How to calculate needed energy

[Vultur]

How powerful would a weapon have to be to blow through two meters of chitin plating and still have energy to do serious destruction to the creature's body? How would this be calculated?

[Stark]

Define 'chitin' and define 'blow through' and define the creature's physiology. How are you going to 'blow through' so much chitin without pushing some of it into the creature's internal organs and heating the flesh? What kind of weapon is being used?

[Connor MacLeod]

YEah, far too many variables are unknown. You have to be more precise before anything like that could even possibly be determined, such as the weapon's nature and design, the size of the hole in the chitin (is it width or depth?) and the size of the creature (how big is its body, etc.) as well as the damage mechanism (is it a projectile weapon? an energy weapon? Does it just heat up the target or pulverize via some secondary shockwave, ,or a bit of both?)

People just don't "know" this stuff automatically or can't pull stuff out of thin air. We need data to work w ith.

[Ender]

Well, we'd have to know the weapon used, then determine the chemical composition and density of said chitin, know the size of the hole, know the mechanism for "blowing through" (melting, vaporization, explosive vaporization, burning/cremation, etc), know the time over which the event took place, and knew what constitutes "serious destruction" so we could estimate that. Though I would think having a 2 meter deep hole in you would be sufficient. And what the heck kind of creature has 2 meter thick skin and is able to move?

[Gil Hamilton]

Well, "chitin" is a specific thing, that is, a polymer made of N-acetylglucosamine sheets (*closes biochemistry textbook*). Hence it has definite properties too it, though I can't imagine why any creature would grow a chitin shell two meters thick (that's a BIG fucking crab).

However, you are going to have to elaborate what you mean by "blow through". Like penetrate with a bullet? Like vaporize with a laser? Like explode with a bomb? The question is vague and not something I'm prepared to answer without stuffing some ground up chitin in a bomb calorimeter and combusting it (though I suppose the CRC Polymer Handbook MIGHT have data on chitin in it... you might go to your local library and look for N-acetylglucosamine).

Actually, that would be the first step I'd take to investigate the question. Get your hands on a Polymer Handbook and get the specific data you are looking for. There are MULTIPLE handbooks that your local library should have that will have just about every bit of information you could possibly want out there, and I guarantee that a common and commercially/medically useful polymer like chitin will have a breadth of data available for it. Then figure out exactly what sort of nastiness you are inflicting on the poor Omega Crab. Once you know that and have the data available to you, then you are good to go.

[Ford Prefect]

though I can't imagine why any creature would grow a chitin shell two meters thick

Because they've been scouted for a Godzilla film, obviously.

[Ender]

Well, "chitin" is a specific thing, that is, a polymer made of N-acetylglucosamine sheets (*closes biochemistry textbook*). Hence it has definite properties too it, though I can't imagine why any creature would grow a chitin shell two meters thick (that's a BIG fucking crab).

However, you are going to have to elaborate what you mean by "blow through". Like penetrate with a bullet? Like vaporize with a laser? Like explode with a bomb? The question is vague and not something I'm prepared to answer without stuffing some ground up chitin in a bomb calorimeter and combusting it (though I suppose the CRC Polymer Handbook MIGHT have data on chitin in it... you might go to your local library and look for N-acetylglucosamine).

Actually, that would be the first step I'd take to investigate the question. Get your hands on a Polymer Handbook and get the specific data you are looking for. There are MULTIPLE handbooks that your local library should have that will have just about every bit of information you could possibly want out there, and I guarantee that a common and commercially/medically useful polymer like chitin will have a breadth of data available for it. Then figure out exactly what sort of nastiness you are inflicting on the poor Omega Crab. Once you know that and have the data available to you, then you are good to go.

Personally, I'd save some work here and treat it like a 2 meter thick piece of graphite. The chitin will be largely carbon in composition, being organic, and the density won't be too far off (most biological things have a density approximately that of water). If I wanted to refine it I'd dig through, but for an order of magnitude estimate that should be good enough.

[Vultur]

Though I would think having a 2 meter deep hole in you would be sufficient.

It would be, if the creature wasn't half a kilometer long. The 2 meters of chitin is just its (overgrown) top layer of armor, equivalent to a crocodile's scales; it's not really an exoskeleton.

And what the heck kind of creature has 2 meter thick skin and is able to move?

It requires artificial aid to do that, but it's sentient and from a very technological civilization (composed of castes of radically different size; most are a size where building technology is easier). Its type never stops growing; with the things that would kill it naturally (gravity strain on its internal organs, loss of teeth, cancers) removed, it no longer has any limits on its growth.

I was referring to penetrating it with a gun-fired projectile (which would then explode, probably; I don't think a simple bullethole would be significant to a creature bigger than an aircraft carrier.) Later, tactical nukes and maybe nastier stuff will get used, but I was hoping that normal weapon fire (assault rifles and such, and 50-cal machineguns) would be useless. (If not, I'll just have to coat its shell in something tougher (biologically deposited diamond?)

[Count Chocula]

Shoulder-fired arms through 2 meters of graphite/chitin: no. 120mm penetrator from an Abrams? Yes. Honor Harrington-style laser heads? Yes. Standard 155mm artillery shells? Probably not. A-10 30mm rounds? Oh yah.

Basically, you're looking at a creature that needs weapons systems to destroy, not something a modern-day soldier would carry, excepting anti-armor rockets.

[Feil]

Can't high powered rifles shoot clean through several inches of wood? A quick google search says rifles can get penetration around nine inches through hard wood. Two metres is about 9x further than that, so it seems like a ballpark guess to say it would take 10x the energy.

A rifle bullet has about a two kilojoules of kinetic energy, so from this extremely rough look, I'd say somewhere around 20-40 kJ kinetic in a nice small place should do the trick. Use a bullet that punches through the hard material then breaks up or explodes when it hits soft flesh to maximize the actual damage done.

I don't buy this. The same energy that makes a bullet penetrate a target also makes it fragment and deform. While arbitrarily increasing the energy of the bullet will, of course, result in increased penetration, there's no reason to assume without actual study that it's a linear relationship.

[Gil Hamilton]

Personally, I'd save some work here and treat it like a 2 meter thick piece of graphite. The chitin will be largely carbon in composition, being organic, and the density won't be too far off (most biological things have a density approximately that of water). If I wanted to refine it I'd dig through, but for an order of magnitude estimate that should be good enough.

Nah. Chitin and graphite don't have much in common except for that they form sheets. The repeating unit in both are pretty different. Graphite is sheet upon sheet of sp2 carbons (and nothing else barring impurities), while chitin is a polysaccharide. Very different from bonds on up.

I think you might get away with ballparking by using a plastic with really well known structural and thermal properties that are easy to get and don't involve digging through handbooks, like polystyrene or PEO for example, but graphite is a while different animal.

[Gil Hamilton]

It requires artificial aid to do that, but it's sentient and from a very technological civilization (composed of castes of radically different size; most are a size where building technology is easier). Its type never stops growing; with the things that would kill it naturally (gravity strain on its internal organs, loss of teeth, cancers) removed, it no longer has any limits on its growth.

I was referring to penetrating it with a gun-fired projectile (which would then explode, probably; I don't think a simple bullethole would be significant to a creature bigger than an aircraft carrier.) Later, tactical nukes and maybe nastier stuff will get used, but I was hoping that normal weapon fire (assault rifles and such, and 50-cal machineguns) would be useless. (If not, I'll just have to coat its shell in something tougher (biologically deposited diamond?)

Eh. Chitin is tough stuff and two meters of it is a lot. Unless they are shooting RPGs and rockets, man portable things like you describe aren't going to do much if only because of sheer depth of penetration needed.

Besides, if your super crab whale thing is magical enough to simply ignore things like gravity and the square cube problem that is the downfall of most movie monsters, then you aren't obligated to be realistic with it. Do what makes for a good story, you don't have to elaborate on the technical details.