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Fulmen
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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?
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nitro-genes
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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]
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rot
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I think this thread should be a sticky
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Fulmen
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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.
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Microtek
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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.
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Fulmen
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Lenses are exiting, any more details on your experiments?
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nitro-genes
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| 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
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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...
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? 
[Edited on 30-4-2006 by nitro-genes]
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Fulmen
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| Quote: | Originally posted by nitro-genes
| Quote: | Originally posted by Fulmen
I have the liner from an 84mm Carl Gustav RPG.... |
Ebay?
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Sure, when hell freezes over :-)
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Swany
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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.
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Deceitful_Frank
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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]
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Deceitful_Frank
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My second shaped charge.
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]
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Deceitful_Frank
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...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]
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nitro-genes
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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]
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NBK
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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]
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Microtek
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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...
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quicksilver
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| 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?
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Deceitful_Frank
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| 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! 
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!
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]
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NBK
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Whatever happened to a simple "No."?
No.
I don't remember you. Were you that memorable of a K3wL that I should remember you?
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]
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12AX7
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| 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
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nitro-genes
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| Quote: | | ...don't clutter up the board with your whining. |
LOL, quicksilver's reply was was quite funny in my opinion. 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.
[Edited on 2-5-2006 by nitro-genes]
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quicksilver
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| 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]
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12AX7
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| 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.
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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
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nitro-genes
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| 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]
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enhzflep
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Spinning Liners
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?
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NBK
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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]
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