[mdlug] OT - IR jamming

[Aaron Kulkis]

Dave Arbogast wrote:
>> Right now, the worst thing out there is a device called
>> an EFP (explosively formed projectile).  It's an upgrade
>> of a successful assassination method -- the platter charge
>> attached to the bottom of a man-hole cover.
>>
>> An EFP is a steel can, normally set in concrete...the can
>> is filled with explosive, with the detonator near the front,
>> and then covered with a shallow dish made of copper (concave
>> into the can.  When the explosive charge blows, the copper
>> blows-outwards while still maintaining a bond with the
>> rim of the steel can...as pressure builds, the copper
>> distends (easily because it is a ductile metal)...the
>> center of the now outward-bowing bowl is travelling
>> faster than the edges...once the edges release/tear from
>> the rim of the can, they snap inwards...forming a very
>> slender projectile, which by this time is moving at a
>> speed in the range of Mach 4 to Mach 6.
>>
>> As you can imagine, this is extremely devastating to
>> anything it runs into -- even an M1 tank :-/
>>  
>>
> I think you missed one part of the physics of the copper in a EFP - it 
> becomes molten at that point and acts like a plasma cutter when it comes 
> in contact with simple armor.

 From what I've learned about "terminal ballistic", all that really
matters is the momentum.

For example, when figuring out the penetration ability of a
shaped charge (bazooka, law, RPG, panzer-faust), the fact that
the copper cone is vaporized doesn't change the calculations.

They just do the calculation as if it were a slug of copper
travelling at the speed of the plasma jet.


 > That is why the M1 and other advanced
> systems employ composite armor in many places - steel on the outside for 
> conventional projectiles, and other layers of other materials 
> (classified) to stop the plasma injection. The M60 in the Nam had simple 
> steel armor easily penetrated by the Russian RPG with their cone shaped 
> copper in the explosive, so the troops would get badly burned from the 
> molten copper injecting into the tank. This copper at that point did 
> little damage other than burn everything.  So, reactive armor panels 
> were added to the outside of the steel - basically explosive charges 

Right.
Reactive armor is what defeats shaped charges -- the explosive
in the reactive armor prevents the shaped charge from properly
forming a plasma jet against the vehicle armor.

The composite armor you speak of is more for defeating solid shot.

> that would detonate when the molten copper entered them, thus blowing 
> the plasma away.
> -dave
> 
> PS - the demolition crews world wide use this technique to topple steel 
> structures like old buildings - they have sticks of plastic explosive 
> about 2.5" in diameter with about a 1" copper piece in the shape of a 90 
> degree right angle running the length of the explosive. It will cut 
> through quite a chunk of structural steel.

shaped charges are fun ;-)