Non-initiating Precursor Shaped Charges

[Bronezhilet]

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 E_k=0.5*m*v^2,, 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.

 

 

[anwaralsharrad]

Tanks Bronezhilet .. i am realy grateful.

[anwaralsharrad]

One question please ,, some sources in the web say that russian grenades or missiles use some kind of non-initiating Precursor on there warheads !! do you have information about this ??  

[Bronezhilet]

Sorry, personally I have no idea, but @Militarysta does claim it, although I don't know his sources:

 

 

And from the same post: According to Dynamit Nobel the precursor in the Panzerfaust 3-T is non-intitating, but there's photographic evidence of the Panzerfaust 3-IT-600 being an initiating percursor.

 

That post also has a few nice pictures from simulations and tests.

[anwaralsharrad]

Thanks again 

[Collimatrix]

While we are on the subject, what is the thinking on precursor charges that are not co-axial with the main charge, like in the French MMP:



And the Javelin?

 

[roguetechie]

Bronez,

 

1006032.pdf available on dtic.mil

26th international symposium on ballistics.... Year is 2011 location Florida

 

It covers a BUNCH of stuff you guys are talking about here, the nera thread, reactive armor thread, covers noninitiating charges wrt reactive armor, and basically a fuck ton of other stuff you will like...

 

It's like1200 pages but it's worth it. If you can't successfully get dtic to cough it up I'll retrace my steps and get you a link to download.

[roguetechie]

Forgot to add that glass as a charge liner material presentation is also included... For some reason i think that may be interesting, and or a glass / secondary material mix

[Collimatrix]

1 hour ago, roguetechie said:

Forgot to add that glass as a charge liner material presentation is also included... For some reason i think that may be interesting, and or a glass / secondary material mix

 

I've read about glass being used as a liner material briefly in some technical literature, but it only said that it had been used, not if it was particularly useful for anything.

There's an entire world of specialized industrial shaped charges used in oil exploration, steel foundries, and doubtless some exotic and arcane fields I'm not aware of.  They are all quite specialized, at this point, for their particular jobs.  It would not surprise me to learn that they use exotic liner construction.

[roguetechie]

This is for combat though...

 

 

[Bronezhilet]

On 9/12/2017 at 7:20 AM, roguetechie said:

Bronez,

 

1006032.pdf available on dtic.mil

26th international symposium on ballistics.... Year is 2011 location Florida

 

It covers a BUNCH of stuff you guys are talking about here, the nera thread, reactive armor thread, covers noninitiating charges wrt reactive armor, and basically a fuck ton of other stuff you will like...

 

It's like1200 pages but it's worth it. If you can't successfully get dtic to cough it up I'll retrace my steps and get you a link to download.

I didn't actually know that a few of the ballistic symposiums were public, nice.

[Bronezhilet]

@Collimatrix @Xlucine

 

[Indigo]

On the topic of different types of shaped charges. I seem to remember awhile back reading about cumulative jets and non-cumulative jets, but I rarely see anyone make the distinction. I have source amnesia so I have no guarantee that it's a legitimate thing, but assuming it is, what is the difference in functionality, construction etc between charges that produce cumulative vs non cumulative jets? If this is complex enough to warrant its own topic let me know.

[Belesarius]

9 hours ago, Indigo said:

On the topic of different types of shaped charges. I seem to remember awhile back reading about cumulative jets and non-cumulative jets, but I rarely see anyone make the distinction. I have source amnesia so I have no guarantee that it's a legitimate thing, but assuming it is, what is the difference in functionality, construction etc between charges that produce cumulative vs non cumulative jets? If this is complex enough to warrant its own topic let me know.

Welcome to SH!.

 

[Collimatrix]

On 9/17/2017 at 3:56 PM, Indigo said:

On the topic of different types of shaped charges. I seem to remember awhile back reading about cumulative jets and non-cumulative jets, but I rarely see anyone make the distinction. I have source amnesia so I have no guarantee that it's a legitimate thing, but assuming it is, what is the difference in functionality, construction etc between charges that produce cumulative vs non cumulative jets? If this is complex enough to warrant its own topic let me know.

 

I have seen this terminology in some technical literature, but I have no insight as to what it means.

 

[A_Mysterious_Stranger]

On 9/17/2017 at 4:56 PM, Indigo said:

On the topic of different types of shaped charges. I seem to remember awhile back reading about cumulative jets and non-cumulative jets, but I rarely see anyone make the distinction. I have source amnesia so I have no guarantee that it's a legitimate thing, but assuming it is, what is the difference in functionality, construction etc between charges that produce cumulative vs non cumulative jets? If this is complex enough to warrant its own topic let me know.

 

Hi I know this is months out of date so apologies if this is redundant but these may or may not help you:

 

A Brief History of Shaped Charges

 

Quote

This brief overview of the development of shaped charges begins with a definition of a shaped charge. In the opinion of the author, a shaped charge is defined as a cylinder of explosive with a hollow cavity at the end opposite the initiation train. If the cavity does not contain a liner, it is referred to as a hollow charge or an unlined-cavity charge. If the cavity contains a liner made from a metal, an alloy, glass, ceramic, wood, or another material, the device is termed a shaped charge or cumulative charge (in the former Soviet Union) or Hohlladung (in Germany). The liner geometry may be conical, hemispherical, parabolic, or any arcuate device.

 

MODELING AND SIMULATION OF SHAPED CHARGES

 

This second one includes text from the first link as far as explaining shaped charges but it also explainsWHY shaped charges with liners are called 'cumulative.'  For example:

 

Because of the changing collapse velocities and angles both the jet velocity and slug velocity are changing during the entire process. In the case of the jet, a positive velocity gradient causes jet stretching and a negative gradient causes mass accumulation.

 

Assuming I am correctly interpreting the data the difference is the presence or absence of a liner and how that affects shaped charge behavior.     That said I may be wrong:

 

How to pierce tank armor. Lavrentiev’s theory of shaped explosive

 

Wikipedia says that traditional large caliber, high velocity anti-tank guns are used nowadays only by the Russians, and “some other countries”, which means that all anti-tank weapons produced in the West is based on the cumulative effect. A mathematical theory of Munroe effect (which is called cumulative effect in Russian) was developed by M.A Lavrentiev during the WW II.

 

Setting aside the fact the document uses wikipedia as a source, this alternate interpretation assigns 'cumulative' to the Munroe effect (which I think is independent of a liner).   In that case 'cumulative' vs 'non-cumulative'  may mean focused vs non focused explosive (which isn't a 'jet' so much as a normal HE detonation.  Go figure.)