Shaped Charges

#1
I was chatting to my boss earlier this week about an RPG strike where we operate and tried to explain how shaped charges work. It turns out that he, being an ex (civilian) engineer was very knowledgable on the subject - he had been trained to use shaped charges to bore through rock.

I had always thought that the jet of molten soft metal penetrated things (armour) but he told me that it was the extreme pressure from the shockwave that caused heat that melts armour or rock. Sounds logical - does anyone know if this is actually the case, or a combination of the two?

Neither of us really knew what role the metal in the cone played - I remembered most munitions using copper in the cone and he, with an industrial background, recalled compressed powdered metals of various types and mixtures, depending on the rock to be penetrated, being used. Can any of Arrse experts on the subject enlighten us on the interaction of pressure and molten/vapourised metal (I have googled munroe ffect with little success).
 
#3
AIUI its the metal ( usually copper?) that is turned into hot nasty plasma with a hell of a lot of KE behind it.
 
#4
@ PX4 - that was my understanding

@BB - that was my understanding as well. But my boss, who is extremely knowledgable about pressure and heat having worked in oil & gas for a few decades, insisted otherwise. I suspect that the copper slug is Miznay Shardin rather than Munroe effect.
 
#5
Google the Munroe effect.

Interesting stuff.
 
#6
To go really in depth look into the Munroe or Neumann effect.

The liner (usually copper) is an enhancer and is there to focus the effect of the detonation wave. The cone inverts into a jet which punches a hole through the material. This is kinetic, not pyretic.
 
#7
Google the Munroe effect.

Interesting stuff.
Agreed, but I cannot really find explantations of the interaction of pressure and the molten metal jet. My intuition says the presuure lelts it ant the jet clears the molten target. I just can't find a definitive answer - let alone why different metals work better with certain targets.
 
#8
The copper of a shaped charge isn't molten as such, it just behaves like a liquid.
At the kind of speeds we're talking about - 8km/s or so - the interaction of the jet tip with the target generates such pressure, that the yield strength of both materials is exceeded by enough of a factor to make strength essentially irrelevant. In this case - known as hydrodynamic penetration - the only things that really matter are the material densities, and length of the jet.

Off to chortle at The Big Bang Theory now...

Sent from my GT-S5830i using ARRSE mobile app
 
#10
Agreed, but I cannot really find explantations of the interaction of pressure and the molten metal jet. My intuition says the presuure lelts it ant the jet clears the molten target. I just can't find a definitive answer - let alone why different metals work better with certain targets.
Munroe is the action of the blast force concentrating pressure waves from detonation by having a hollow on the face of a charge. Misznay is an expansion of the same effect by having the hollow spherical and lining it with metal.
 
#11
To go really in depth look into the Munroe or Neumann effect.

The liner (usually copper) is an enhancer and is there to focus the effect of the detonation wave. The cone inverts into a jet which punches a hole through the material. This is kinetic, not pyretic.
Thanks Dingerr,

Does the copper clear the molten (caused by extreme pressure) target?
 
#13
I don't understand the question.
My boss' understanding was that extreme and focussed (from the shape of the charge) pressure caused heat that would make the target melt. I had heard of improvised shaped charge projectiles that used steel cones or no metal cone that just did not work, so I was wondering what role the cone played if the target had already melted. My thought was that the jet of molten malleable metal would hose out the target molten material.
 
#14
I don't understand the question.
I think he wants to know, what actually causes the penetration. Is it the pressure wave or is it the soft molten copper?

Its the copper isnt it? High velocity negates how soft it is and it will go through by shear speed of force.
 
#15
No it's a jet. The copper follows through as a slug. An added bonus when hitting armour.
 
#16
No it's a jet. The copper follows through as a slug. An added bonus when hitting armour.
I had thought it was a slug in miznay shardin effect (as in off-route mines) but a jet with Munroe effect (as in RPGs etc). I think Pebbles is close to what I am trying to understand: the relationship between the extreme high heat caused by pressure waves and the ductile metal cone.
 
#17
There are shaped charges and there are hollow charges, you are confusing the two. Shaped charges generate a massive shock wave which is nice for smashing concrete, you can make one quite easily, hollow charges form a jet of hot gas usually through the use of a copper funnel, usefull for cutting through steel.

Self forging fragment is a hollow charge with a copper projectile which is fired through the armour, but hey why not just wiki the terms I've used?
 
#18
When a metal liner is used, it turns into a molten metal slug moving at high speed with enormous kiinetic energy. Followed by the shock wave and gasses. All of this will strike whatever target it is used upon.

The shaped charge effect will also work when a metal liner is not used, although in this case there won't be the slug of molten metal, just the shock wave and gasses but as energy isn't used to transform the metal liner a higher detonation velocity could be achieved.

However, there are many variables that prevent you getting a definitive but general answer. The diameter of the charge and it's stand off height have an effect, but more importantly the specific detonation velocity of the type of explosive used and the angle of the conical shape (in a round shaped charge). For example, a higher velocity explosive such as ICI's Plaster Gelatine (no longer made unfortunately) worked best with an included angle of 60 degrees; but ICI's Special Gelatine 80 worked better with an 80 degree included angle. However, Special Gelatine had both a low and a high detonation velocity depending on weather a booster was used to initiate the charge. For example using just a ICI Standard No 6 detonator directly would often just produce the lower velocity but using some Superflex as a booster or a few short lengths of Cordtex would reliably produce the higher velocity of detonation. This was noticable when used against rock targets or agianst steel targets underwater.

So to get definitive answers would require one to specify the lining material, the stand off height, the type of explosive used the size of the charge and it's method of initiation. An RPG round would have much different characteristics from, say, a plastic commercially made container designed to take a slurry with a plastic cone and filled with foam.

One claim to fame I once held was to use a small shaped charge underwater on a shipwreck called Filrix wich had gone aground just round the corner from the old Fort Bovisand in Plymouth. The charge was 2just 250g of ICI Special Gelatine 80 with two short lengths of Superflex taped to a Cordtex line, both the shape and the stand-off was made by using a Candle shaped light bulb which also provided an air gap. When fired, the charge successfully punched a perfectly nice hole with which I was later able to fit an eyebolt. Those were back in the happy days when the Filrix still had pretty clean paint on it and restrictions were fewer...
 
#19
Why copper, if metal improves the "effect" and steel isnt as good, too hard? what about lead or aluminium? soft and heavy/light, more/less usable KE?
 

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