Talk:Shaped charge

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[edit] Error in "Liner" section re: usefulness of skirts today?

Paragraph 4 of the Liner section ends with the statements The use of skirts today would, depending on the warhead, probably increase penetration by providing a more optimal standoff distance. The new Stryker vehicle was recalled from Iraq specifically to fit it with slat armor, a form of skirt armor, to protect it against RPGs etc. I have removed this sentence until its accuracy can be assertained or clarified.

Good call. That sentence is nonsense. Riddley 10:50, 28 August 2006 (UTC)
There is no error is the previous text, abet maybe my poor grammar and spelling? The use of basic thin mild steel side skirts will, in many cases, improve a modern shaped charge (SC) warhead's effectiveness. It is only when the skirting is extremely thick, or armour arrays using ceramic, composite, explosive reactive armour (ERA), or non explosive reactive armour, will this be decremental to the warhead's penetration. It was found that in some cases the spacing provided by the skirting actually improved penetration by providing a more optimal standoff distant from the warhead to the tanks side armour (more below).
Shaped charges require a standoff for the jet to form correctly. Early warheads required about 2-3 charge diameters (CD), 2nd generation 70's era, 6-7 CDs and modern up to and above 10 CDs. Degradation to penetration (due to jet breakup and dispersion) happens after 4-6 CDs for WWII era SCs, 2nd gen after 16 CDs and for modern SCs the distance is mostly classified information. If you plug some numbers into that data, you get some interesting results. Here is an example attack: for a 75mm projectile with a 65 mm SC warhead, the spacing distance needed to make an appreciable drop in penetration would be 260-390mm for WWII SCs and over 1m for a more modern warhead. Most modern anti-tank missiles have a SC warhead diameter between 100-150mm, bringing the optimum standoff to 1-1.5m and the a degraded standoff up to a ridiculous 1.6-2.4m! You can see that the use of skirting in these cases, does in fact, do diddlely squat to distance the armour away from the shaped charge's jet before it has degraded, as the skirting is only some 300-500mm away from the tank's side armour!
The original use for the skirts (Schürzen) was firstly to defeat small calibre armour piercing (AP) projectiles and secondly to degrade, but not defeat, the larger calibre ones. For small calibre, by direct defeat or destabilisation and for large calibre, by a combination of destabilising the projectile and damaging the penetrating cap. On very small calibre, or the more crude of WWII SCs, the armour could also degrade the SC's penetration to some extent. The use of slat, chain, or bar armour in modern armoured fighting vehicles (AFVs) is to damage/short circuit the fuzing system on some shaped charge projectiles. The fuzing system on some RPG-7 (Ruchnoy Protivotankoviy Granatomet [Handheld Anti-Tank Grenade Launcher] -7) projectiles use the inner and outer nose cone (ogive) to transmit the firing pulse from the small diameter piezoelectric nose probe to the rear mounted fuze and detonator. If the inner and outer sections of the ogive are forced together, the fuze short circuits, the detonator at the rear cannot initiate the main charge, and the shaped charge jet cannot form. Slat/bar/chain armour is used on AFV's for this reason and not the reason stated before. It should be noted that if the nose probe hits a slat/bar/chain element, then the warhead will function correctly, the jet will form and on a poorly protected vehicle the armour behind will more than likely be penetrated. Another note is that the high speed impact of the RPG-7 projectile with the armour, may cause the projectile's filling to deflagrate (a low order subsonic explosion), not detonate, causing some local fragmentation and blast damage.NeilGibson 08:33, 1 October 2006 (UTC)
Having done a bit of reading, I accept that slat armour is primarily designed to disrupt the fusing mechanism rather than change the standoff, just goes to show you learn something new everyday. I still don't understand what you are saying regrading optimum standoff though - if modern HEATs need a standoff of say 10 or more CDs "for the jet to form correctly" then how could any impact-fused modern weapon achieve a correctly formed jet? Why not use proximity fuses to get the optimum standoff? Riddley 10:02, 1 October 2006 (UTC)
Well a standoff of 10 CDs may be the optimum for some of the most advanced warheads, but most are still only 5-7 CDs. Although there is an optimum standoff, you can lose a few CD here and there and still achieve good penetration, you’ll just not get the max capability out of the warhead. For some warheads, the cone angle may also be wider, this results in a thicker jet which improves lethality and lowers the standoff, but negatively, decreases the depth of penetration. Those warheads which do not use a proximity sensor, have to rely on some form of inbuilt standoff. The standoff can come from just the nose, a nose probe, an extending nose probe, or by placing the warhead as far to the rear of the missile/projectile and allowing the jet to travel along a channel in the centre axis of the weapon. Although proximity sensors are used on many heavyweight systems (HOT 3, Brimstone, Hellfire, BILL RBS 56, etc) and on more advanced lightweight systems (Javelin, NLAW, etc), the exact nature of the proximity sensor used (magnetic, laser, optical or radar) and it's capability is not normally released due to security reasons. NeilGibson 16:18, 1 October 2006 (UTC)

[edit] Shaped Charge (Munition) Image

Hi, what is the exact round in the new image? Checking the image, the name of the file gives the origin as French. It seems most likely to be of 90 mm calibre and for either the Giat 90 mm CN 90 F1, Cockerill or Engesa guns due to the length of the cartridge case. If for the CN 90 F1 gun this makes it a HEAT-T, OCC F1 and if for the Cockerill or Engesa guns, the NR478 HEAT-T. NeilGibson 18:54, 8 February 2006 (UTC)

This looks like another view of the same round, with some more markings visible: http://commons.wikimedia.org/wiki/Image:Mines_501607_fh000003.jpg BillFlis 16:31, 10 February 2006 (UTC)

[edit] Linear Shaped Charge Image

Oh I forgot to say thanks for the linear shaped charge image, but there are two problems. LSCs are not normally initiated in the way depicted in the image, e.g. by a detonator applied to the top of the charge. In general they are initiated from one end using some form of coupling between the explosive fill and the detonator, be it only a blob of PE. Also they tend to have a triangular top section, as the explosive to the sides is not used in the collapse of the internal apex. If this profile was used it would just raise the cost and enlarge the danger area. NeilGibson 19:28, 8 February 2006 (UTC)

You're quite right about my sketch not resembling the commercial product, a photo of which would be a good addition, but I'm reluctant to steal one from, say, Ensign-Bickford. My image looks like what I would have made in a machine shop, if I had to. The central initiation would give a symmetric jet. It also resembles Figure 63 of Walters's book.BillFlis 20:22, 8 February 2006 (UTC)
Yes I have contemplated 'acquiring' images from the above fore mentioned website, but have resisted the temptation. There a loads of other LCS manufacturers too which have images on their websites? Perhaps if we contact one of them and give a link to their website at the bottom of the article, they may be interested? Anyway for now it’s the best we have, I'll have a look around myself and see if I can find a more representative image. The profile in you image is used though, but not for LSCs in general. Your image profile is used to produce a linear self forging fragment, abet with a different liner cross-sections, the addition explosive being a bonus this time. I've seen a few of these in technical papers and reference books. NeilGibson 09:37, 9 February 2006 (UTC)

[edit] Explosive lens

I think the section on Explosive Lenses should be moved to a separate article. It's not really a "shaped charge" as the phrase has come to be used. Granted, it's a charge of explosive and it's shaped, but that doesn't make it a shaped charge any more than heating up a dog turns it into a hot dog (frankfurter).

Also, I think an explosive lens is something that someone (reading, say, about nuclear weapons) might reasonably be expected to want to look up. So it deserves its own heading. Cross-referencing to Shaped Charges would be appropriate, because SCs-proper sometimes incorporate them (mainly for research purposes).BillFlis 22:54, 7 February 2006 (UTC)

Yes I quite agree that lens and plane wave generators should be in a separate entry. I did not move it myself as I had changed so much the first time I edited the article, I though someone might be offended. There is the point of view though that shaped charges share many of the aspects of explosive lens, especially shaped charges that use a barrier within the explosive to shape the detonation wave? I also though about starting an article on warhead mechanics, which all of these separate articles could fit within, but I haven't taken it further as of yet? NeilGibson 18:54, 8 February 2006 (UTC)
The terminology that has arisen for the "barriers" you mention is "waveshaper." No ordnance charge that I know of uses a true explosive lens, and indeed I think it would be an unnecessary and expensive complication. The lens analogy is a good one--as in an optical lens, the effect is based on a difference in wave velocities. A waveshaper affects the shape of a detonation wave rather by changing its path, rather than its speed.BillFlis 20:35, 8 February 2006 (UTC).
There are various ordnance charges that shape the detonation wave, whether by multipoint initiation or by using inert barrier materials. There may also be some that use active barrier materials (varying speed explosives). Some of the cross sections of these charges show different materials between the initiation point and the main explosive fill. Whether or not this is another explosive, or just some form of inert barrier tends to be classified. Either way feel free to set up another article on the subject as I think it’s a very good idea. For your info I didn't write the original nuclear weapons part of the article, just tidied up a few things. NeilGibson 09:37, 9 February 2006 (UTC)


[edit] Fluted Liners

Someone should add some extra detail re. fluted liners for shaped charges. --Nabokov 10:24, 6 May 2006 (UTC)

[edit] WPMILHIST Assessment

There really should be in-line citations, but your sources are listed at the bottom, and the material is lengthy, thorough, and well-written. LordAmeth 16:44, 3 February 2007 (UTC)

[edit] Commercial shaped charges

There is a commercial use of lined conical shaped charges that is not mentioned in this article. Oilfield service companies, e.g. Schlumberger and Halliburton, use small shaped charges to perforate the casing of a wellbore. See Oil well completion, Schlumberger, and AnaLog. Millions of these shaped charges are produced and used annually.

This article, being in a military category, is probably not the place for this information. I am not familiar enough with the practices here to make another article myself, though. Suggestions?

wysiwyg 15:39, 18 February 2007 (UTC)

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