nbk2000
July 27th, 2002, 05:00 AM
It's a well known fact that when two waves (of any type) interact, there'll be two types of interaction between the two, constructive interference, and destructive interference.
In our line of work, we're interested in the constructive, rather than the destructive (strange, huh? <img border="0" title="" alt="[Wink]" src="wink.gif" /> ) type of interference.
It's constructive interference that comes into play with shaped charges of all types. Without it, we wouldn't have SC or LSCs of any sort.
Now, usually, we tend to think of explosions have a single source of initiation...the detonator. Usually this is fine. But, by expanding our thinking to more than one point of initiation, we greatly expand our abilities.
As an example, look at the design of anti-aircraft missle warheads. They're limited in size and weight, yet have to be able to effectively engage a target at great passing speeds and unknown orientation anywhere within a 360 degree sphere on all axis.
To address this problem, weapons designers have incorporated the multipoint initiation principle into warhead design.
In this picture we see the pressure contours immediately after a 3 point initiation. The initiation points are the top, center, and bottom on the left hand side. The target is on the right hand side, center.
<img src="http://server3001.freeyellow.com/nbk2000/Warhead1.gif" alt=" - " />
By the time the pressure waves have traveled to the target side, they have constructivly interfered with each other to form a broad, and nearly flat, pressure wave of greater intensity than any single initiation could generate. (Notice the band of red, as compared to the original yellow in the first picture)
<img src="http://server3001.freeyellow.com/nbk2000/Warhead2.gif" alt=" - " />
The effect of this can be seen by the large area of red centered in a larger field of orange. Note how these colors are predominant on the target side, and nearly absent on the side where the initiations originated from.
<img src="http://server3001.freeyellow.com/nbk2000/Warhead3.gif" alt=" - " />
The sum effect of this can be seen in the dense ring of fragments with the highest velocity (red) fragments being present on only one side (asymetric).
<img src="http://server3001.freeyellow.com/nbk2000/Warhead4.gif" alt=" - " />
This principle is also used in a patent for a MOUT weapon to blast mouseholes through reinforced concrete walls big enough for men to crawl through to assualt the enemy within.
In this case, a cylindrical charge of explosive is initated simultanously at both ends so that the wave fronts collide in the middle of the device, which is a machined cylinder of aluminium with a radially symetrical cavity in the center to provide a shaped charge effect.
The colliding waves expand out from the center in a radial manner, destroying the target wall from the inside.
Naturally, the question becomes one of how do we use this technique in our own experiments. Well, before you can run you have to learn how to walk, and before you can walk you have to crawl.
Meaning you have to first overcome the problem of making detonators that explode within a millisecond of each other. Because without such precisely synchronized intitiation, you'll not achieve the needed symetry.
Regular bridge-wire initators that use a hot nichrome wire to light up a pyrotechnic charge to set off the primary are unsuitable for this. There's too many variables in the design, even in carefully controlled factory conditions that the home experimenter could never hope to duplicate.
For the precise timing needed, an SCB (Semi-Conductor Bridge) initator is used, along with the capacitor bank and timing circuits to complete the device. But this is also expensive and complicated.
What's needed is a simpler way to duplicate the same principles without the high-end costs.
Fortunately, if you have det-cord, it's possible.
This is done by cutting precisly duplicate lengths of det-cord and attaching them to a central detonator. This way, the need for synchronization is removed since the det-cord will carry the explosive impulse to the secondary initiators in the device at the same time since they're of uniform length and velocity, and all using just one main detonator who's construction can be of simple design.
Since det-cord can be a pain to improvise, which also introduces variables of density and velocity which would ruin the whole point, we could borrow an idea from the electronics industry and lay down "traces" of explosive compositions (much the same as a circuit board) that would carry the impulse to the initiators.
For this purpose, I'm envisioning casting a sheet of explosive putty (PETN/Blu-tak binder) that will have a uniform density, and cutting out strips of the explosive to be layed out on the device and held in place with a coating of (paint/resin/whatever).
Because the "traces" were cast they'll be of uniform density and can be precisely measured and cut.
Another way would be to use tubes filled with a liquid explosive composition. Liquids are always of uniform density, thus removing that problem.
So, what purposes would you use the asymetric effect for?
<small>[ July 27, 2002, 04:05 AM: Message edited by: nbk2000 ]</small>
In our line of work, we're interested in the constructive, rather than the destructive (strange, huh? <img border="0" title="" alt="[Wink]" src="wink.gif" /> ) type of interference.
It's constructive interference that comes into play with shaped charges of all types. Without it, we wouldn't have SC or LSCs of any sort.
Now, usually, we tend to think of explosions have a single source of initiation...the detonator. Usually this is fine. But, by expanding our thinking to more than one point of initiation, we greatly expand our abilities.
As an example, look at the design of anti-aircraft missle warheads. They're limited in size and weight, yet have to be able to effectively engage a target at great passing speeds and unknown orientation anywhere within a 360 degree sphere on all axis.
To address this problem, weapons designers have incorporated the multipoint initiation principle into warhead design.
In this picture we see the pressure contours immediately after a 3 point initiation. The initiation points are the top, center, and bottom on the left hand side. The target is on the right hand side, center.
<img src="http://server3001.freeyellow.com/nbk2000/Warhead1.gif" alt=" - " />
By the time the pressure waves have traveled to the target side, they have constructivly interfered with each other to form a broad, and nearly flat, pressure wave of greater intensity than any single initiation could generate. (Notice the band of red, as compared to the original yellow in the first picture)
<img src="http://server3001.freeyellow.com/nbk2000/Warhead2.gif" alt=" - " />
The effect of this can be seen by the large area of red centered in a larger field of orange. Note how these colors are predominant on the target side, and nearly absent on the side where the initiations originated from.
<img src="http://server3001.freeyellow.com/nbk2000/Warhead3.gif" alt=" - " />
The sum effect of this can be seen in the dense ring of fragments with the highest velocity (red) fragments being present on only one side (asymetric).
<img src="http://server3001.freeyellow.com/nbk2000/Warhead4.gif" alt=" - " />
This principle is also used in a patent for a MOUT weapon to blast mouseholes through reinforced concrete walls big enough for men to crawl through to assualt the enemy within.
In this case, a cylindrical charge of explosive is initated simultanously at both ends so that the wave fronts collide in the middle of the device, which is a machined cylinder of aluminium with a radially symetrical cavity in the center to provide a shaped charge effect.
The colliding waves expand out from the center in a radial manner, destroying the target wall from the inside.
Naturally, the question becomes one of how do we use this technique in our own experiments. Well, before you can run you have to learn how to walk, and before you can walk you have to crawl.
Meaning you have to first overcome the problem of making detonators that explode within a millisecond of each other. Because without such precisely synchronized intitiation, you'll not achieve the needed symetry.
Regular bridge-wire initators that use a hot nichrome wire to light up a pyrotechnic charge to set off the primary are unsuitable for this. There's too many variables in the design, even in carefully controlled factory conditions that the home experimenter could never hope to duplicate.
For the precise timing needed, an SCB (Semi-Conductor Bridge) initator is used, along with the capacitor bank and timing circuits to complete the device. But this is also expensive and complicated.
What's needed is a simpler way to duplicate the same principles without the high-end costs.
Fortunately, if you have det-cord, it's possible.
This is done by cutting precisly duplicate lengths of det-cord and attaching them to a central detonator. This way, the need for synchronization is removed since the det-cord will carry the explosive impulse to the secondary initiators in the device at the same time since they're of uniform length and velocity, and all using just one main detonator who's construction can be of simple design.
Since det-cord can be a pain to improvise, which also introduces variables of density and velocity which would ruin the whole point, we could borrow an idea from the electronics industry and lay down "traces" of explosive compositions (much the same as a circuit board) that would carry the impulse to the initiators.
For this purpose, I'm envisioning casting a sheet of explosive putty (PETN/Blu-tak binder) that will have a uniform density, and cutting out strips of the explosive to be layed out on the device and held in place with a coating of (paint/resin/whatever).
Because the "traces" were cast they'll be of uniform density and can be precisely measured and cut.
Another way would be to use tubes filled with a liquid explosive composition. Liquids are always of uniform density, thus removing that problem.
So, what purposes would you use the asymetric effect for?
<small>[ July 27, 2002, 04:05 AM: Message edited by: nbk2000 ]</small>