dissolve PIB, there should be no problems?

I can mix it all wet and then evaporate down to calculated weight for a dence plastique that really packs some punch! :D

[Edited on 15-5-2006 by Deceitful_Frank]

nitro-genes - 15-5-2006 at 14:26

If you could obtain any self vulcanising tape, you are far better of isolating the Pib from this than from bluetac. I tried both, and the bluetac does seem to have a slightly better binding ability, but is a mess to isolate in large quantaties. For the isolation from the self vulcanising tape, just dissolve all of the tape at once in about 100 ml of gasonline, let it sit for a week, filtering out the tape is very easy, and precipitate the Pib with 50 ml of acetone. Yield is about 18 grams of Pib, enough for >400 grams of plastique! Pib is precipitated very well by acetone, so I'm quite sure that NM won't dissolve Pib very well also. :(
Most simple solution is to use nitrocellulose from ping pong balls in combination with NM, this can form anything from a stiff gel to a viscous liquid with more or less NC dissolved...

There is however another binder you can use. I've experimented a little with this one, in combination with DEP, but with much less results than with Pib. You can find it in the typical clear school glue. It consist of nothing more than polyvinyl acetate with a solvent. PVA dissolves very well in acetone and NM and can form high density PBX type explosives by pressing...
I've been thinking to use this also for the PETN/NG composition, since you reminded me that the 1,65 g/cc density figure from COPAE probably is the density when pressed.
Under: "Penthrinits" in PATR there is also some information about the PETN/NG 4:1 composition, but this one gives a loading density of 1,49 g/cc, with a maximum achievable density of 1,72 g/cc. I think these figures a more thrustworthy, since they are from the same reference, but the information in PATR is more complete.

Detonation pressure thus is probably not as high as I had hoped. I wonder if intruducing a few percentages of polyvinyl acetate in PETN/NG will give slightly higher densities. Another option is a melt cast of PETN/ETN, but even than, that air is just so hard to get out! Maybe I will give my vacuumpump from the destilation setup another use soon! :D:D:D

[Edited on 15-5-2006 by nitro-genes]

enhzflep - 15-5-2006 at 16:16

Yeah, thanks again nitro. Turns out I had the wrong sort of wheels in the garage ;)
The blutak's been dissolved for ~1month, so had settled quite nicely. No real reason not
to finish that wheel off.

You mention NC and NM. Well have only got about 40 ping-pong balls left, Buuuut - what about double base powder? Have still got about 1.75kg:cool: of AS-30N kicking about. Bit more punch? (and cheaper to boot) $210 Aus for 2kg :D 10.5c/gram

Thank-you also quicksilver. I'd thought that method of mixing to be the better option, however was just a little impatient, and wanted plastique in under 45mins. But will have a bash at the method you mentioned.
Man, I hate being a lazy, impatient bastard...

Find below the pictures of the concrete & a star-stake.... Sorry for the shit quality - they're captured frames from a low quality vid.
4gms and then 3gms

HMTD-Tak.jpg - 66kB

nitro-genes - 16-5-2006 at 07:03

Just finished my new SC. :)
This time I used only prefabricated PVC parts from plumbing supplies. So, no sawing, sanding etc. was necessary to align the charge and liner properly, which is bound to make a SC less precise...

The charge consists of, from left to right:

1: 60 deg. (no tulip shape this time), 0.5mm thick copper liner with rouded apex, total height of 21mm and diameter of 25mm.
2: PVC tube endcap, with the innerdiameter of the liner sanded out in the middle, acts as a fitting to hold the liner in place.
3: PVC screw endcap, as explosives container (38mm high, so 0.8 headheight) and as an endcap for the charge.



And assembled it looks like this:



Still some doubt about the filler, but probably just the PETN/NG. Volume of the container with the liner in place is 18 ml, so with a denisity of 1.5 g/cc for PETN/NG 4:1, It will need about 27 grams of HE, and thus only 5.5 grams of NG. This is still acceptable for me. The only thing I still worry about is whether the NG will weaken the PVC to a great extent...Does anybody know this?

[Edited on 16-5-2006 by nitro-genes]

quicksilver - 16-5-2006 at 07:57

Tasking for granted that the NG is acid free I don't believe that you need have any concerns what-so-ever. The only issue with nitric esters and plastic containers is a wierd one: IF diphenylamine is used as a stabilizer and there is still some acid in the material you will get a deep BLUE stain. It has been one of the methods used time and again to identify a less than complete wash of nitric esters.
ETN is a wonderful thing. The more one delves into the mfg of ETN the more it seems a simple replacment for PETN. I highly recommend US1691954 as it's some of the better work published. Merck v12 has it. And you could check out various threads too. The biggest issue is purity, crystal formation, and nitration time. Once those issues are settled to your satisfaction, the material is truely awe inspiring in it's utility and stability.

rot - 16-5-2006 at 08:52

Nitro, Where is the standoff?

Rosco Bodine - 16-5-2006 at 12:45

Hmmm....I have never experimented with shaped charges
using liners , but just off the top of my head it looks wrong to me to me to have the conical cavity OD come
all the way out to the cylindrical OD of the columnar charge . The thin V shaped section just looks wrong
to me . If I were designing the thing , just going on intuition , the OD of the cone opening would be about
two thirds of the OD of the cylindrical columnar section ,
the end of the charge being a flat ring , rather than a
sharp edge like an open cored punch . I might even
make the flatted ring a bit wider so that the flat is
even a quarter the width of the column . The end section
of charge just seems to be too thin to be doing much of anything on that section of charge where the liner
comes all the way out to the OD of the column , it just
doesn't have sufficient cross section to be doing much
in the way of work of holding and forming a tight jet ,
but that is just my own visualization and thinking .....
I don't really know .....I just know that I would probably
build it the way I think it should work :D

It may even be that the columnar shape itself is not as
good as would be a gradually flaring column , something like
a trapezoidal keystone shape , to add some thickness even
further surrounding the conical liner . Anybody else
follow what I am saying here ?

Another thought I have had is a torus shaped charge
which has a trapezoidal cross section , but is a flared ring
having a conical shape , and detonated around the upper edge continuously by a synchronizer cylindrical charge which is apex initiated . This would function as a lens to collimate
the initial jet and reenforce it .


[Edited on 16-5-2006 by Rosco Bodine]

Deceitful_Frank - 16-5-2006 at 13:33

They call it subcalibration and IIRC the cone should be around 70-80% the ID of the SC casing.

My last EGDN SC had a cone of 20mm width and an ID of the casing of 28 so 5/7 or 71%

This can be built into the design of the SC or the space in the casing around the base of the cone can be filled with an inert material to save explosive.

For small devices however its often not worth the effort to save a gram of two of plastique... may as well just ignore the first few millimetres from the base of the cone and use 70-80% of its diameter when calculating your standoff and headheight :)

Boat-tailing (beehiving) also helps to save explosive and increase efficiency. SC's could be designed in all manner of shapes but not everyone has access to CAD software and a full metalshop... its often so much easier to stick with simple proven designs and just nitrate 30% more polyol! :cool:

[Edited on 16-5-2006 by Deceitful_Frank]

Rosco Bodine - 16-5-2006 at 13:51

I see , the " effective dimension " of the charge
is visualized as having that " dead end " thin
section being " sawed off " for purposes of calculating the standoff distance .
I just wonder if that thin
section could have unfavorable steering effect on the jet ,
because of the asymmetry of the detonation wave
cutoff where it goes below critical diameter in the thin
section . I guess it would depend on the explosive being
used , the degradation of the jet would be worse for
lower velocity and higher critical diameter explosives ,
and little concern for the faster and small critical diameter stuff .

[Edited on 16-5-2006 by Rosco Bodine]

nitro-genes - 16-5-2006 at 14:53

Quote:
Originally posted by rot
Nitro, Where is the standoff?


Lol, forgot to mention, I still have to saw off about 5 cm of 32mm pvc tubing that will be the standoff (2 times CD). This does not have to be very precise though...

Subcalibration indeed ensures that the base of the cone also participates in jet formation. For PETN the critical diameter for high order detonation is about 2mm, so for my charge about 20 mm of the 25 mm will be 100% effective maybe, but using subcalibration in combination with a composition containing NG is just very difficult to realise. NG attacks almost every glue and plastic there is and the subcalibration has to be done by hand, which makes a good alignment more difficult. Steel or other metal tubing instead of PVC is not an option, I really don't like shrapnel for that matter...
As I noticed with the beehive charge, very small aberrations in the alignment will have a dramatic effect on jet formation, so although subcalibration improves efficiency quite a bit, it also complicates things quite a bit.
I don't think subcalibration is that critical btw since Axt his .357 magnum bullets still did 2.5 cm of steel IIRC!

The most difficult things for a home made shaped charge are liner symmetry, the alignment of the liner in the explosives container and to a lesser extend, the point of initiation in combination with the headheight. If one of these is slightly off, there will be no penetration at all, especially with cone shaped liners. The rest, like heavy confinement, subcalibration, explosives composition etc. will only have an effect on the overal efficiency or CD's of penetration...

[Edited on 16-5-2006 by nitro-genes]

Chris The Great - 16-5-2006 at 23:08

Remember that the jet travels much faster than the speed of the collapsing liner (6-10km/s vs ~2-3km/s). Most of the jet will be through the target by the time the last edges of the cone finish collapsing, so even if they had a unfavourable effect, it wouldn't matter. It certainly wouldn't be able to "catch up" to the rest of the jet and knock it off course or have other unfavourable effects.

Deceitful_Frank - 17-5-2006 at 01:43

You took the words right out of my mouth! ...or should I say fingertips! Yep, thats all I have to contribute this morning :)

Boomer - 17-5-2006 at 04:19

While speaking of fingertips...

Enhzflep I noticed you're a lucky bastard, since on that pic said body parts
are still present. NEVER mix HMTD with anything, it is chemically unstable
and much worse in this respect than its acetone sister. I personally
had it detonate into my face while plasticising, while it was already
a goo and the force used was less than what would have set off
dry powder. There are SEVERAL similar stories from other peaple,
IIRC two including auto-detonation sitting on a shelf.

Obviously you were lucky this time, or used a combination that is more inert,
but do you KNOW it would not have 'misbehaved' had you aplied
a little more force while mixing, or had used more/less/another solvent etc?

Try writing with your non-dominant hand, or even wipe your ass - it sucks believe me.

nitro-genes - 17-5-2006 at 04:35

Had the same thing, 7 grams of HMTD/NC plastique just went BOOOM! suddenly...I was sitting about 60 cm away from it, since I just stopped mashing it. Small pieces of the cardbord and foil it was lying on went through my trousers in my knee (!) and I couldn't hear for two days. It's years ago now, but still my right ear is not as good as my left. :( Still, I think I was just very lukcy...
It is such a terrible experience really, the first few minutes I just walked around without knowing what had happened, then I saw the blood al over my knee and the crater in the table... I stopped making HE's for more than a year after this, sometimes I wonder what is wrong with me to continue to do this...

Boomer is right, PLEASE stop fucking around with that shit! If you continue using HMTD like this it is not the question IF an accident is going to happen, only WHEN. :(

[Edited on 17-5-2006 by nitro-genes]

HMTD - 17-5-2006 at 06:49

Hello! I really like this thread. I saw the pictures with such amount of HMTD plastique with fingerprints on it. Now, Enhzflep, imagine: You just mixed 7 gramms of plastique, you knead it with you WORK hand - this is more comfortable for you. You like it's consistency, it's so softy, you think where to use such a good thing? Next moment it all disappears, you don't feel any pain, but the next second you see your hand, if it can be so called now. The blood from broken arteries flows to the floor in the rythm of your heart. YOU HAVE NO FINGERPRINTS ANYMORE. You trying to stop bleeding, you call to emergency, later you will spend a month in a hospital. Now you feel pain. Such a pain that you can't sleep. But it will be later, when nothing you can change. But you still can. You think this is joke? The friend of mine partially lost his two fingers when only 0,3 g ( not 7!) of such a plastique detonated in his hands when he tried to form it. The rest amount spontaniously detonated after 5 days after accident. The binder was clear Pib/polybutene liquid. Please, don't use HMTD in mixes and your devices!!! There are beautifull substances - high explosives, for example, PETN. With such a binder they are more dense(I had 1.59 for 89/11) and powerful than anything with HMTD. As for me, now I use small amounts of primary - just 0,02-0,05 g of PbN6 with powdery PETN. Good luck. Sorry for my English.

rot - 17-5-2006 at 07:24

I'dd say don't even use sensitive primary's like HMTD or acetone peroxide. they're just too dangeroes. I use Silver Acetylide, Wich is much safer (didn't detonate when I crushed it between 2 metal plates).
I used to use Acetone Peroxide as primary but started using Silver acetylide after I once had it detonate when pressing it into a plastic tube. It was 0.5g, thank god I was holding the tube with pliers or I would have been a finger shorter.

a_bab - 17-5-2006 at 07:37

I once got a nasty explosion because of the Ag2C2; I'd say it's far more sensitive than the AP; maybe something like the mercury MF. Very static and flame sensitive that is, if is well dried. It can bite.

I still have a small mark of embeded carbon/silver oxide under the skin as to remind me. The amount involved in the accident was maybe 1 gram, in a plastic box no bigger than a film can but all the palm was heavily bruised and it really did hurt. Alot.

quicksilver - 17-5-2006 at 08:04

Quote:
Originally posted by nitro-genes
Had the same thing, 7 grams of HMTD/NC plastique just went BOOOM! suddenly...I was sitting about 60 cm away from it, since I just stopped mashing it. Small pieces of the cardbord and foil it was lying on went through my trousers in my knee (!) and I couldn't hear for two days. It's years ago now, but still my right ear is not as good as my left. :( Still, I think I was just very lukcy...
It is such a terrible experience really, the first few minutes I just walked around without knowing what had happened, then I saw the blood al over my knee and the crater in the table... I stopped making HE's for more than a year after this, sometimes I wonder what is wrong with me to continue to do this...

Boomer is right, PLEASE stop fucking around with that shit! If you continue using HMTD like this it is not the question IF an accident is going to happen, only WHEN. :(

[Edited on 17-5-2006 by nitro-genes]


The horrable but interesting thing is that the material detonated AFTER any physical contact or stimulus. THAT is exactly why I just can't see experimenting with peroxcides. And 7 grams of HMTD/NC plastique is no small chunk of change! To propel cardboard into flesh is really something to contemplate.... I suppose that the issue is that from an experimentor's perspective it's availability and lack of expense is attractive. but there are so damn many alternatives. Especially if one buys several pounds of Erythritol or Mannitol. The thing is that those sweeteners are available to anyone for pennys (send me mail & I'll be happy to give URLs).
It just goes to show how vastly unpredictable HMTD / AP are and how uniquely addictive this damn hobby is as well.

rot - 17-5-2006 at 10:07

Let's go back on topic.

enhzflep - 17-5-2006 at 19:42

Shit, God dammit. So those pics I've seen of a hand missing fingers were from you Boomer, the very one and the same? Along with the little boy that chewed on a detonator, the BP fountain imbedded in knee and the CO2 bulb that passed through somebody's leg. OUCH. Never mind the guy that was cubed by a pipe bomb. :D

It is therefore the case that I must say thank-you to Boomer. For I never tried plasticizing the shit until after I read your post at RS.org. Read about (kewlish) efforts to 'plasticize' AP with double base powder (10%Ng, 90%NC). Hey I even gave it a bash once, but that stuff is not very friendly - the AP recrystalizes into HUGE crystals. So, reading your post along with the AP experiment and seeing that picture of your hand caused me to never, ever want to try mixing it with NC and or NG.

So, anybody got an idea of what I should do with the 15gm chunk of the stuff I've had sitting outiside for the last 5 days? Guess I should leave it away from the 50gms sitting in the pyrex jug...

But seriously - I guess you could put it down to having somewhat of a cavalier attitude towards the stuff, not (just) simple ignorance. I first spent about 10 hours looking across the net for accidents involving the stuff. The thing that was overwhelmingly in common with these accidents was (A) mixing with NC, (B) mixing with DB powders or (C)pressing into containers made of incompatible metals(in which case, any moisture would increase rate of decomposition). To be perfectly frank, the remainder I put down to "operator error" as it were, judged on account of the apparent poor grammar, scientific technique and lack of understanding of the seriousness of the compound exhibited by those unfortunate many.

Over the course of several dozen batches I have altered the method used to wash and neutralize it. It is in my experience, much, much harder to free the substance of all traces of potassium carbonate or sodium bicarbonate than it is to free the substance from citric/hydrochloric acid. Therefore I don't neutralize it, but merely wash it. I borrow a ph meter with 3 sig figures, and use a biometric sensor too (my tongue;))

Anyway- after 4months of sitting, a mixture that has been neutralized detonates with a distinctly different smell and much reduced flame. Not to mention the fact that said powder retains clumps as a result of moisture retention. Almost smells like a coke fire furnace.

After the same period a batch that has been washed and washed and washed again (some 10 - 15 times) reacts _precisely_ the same as it did on the first day it was dried. Not only is there no funny smell or flame reduction, but the powder is as free flowing and fine as powdered glass - an indication of the lack of water absorption/retention.

The binder from blu-tak was chosen for several reasons.

1) It's non-toxic and safe for children to play with/eat (so long as they don't choke on the stuff) This is an indicator that it is an inert substance. Along with the claim of the inertness of its binder in Bostik's MSDSs. One may leave a blob of the suff sitting in the open air for months and months and months at a time without any observable change on the surface - it never hardens or dries out i.e no observable volatility or oxidisation taking place. Although UV light's not its best friend.

2)Its readilly available and comes from a well respected company with too much of a reputation to protect to produce batches with significant varience in physical/chemical properties. Though I'd obviously be in no position to sue for a change in composition;)


In addition to these facts, I started out mixing some 0.2 - 0.3gms of hmtd with the blu-tak binder. This first sample was divided into two. One sample went into the oven at 60deg C where it sat without incident for 4 days, while the other half went into the freezer. At the end of the four days, each sample was again divided into two, meaning that I now had 4 balls. One ball from each storage method was tested with hammer and anvil, the other 2 balls were tested with flame.

Results: Hammer testing was significantly harder to initiate than straight powder - with no discenrable difference between two two storage methods. - Also noted was the fact that incomplete detonation was observed, a small blob remained on anvil after testing. Scraped up, this was still dentonatable.

Flame testing was similarly uneventfull,although very nearly as sensitive to flame/spark as straight powder - it must be noted that the burning did in fact proceed somewhat slower than a similar quantity of straight powder would.


NOW,
All that said. Thank-you, one and all for your concern. This is pehaps the appropriate time to get a new flavour of the month. (while i can still type & shit with gay abandon:)) Programming the new version of HECalc is hard enough with two hands

I guess ETN should be next. Besides, as video from Axt and Nitro-genes have clearly shown this material has great utility for the construction of shaped charges.

Has anybody thought along the same lines as myself, in that a flexible linear SC could be quite effortlessly constructed using copper powder and latex-rubber? (or other similarly flexible, curable product- possible silicone sealant...)

*Imagine if you will, firstly filling the bottom ~ 1/2 of U-channel with latex rubber. Then laying a piece of 90deg angle into this
*Following this, a thin layer of (safe) plastique would be inserted, before having a cavity formed in it with a square rod.
*Next would come the pouring in of a latex/copper mixture, to act as the liner. This too would have a cavity former inserted
*Finally, latex could be poured ontop and allowed to cure.

-I imagine this to be somewhat similar to the method utilized by commercial manufactures of said product. Albeit with certain efficiency (and possible continuous, i.e extrusion) techniques.

I have attached a diagram that should better describe what I mean below.
[/cavalier attitude]
Look forward to the new version of HECalc coming in the next week or so. Includes library of explosives, better numerical methods, Calculation of OB and VDet for multiple compounds, output saving and comprehensive help.
enhzflep.

EDIT:
And yeah. I do realise I've misspelled mold as mould in the very first line. Oh well, too lazy to edit image and re-post....

[Edited on 18-5-2006 by enhzflep]

Flexible Linear Shaped Charges.jpg - 95kB

nitro-genes - 18-5-2006 at 02:51

Last night I tested the 25mm shaped charge with PETN/NG. This stuff is dense! I measured the volume of the container to be about 18 ml, and because PATR mentioned PETN/NG 4:1 to have a loading desity of 1.49 g/cc I thought I'll make 28 grams total to be sure to have enough. Turned out I was still about 1-2 grams short...

What can I say, the report was an incredibly thight thumb really, in that sense noticably different from the PETN/Pib composition. The movieclip is nothing special, since the mixture is pretty oxygen balanced. But the reverb coming from the nearby water was great. :D

Fairly good results this time, I used the length of the small block of steel this time, which is 7.5 cm long and 2.5 cm thick! The jet came very close to penetrating the whole block, as well as almost completely splitting it. :o
I measured the depth of penetration with a long thin needle and came to a decent 6.8 cm. Still, not even close to the 4 CD+ specs such a charge should do. :(
Again there was the same copper coloured dimple (grey circle in the first picture) next to the enrtyhole, just like with the last one. Very strange, since the first shaped charge did not show this. There was no carrot in the penetration hole, so that may have been the cause of the dimple. Precision really is key for a good shaped charge I think...Then again, how can there be a reasonably good jet formation with the carrot beeing more than a centimeter off center?!





I've systematically demolished all of my steel blocks now, so I'll have to find some replacements. :D The next charge will be done underground, so with good sand tamping. and some subcalibration. I expect a much tighter and deeper penetration for this setup, maybe 4 CD will be within reach! :)

[Edited on 18-5-2006 by nitro-genes]

Attachment: 25mm PETN+NG SC small compressed.avi (919kB)
This file has been downloaded 1609 times


enhzflep - 19-5-2006 at 00:00

:o :o
Now, that is a pretty picture.:D
From previous experiments with last month's flavour of the month, I was able to determine that when I used a plastic body rather than a metal one, I only got about 1/2 as much penetration. Certainly, i think the effect may well be less with a faster compound, but applying the same formula to the penetration shown above would give you about 13.6 cm - some 5.5 CDs. I forget the name and location of the file, but I believe Axt has posted a file detailing a study into the effects of changing the strength of confinement.
(It was a jpg from memory)

I really wouldn't have been doing more than pissing into the wind about the dimple, UNTIL i read some posts in the last 2 or so pages of this forum, Re: critical diameters of explosives. My $5 says that once you get subcallibration with at least the critical diameter of your explosive around the base of the cone, that you will no longer have the carrot being blown off center.

nitro-genes - 19-5-2006 at 02:34

Quote:
Originally posted by enhzflep
I really wouldn't have been doing more than pissing into the wind about the dimple, UNTIL i read some posts in the last 2 or so pages of this forum, Re: critical diameters of explosives. My $5 says that once you get subcallibration with at least the critical diameter of your explosive around the base of the cone, that you will no longer have the carrot being blown off center.


It can't be the whole story, since the beehive charge with the 25 mm liner had the largest subcalibration of the three charges (2.5mm), and had the dimple/stain next to the entry hole also!
I think I might have been not precise enought with the drilling of the detonator hole in the endcap. But this could be half a millimeter at the most. Another thing could be fluctuating densities or even small airgaps in the explosive at the base of the cone. I agree that the collapse of the base of the cone is most likely the problem, but again, the beehive charge did also have this problem... It can't be the liner though since the penetration of the first charge was perfectly symmetrical with a smooth appearance...:)

Confinement is something I still want to try, although sandtamping probaly is not as effective as a steel wall...

quicksilver - 22-5-2006 at 06:14

Could it be that the strength of the whole need be equal? That is that if there exists a greater strength to the cone than the body or visa versa that differing results occur? The example of a small cone made from a bullet casing comes to mind. Here the cone is weaker than the body. However, the elastisity of the whole is mostly equal. PVC, etc may be quite strong in terms of containment due to it's flexability. Could that very factor be an influence?
Most commercial SC have less varience in wall and cone flexability it appears....just a thought.

Joeychemist - 24-5-2006 at 15:50

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:)

[Edited on 24-5-2006 by Joeychemist]

enhzflep - 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]

nitro-genes - 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]

quicksilver - 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...

Fulmen - 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.

nitro-genes - 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?

Fulmen - 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%.

nitro-genes - 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...

Deceitful_Frank - 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 :)

Fulmen - 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.

Deceitful_Frank - 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?

Fulmen - 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 :-)

nitro-genes - 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]

Deceitful_Frank - 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]

nitro-genes - 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]

Boomer - 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.

Deceitful_Frank - 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?

nitro-genes - 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)
This file has been downloaded 1976 times


Fulmen - 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.

nitro-genes - 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

Fulmen - 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

nitro-genes - 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]

Fulmen - 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.

Chris The Great - 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)
This file has been downloaded 1702 times


Fulmen - 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.

Cube - 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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