How tough is BPC actualy?

[Leila Ross]

As far as I can see as with most types of Handwavium, Biphase Carbide is as tough as the game needs it to be and no tougher.

And with this (un)helpful comment, I shall now leave the thread.

[twb3]

I'm afraid a straightforward comparison of blast overpressure to material tensile strength is not useful as even a first-approximation analysis of the vulnerability of a vehicle to blast effects. Yes, they are both in units of force per unit area, but it's still an apples-to-oranges comparison.

An answer really requires a more detailed engineering analysis of possible failure modes. For example, say the driver's hatch has an area of 2.5 square feet and we are looking at a 1,200 psi overpressure. The load on the hatch from the overpressure is 3,000 pounds evenly distributed. I can think offhand of three failure modes that would have to be analyzed:

1 - Is the hatch sealing good enough to prevent the 1,200 psi blast wave from propagating into the crew compartment and injuring / killing the crew?

2 - Will the structure supporting the hatch (hinges, hatch seat, etc.) fail under the 3,000 pound blast load?

3 - Will the hatch itself fail structurally due to the blast load?

Answering #2 and #3 will require an analysis of the bending and shear loads imposed on the structures. The strength of the material will be key to this analysis, but it's not a simple matter of comparing overpressure to tensile strength. Rather, the peak stresses will have to be calculated and compared to the strength of the material.

Qualification: I am a degreed engineer.

TWB

[drow]

its classic science. if we assume the tank is a perfectly regular sphere...

[terryocarroll]

The original post is off by a factor of 1,000,000.

To quote from the rulebook:

The first, of course, was the development of biphase carbide (BPC) armor. Stronger than any steel, it was also so light that even an air-cushion
vehicle could carry several centimeters of protection. The equivalent of a ton of TNT was needed to breach even this much BPC armor – which meant that, in practice, nothing less than a tactical nuclear device was likely to be effective.

Note that it's "a ton" not a megaton. Megaton sized weapons are strategic nukes, delivered by ICBMs. Ogreverse cruise missiles are probably a few kilotons in yield. The nukes thrown around by tanks are very small indeed, as nukes go. I reckon that getting close enough with even a ton of TNT would kill the crew of a tank quite messily, though, whether or not the armour was breached. I like the idea of "hiveloc" rounds that are so fast that the BPC "flow[s] like wax". That seems more realistic to me.

[gjc8]

Originally Posted by twb3

Answering #2 and #3 will require an analysis of the bending and shear loads imposed on the structures. The strength of the material will be key to this analysis, but it's not a simple matter of comparing overpressure to tensile strength. Rather, the peak stresses will have to be calculated and compared to the strength of the material.

Made even more complicated by the fact that "biphase" means it is almost certainly not homogeneous and probably not isotropic.

[DouglasCole]

Originally Posted by twb3

For example, say the driver's hatch has an area of 2.5 square feet

2.5 square feet = 360 square inches

and we are looking at a 1,200 psi overpressure.

1200 pounds per square inch

The load on the hatch from the overpressure is 3,000 pounds evenly distributed.

432,000 lbs evenly distributed, no? 216 tons on a slab 19" square, more or less.

1200psi is pretty serious overpressure, I think. That's like 80 atm.

[ReconCS6]

This is what I'm talking about. I'm a friggin english major. We need more technical discussion. I like actual math, and what I came up with originally took me about an hour and a half of digging and research. I simply couldn't imagine that some part of the tank wouldn't fail under the stress of pressure or even a tac-nuke and point blank range. The largest atomic cannon shell had a yield of 15 kilotons (15,000 tons of tnt, same size as Hiroshima). each shell is 365 kilos (about 800 pounds) and is 1384mm or 4 and a half feet long. The M65 Atomic Cannon from which it was fired had a muzzle velocity of 625 m/s (2060 ft/s), for a nominal range of 32 km (20 mi), and weighed 77 metric tons. The shell alone (never mind the nuke inside) at that speed and weight causes how much force? 1/2mv squared right? that equals over 71 thousand kilo-joules if my crappy math is right.
Is that not a significant amount of force?

[Apache]

I would just be happy to know what one centimeter of BPC is rated in 4e GURPS terms.

Whats its DR?

Yes, I'm working on my own G:OGRE 4e project.

[JLV]

Originally Posted by drow

its classic science. if we assume the tank is a perfectly regular sphere...

Oooo, even better; let's assume the tank is a point! ;-)

[twb3]

Originally Posted by DouglasCole

2.5 square feet = 360 square inches




1200 pounds per square inch



432,000 lbs evenly distributed, no? 216 tons on a slab 19" square, more or less.

1200psi is pretty serious overpressure, I think. That's like 80 atm.

You are correct, of course. That's what I get for working pressures in lb per square foot for so long.

TWB