Reactive Liner Shaped Charges - For when you really don't like something

[Bronezhilet]

So, 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:

Quote

Reactive materials are a class of solid energetic materials that are formulated to release energy under highly dynamic loads. [...] Remarkably different from traditional energetic materials, they have features of high mechanical strength and sufficient insensitivity so as not to sustain a deflagration reaction using traditional initiation techniques, such as exploding bridge wires or flame initiation. As such, the mechanical work of a high-strain-rate plastic deformation process is required to provide the necessary energy to drive the reaction

(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:

Quote

The results showed a tremendous increase in steel target damage over a standard mass matched shaped charge lined device (Wang et al.)

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:

 

Quote

The liner of this charge was 40 mm in diameter and 55 degree in cone angle. Related parameters of three experimental operating conditions are listed in Table 1, where CD, L, S, M, and h are charge diameter, charge height, standoff distance, liner mass and liner thickness, respectively.

 

 

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:

Quote

The jet formed by reactive material liner is thicker and longer, with a shorter formation time. There are some disadvantages for reactive material jet, such as low density, and poor ductility, which makes it easier to break out and go against improving penetration depth. Furthermore, there are observed cavitations of the reactive material during jet formation.

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.

[Xlucine]

How does the energy released compare to the typical energy delivered to the target by a conventional shaped charge? I suspect the numbers are comparable, as while you've got a lot of explosive driving the SC, that probably has a lower TNT equivalence and SC efficiency must be ass

[roguetechie]

Tnt equivalence factor is up to 7.7...

 

This seems pretty damn spiffy to me. Is that not what you're talking about?

 

Also with such a high potential tnt equivalence can it not actually afford to have pretty low efficiency for a shaped charge?

 

I get the impression that It's so freakishly destructive BECAUSE OF it's inefficiencies compared to an ideally efficient shaped charge. (This is based on my assumption that shaped charge efficiency essentially relates to keeping the "jet" tightly coherent with all areas of it maintaining both tight physical proximity but also as close to uniform velocity throughout for as long as possible)

 

Whereas this has poor efficiency breaks up and gets chaotic quickly etc, but this spreads the damage and stresses much more. Since in military usage you want both penetration AND a large damage pattern once through the initial barrier, this is actually an advantage much of the time.

 

Or am i completely wrong?

[Bronezhilet]

10 hours ago, Xlucine said:

How does the energy released compare to the typical energy delivered to the target by a conventional shaped charge? I suspect the numbers are comparable, as while you've got a lot of explosive driving the SC, that probably has a lower TNT equivalence and SC efficiency must be ass

Quote

When the average velocity of a 1 kg jet varies from 2000 to 6000 ms^-1, the kinetic energy could reach 0.6–5.4 times TNT equivalence.

"Demolition Mechanism and Behavior of Shaped Charge with Reactive Liner", Xiao et al.
 

But a 1 kg jet is rare. a (really) rough estimation on a liner with a diameter of 110 and an internal angle of 50 degrees gives me ~380 grams for a 2 mm liner, ~500 grams for a 3 mm liner, and ~750 grams for a 4 mm liner. And we know that not all liner material will go into the jet or slug and we know that the jet itself has a very low weight compared to the slug.

 

Using the following info:

(Liner material is copper)

 

 

I'm getting an RE factor of 2.39. (500/50 = 10 kJ per gram for the total jet, TNT is 4.184 kJ per gram -> 10/4.184=2.39)

 

3 hours ago, roguetechie said:

I get the impression that It's so freakishly destructive BECAUSE OF it's inefficiencies compared to an ideally efficient shaped charge. (This is based on my assumption that shaped charge efficiency essentially relates to keeping the "jet" tightly coherent with all areas of it maintaining both tight physical proximity but also as close to uniform velocity throughout for as long as possible)

 

Whereas this has poor efficiency breaks up and gets chaotic quickly etc, but this spreads the damage and stresses much more. Since in military usage you want both penetration AND a large damage pattern once through the initial barrier, this is actually an advantage much of the time.

 

Or am i completely wrong?

Yes, you're wrong. It's so destructive because a reactive liner literally blows the fuck up, a normal liner doesn't do this.

[roguetechie]

Right i get the blows the fuck up part... That part makes sense.

 

My question is, in the blowing up does it technically lose a shit ton of it's efficiency rating as a shaped charge? 

 

Or are the two things unrelated?

 

However, to be clear here LOL I'm completely on board with the blowing the fuck up part. I just want to know what it does to the technical efficiency rating of the shape charge on the math side.

[Bronezhilet]

20 minutes ago, roguetechie said:

Right i get the blows the fuck up part... That part makes sense.

 

My question is, in the blowing up does it technically lose a shit ton of it's efficiency rating as a shaped charge? 

 

Or are the two things unrelated?

 

However, to be clear here LOL I'm completely on board with the blowing the fuck up part. I just want to know what it does to the technical efficiency rating of the shape charge on the math side.

In the tests done by Wang et al., the Al/PTFE liner had slightly less penetration in steel than a copper liner. Which is interesting because a copper liner should have significantly more penetration than for example a pure aluminium liner. It appears that the charges were dimension-matched, and then it doesn't make sense that an Al/PTFE liner has almost the same penetration as copper.

 

Someone should do some tests with dimension and mass matched shaped charges to compare Al/PTFE to aluminium and copper.

[barbaria]

If I understand it correctly, this thing will blow up the internals of an integrated special armor array and will leave a huge hole in a adapted special armor array? (thnx SH_MM)

 

Will this make backplates even more important to stop the jet from penetrating?

[roguetechie]

2 hours ago, Bronezhilet said:

In the tests done by Wang et al., the Al/PTFE liner had slightly less penetration in steel than a copper liner. Which is interesting because a copper liner should have significantly more penetration than for example a pure aluminium liner. It appears that the charges were dimension-matched, and then it doesn't make sense that an Al/PTFE liner has almost the same penetration as copper.

 

Someone should do some tests with dimension and mass matched shaped charges to compare Al/PTFE to aluminium and copper.

 

Yeah you were mentioning that earlier and how it makes certain comparisons hard or nearly impossible to do.

 

It's that whole change only one variable to get good data thing.

[Bronezhilet]

1 hour ago, barbaria said:

If I understand it correctly, this thing will blow up the internals of an integrated special armor array and will leave a huge hole in a adapted special armor array? (thnx SH_MM)

 

Will this make backplates even more important to stop the jet from penetrating?

I'm seriously doubting that claim about it penetrating about the same as a copper liner, since that goes against basically everything we know about HEAT jet penetration.

 

But yes, it would blow up the internals of whatever it hits. And I guess that if it hits ERA, there won't be much ERA left. It'll either detonate from the impact or the reactive jet will blow it sky-high. In my opinion RLSCs will be quite effective as multi-purpose warheads. If you have something like a 40 mm autocannon with RLSC warheads you'll have significant destructive power versus a lot of different types of targets.

[SH_MM]

Are reactive shaped charge liners identical with energetic shaped charge liners? Would make sense if they were...

 

Energetic shaped charges are already in use.

"DPEX energetic liner shaped charges substitute a defined amount of the inert liner components with reacting metals. These energetic components are transferred into the perforating tunnel together with the jet where a strong exothermic reaction takes place.

The result is an extreme pressure spike inside the perforating channel that will follow the path of least resistance and initiate a flow back into the wellbore. This backflow will break up the crushed zone and transport it out of the perforating channel resulting in a cleaner tunnel with increased diameter. Any possible slugs that have been created will also be eliminated. In addition, depending on the rock type and down hole conditions, small fractures may be initiated on the walls and the tip of the perforating channel."

 

http://www.dynaenergetics.com/products/energetics-systems/shaped-charges/dpex-shaped-charges

[Bronezhilet]

12 minutes ago, SH_MM said:

Are reactive shaped charge liners identical with energetic shaped charge liners? Would make sense if they were...

 

Energetic shaped charges are already in use.

"DPEX energetic liner shaped charges substitute a defined amount of the inert liner components with reacting metals. These energetic components are transferred into the perforating tunnel together with the jet where a strong exothermic reaction takes place.

The result is an extreme pressure spike inside the perforating channel that will follow the path of least resistance and initiate a flow back into the wellbore. This backflow will break up the crushed zone and transport it out of the perforating channel resulting in a cleaner tunnel with increased diameter. Any possible slugs that have been created will also be eliminated. In addition, depending on the rock type and down hole conditions, small fractures may be initiated on the walls and the tip of the perforating channel."

 

http://www.dynaenergetics.com/products/energetics-systems/shaped-charges/dpex-shaped-charges

For as far as I understand, no, they're not the same thing. They're being a little vague, but it seems they're using something like a multi-layer liner or something. They specifically say "these energetic components are transferred [...] together with the jet", with a reactive liner, the jet is both the reactive material and penetrator. With this charge the two functions seem to be separate. And while it does say "strong exothermic reaction" and "extreme pressure spike" it doesn't say it's an explosion. The function of the energetic material is to transport debris out of the tunnel and thus making it wider. With a reactive liner you'll also be making the tunnel wider, but you'll be doing that by blowing up the target, which will inherently create more debris. So while they are talking about "extreme pressure", it doesn't seem to be a 'proper' explosion, just a reaction which creates enough gas to produce an overpressure in the perforating channel to create a backflow. It also says "small fractures may be initiated" (emphasis mine), but you've seen the damage a reactive liner can do to concrete.

 

But then again, it might be the same thing, just with a reactive liner with a lower RE factor, but I don't think it is.

[Collimatrix]

On 8/29/2017 at 2:27 PM, Xlucine said:

How does the energy released compare to the typical energy delivered to the target by a conventional shaped charge? I suspect the numbers are comparable, as while you've got a lot of explosive driving the SC, that probably has a lower TNT equivalence and SC efficiency must be ass

 

TNT's energy density is, by convention, 4.184 MJ/KG.  Since KE is 1/2 MV^2, energy densities are dimensionally identical to half the square of the velocity.  So I get that anything that's moving at 2.9 KM/S has the equivalent energy density of TNT.  2.9 KM/S is about the right velocity for the slug of a shaped charge jet, but the tip (which is a small percentage of total mass) is moving quite a bit faster than that.
 

[Bronezhilet]

To clarify a little on the above post, the paper from which those screencaps are considers everything moving at a velocity less than 2 km/s not part of the jet.

[Collimatrix]

If I could find a document that has an example shaped charge with explosive charge mass and type, and a mass/velocity distribution that I could actually take some sort of integral from, I could work out average kinetic energy and efficiency figures for a typical shaped charge.

Now, this opens up an interesting question about NERA.  The little material that's available about reactive liners says that the flouropolymer is undergoing some sort of exothermic reaction that can only occur under intense pressure.  Does this mean that the polymer in NERA isn't just vaporizing?  Might it be deflagrating as well?

[Bronezhilet]

That would explain the warning about explosives on the Merkava NERA.

[Bronezhilet]

On the other hand, if it was reactive, wouldn't a single hit detonate a complete NERA layer? For as far as I know NERA isn't segmented in blocks like ERA, which suggests that it isn't reactive (or at least not self-sustaining).

[SH_MM]

I think the Merkava uses proper SLERA (self-limiting explosive reactive armor), which for example can contain only small amounts ("pockets") of explosive materials inside a larger layer of an elastic material. It is also possible to combine reactive/energetic materials with explosives for use as SLERA/ERA.

 

http://www.ciar.org/ttk/mbt/papers/symp_19/TB611523.pdf

[roguetechie]

On 8/30/2017 at 2:05 AM, Bronezhilet said:

In the tests done by Wang et al., the Al/PTFE liner had slightly less penetration in steel than a copper liner. Which is interesting because a copper liner should have significantly more penetration than for example a pure aluminium liner. It appears that the charges were dimension-matched, and then it doesn't make sense that an Al/PTFE liner has almost the same penetration as copper.

 

Someone should do some tests with dimension and mass matched shaped charges to compare Al/PTFE to aluminium and copper.

 

Thanks for answering a bunch of my questions, I've been reading about shaped charges efps heat warheads reactive armor and etc basics all day...

 

Hopefully my questions won't suck as much soon LOL

[Mighty_Zuk]

23 hours ago, SH_MM said:

I think the Merkava uses proper SLERA (self-limiting explosive reactive armor), which for example can contain only small amounts ("pockets") of explosive materials inside a larger layer of an elastic material. It is also possible to combine reactive/energetic materials with explosives for use as SLERA/ERA.

 

http://www.ciar.org/ttk/mbt/papers/symp_19/TB611523.pdf

Albeit IMI is the main producer of the Merkava's armor, it and RAFAEL are both government owned and certain divisions inside them act as separate units, enabling a rather uncomplicated process for producing products of one company in another.

And so far the only patent I'm aware of, on an armor solution by an Israeli company so closely related to the Merkava project (as a whole), is of a NxRA type armor by RAFAEL (The link was given in this forum actually, don't remember by whom).

Now, the responsible division for this patent works in close cooperation with MANTAK, it has to be. Same with parallel divisions in IMI. So if one holds a strong opinion on the conception of a given armor type, there should logically be a consensus among these bodies I've mentioned above.

The patent was filed in 2005, which was shortly after the Merkava 4 entered service. Obviously, armor development hasn't stopped there and the armor array has been changed at least once.

https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=7360479B2&KC=B2&FT=D&ND=1&date=20080422&DB=&locale=

 

So if RAFAEL choose to head on with NxRA over SLERA and NERA for heavy applications, and we assume that so do MANTAK and IMI, then the Merkava 4 is unlikely to use SLERA over the described NxRA.

 

[Lord_James]

Necro (sorry), but this topic was too cool for me not to post on! 

 

When researching about this, I found some enlightening (for me) information about this: 

 

Per Wikipedia (taken with large helpings of salt), Teflon and other PTFEs react with metals like aluminum at high temperatures. Along with the surrounding air, could these reactions explain why Al/PTFE liners have such powerful explosions? 

 

PTFEs have strong bonds between their fluorine and carbon atoms, as well as a very low coefficients of friction. Could this also explain the powerful explosive force (due to the release of this energy), and its ability to penetrate armor (low friction between the armor and the jet), respectively? 

 

This sounds like a very good precursor charge for tandem warheads. The Al/PTFE pre-charge doesn’t need to be very big to do large amounts of damage; I would think a 40mm (or even smaller) RLSC on a 120mm would literally blow up the first couple of layers of NERA /ceramics /whatever (and itself, so no remaining jet tip to penetrate as well) and leave a big hole for the main jet to pass through undisturbed. 

 

But, I can see why this isn’t being fielded whilst being very efficient (and surprisingly easy to make): fluorine is not the nicest of chemicals to have reacting in air. I can imagine what all the environmentalists would tout about the military using ammo with fluorine compounds as products. 

[Zadlo]

On 3/21/2019 at 2:13 PM, Lord_James said:

This sounds like a very good precursor charge for tandem warheads. The Al/PTFE pre-charge doesn’t need to be very big to do large amounts of damage; I would think a 40mm (or even smaller) RLSC on a 120mm would literally blow up the first couple of layers of NERA /ceramics /whatever (and itself, so no remaining jet tip to penetrate as well) and leave a big hole for the main jet to pass through undisturbed.

 

If you want a thermobaric warhead to be a precursor for tandem...

Al/PTFE is not a classic explosive but a pirolant which is useful for thermobaric warheads or SLERA.

[Collimatrix]

On 3/21/2019 at 7:13 AM, Lord_James said:

Necro (sorry), but this topic was too cool for me not to post on! 

 

But, I can see why this isn’t being fielded whilst being very efficient (and surprisingly easy to make): fluorine is not the nicest of chemicals to have reacting in air. I can imagine what all the environmentalists would tout about the military using ammo with fluorine compounds as products. 

 

I'm pretty sure the pyrotechnic flares used for luring away heat-seeking missiles use a similar PTFE/aluminum mix.