How tough is BPC actualy?

[ReconCS6]

Inspired by the how much does an Ogre actually weigh debate, I took some time to look up some material densities, grams per cubic centimeter, tensile strength measurements, etc.

Also did some research of PSI, Megapascals and nuclear blast overpressure/f5 tornado winds.

So, current technology armor is typically Rolled homogenous armor, alluminum armor, or chobham armor.

Basic RHA has a tensile strength of about 900-1100 MPa, and a density of 7.84 grams/cubic centimeter.

The average 1 megaton nuclear weapon produces a peak overpressure of 50 PSI (or 0.344737864500 Megapascals), and the fireball itself will be 5700 meters across. We will assume that the tank in question is a few feet further out.

In terms of tensile strength, the tanks armor has a tensile yield strength of roughly 137785 PSI. The tanks armor plates can take the force. Most tanks have a frame built of RHA these days, and tougher armor.

Chobham armor is supposed to be made primarily from Silicone Carbide, which has a yield strength over 3000 MPa (or 435113 psi)and 3.21g/cubic centimeter. so chobham armor is roughly three times tougher than RHA. It can completely survive the overpressure by itself.

Now a force 5 hurricane has winds around 150mph. Reports have stated that most tanks won't even budge when hit with winds of this velocity.

I'm pretty sure that a tank hit with 50 psi at 900mph is gonna do some moving, and while the armor may not breach, the tank might due to being thrown like a rat by a terrier.

Comments?

PS my math has always sucked, and I know this.

[sir_pudding]

Conventional tanks can be flipped by comparatively modest conventional explosives, and the crews can be killed by overpressure that leaves the tank mostly intact.

[Wei Po Yang]

Your blast overpressure numbers seem low. A few ounces of C4 can produce over 100 PSI within 10 feet of the blast. 50 PSI is a serious injury (blown eardrums and membranes) but likely not a lethal pressure wave to a human. Mythbusters did several episodes discussing the lethality of G-force and pressure forces, if you'd like to see some examples. For reference, 14.7 PSI = 1 atm, and the numbers above would actually be PSIg, or PSI above normal atmospheric. Therefore, a 50 PSI wave is about 3.5 atm, or the force on the human ears at the level of a 35 foot dive in a lake, if I recall what my SCUBA diving friend once told me correctly.

I've also never seen tensile strength measured in PSI. Tensile strength is usually measured in force units, and usually refers to the force that can be applied to a cord or cable before it breaks. PSI and MPa are units of pressure - I would expect those units to be a measure of crush strength/compression resistance, not tensile strength.

[KevinR]

Originally Posted by Wei Po Yang

Therefore, a 50 PSI wave is about 3.5 atm, or the force on the human ears at the level of a 35 foot dive in a lake, if I recall what my SCUBA diving friend once told me correctly.

1 atmosphere is about 10 meters of water.

[offsides]

10 PSI overpressure from a nuclear detonation is generally considered sufficient to kill most people exposed to it, though I don't know how much of that is from the total destruction it causes on the rest of the environment the people are in. 5-7 PSI will destroy most non-hardened structures...

[Toltrin]

I think they finally made a tank out of the stuff black boxes were made of... someone had to do it sometime.

[DouglasCole]

Originally Posted by Wei Po Yang

Your blast overpressure numbers seem low. A few ounces of C4 can produce over 100 PSI within 10 feet of the blast. 50 PSI is a serious injury (blown eardrums and membranes) but likely not a lethal pressure wave to a human. Mythbusters did several episodes discussing the lethality of G-force and pressure forces, if you'd like to see some examples. For reference, 14.7 PSI = 1 atm, and the numbers above would actually be PSIg, or PSI above normal atmospheric. Therefore, a 50 PSI wave is about 3.5 atm, or the force on the human ears at the level of a 35 foot dive in a lake, if I recall what my SCUBA diving friend once told me correctly.

I've also never seen tensile strength measured in PSI. Tensile strength is usually measured in force units, and usually refers to the force that can be applied to a cord or cable before it breaks. PSI and MPa are units of pressure - I would expect those units to be a measure of crush strength/compression resistance, not tensile strength.

He's got this one right. Tensile "strength" is almost always normalized by the area over which it's applied, making it a stress, which has the units of pressure (force per unit area) or, as is sometimes equally valid, energy per unit volume.

Stress can be either compressive or tensile, of course.

[Wei Po Yang]

Originally Posted by KevinR

1 atmosphere is about 10 meters of water.

I sit corrected. 35 meters of water, then. :-D

Thanks for the other correction on tensile strength. Makes sense.

[ReconCS6]

I believe that the reason c4 produces a high overpressure is due to its high propogation speed during detonation. I think that plastique is orders of magnitude faster than any other explosive of equivelant yield...imagine a 1 megaton c4 explosion. **** would fly.

[JLV]

Nuclear weapons have four primary damage mechanisms -- Blast, Frag, Radiation and Heat.

The Blast is actually from both the initial shock wave, and from the "transient winds" caused by the passage of that shock wave (and the subsequent desire of the atmosphere to fill in a vacuum or area of lower pressure). The transient winds can be quite effective in that they introduce new pressure waves of considerable magnitude that may move against the way a target is braced (for buildings, it can cause complete failure and collapse, and for vehicles, if the transient winds apply pressures latitudinally instead of longitudinally, they can flip even surprisingly heavy vehicles).

The Frag is composed of items picked up by the blast wave (secondary translation) which can include people, bricks, glass shards, cars and trucks, dogs and cats, you name it). Many of these objects will be moving at quite respectable speeds and can cause enormous damage on impact.

Radiation is fairly self-explanatory, and can cause anything from immediate death, to cancer 25 years from now (or even nothing at all). Radiation generally lessens over the square of the distance from the detonation, though that varies widely depending on circumstances. For game purposes we can assume the other damage mechanisims overcome the radiation effects in the immediate tactical environment and thus can ignore this one.

Heat is a major damage mechanism but is unpredictable by its very nature. We used to say "we don't weaponeer the flash" because we frankly lacked the math to do so in a reasonable time frame (i.e. within a sufficiently small time frame to permit a decision maker to determine whether or not he was actually going to pop a nuke). Suffice it to say that fire WILL result, and anything flammable within a reasonable distance of the detonation WILL burst into flames. Additionally, secondary damage effects (damaged gas mains and the like) will also cause fires to break out even well beyond the range at which spontaneous combustion would occur. As a side note, that flash can temporarily or even permanently (in rare cases) cause blindness. Even temporary blindness in a fast-moving tactical environment can cause significant tactical disadvantage to the blinded personnel.

I know this doesn't address the basic issue of stress versus tank parts, but it's well to understand the damage mechanisms as you get into these discussions since your straightforward math about pounds of pressure per square inch can easily be skewed when a tractor-trailer rig impacts your LGEV at several hundred feet per second....