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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:

348c2015d7.png

(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:

446c46fa08.png

(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:

fc3f4c8558.png

(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:

28374b5038.png

(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:

0ca6fc0fdb.png

(Figure from "The Legacy of Manfred Held with Critique" by EV2 Florian Bouvenot)

 

 

But the most important one for us, is projectile material:

e9061e45de.png

(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.

 

 

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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.

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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.

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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.

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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.

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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.

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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!.

 

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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.

 

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