Physics of a tank impact...

[Johnny1A.2]

Suppose hypothetically that a one kilogram (or close enough) piece of dense rock (like basalt or granite) slammed into the main-body armor of a modern-day battletank at a velocity of about 740 meters/sec (never mind how the situation arose).

What exactly is likely to happen? Is it going to penetrate, or tear a gash in the armor, or will it shatter and a lot of the energy be carried away?

I'm sure it would disable the main gun if it struck that, but what about the main body armor? Or the turrent armor, or the treads? (I'm pretty sure it would be Very Bad Indeed for the treads or motive machinery if it hit them, actually.)

[Anthony]

Originally Posted by Johnny1A.2

Suppose hypothetically that a one kilogram (or close enough) piece of dense rock (like basalt or granite) slammed into the main-body armor of a modern-day battletank at a velocity of about 740 meters/sec (never mind how the situation arose).

What exactly is likely to happen?

Well, to give a comparison, a kinetic penetrator from an M1 tank is 4 kg at 1740 m/s, and will have many times the sectional density because made of a material that's 3-4x as dense and shaped as a long narrow dart instead of a chunk of rock.

So, most likely, it damages the paint job. I doubt it would even go through side armor.

[DouglasCole]

Originally Posted by Johnny1A.2

Suppose hypothetically that a one kilogram (or close enough) piece of dense rock (like basalt or granite) slammed into the main-body armor of a modern-day battletank at a velocity of about 740 meters/sec (never mind how the situation arose).

What exactly is likely to happen? Is it going to penetrate, or tear a gash in the armor, or will it shatter and a lot of the energy be carried away?

I'm sure it would disable the main gun if it struck that, but what about the main body armor? Or the turrent armor, or the treads? (I'm pretty sure it would be Very Bad Indeed for the treads or motive machinery if it hit them, actually.)

about 32d pi++ of damage. :-) Call it 6dx5, but it's not going to be a great penetrator overall. Might be 6dx5(0.5). This is about an 86mm basalt spheroid.

[lwcamp]

Rock is relatively low density and is not very strong compared to armor. At ~700 m/s, dynamic pressure will not be enough to plastically deform even steel, never mind advanced modern armors. My best guess is that the rock shatters and the tank is unharmed. If it hits someplace with a thickness less than the rock diameter, it might dent or crack that section.

Luke

[Phoenix_Dragon]

Originally Posted by Johnny1A.2

I'm sure it would disable the main gun if it struck that, but what about the main body armor?

I strongly doubt it.

In fact, a single strike from that rock will probably have no effect other than scratching the paint. If you hit the lens of an optic, you might impair it (Cracked external lens), and you might damage some of the external features (Such as the external MGs). Chances of knocking out a track or damaging the engine is probably negligible, particularly given rock's low density compared to a metal round.

Compared to the kinetic rounds that are a threat to a tank, that thing is lightweight, slow, low-density, has a high cross-section, and is fragile (The rock is most likely going to shatter on impact, making its already-poor performance even worse).

[smurf]

Originally Posted by DouglasCole

about 32d pi++ of damage. :-) Call it 6dx5, but it's not going to be a great penetrator overall. Might be 6dx5(0.5). This is about an 86mm basalt spheroid.

Old rules used to state sub sonic rounds had a 0.5 divisor but this is supersonic?

So it must have come from space to have a lump of rock go super sonic. Rocks that have no aerodynamic shape will not go super sonic. The sound barrier would break it apart.

[DouglasCole]

Originally Posted by smurf

Old rules used to state sub sonic rounds had a 0.5 divisor but this is supersonic?

No. Subsonic includes the .45ACP which is 2d pi+ just fine, no armor divisor.

I gave it the armor divisor because of the brittle-and-shatter thing Luke mentioned above.

[ronom]

And Douglas Cole has a pretty good ballistic formula, so that should be about right.

[malloyd]

Originally Posted by Phoenix_Dragon

Compared to the kinetic rounds that are a threat to a tank, that thing is lightweight, slow, low-density, has a high cross-section, and is fragile (The rock is most likely going to shatter on impact, making its already-poor performance even worse).

That last bit not really. Once you are up in the supersonic range how fragile a missile is doesn't matter so much - in a sense it doesn't have enough time to shatter, it's through the target before a stress that would break it apart can propagate through it. Note that our many of our anti-tank penetrators are actually liquids (molten metal jets) at the moment they actually hit the armor.

[Fred Brackin]

Originally Posted by DouglasCole

I gave it the armor divisor because of the brittle-and-shatter thing Luke mentioned above.

It's low density too. Better than wood but less than half of steel or 1.8th of DU.