megalomania
June 26th, 2003, 03:27 PM
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted March 20, 2001 01:27 PM
--------------------------------------------------------------------------------
Topic Starter:
The design of conventional shaped charges is based on the fact that propagation of the detonation wave is always perpendicular to the explosive surface. In linear applications where two flat strips of explosive are detonated at an angle to each other, the detonation waves converge on a plane bisecting this included angle and form a "sheet" of explosive force. Where a liner is used, this "sheet" becomes the "blade" that does the actual cutting. In this system the effect is progressive and two-dimensional, with the period of cutting action (width of the "blade") determined by the width of the explosive strips, standoff distance, etc.
If an explosive profile of cylindrical (or parabolic) section were to be used instead of the usual "V" configuration, the detonation wave(s) would converge on a *line* along the target surface (rather than on a plane perpendicular to that surface). In such a system the effect would be instantaneous and one-dimensional (rather than progressive and two-dimensional) since *all* available energy would be focused along this line at the same instant. Theoretically, while there would be little or no cutting effect, the shattering force concentrated along this narrow line would be tremendous.
The greatly enhanced spalling effect of a "focused" charge of this type might prove superior against hard or brittle targets such as steel, concrete or glass. The familiar conical spalling of thick glass that results from the impact of a low velocity BB illustrates the effect, and suggests that unconventionally small charges could be used to breach these sorts of materials.
Naturally, the same principle ought to apply to conical as well as linear V charges.
Any thoughts on this supposition, or any useful references on the practical design of cylindrical or parabolic shaped charges?
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 08:41 AM
--------------------------------------------------------------------------------
When I understand you correctly you want to know the effect of different shapes of the cavity/liner in linear shaped charges. The only thing I know is that a shockwave can be compared to the waves in water when a stone is thrown in. And the effect of colliding shockwaves is like waves created by two stones that meet and interfere with another. And which results in a different pattern with the wave getting a different direction and force at certain points.
Now, it seems that the V-shaped cavity with a certain angle gives the best result: that is it creates the strongest, focused resulting shockwave. And when you use other shapes a different resulting shockwave is produced that is probably not as strong and focused as with a V-shape. In the improvised munitions manual a linear shaped charge constructed with a metal pipe cut in half (and producing a cyllindrical shaped cavity) doesn't penetrate armor as deep as the V-shaped linear charges (but this could be caused by other factors I'm not sure). And I'm not sure a "line" is produced as you say instead of a "sheet" or "blade" with a V-shaped cavity. Maybe there is a computerprogram that simulates colliding waterwaves? (there must be one somewhere). You could then easily see what kind of effect different shapes of the cavity have on the resulting shockwave.
I'm also curious to the effects of different shapes and specially the effect of a linear shaped charge consisting of two tubes of explosive with a V-shaped profile in the middle. Would the colliding shockwaves result in a fluid metal jet and would it be focused and how effective would it be?
And about the effects on (safety) glass: glass is far more sensitive to pressure- and shochwaves because, unlike steel, it will not bent it just breaks. It cannot absorb the energy. So to "cut" glass you need far less explosive than for steel.
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted March 21, 2001 01:24 PM
--------------------------------------------------------------------------------
It's my understanding that a detonation shock wave (or any portion thereof) will *always* propagate at an angle of 90 degrees relative to the surface of the explosive producing it. If the explosive surface is flat, as in one "leg" of a V-shaped linear charge, the detonation wave is consistent and the force-direction from any point of the surface is parallel to that from all other points (think ray theory). If diagrammed, the collision of these "rays" would resemble a fish skeleton, i.e. parallel lines of force (the fish ribs) converging and being redirected along a central plane (the fish backbone).
If the explosive surface is concave the "rays" will be convergent, not parallel, and therefore all energy will focus instantaneously on a central point without collision or redirection.
If the explosive surface is convex (as with a tube) the "rays" will instead be divergent, with no point of focus, and incoherent convergence angles producing little or no redirection or jet (i.e. a scattering effect).
If the above assumptions are correct, the explosive energy directed at the target using a tubular charge (or charges) would be almost entirely dependent on the countermass, with *none* of the advantages associated with shaped charges. While two cylindrical charges would undoubtedly collapse a central V in some manner, this collapse would be partial at best and would not result in a "blade" shaped jet. The interference effects of an infinite multiple of divergent force lines (or "rays") would also tend to cancel rather than augment each other, so I think attempting to use tubes is essentially a non-starter.
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 02:03 PM
--------------------------------------------------------------------------------
Sorry, I don't think I understand you. Maybe you could make a diagram and not use so many terms I don't know the meaning of or haven't heard of at all (is english your native language?). But what I do know is that a shockwave is not flat, it's moves in all directions (except backwards) from the small starting point (in the detonator). It moves from that point on like a balloon you blow up.
That's the reason a linear shaped charge with V-cavity even works and creates a metal jet and shockwave directed to the surface despite the fact that the original shockwave is parallel to the surface and pointed to the end of the linear shaped charge: but the shockwave on each side of the V-shape move also downward and collide with eachother and this results in a focused shockwave. So the cutting (focused) shockwave and metal jet are directed to the surface. If a shockwave would be flat and moving only in the direction from the point of initation to the end, a linear shaped charge would have no effect at all. Except for the pressurewave that moves in all directions (but that will not cut steel).
[This message has been edited by outsider (edited March 21, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 02:49 PM
--------------------------------------------------------------------------------
But I believe you already know that. And you say that with a V-shape cavity the shockwaves moving downwards to the surface collide and get focused. And with a cyllindrical cavity they focus on a central point without collision. And finally when using tubes the shockwaves would disperse. But this way you compair shockwaves with rays of light hitting a mirror with a V- or parabolic shape and I don't think that's possible. Shockwaves are waves and the interfere with each other as waves: re-enforcing each other at some points, changing direction on collision, etc. So using a simulation programm of colliding waves would be helpfull to understand the effects of different shapes.
Ctrl_C
Frequent Poster
Posts: 244
From:
Registered: NOV 2000
posted March 21, 2001 03:51 PM
--------------------------------------------------------------------------------
is this right?
damn....pic wont work...copy this into your browser, dont use the link or it wont work: http://badsektor.9ug.com/images/linearshaped.jpg
[This message has been edited by Ctrl_C (edited March 21, 2001).]
[This message has been edited by Ctrl_C (edited March 21, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 04:12 PM
--------------------------------------------------------------------------------
I did a quick search on the internet looking for "linear shaped charges animation" and found some interesting sites with animations of exploding (linear) shaped charges: www.feainformation.com and www.hydrosoft.com. The first shows an animation of an exploding linear shaped charge as well as a conical shaped charge (click on "warhead analysis" and then on the SC you want to see). With hydrosoft, click on "animation" and then "shaped charge". This might clarify some things. But what we need is some animations of FLSCs with other (cyllindrical) shaped cavities. And one of two tubes with a profile in between. Although I think/hope it won't differ much from a normal FLSC. Probably just the shape of the metal jet differs (and thus it's effect).
[This message has been edited by outsider (edited March 22, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 04:19 PM
--------------------------------------------------------------------------------
A picture is better than a thousand words but there's just a small mistake: the detonator is put in one side (begin/end) of a FLSC not on top. Maybe that's possible/done with bigger demolition type charges but not with FLSCs (I think). But it doesn't make a big difference anyway because the shockwave will be traveling parallel to the surface anyway when it proceeds through the charge.
[This message has been edited by outsider (edited March 22, 2001).]
wantsomfet
Frequent Poster
Posts: 233
From: EU
Registered: JAN 2001
posted March 24, 2001 07:45 AM
--------------------------------------------------------------------------------
What about: http://www.warheadanalysis.com/
or http://www.cc.gatech.edu/gvu/animation/explode/shaped.html
And this posting from alt.engr.explosives by Gerald Hurst is interwsting, too.
Subject:
Re: Shaped charges?
From:
glhurst@onr.com (Gerald L. Hurst)
Date:
1996/10/30
Message-Id:
<556vpk$qgq@geraldo.cc.utexas.edu>
Newsgroups:
alt.engr.explosives
In article <556g4t$ge7@news1.t1.usa.pipeline.com>,
hummas@usa.pipeline.com(Bill M) says:
>I might also add, for those
home experimenters out there, that, along with the forward jet of material,
there is also a backward moving mass of material (how much >depends on
the configuration of your explosive and container). Considerations which
make shaped charges difficult for kitchen chemists are the uniformity (both
in density >and quality) of the explosive and of the detonation.
If you are referring to the
slug or "carrot" which is formed along with the particulate jet, the former
also moves forward but only at a fraction of the velocity of the jet.
The slug, which is often shaped like a carrot, can sometimes be found nestling
in the (steel) target hole left by the jet.
The only part of the assembly
that actually moves backward is a portion of the gas cloud. Momentum
conservation dictates that the gas blast to the rear must be greater than
forward.
The velocity of the jet
increases and its mass decreases as the cone angle is decreased until it
approaches twice the velocity of the explosive and zero mass (in theory).
In practice, the optimal cone angle for good penetration depth is usually
about 60 degrees with a stand-off of about 2.5-3.5 diameters. These
values are a compromise for penetration because greater stand-off would
give even better penetration if the charge and cone were perfect. With
most real charges the jet is imperfectly focused and threfore spreads and
becomes less effective over large distances.
A pound of C-4 in even a
field packed shaped charge will pierce 7" of steel. This would be
considered poor performance per unit size compared to the penetration the
oilfield casing perforation guys get with their precision pressed RDX and
HMX charges combined with equally precise special metal linings.
Jerry (Ico)
[This message has been edited by wantsomfet (edited March 24, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 24, 2001 09:01 AM
--------------------------------------------------------------------------------
The first site I already mentioned. But the second is really great! Like it a lot. Thanks very much. I owe you (probably not spelled right but you know what I mean I think).
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted March 20, 2001 01:27 PM
--------------------------------------------------------------------------------
Topic Starter:
The design of conventional shaped charges is based on the fact that propagation of the detonation wave is always perpendicular to the explosive surface. In linear applications where two flat strips of explosive are detonated at an angle to each other, the detonation waves converge on a plane bisecting this included angle and form a "sheet" of explosive force. Where a liner is used, this "sheet" becomes the "blade" that does the actual cutting. In this system the effect is progressive and two-dimensional, with the period of cutting action (width of the "blade") determined by the width of the explosive strips, standoff distance, etc.
If an explosive profile of cylindrical (or parabolic) section were to be used instead of the usual "V" configuration, the detonation wave(s) would converge on a *line* along the target surface (rather than on a plane perpendicular to that surface). In such a system the effect would be instantaneous and one-dimensional (rather than progressive and two-dimensional) since *all* available energy would be focused along this line at the same instant. Theoretically, while there would be little or no cutting effect, the shattering force concentrated along this narrow line would be tremendous.
The greatly enhanced spalling effect of a "focused" charge of this type might prove superior against hard or brittle targets such as steel, concrete or glass. The familiar conical spalling of thick glass that results from the impact of a low velocity BB illustrates the effect, and suggests that unconventionally small charges could be used to breach these sorts of materials.
Naturally, the same principle ought to apply to conical as well as linear V charges.
Any thoughts on this supposition, or any useful references on the practical design of cylindrical or parabolic shaped charges?
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 08:41 AM
--------------------------------------------------------------------------------
When I understand you correctly you want to know the effect of different shapes of the cavity/liner in linear shaped charges. The only thing I know is that a shockwave can be compared to the waves in water when a stone is thrown in. And the effect of colliding shockwaves is like waves created by two stones that meet and interfere with another. And which results in a different pattern with the wave getting a different direction and force at certain points.
Now, it seems that the V-shaped cavity with a certain angle gives the best result: that is it creates the strongest, focused resulting shockwave. And when you use other shapes a different resulting shockwave is produced that is probably not as strong and focused as with a V-shape. In the improvised munitions manual a linear shaped charge constructed with a metal pipe cut in half (and producing a cyllindrical shaped cavity) doesn't penetrate armor as deep as the V-shaped linear charges (but this could be caused by other factors I'm not sure). And I'm not sure a "line" is produced as you say instead of a "sheet" or "blade" with a V-shaped cavity. Maybe there is a computerprogram that simulates colliding waterwaves? (there must be one somewhere). You could then easily see what kind of effect different shapes of the cavity have on the resulting shockwave.
I'm also curious to the effects of different shapes and specially the effect of a linear shaped charge consisting of two tubes of explosive with a V-shaped profile in the middle. Would the colliding shockwaves result in a fluid metal jet and would it be focused and how effective would it be?
And about the effects on (safety) glass: glass is far more sensitive to pressure- and shochwaves because, unlike steel, it will not bent it just breaks. It cannot absorb the energy. So to "cut" glass you need far less explosive than for steel.
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted March 21, 2001 01:24 PM
--------------------------------------------------------------------------------
It's my understanding that a detonation shock wave (or any portion thereof) will *always* propagate at an angle of 90 degrees relative to the surface of the explosive producing it. If the explosive surface is flat, as in one "leg" of a V-shaped linear charge, the detonation wave is consistent and the force-direction from any point of the surface is parallel to that from all other points (think ray theory). If diagrammed, the collision of these "rays" would resemble a fish skeleton, i.e. parallel lines of force (the fish ribs) converging and being redirected along a central plane (the fish backbone).
If the explosive surface is concave the "rays" will be convergent, not parallel, and therefore all energy will focus instantaneously on a central point without collision or redirection.
If the explosive surface is convex (as with a tube) the "rays" will instead be divergent, with no point of focus, and incoherent convergence angles producing little or no redirection or jet (i.e. a scattering effect).
If the above assumptions are correct, the explosive energy directed at the target using a tubular charge (or charges) would be almost entirely dependent on the countermass, with *none* of the advantages associated with shaped charges. While two cylindrical charges would undoubtedly collapse a central V in some manner, this collapse would be partial at best and would not result in a "blade" shaped jet. The interference effects of an infinite multiple of divergent force lines (or "rays") would also tend to cancel rather than augment each other, so I think attempting to use tubes is essentially a non-starter.
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 02:03 PM
--------------------------------------------------------------------------------
Sorry, I don't think I understand you. Maybe you could make a diagram and not use so many terms I don't know the meaning of or haven't heard of at all (is english your native language?). But what I do know is that a shockwave is not flat, it's moves in all directions (except backwards) from the small starting point (in the detonator). It moves from that point on like a balloon you blow up.
That's the reason a linear shaped charge with V-cavity even works and creates a metal jet and shockwave directed to the surface despite the fact that the original shockwave is parallel to the surface and pointed to the end of the linear shaped charge: but the shockwave on each side of the V-shape move also downward and collide with eachother and this results in a focused shockwave. So the cutting (focused) shockwave and metal jet are directed to the surface. If a shockwave would be flat and moving only in the direction from the point of initation to the end, a linear shaped charge would have no effect at all. Except for the pressurewave that moves in all directions (but that will not cut steel).
[This message has been edited by outsider (edited March 21, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 02:49 PM
--------------------------------------------------------------------------------
But I believe you already know that. And you say that with a V-shape cavity the shockwaves moving downwards to the surface collide and get focused. And with a cyllindrical cavity they focus on a central point without collision. And finally when using tubes the shockwaves would disperse. But this way you compair shockwaves with rays of light hitting a mirror with a V- or parabolic shape and I don't think that's possible. Shockwaves are waves and the interfere with each other as waves: re-enforcing each other at some points, changing direction on collision, etc. So using a simulation programm of colliding waves would be helpfull to understand the effects of different shapes.
Ctrl_C
Frequent Poster
Posts: 244
From:
Registered: NOV 2000
posted March 21, 2001 03:51 PM
--------------------------------------------------------------------------------
is this right?
damn....pic wont work...copy this into your browser, dont use the link or it wont work: http://badsektor.9ug.com/images/linearshaped.jpg
[This message has been edited by Ctrl_C (edited March 21, 2001).]
[This message has been edited by Ctrl_C (edited March 21, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 04:12 PM
--------------------------------------------------------------------------------
I did a quick search on the internet looking for "linear shaped charges animation" and found some interesting sites with animations of exploding (linear) shaped charges: www.feainformation.com and www.hydrosoft.com. The first shows an animation of an exploding linear shaped charge as well as a conical shaped charge (click on "warhead analysis" and then on the SC you want to see). With hydrosoft, click on "animation" and then "shaped charge". This might clarify some things. But what we need is some animations of FLSCs with other (cyllindrical) shaped cavities. And one of two tubes with a profile in between. Although I think/hope it won't differ much from a normal FLSC. Probably just the shape of the metal jet differs (and thus it's effect).
[This message has been edited by outsider (edited March 22, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 21, 2001 04:19 PM
--------------------------------------------------------------------------------
A picture is better than a thousand words but there's just a small mistake: the detonator is put in one side (begin/end) of a FLSC not on top. Maybe that's possible/done with bigger demolition type charges but not with FLSCs (I think). But it doesn't make a big difference anyway because the shockwave will be traveling parallel to the surface anyway when it proceeds through the charge.
[This message has been edited by outsider (edited March 22, 2001).]
wantsomfet
Frequent Poster
Posts: 233
From: EU
Registered: JAN 2001
posted March 24, 2001 07:45 AM
--------------------------------------------------------------------------------
What about: http://www.warheadanalysis.com/
or http://www.cc.gatech.edu/gvu/animation/explode/shaped.html
And this posting from alt.engr.explosives by Gerald Hurst is interwsting, too.
Subject:
Re: Shaped charges?
From:
glhurst@onr.com (Gerald L. Hurst)
Date:
1996/10/30
Message-Id:
<556vpk$qgq@geraldo.cc.utexas.edu>
Newsgroups:
alt.engr.explosives
In article <556g4t$ge7@news1.t1.usa.pipeline.com>,
hummas@usa.pipeline.com(Bill M) says:
>I might also add, for those
home experimenters out there, that, along with the forward jet of material,
there is also a backward moving mass of material (how much >depends on
the configuration of your explosive and container). Considerations which
make shaped charges difficult for kitchen chemists are the uniformity (both
in density >and quality) of the explosive and of the detonation.
If you are referring to the
slug or "carrot" which is formed along with the particulate jet, the former
also moves forward but only at a fraction of the velocity of the jet.
The slug, which is often shaped like a carrot, can sometimes be found nestling
in the (steel) target hole left by the jet.
The only part of the assembly
that actually moves backward is a portion of the gas cloud. Momentum
conservation dictates that the gas blast to the rear must be greater than
forward.
The velocity of the jet
increases and its mass decreases as the cone angle is decreased until it
approaches twice the velocity of the explosive and zero mass (in theory).
In practice, the optimal cone angle for good penetration depth is usually
about 60 degrees with a stand-off of about 2.5-3.5 diameters. These
values are a compromise for penetration because greater stand-off would
give even better penetration if the charge and cone were perfect. With
most real charges the jet is imperfectly focused and threfore spreads and
becomes less effective over large distances.
A pound of C-4 in even a
field packed shaped charge will pierce 7" of steel. This would be
considered poor performance per unit size compared to the penetration the
oilfield casing perforation guys get with their precision pressed RDX and
HMX charges combined with equally precise special metal linings.
Jerry (Ico)
[This message has been edited by wantsomfet (edited March 24, 2001).]
outsider
Frequent Poster
Posts: 91
From:
Registered: FEB 2001
posted March 24, 2001 09:01 AM
--------------------------------------------------------------------------------
The first site I already mentioned. But the second is really great! Like it a lot. Thanks very much. I owe you (probably not spelled right but you know what I mean I think).