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Author: Subject: Unconventional Shaped Charges
Axt
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[*] posted on 14-6-2006 at 20:23


That does make some sense. Its why they use exotic liners in cylindrical liner studies, usually beryllium.

"Differential cones transfer momentum from the explosive to another material, usually a metal such as copper, with a speed of sound different from the speed of the blast in the explosive. The slope of the cone is chosen so that the speed of the blast at the surface of the cone is equal to the speed of sound of the metal on the surface of the cone. The result is a hypersonic jet. This jet then penetrates the armour. This is also called the Munroe effect, discovered in 1888. This is the basis of high explosive anti-tank (HEAT) weapons."

Meaning the "speed of the blast" is relative to the angle of the cone, with cylindrical being the upper limit.

See pg. 106 of FoSC for more info, "For shaped charge applications, the major criterion for jetting is that the formation process be subsonic. Otherwise the jet will be incohearent and spread out radially.....".

Though there is the book, "Evaluation of Improvised Shaped Charges" search amazon for it, still available on special order. Essentially the book is a reprint of a study on cylindrical lined charges. Its just a heap of tables with charge dimensions, materials and penetrations. I cant remember much from it, only that a short standoff was desirable ~1/4" or something. I had it opened it once, then lost it :( It was for Al/steel/Cu tubes but unsure what explosive was used, C4 or equivalent plastic explosive I think.

Cube, give more information on that charge. explosive/dimensions/thickness of steel etc. I'm quite sure that if I'd used thicker steel thats what my result would have been, where the steel was too thick for a "hole punch" effect.

[Edited on 15-6-2006 by Axt]
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[*] posted on 14-6-2006 at 21:56


Quote:
The slope of the cone is chosen so that the speed of the blast at the surface of the cone is equal to the speed of sound of the metal on the surface of the cone. The result is a hypersonic jet.


That just answered so many questions about designing a shaped charge it is unbelievable. Why different angles and materials? Speed of sound considerations.

I've seen a lot of questions about "what angle is best" and no one offered a good explanation... and here Axt solves it all with one little quote.

In other words it is a piece of cake (as much as a bunch of trig is a piece of cake) to choose the optimum angle for your chosen explosive, assuming your VoD is right.



Still bugs me that I'll need some really weird liner materials to do a high VoD cylindrical charge.
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[*] posted on 15-6-2006 at 08:38


the steel plate was 5cm thick
i tried to copy your charge, so i had nearly the similar dimensions
the sc inside diameter was 4,7cm and 10,5cm high . copperpipe as a liner. its outside diameter is 15mm, 1mm thick and 65mm long
no standoff
i think i used about 110g ANNM

[Edited on 15-6-2006 by Cube]
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[*] posted on 15-6-2006 at 14:55


Axt, nice to see a post from you again in this thread. :D I suppose you finished all your research about the extremely interesting diaminofurazan derivatives... Have you ever thought about meltcasting some of your precious DNAF into one of your bullet shaped charges?

Nice article btw Chris, although like fulmen, I'm rather puzzled how very fast explosive compositions like Octol and LX-14 in combination with copper cones with slopes as low as 42 deg. can be justified. Molybdenum is known to be better liner material then copper and does have a higher speed of sound (5400m/s), but then again DU has an even slower speed of sound than copper though is slightly better than the former.

I think every liner material is a tradeoff of between favorable and less favorable properties, like density, dynamic stength, ductility etc. There just is no material that has the perfect combination of these properties, and a favorable speed of sound is just another desirable property that maybe is not that critical as some of the other properties like for example the incredibly high density of DU...

I think the problem is that for a cylindrical shaped charge, the mass percentage of the liner that is accelerated is so small, that the radial expansion will make the liner much faster incoherent (less dense) than in a liner of say, 60 deg. with a much larger mass consistancy. So in this case the speed of sound may become much more important than the other properties. (Small mass and jet lenght, so density and dynamic strength may be less important liner material properties in this case)

This is a nice link which gives some speed of sounds in different materials:

--> http://hypertextbook.com/physics/waves/sound/

Glass has also got a decent speed of sound, maybe this is one of the things that accounts for it's relative high performance as a liner material. :)

[Edited on 15-6-2006 by nitro-genes]
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[*] posted on 15-6-2006 at 22:53


In the interests of science, I bring you- calculations! First, general rules, and then the equations used to find those conclusions. The actual problem was solved by my friend in about 15 minutes (including re-doing them to double-check), it would have taken me much longer on my own.
I made the assumption that the liner collapse would be perpendicular to the liner material, otherwise it would start getting way too complicated.

Also, these diagrams are not to scale. The lines aren't at the right angles and such. They are just to show you which variables go where, since that is important in this.

First, find the VoD and speed of sound in the liner material. These are variable Ud and Cv respectively. You also need the radius of the charge, which shall be r.

Now, we want to find the maximum angle of x. The triangle is our liner in case you couldn't tell.


First, we find Q, which is Ud/Cv

The hieght of the cone apex will be h.
r<sup>2</sup> = (Q-1)h<sup>2</sup>
A quick calculation gives the hieght.

To find the maximum angle, it's easy trig:
tan<sup>-1</sup>(h/r)

Tada! An example will be an explosive detonating at 8325m/s and a copper cone with a speed of sound of 3800m/s. The radius was chosen to be 38.1mm.

Q = 8325/3800 = 2.191

(38.1)<sup>2</sup> = (2.191 - 1)h<sup>2</sup>
h = 34.912mm

tan<sup>-1</sup>(34.912/38.1) = 42.5*

NEAT!



Now, the proof of how the hell we got these! You need to use actual numbers when solving or you wouldn't have noticed stuff like the (Q-1) and stuff. In this case we used methyl nitrate at 8000m/s and copper at 3800m/s, the radius being 19.1mm. These equations have been checked.

We also have this fancy diagram. Triangle I is the cone, triangle II is the area that the liner will go through during the collapse.


Q = 8000/3800 = 2.11

a + b = 2.11a
r = 19.1
b = 1.11a

a<sup>2</sup> + r<sup>2</sup> = c<sup>2</sup>
(1.11a)<sup>2</sup> + r<sup>2</sup> = d<sup>2</sup>

Therefore
c<sup>2</sup> + d<sup>2</sup> = (2.11a)<sup>2</sup>
c<sup>2</sup> = (2.11a)<sup>2</sup> - d<sup>2</sup>

Substituting in equation one:
a<sup>2</sup> + r<sup>2</sup> = (2.11a)<sup>2</sup> - d<sup>2</sup>
r<sup>2</sup> = 4.4521a<sup>2</sup> - a<sup>2</sup> - d<sup>2</sup>
r<sup>2</sup> = 3.4521a<sup>2</sup> - d<sup>2</sup>

Then, we add that two equation two:
( r<sup>2</sup> = 3.4521a<sup>2</sup> - d<sup>2</sup> )
+ ( (1.11a)<sup>2</sup> + r<sup>2</sup> = d<sup>2</sup> )

We get
(1.11a)<sup>2</sup> + 2r<sup>2</sup> = 3.4521a<sup>2</sup>
2r<sup>2</sup> = 3.4521a<sup>2</sup> - (1.11a)<sup>2</sup>
2r<sup>2</sup> = 2.22a<sup>2</sup>
Hmmm
Notice 2.22 is 2(Q-1). Twos cancel and give us r<sup>2</sup> = (Q-1)a<sup>2</sup>
Would not have seen that without plugging in some numbers.

Anyway, start solving from there.
a = 18.1
b = 20.1
c = 26.3
d = 27.7

Anyway, it's easy to solve for the angles once we find some of the measurements.
tan<sup>-1</sup>(a/r) = xi



Now, There are a few problems with this method. The main one is that the time in which the liner collapses will be longer than the time in which the detonation impacts the entire cone. So in reality, this will NOT give the maximum angle. However, it seems to be a good way to estimate what will work.

If you wanted to know the EXACT maximum angle, you'd have to incorporate Gurney velocities to find out how long it will take the cone to collapse... which will depend on the angle. So now you have just introduced ANOTHER variable to the system. You'd also have to complicate things by knowing that the cone collapse will not be perpendular to the liner.
How about no :D

I've got more spares tommorrow, we'll see what we can do. Math is pretty fun when you're doing it with someone who has a clue.

However, from these calculations and knowing that it does not give the maximum angle, it is perfectly reasonable IMO to have 50* copper cones with explosives VoDing in the 9000m/s range.

[Edited on 16-6-2006 by Chris The Great]

[Edited on 16-6-2006 by Chris The Great]
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[*] posted on 16-6-2006 at 03:43


I don't understand why you calculate the tangent angle X... I thought that the liner angle was usually given for the cosinus angle (twice that is) in your picture. (LA in the picture below)



So with calculated maximum of X of 42,5 deg. this would mean that the maximum liner angle would be 180-42.5*2 = 95 deg...

The liner angle of a cylindrical shaped charge is taken as 0 deg. I think? So your not looking for a maximum angle but for a minimum I guess...

And in this article they use a simple equation that includes the slope of the cone...

An analytic model for the prediction of incoherent shaped charge jets
R. J. Kelly

It is now a well recognized fact that the jet from a shaped charge can be overdriven in the sense that the fastest moving particles are not produced as a cohesive mass of material. Rather, the tip material may be produced as a number of discrete particles which possess different nonzero radial components of velocity and hence spread out from the axis of symmetry of the charge. Such a jet is classed as incoherent and when this incoherency occurs the jet's target penetration capability is invariably degraded. This physical phenomenon is the subject matter of this article. Several experimental results using common shaped charge materials are presented first. An analytic model which predicts the jet speed at the transition point between a coherent and incoherent state is then described. This model is based on the assumption that a stagnant core with circular boundaries exists in the flow region. Further, the flow field is assumed to be compressible with circular streamlines. The Murnaghan equation of state is used to relate the pressure and density in the flow region where the jet is produced. It is postulated that the transition between a coherent and incoherent state occurs when the circular flow becomes wholly supersonic. The critical Mach number for coherency is shown to be approximated to high accuracy by a simple formula depending on the collapse angle of the flow and the incoming flow speed. Excellent agreement between the model predictions and the experimental data is demonstrated.

This would be helpfull too:

Criteria for jet formation from impinging shells and plates
Pei Chi Chou

Criteria on jet formation and jet cohesiveness are proposed for collapsing solid plates and shells. These criteria are also applicable to impinging fluid sheets from plane or annular nozzles. Under the high impact speeds treated here, the solid plates or shells behave as compressible fluids; for the impinging fluid sheets compressibility effects will also be assumed important. Jetting will occur if either the collision is subsonic or the impinging angle is large enough such that the shock in the flow is not attached at the collision point. Jets formed from subsonic collisions are coherent; those from supersonic collisions are not coherent. The criteria are shown to be in general agreement with available experimental evidence. Further, the proposed criteria are also verified by two-dimensional unsteady finite-difference computer calculations. In addition, these calculations indicate the mechanical reasons for the coherency or noncoherency of the jet under various impact conditions. The practical applications of these criteria include collapsing shaped-charge liners, the explosive welding of plates, and steady impinging fluid sheets from annular nozzles. Journal of Applied Physics is copyrighted by The American Institute of Physics.

If someone has acces to these articles, could they be uploaded? (Edit: Please? :))

[Edited on 17-6-2006 by nitro-genes]
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[*] posted on 17-6-2006 at 12:41


Found some information about the machnumber: :)

Current shaped-charge jet theory maintains that a stable jet cannot form if the Mach number of the collapsing liner relative to the collapse point (that is, the Mach number of the material entering the collapse point) is greater than a critical value (this is called the sonic criterion). Jets formed at greater Mach numbers are said to be overdriven and show splashing, hollowness, and particulation, which reduce the performance of the jet. A critical Mach number of 1.23 (based on the static speed of sound) is often used for a copper liner. A design in which the Mach number of the collapsing liner is less than but close to the critical Mach number is said to be extreme...

So they define the machnumber to be dependant of the velocity of the liner material entering the collapse point. Wouldn't this be equal to the VoD of the explosive? I would really like to know the connection between the cone angle and the Vmax of the accelerated liner wall. And wouldn't the velocity at the collapse point also be dependant of the thickness (mass) of the liner then? I mean, a larger mass is accelerated slower, but then again, propably the acceleration is so fast that Vmax is generally reached before the two walls collapse. Acceleration time is the reason though why the cone with the rounded apex is a better liner shape than a sharply pointed cone...

[Edited on 17-6-2006 by nitro-genes]
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[*] posted on 17-6-2006 at 16:31
Some thoughts


Here are some software generated kinematic depictions of

shaped charges in action -> http://www.warheadanalysis.com

Two more not shown on that page _

http://www.feainformation.com/avilib/83.avi

http://www.feainformation.com/avilib/62.avi

My favorite, Von Mises stress on twin hemispherical liners

wouldn't mind lighting the fuse on that one :)

http://www.feainformation.com/avilib/61.avi


In viewing the posts here I don't see any mention of the use

of tamping. Tamping is not practical for muntions and largely

unecessary since the charge is contained within a steel casing

and is in motion toward the target when set off. In stationary

shots adding tamping significantly improves penetration.

Glueing the charge to the inside bottom of a plastic jug so it

can be filled with water will work well.


Does anyone have information to post or links refering to the

use and application of metal Interstitial hydride cavity liner.

The secondary incendiary effect should be quite spectacular.

.

[Edited on 18-6-2006 by franklyn]
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[*] posted on 18-6-2006 at 02:58


This article could also cover the relation between critical mach number and liner angle:

Considerations about the Analytical Modelling of Shaped Charges
Pierre Yves Chanteret

Propellants, Explosives, Pyrotechnics
Volume 18, Issue 6 , Pages 337 - 344


Abstract
The problem of building and using analytical codes for shaped charge simulation is reviewed. The basic physics of the whole shaped charge functioning is considered, starting from explosive liner interaction, going through jet formation and jet break-up, down to cratering into the target. For each stage of the phenomenon, a critical look is given to the existing analytical models, with the idea of determining which models are able to adequately predict the shaped charge behavior with keeping an as low as possible degree of complexity. On reviewing these analytical models, it is shown that some parameters have to be taken into account for a better understanding of what governs shaped charge performance.
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[*] posted on 4-7-2006 at 04:54


Some information that I found in the abstract of:

"An Unsteady Taylor Angle Formula for Liner Collapse"
Authors: Pei Chi Chou; Eitan Hirsch; Robert D. Ciccarelli

An analytical formula for determining the direction of motion for an explosively driven metal liner under unsteady conditions is presented. This direction is defined by the angle delta between the velocity vector of the liner element and the perpendicular to the initial liner surface. A formula for determining the angle delta was first proposed by G.I. Taylor as sin delta = V/ 2U, where V is the final liner element velocity and U is the velocity by which the detonation wave front sweeps past the liner. This formula is, however, accurate only under steady-state conditions where the detonation wave sweeps past identical cross sections of the explosive-liner geometry. For non-steady cases, the Taylor formula is not applicable since the existence of a velocity gradient or a gradient of the typical acceleration duration along the liner may significantly affect the angle delta.

So the collapse angle for a liner of even thickness can be calculated from: Sin (collapse angle delta) = V/2U

In which V is the velocity of the liner wall. So, the V should stay below the critical machnumber of 1,23. Bulk speed of sound for copper is 3800 thus V should stay below 1,23 * 3800 = 4600 m/s.

But how can you calculate U, the speed by which the detonation wave passes the liner surface? From "Explosive with lined cavities" I found out that this is simply the VoD of the explosive (detonation wave) divided by the cosinus of half the liner angle A. This gives U = VoD for liner angle 0 deg. and with U approaching infinity for a liner of 90 deg. This makes sense, if the liner is a completely flat disc at the bottom of the charge, the detonation wave will hit the whole surface at once. (The collapse angle delta is 0 deg in this case in accorance with the Taylor equation since V divided by infinity will approach zero)

The Taylor equation is a simplified form of the equation in "Explosives with lined cavities" that says :



In which Ud is the VoD of the explosive, V0 is the final liner element velocity (V in the Taylor equation), a is half the liner angle and (b-a)/2 is the collapse angle (delta in the Taylor equation). Picture of the liner collapse below:



Of course the liner will have a certain mass, and as I posted earlier I wondered where this was included. But a higher mass will probably result in a slower inward collapse velocity, while as the velocity U by which the detonation front passes the surface of the liner will remain the same. So with U remaining constant but the velocity of the collapsing liner wall becoming smaller, the collapse angle delta will become smaller. So the mass/velocity relation is incorporated in the collapse angle of the flow I think... :)

Unfortunately, the collapse angel variable makes this formula not very usable in practice, since you can't determine this by any easy means. I did some calculations with the assumption that cos A (liner angle) = tan (collapse angle/2) for an ideal collapse. (collapse perpendicular to the liner wall, with speed = VoD of the explosive):



But pluggin in some numbers doesn't give any usable data, of course. Since the process is undoubtly much more complictated than this simple approach... :P

[Edited on 5-7-2006 by nitro-genes]
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[*] posted on 4-7-2006 at 07:13


If you test the Taylor equation using some X-ray recordings of the liner collapse of a 42 deg liner with comp. B (VoD ~ 8000 m/s) as explosive filling:



Sin(delta) = V/2U ---> V = Sin(delta) * 2U

U = VoD/cos A (A = half the liner angle)

angle delta = (b-a)/2 from the liner collapse drawing from "explosives with lined cavities" = B/2 in the picture above

So:

V = sin(B/2) * 2 * VoD/cos(A/2) in which A is the liner angle (42 deg.)

V = sin (20/2) * 2 * 8000/cos(42/2)

V= sin(10) * 2 * 8000/ cos(21)

v = 2976 m/s, far below the speed of sound in copper!

(You can see by this that the ideal collapse angle from cos A = tan(collapse angle/2) = much larger then the real angle. Ideal would be cos(21) = tan (43/2) giving a collapse angle of 43/2 = 21 degrees, almost twice as large as the real collapse angle! Since the velocity by which the detonation wave passes by the liner wall is determined by 8000/cos(21) , the liner element velocity V must be much slower in the real situation.) I wonder if it is purely the mass of the liner that accounts for this slower liner element velocity compared to the ideal situation...

It is strange though, if you use the Taylor equation to predict the liner element velocity (V) for a liner angle of 0 degrees (cylindrical shaped charge) you would get only a V of 6200 m/s for the ideal collapse angle of 45 degrees.. Not the high numbers you would expect to justify the use of berillium liners. The liner element velocity cannot exceed the VoD of the explosive anyway...

[Edited on by nitro-genes]
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[*] posted on 8-7-2006 at 03:22


Wow nitro-genes. That's some great stuff. I've not had the need nor inclination to use any half-way serious math now for quite some time. This will in fact, be quite a joy to chew over.

This may help the winter-time pass more quickly than is the case currently.

Actually came to this thread to post something that's reasonably old hat, but that I'd not seen before. -- A method of repeatedly and relatively inexpensively defeating shaped charge warheads..

It would seem that a bright bunny has had the ingenious thought (albeit intuitive once mentioned) of defeating the jet itself. In contrast to the current paradigm which involves causing the jet to do more work than would be necessary to effect penetration.

Though I won't spoil it, the idea is to in fact ________ the jet. :o :o upon contact with the armour of a tank. This has apparently been necessitated by the change in tactics that we've all seen in the current conflicts in the middle-east.

Sure, you can make a tank with 10 tonnes of armour, and they can bring out a roadside bomb with X amount of explosive. So then you bring out a tank with 20 tonnes of armour, then the bastards use a bomb with Y amount of explosive. So on and so forth, adnauseum. Problem is however, A tank with 20 tonnes or more of armour is both hard to transport to a area of conflict, additionally - they become less and less agile and are an even easier target.

Solution? Take a tank with only 2 tonnes of armour, apply a skin that has the capability of defeating a shaped charge jet repeatedly and you have a serious counter measure on our side. Rounds that employed a double shaped-charge effect would need to be able to direct the second SC jet onto exactly the same point to even begin to have a chance against this system. Good luck with a tank that's moving.

So how's this all work you might ask..
Think along the lines of "How do I make a bridge-wire dissapear" ;)
Look here for further details.
-->Missile Defence Shield
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[*] posted on 8-7-2006 at 03:58


Great stuff! But how about using glass liners? Or even sintered liners like they use in the oil industry. These would make non-continuous jets that would not be affected by any current I guess...

Thats funny, even have a PDF hanging around dealing with the concept (see attachment)

I think I know now why beryllium is used for 0 degree liners (cylindrical) btw. :) From: "Structure of a Shaped Jet Formed in an Oblique Collision of Flat Metal Plates by O. B. Drennov" It seems that jet formation is dependant very much on two things at these small liner angles:

1 very high dynamic strength
2 subsonic liner velocity

Beryllium has a very high dynamic strength and elasticity modulus AND a high bulk speed of sound. Tantalum and DU also have very high dynamic strengthts (tantalum is the best material for EFP's) but these lack the high speed of sound required. (~3400 m/s for both)
Beryllium is probably the only metal having the right combination of these properties. So, the 12.000 m/s sound speed probably is pretty excessive, since I'm sure now that the liner velocity cannot exceed the VoD...:)

[Edited on 8-7-2006 by nitro-genes]

Attachment: Disruption of Shaped-Charge Jets by a Current.pdf (212kB)
This file has been downloaded 1079 times

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[*] posted on 8-7-2006 at 04:07


Oh yeah. (bangs head repeatedly) Of course.
Such a simple and elegant solution. How on earth could such an idea have been overlooked. And it all seemed so good.

Guess I was so overwhelmed by the neatness of the idea that I (along with others) completely disregarded my usuall approach of searching for the simplest, cheapest counter-measure.

Oh well, at least somebody here is still thinking ;)
Well done once more, nitro.

[EDIT: Half a million amps :o :o - That'd be quite some fireworks show]

[Edited on 8-7-2006 by enhzflep]
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[*] posted on 8-7-2006 at 04:41


I have zero knowledge of electricity...Could it be that under these tremendous pressure glass becomes conductive to? :) Although I seem to remember that higher temperatures only increases resistance...

[Edited on 8-7-2006 by nitro-genes]
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[*] posted on 8-7-2006 at 05:29


Ha, I know that the Red terminal's positive and the Black one's negative :D

No, seriously though - that's an interesting propostion. Couldn't locate any hard data on the phenomenon. (pressure vs conductivity) I'm certainly not clever enough to postulate on that effect. I'd be talking entirely out of the thing I sit on. ;)

However, according to http://www.glass-ts.com/PDFs/htelec.pdf, it is possible to melt glass electrically
Quote:

Electrical melting of glass utilises the bulk resistivity of the glass, hence it is essential to know what this is and how it varies at elevated temperatures. Different types of glass can have very different resistivities so it is also necessary to take this into account. Changes in composition, particularly in alkali type and content, can strongly influence electrical properties.

Though to be perfectly frank, I'd be amazed if such a capacitive discharge system could effect anywhere near the same result as it would on a metal-based jet.

Gimme theoretical physics any day and practical chemistry every other day..

Another refference I've just read seemed to suggest that up to temperatures of "20 K" (I assume they mean 20,000 C as opposed to 20 deg Kelvin - it doesn't make a huge percentage difference at 20,000 ~ 1 and a bit %) that electron mobility increases and results in a lowering of the resistance. After this temperature is reached the trend is reversed, and conductivity once more recedes.

Though, with copper jets being measured in the 300->400 deg C range, this effect is hardly going to be of much assistance in this case one would think. Even allowing for the difference in heat capacity of metals and glass, it's not going to be up around this temperature.

Oh well, guess that means we can roll out millions(billions?) of dollars worth of research and the bastards can destroy us with super-sized Martini glasses. :) Ha, they'll be happy to know that perhaps our love of alcohol will be our downfall. ;)
Either that or they'll start putting 500kg charges under the road and play a game of Who can launch a tank the farthest....
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[*] posted on 8-7-2006 at 06:22


Quote:
Originally posted by enhzflep
Oh well, guess that means we can roll out millions(billions?) of dollars worth of research and the bastards can destroy us with super-sized Martini glasses. :)


Glass lamp shades would do fine I think...:D
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[*] posted on 8-7-2006 at 12:58


Or, they might just switch to using EFPs like the kestrel variant of the predator missile already does. EFPs are immune completely to every form of defense against shaped charge, since each one tries to desrupt/destroy the jet, which the EFP does not have. And, if you think that an EFP cannot pierce armour, see this wonderful picture of the EFP from a predator missile going clean through a tank! :o



Taken from http://www.army-technology.com/projects/predator_kestrel/index.html#predator_kestrel5

[Edited on 9-7-2006 by Chris The Great]
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nitro-genes
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[*] posted on 8-7-2006 at 15:35


Wow! Impressive performance for a warhead of under ten kilograms, especially when you consider that most of the weight will be in use for the propulsion and targetting systems onboard! You can even see the exit point at the left in the bottom of the tank...

An EFP will do little over 1 time diameter penetration in armor I believe, but the advantage is that considerably less explosive material is needed for a given diameter in comparison with a shaped charge. The successful formation of an airstable, long stand-off EFP however demands a much more intimate knowledge of detonation dynamics and material behaviour under high pressures than for making a conventional shaped charge though.
I've seen several studies and programs though that can predict the speed and mass of the EFP and even the number of "fins" on the EFP after it's formation...Neat! :)

To bad tantalum isn't OTC available. :P I'm planning to try some copper lined EFP's somewhere in the near future anyway. They won't be effective at very long-standoffs probably, but ok...

[Edited on 8-7-2006 by nitro-genes]
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[*] posted on 8-7-2006 at 17:34


Oh, they will form balls instead of the "bullets" a precision designed one will form. They will still travel a long, long way with a large amount of kinetic energy. I've been wanting to try my hand at one too :)
But to form those fancy aerodynamic bullets one needs to do a lot of computer calculation and unless somebody finds a program to design them, we'll be stuck with ball shaped projectiles...

The actual predator missile is only 6.4kg. The entire launcher is under 10kg when loaded.

Check this one out though. Now that is a well formed projectile:


From http://www.military.com/soldiertech/0,14632,Soldiertech_EFP,,00.html

[Edited on 9-7-2006 by Chris The Great]
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[*] posted on 9-7-2006 at 08:54


On the topic of high speed impact on solid material...to illustrate the effect of something other than gaseous..

Here, a 1.2 cm Al ball is shot into solid Al at 6.8 km/sec. The Al ball is obliterated of course...the ball shown is for illustration only.



Now imagine what an asteroid of 100x100x100 m can do to earth, at triple that speed...which is the lower limit of asteroid/meteorite speeds...!!!! :o


[Edited on 10-7-2006 by chemoleo]




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[*] posted on 10-7-2006 at 13:48


Quote:
Originally posted by enhzflep
A method of repeatedly and relatively inexpensively defeating
shaped charge warheads..
Think along the lines of "How do I make a bridge-wire dissapear" ;)

Quote:
Originally posted by nitro-genes
Great stuff! But how about using glass liners?
a PDF hanging around dealing with the concept (see attachment)

I do not see the benefit of this technique over reactive armor applique. The
trend now to have tandem charges impacting in a sequence just results in an
arms spiral. It seems to me money and effort is better spent preventing the
projectile from acting on the armor in the first instance. Israel supossedly has
experimented with a device that produces an electromagnetic pulse as the
munition approaches. This induces sufficient current in the wiring to fire the
detonator. Of course this requires extraordinary timing given the brief window
for effective countermeasure. This also can be countered by a munition using
coaxial wiring and Faraday shielding. A gun fired APDS round is still the most
effective trenchant penetrator, requiring 30 inches of cobham armor to stop,
a reason for the shift in tactic to death from above, 30mm caliber as apposed
to 120mm plus coming from the side.

.
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[*] posted on 19-7-2006 at 09:26


Quote:
Originally posted by chemoleo
Here, a 1.2 cm Al ball is shot into solid Al at 6.8 km/sec. The Al ball is obliterated of course...the ball shown is for illustration only..


More than 11 km/sec with only blackpowder as the propellant...light gas guns are fun! :D They are used by NASA indeed to describe possible meteorite impacts on earth, but they also plan to shoot satellites directly into orbit with much larger designs. :)

The design of such a device doesn't even seem all that complicated at first glance, low detailed schemes can even be found on the internet, with the "breakthrough" valve beeing the most difficult part probably. I wouldn't be surprised if such a thing could be built in a couple of years in a garage. (Make sure though you don't have to explain the neighbours what you are building) That would really be a madscientist project! :D
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[*] posted on 22-7-2006 at 03:16


It turns out that with the semtex-like explosive (160-170 kbar range) I was using, penetration of more than 2,5 times cone diameter is not possible, so the 28 mm copper cone thus was already very close to the limit probably with 5 cm of steel and over 10 cm of soil.

Completely by accident found this graph of the chapman-jouguets detonation pressure versus penetration in PATR. It is a pitty though they don't mention the test setup, liners used, explosives etc...:(




[Edited on 22-7-2006 by nitro-genes]
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[*] posted on 29-7-2006 at 22:12


A question for the esteemed membership that's been stumping me, and that someone here may perhaps be able to answer.

The question is, if you have two seperate plates of metal, say copper, arranged in a configuration like that of a typical shaped charge and touching at the apex, would the plates flow like a typical shaped charge liner into a jet?

Or, would they behave as two seperate entities and collide into each other, in an explosive-weld?

Mind you that these plates are free to move relative to each other, meaning that they're not welded together, only mechanically held together by spring-tension or such, not massive confinement.

I've checked through my copy of FoSC, and other texts, and found no answer. Perhaps someone here has experimented with such liners?

[Edited on 7-30-2006 by NBK]




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