Physics Guy wrote: ↑Thu Oct 13, 2022 5:34 am
The little HIMARS slugs won’t penetrate armor. You could drive through the burst of one of these munitions in a tank, and it would just be a hard, loud rain on the roof.
Although tungsten is dense and hard, the small HIMAR shot simply does not have enough kinetic energy to pierce heavy armor. The kinetic energy of a projectile is equal to 1/2 times its mass times the square of its velocity (KE = 1/2 mv^2).
The most successful armor-piercing munitions use high-density, high-velocity penetrators with a small cross-section to concentrate a large amount of energy onto a small area at the target. These munitions rely on kinetic energy alone to pierce armor.
Heavy armor-piercing rounds use strong high-density metals such as depleted uranium or tungsten as the penetrator component. The muzzle velocity of the 120 mm armor-piercing sabot rounds used by the M1 Abrams and other NATO tank main guns is about 4,000 ft /sec (1,700 m/s) or 3,500 mph. The weight of the penetrator rod is 56 pounds (25 kg)
*.
Depleted uranium (U238) has a density of 19 grams per cubic centimeter (g/cm^3). The density of tungsten is about the same. Lead is 11 g/cm^3. For comparison, solid ice is just less than 1 g/cm^3.
The DU penetrator of the Sabot round used as a 120 mm anti-tank munition is a long, thin rod with a point in front and stabilizing fins on the back. After it leaves the smoothbore gun tube, the aluminum encasement (see image below) breaks away leaving the penetrator to hit the target.
These rounds can get the job done with a single hit. The image below shows a tank turret that was struck by a 120 mm sabot round. From the outside, it doesn’t look too bad. Inside the turret is a different story.
When the penetrator rod hit the turret, the kinetic energy released essentially melted the DU metal, as well as some of the armor with which it came into contact. A metal splash pattern can be seen burned into the outside of the turret.
The white-hot metal, along with the solid steel armor shrapnel that spalled off the inside walls of the turret, incinerated the combustible material inside the tank, including the crew. The flying metal left holes in every piece of equipment in the crew compartment except for the breach of the main gun which is a large rectangular steel block.
The two soldiers in the image below are holding 120 mm armor-piercing depleted uranium (DU) sabot rounds for their M1A2 Abrams tank behind them. The encasement is aluminum and breaks away once the round leaves the barrel.
Both the 120 mm anti-tank round, and the 30 mm round (shown below) used by the autocannon on the A-10 Thunderbolt (Warthog), use depleted uranium as the penetrator.
The 30 mm GAU/8 7-barrel autocannon shown below on the A-10 has a rate of fire of 3,900 rounds per minute. Needless to say, the weapon is fired in short bursts. When the gun platform is moving at, say, 200 mph, there isn't more than a few seconds on a tank-sized target. Depending on the angle of incidence, the 30 mm armor-piercing round can punch holes in most tank armor, especially the thinner turret top armor found on most main battle tanks as well as that normally used on armored personnel carriers.
The tank shown below was hit by 30 mm DU fire from an A-10. The heavier armor in the front of the tank was breached, as were the turret and main gun tube.
30 mm DU rounds also punched through the armor of what looks like an APC. Depending on the range and angle of incidence, modern APC armor can usually stand up to .50 cal armor-piercing rounds. For example, the armor on the Bradley fighting vehicle was specified to resist armor-piercing rounds slightly larger than .50 cal at 500 meters. When it comes to APC armor, however, the 30 mm DU rounds will get the job done.
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*By comparison to a 120 mm sabot round, the HIMARS tungsten shot, which appears to be 4 to 6 mm in diameter, would weigh a few grams or so at most. As a rough approximation, assume that the impact velocity is the same for both projectiles, and give the HIMARS shot a factor of 5 or so for the larger cross-section of the Sabot penetrator. To get an estimate of the relative impact energy per square inch of the two projectiles, just compare the masses adjusted for the cross-section. The difference in armor-piercing capability becomes apparent.
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ETA 1.
While working in Kuwait, a colleague from Sikorsky found out that I had been a tanker in the military. He invited me to spend a Friday afternoon with him at the boneyard for Iraqi (read Russian) armor recovered from the Desert Storm battlefield. It took some time but we eventually found a tank with its turret still on the hull. There were two clean GAU/8 holes in the turret. No other damage was visible from outside the tank.
"Take a look inside", he suggested. I opened the hatch and the scene was pretty much as described for the tank shown above. While there were two neat 30 mm holes from an A-10 attack on the outside, on the inside of the turret the armor had spalled off over an area of several square feet. The paint had been burned off of every surface. The interior was now rusted from the intense fire and there were oddly shaped jagged shrapnel holes in nearly every interior surface except for the breach block. "In the world of aviation", he said, "tanks are targets."
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ETA 2.
Ukraine could have had all the A-10 Warthogs that they could possibly fly or use for spare parts, but declined. As described earlier, they opted instead for late-block F-16s and F-15s. ("When you care enough to send the very best", I guess.)
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ETA 3.
It goes without saying that the effects inside the tank turret from the 25kg penetrator of a 120 Sabot round would not be the same as those from a 30 mm DU round in which the penetrator weighs less than 1 kg. (KE=1/2 mv^2)
The tank in the Kuwait boneyard had been hit by two 30 MM rounds and the damage described inside was mainly from spalling armor fragments. The tank in the image in that post had been hit by a 120 mm Sabot penetrator. I have not personally seen the results of a 120 mm Sabot round hit, but have been told that any identification of the crew members would have been impossible since the bodies were essentially "liquified".
