DR derivation in GURPS?

[Anthony]

Originally Posted by sir_pudding

Diamond ignites at 850 to 1000 C. Napalm burns at about 800-1200 C.

Diamond is a very very good heat conductor; you are unlikely to reach that temperature on a large object with any remotely small point source.

[Anaraxes]

Napalm is a point source?

[Varyon]

If you have Pyramid #3/52, there's an article in there on Low Tech Armor Design which, despite its name, will work for designing armor of pretty much any TL, so long as you have the relevant data for the material. These relevant data are flexibility, DR/inch (or DR/lb), and density. Of these, DR/inch is the toughest one to figure out. Many materials are in GURPS in one form or another and can give you a good idea of their DR/inch or DR/lb by using the equations in the article to back-calculate. Other considerations can also come into play here - for example, aramid fiber (and its descendents in Ultratech) has greatly increased DR against piercing and cutting attacks, while brittle materials (like diamond) are semi-ablative. Offhand, I'd say diamond is essentially semi-ablative Diamondoid, although you could justify it being a bit less effective, using the stats for Nanocomposite instead. I worked out the stats of lot of UT materials for use with the article here, and the user Kallatari did the same (albeit earlier and with slightly different numbers) here.

[The_Ryujin]

Sadly there is no formula that GURPS applies to figuring how much DR an object gives (that I know of at lest) and instead mostly either useses imperical data based on any known ballistics data for modern materials, penatration test studies done of recreations of old school armor for low tech armor and or a heaping of just plain ok' guess work.

That being said if you send David l Pulver a PM I'm pretty sure you can wrangle some of the rules of thumb he uses out of him.

Lastly, as others have said, diamond makes for poor armor do to a little problem called cleavage-any attacks that hit it at a right angle will chop through the armor like butter but if you still want some figures on it diamond has DR9 per inch, a WM of 0.99 but is semi ablative. I'd also rule that on a critical hit or after an successful Jeweler, Geologists or Expert Skill (Mineralogy) roll to treat attacks as having an AD of 10 to simulate hitting it at a 90 degree angel. If you want a type of diamond that doesn't suck there's TL 11 diamondiod armor which has DR ~250/in and a WM of 0.06.

[Anders]

Such a rule would probably be impossibly complex, if it's supposed to encompass even a fraction of the materials and modes of deploying them that are available.

[evileeyore]

Originally Posted by Anaraxes

Napalm is a point source?

If you're of the opinion that "just a dab will do".

[Anthony]

Originally Posted by Anaraxes

Napalm is a point source?

If it's smaller than the vehicle, yes. A napalm bomb sufficient to cover and heat an entire vehicle will kill the vehicle no matter what it's made of.

[sir_pudding]

Originally Posted by Anthony

Diamond is a very very good heat conductor; you are unlikely to reach that temperature on a large object with any remotely small point source.

Even with synthetics, could you make diamond armor with large plates? Diamond scale or brigandine is going to ignite when doused in napalm, I think.

[Polydamas]

Originally Posted by Anders

Such a rule would probably be impossibly complex, if it's supposed to encompass even a fraction of the materials and modes of deploying them that are available.

And for many materials and threats, the data does not exist, so one would start by doing tests and trying to work out best-fits. Someone could easily do a whole PhD on different factors which influence the protective qualities of Japanese kozane made from traditional materials.

[Anthony]

Originally Posted by sir_pudding

Diamond scale or brigantine is going to ignite when doused in napalm, I think.

The person inside the armor will be dead before the diamond ignites, so it doesn't much matter. For that matter, diamond is not particularly more flammable than, say, kevlar (which decomposes at lower temperatures than diamond ignites)