I’ve been working on a project for several months, that is going to turn into a post, hopefully in about a week or so. I’m looking forward to publishing the final results.
As I gear up for it, I was thinking about other work I have done in this area and wanted to share some of that with you.
I don’t have much in the way of impressive skills. I’m not an artist or a musician. I can’t dance. My writing sucks.
What I am, though, is an extremely good metallurgist. And a bit of a sick evil fuck. That makes for an interesting combination.
What I am exceptionally good at is using metallurgy to kill things better.
Once upon a time, I was classified by the DOD as an “enhanced lethality engineer.” I really wish I had gotten business cards with that printed on them.
Here was the nature of that job.
Let’s say you have a missile system, like the TOW or Javlin.
It exists and has existed for a while. There are (or were) many in inventory. Soldiers have been trained on them. There is an entire production infrastructure that exists to make them.
But they are not as effective as they once were on the newest generation of armored vehicles.
Rather than scrap them, my job was to improve the warhead, so that existing systems could be upgraded to be more effective.
I enhanced the lethality of an existing system, hence, I was an enhanced lethality engineer.
This type of system upgrade happens all the time. Guidance improvements for accuracy, rocket improvements for range and speed, etc.
I did warheads.
The explosive physics of a shaped charge is not terribly complicated.
There is a cone of metal backed by a charge of explosives. The explosive detonates. That sends a shockwave into the back of the cone at a speed of 8,000+ meters per second. The cone collapses. As the walls of the cone impact each other, the material at the inner surface of that cone experiences forces in the range of tens and hundreds of gigapascals. That much pressure causes the metal to undergo shear and act like a liquid. It literally squirts out of the cone, sort of like how you can shoot a watermelon seed from between your fingertips by squeezing it.
The front of that jet is moving at about 12 kilometers per second. The back of the jet at about 6 kilometers per second.
The jet takes a short distance to form, which is your optimal standoff distance for the warhead.
Only the inner layer of the cone forms the jet, the rest of the cone becomes a slug and travels behind the jet at about 3 to 4 kilometers per second.
When the fully formed jet hits the target, it erodes it, like a water jet cutter. When you were a kid, did you ever squirt a hole into the dirt with the jet nozzle on a garden hose? Same thing.
The penetration of the jet is a function of the length of the jet and the relative densities of the jet and the armor. If you wondered why some tanks use depleted uranium armor, this is why. No metal is strong enough to resist impact at velocities of 12 kilometers per second and tens of gigapascals of force, so you just use the densest material you can to limit the depth of jet penetration.
The length of the jet is determined by the diameter and angle of the cone. The optimal angle for a deep penetrating jet is 42°. The diameter is limited by the size of the missile.
All you can do is play with the density of the metallic liner.
Typically, the liner is copper. Copper has a higher density than steel and is very ductile. The liner material has to be ductile, or the liner will shatter and not form a good jet.
The amount of precision that goes into making shaped charge liners is very high. Tolerances in the tenths of thousands of an inch. Little imperfections alter how the jet forms and reduce its penetrating capacity. Military shaped charge liners are very expensive.
As an aside, the shaped charge liner design for perforating charges in oil and gas is different. In a military setting, you only get one shot to kill a tank. If you don’t it will shoot back. In oil and gas, rocks don’t shoot back. You use lots of charges to perf a rock so shaped charge liners have to be cheaper to be cost-effective. Oil and gas love powder metal liners because they are less ductile and the slug breaks up and doesn’t plug the perf hole.
One of the metals that makes better liners is molybdenum. It’s more dense than copper and forms a jet very well. The problem is, it doesn’t deep draw easily like copper does, so making liners is harder.
I started out on an additive manufacturing process that created full-density moly liners that had the metallurgical properties to make good jets. There is a lot of metallurgy, grain size, orientation, etc, that affects jet formation and we wanted to optimize for that.
But then I got to thinking.
We know that only the inner layer of the cone forms a jet and the rest forms a slug.
You need the cone to have a certain thickness, if you try to make it thinner so that only that jet-forming layer is there, it won’t form a jet. The backing layer of the cone is what drives the jet formation.
The good news is that we know just how thick that jet-forming layer is.
So, what can we do?
I made a bi-metallic liner.
The inner layer was jet-forming molybdenum.
What to make the driving layer from?
How about zirconium? It bonds well to molybdenum so you don’t get delamination during jet formation. It can be applied with the same additive manufacturing process as the moly.
Oh yeah, and it’s pyrophoric and burns at a few thousand degrees in air.
When the charge goes off, the bi-metallic cone collapses. The molybdenum inner layer shears and turns into a jet at 12 kilometers per second and erodes a hole through the armor. The zirconium slug traveling behind hits the hole made by the moly jet. The zirconium slug sheers through the hole and comes out the other side having been adiabatically heated to a few hundred degrees.
The hot zirconium exits the hole into the crew compartment of the armored target and ignites, spraying everywhere.
I just punched a hole through the side of your armored vehicle with a hypersonic jet of molten metal and then sprayed your crew, your ammo, and your fuel with 3,000° burning metal with three times the muzzle velocity of a 5.56.
Because it was fucking fun to design this shit and set it off.
The word engineer means “one who builds engines.”
The word engine, in its origin, meant a siege engine, a machine for breaching fortifications.
Metallurgy is the oldest form of science. It is what made us take that first step from using the materials we found around us in the Stone Age to making the materials we needed with smelting in the Bronze Age. All of civilization became possible when we started making metal tools.
I embrace the roots of my field.
I am a metallurgical engineer.
I use my knowledge of metal to build more effective machines for breaching fortifications.
Better killing through metallurgy.
4 thoughts on “Better armor killing with metallurgy”
I, personally, don’t know any man that doesn’t enjoy making things go BOOM. Some better than others, you gooder. 😉
Fascinating. As are many aspects of … energetic systems.
Very much looking forward to the follow-up post. And, may I request an article on explosive bonded materials, if that’s in your wheelhouse? We’re now using a few such components at work, and it’s caught my interest.
Armed with a dangerous mind….
Neat. I never figured such precision was required for a shape charge, it gets exploded afterall. but it makes perfect sense as you explain it!
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