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At the request of @anwaralsharrad a topic about non-initiating precursor shaped charges. Basic principle of non-initiating precursors As the name implies, these are specialised shaped charges designed to not initiate something, which in this case is an ERA sandwich. The purpose of this is to punch a hole through the ERA sandwich for the main charge to go through, without setting the ERA off. Achieving this means that the detonation of the ERA sandwich cannot influence your projectile in any way shape or form. The explanation on how this works is fairly simple: Every energetic material (explosive) needs to be initated, if it isn't initiated it will act like any other material when hit by a projectile. In our case the initiation is done (or not done) via an impact. For an explosive to not initiate by impact, the impact energy needs to be lower than the critical energy* of the explosive. So you basically throw something at the ERA sandwich fast enough to punch a hole through it, but not fast enough to introduce critical energy in the explosive. This is usually achieved by using a special liner material, usually something lighter than copper (in theory you can make the jet slower to make it non-initiating, but then the main charge might catch up with your precursor jet, which you don't want). I've seen PTFE thrown around as a liner material for a non-initiating precursor warhead. The formula for kinetic energy is Ek=0.5*m*v2,, the kinetic energy of something is half the mass multiplied by the square of its velocity. So to lower the energy you can either go lighter or slower. * The impact/shock initiation point of explosives can be quantified by multiple units like J*cm-2, v2d, u2d, ρv2d, √ρv2d, Pd, and probably a whole bunch more. In this topic I will keep it simple and try to not use units. Things that influence non-initiating precursors However, it is quite tricky to get right since a plethora of factors influence the initiation point of an explosive. For starters, the type of explosive used in the ERA block is important: (Table from "A General Model for the Shock Initiation of Explosives" by F. E. Walker and R.J. Wasley) As you can see, explosives can have wildly varying critical energy points. Although these values are for pure explosives and not the desensitised explosives used in ERA, but this should give you an idea about not all explosives being equal. So a precursor might be non-initiating versus one type of ERA, but not versus another type of ERA simply because they use different types of explosives. A different graph showing the same thing: (Figure from "The Legacy of Manfred Held with Critique" by EV2 Florian Bouvenot) Furthermore, the impact velocity to initiate an explosive changes when the explosive is protected by a barrier of another material. The effectiveness of this barrier, which in the case of ERA is a flyer plate, depends on its thickness: (Figure from "The Legacy of Manfred Held with Critique" by EV2 Florian Bouvenot) In this graph everything above the line means "Boom" and everything under it means "No Boom". So to initiate an explosive protected by a barrier, you can either go faster, or go heavier. And again, this means that a non-initiating precursor might not be non-initiating because one type of ERA might have a thinner flyer plate than an other type. Even the material used for the barrier has an effect: (Figure from "The Legacy of Manfred Held with Critique" by EV2 Florian Bouvenot) Again, a non-initiating precursor might be an initiating precursor depending on the material of the flyer plate. There has been research about using glass or ceramic flyer plates. It might be that a precursor that's non-initiating versus a steel flyer plate, is initiating versus a glass flyer plate. Another thing to take into account, is whether or not the explosive is confined on all sides. For example, Nozh has a non-uniform confinement, so Nozh might react differently to a non-initiating precursor. The effect looks like this: (Figure from "The Legacy of Manfred Held with Critique" by EV2 Florian Bouvenot) But the most important one for us, is projectile material: (Figure from "The Legacy of Manfred Held with Critique" by EV2 Florian Bouvenot) As you can see, the lower the material density, the faster the projectile has to go to initiate an explosive. This is what we want, because we want to punch a hole without initiating an explosive. However, a lighter material also means that it has less penetration compared to a liner with a heavier material. ...but a lighter material can be accelerated to higher velocities, which means a higher penetration than a slower jet with the same density. So basically, whether or not a non-initiating precursor is actually non-initiating depends on a significant amount of variables, each of which influences the other. Basically it's a giant mess of variables to keep an eye on, but the desired result is clear: Punching a hole through a metal-explosive-metal sandwich without setting off the explosive. After that you can throw whatever you want through that hole without having to worry about setting off an explosive, which means that you can use the best penetrator you can make. ... @anwaralsharrad does this answer your questions? If not, feel free to ask anything.
Bronezhilet posted a topic in Ballistics Science DiscussionSo, recently I stumbled upon something fairly interesting. Most of the people here know about shaped charges and how they work, the principles behind it are fairly well known. Recently however, there has been research about a new 'class' of shaped charges: Reactive Liner Shaped Charges. As the name implies it's a shaped charge with a liner made out of a reactive material. Please note that I still do not fully understand the workings of Reactive Liner Shaped Charges, this post may be changed or updated depending on new information and/or discussions. What is a reactive material, you say? One of the papers explains it like this: (Demolition Mechanism and Behavior of Shaped Chargewith Reactive Liner, Jianguang Xiao et al., 2016) In simple terms, it's a material that only explodes when you hit it really really really really hard with a hammer. Or when you fire it into a solid material at several kilometers per second. I dunno. It's one of the two. What this amounts to is a shaped charge which forms an exploding jet. Neato. But... why should you care? We already don't fire explosives at an armoured target because it's not very efficient, so why suddenly care now? To answer that I have to compare it to normal shaped charges and explain a few things about explosives. The most important thing to understand is that no explosive detonates instantly, there is always a slight delay. This delay is (almost) negligible at normal projectile velocities, but become important at high velocities. Think hypersonic velocities, like with... shaped charge jets! The main thing I am not completely sure about is whether the detonation of the shaped charge initiates the liner, or the impact with the target. The self-delay of the reactive material used in most of the tests is ~0.85 and depending on the liner angle the jet can move 2.8 to 5.2 meters before actually exploding. Of course this distance will be a lot less when penetrating because the material slows down. A reactive material with a too low self-delay might detonate during the formation of the jet, or before it actually managed to penetrate the armour (but this only applies in the situation where the reactive liner is initiated by the shaped charge). This is of course not something you want, you want the liner to detonate inside the target to do the maximum amount of damage. And that's the main reason you should care about shaped charges with reactive liners. They do a fuckton of damage. This is your brain: This is the result of a shaped charge with an aluminium liner: This is your brain on drugs: This is the result of a shaped charge with a reactive liner: To give a sense of scale, that's a 1520 by 1520 mm concrete cylinder. The shaped charge had a diameter of... 81 mm. As you can see the reactive liner does a fuckton more damage compared to a normal liner, this is because the jet literally detonates when it's inside the armour. Concrete is one of the materials that cannot deal with certain forces, which makes it weak versus explosives detonating inside of it. Steel for example cares a lot less about it, but even steel will suffer more damage from a reactive liner than a normal copper liner. The entry hole for a reactive liner is around 0.65 CD whereas for a copper liner it is 0.5 CD. A paper also states the following: The paper however does not show or describe the "tremendous increase in steel target damage". It does however give some basic information and show photos of the entry holes: The penetration capabilities of reactive liners in steel targets were "sacrificed slightly" compared to copper liners, but the paper does not elaborate any further. Here's some more information and pictures about the effectiveness of reactive liners against concrete targets, just for shits and giggles: A 'Bam Bam' is the same warhead as the 81mm one (1.8 kg) from the first photos, except scaled to 18.1 kg. The 81mm charge is called Barnie, by the way. The target is the same ~1500 mm too. As you can see the Bam Bam charge is capable of fucking up massive parts of asphalt roads/runways. A 21.6 cm shaped charge completely destroying around 42 square meters of asphalt. But hey, a 21.6 cm charge is fucking massive, lets tone it down slightly. Charges: Test setup: Results: Sadly there's a bunch of information missing in the tables. It is highly likely that different liner thicknesses were used, but these aren't given in the tables. Results can be found in the full version of Table 1: ...that's around 9-10 square meters of concrete fucked up by a ~1 kg warhead. That's fucking insane. Some other things to note is that due to the materials used in these tests (an aluminium-polymer mix) the jet velocity is significantly higher and the jet length longer than comparable copper liners: So the reactive liner used (26% Al, 74% Teflon) has a jet tip velocity that's around twice as high for shallow charges, but drops to around 1.6 at higher angles. The difference in jet tip velocity is most likely due to the lower density of the reactive liner. This is what Wang et al. said about this: This poor ductility also increases the probability of fragmentation (jet break-up), which can be seen here: So because the reactive liner has a lower density, it forms a jet quicker, but because of its poor ductility it starts to break up very quickly. Tests have shown that a stand-off that's longer than 2 CD is undesirable, whereas normal liners do not really care about a longer stand-off. However! The research done to make the Barnie warhead show that it is undesirable to have cavitation during the formation of the jet. This cavitation is visible in the above simulations, but can better be seen in this one: It is very well possible that Wang et al. had a sub-optimal liner design, since the final Barnie jet looks like this compared to a comparable aluminium liner jet: They are quite similar and the Barnie jet does not have the 'blobs' visible in the simulations from Wang et al.. And last but certainly not least, Xiao et al. calculated the TNT equivalence (RE factor) of the reactive liner: In simple terms, the kaboom-effectiveness of this reactive material is 3.4 to 7.7 times as high as TNT. But since these values on their own are kind of meaningless, lets compare them to other RE factors! The RE factor of C4 is 1.34. The RE factor of RDX is 1.6. PETN? 1.66. Torpex? 1.3. Amatol? 1.1. ANFO? 0.74. The explosive with the highest detonation velocity (Octanitrocubane)? 2.38. THIS FUCKING ALUMINIUM/TEFLON MIX!? MOTHERFUCKING 7.77. Interestingly the theoretical energy contained in the aluminium/teflon mix is only about 4 times as high as TNT. The higher values are most likely due to the addition of kinetic effects. So yeah... huzzah for reactive liners. I might add some stuff to this post later, depending on whether or not I forgot something.