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[Valikdu]

I'm faced with defining a lot of materials right now (mostly for body components), so I need to ask:

How exactly do the strain_at_yield tags affect combat?

They *seem* to be determining if the part will be hard or soft and as such, will be fractured or torn instead; but what else?

And in the vanilla metal raws these are all over the place. With weapon-grade metals, the parameter increases as metals get better (copper - bronze - iron - steel), so one would figure that it's oppositely proportional to how much the material will get deformated when yielding, but then I see that the non-weapon grade metals have *less* than the weapon-grade ones - mostly (silver has more). It just hurts my brain.

[Putnam]

http://dwarffortresswiki.org/index.php/Weapon#Material

[Valikdu]

http://dwarffortresswiki.org/index.php/Weapon#Material

I've just been there. It didn't make things more clear.

Unless steel really deforms more than copper, under stress.

[Putnam]

The most important material property is TENSILE_STRAIN_AT_YIELD, which I notice isn't there. SHEAR is just cutting, but TENSILE factors into that and blunt.

(Cutting/blunt calculations include armor)

[smakemupagus]

there's nothing physically inconsistent with a material we think of a stronger (Yield STRENGTH, units of force/area) also having a higher yield STRAIN

don't think of it as "steel deforms more than copper", think of it as "steel can deform more than copper before it fails catastrophically"

http://en.wikipedia.org/wiki/Yield_(engineering)#Typical_yield_and_ultimate_strengths
steel yield strength ~500-800 MPa or more depending on form
copper 70 MPa

edit:  the various formulations of steel have very different properties, some of them have seem to have higher strain at yield than copper, others lower, and some can be strained well beyond the elastic limit and reach an even higher strength in a work hardening regime.  To complicate further it seems different disciplines define the yield point differently on those more complex curves, some people say the yield point is 0.2% strain by definition, some say it's the elastic limit, some say it's the ultimate limit before catastrophic failure.  anyway: Toady's probably not totally off base

In game terms, what I understand this to mean is that the main thing you want is a high Yield Strength in your armor to prevent your arm from getting lopped off (copper fails this test, and steel is quite good).  But assuming the armor does not fail, you also would prefer a small deformation to minimize serious blunt injuries.  If you want to compare the effectness of steel to other metals against a blow of given force, you probably want to look at the *ratio* of yield_strength to strain_at_yield