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[Footkerchief]

The only way to feasibly include materials properties in DF is with a completely abstracted system.  I think the current one has a bunch of values that aren't even being used, so those should probably be cut out unless something is going to be done with in the future.

Toady said that all of the material properties are used during wrestling, I think.  Presumably "pinching" (i.e. ripping) uses tensile and joint breaks use bending.  I'm not sure where torsion comes into play.

[Arrkhal]

The values in the raws must be wrong, then, which is odd since Toady states he's using real-life values.

Some are, for sure.  20,000 KPa (about 2900 PSI) for skin is about right, though it's specifically the epidermis that's 3,000-4,500 PSI, while the much thicker dermis beneath that is about 150-300 PSI, IIRC.  Though after it's dead, leather is also 3,000-4,500 PSI.

For wood: http://www.woodbin.com/ref/wood/strength_table.htm

Parallel to the grain, 980-1680 PSI.  In the raws, it's 40,000 shear yet 10,000 everything else.  I've yet to see a single place list shear strength perpendicular to the grain.  40 MPa (5,800 PSI) is probably actually too low to be perpendicular to the grain, and is actually reasonably correct for compressive strength parallel to the grain.

So the numbers for wood are pretty mysterious.  I'm guessing 40,000 was actually a random buff to make spears and arrows pierce skin, or a misinterpreted compressive strength.

Any comments on this, though? I mean, I guess it does make sense that something impacting something else gets subject to some level of shear stress (since it wants to get "squashed") and not just compressive, but I don't know much about this, and it seems like different types of strain would affect each other in a case like that.

That equation refers specifically to shear in a round rod.  That is, you swing a club at something, and the area above the impact wants to keep moving forward, while the area at and below the impact wants to stay still, thus generating a shear stress.

I believe it's primarily shearing force that generates the Hertzian cone.  http://flintknapper.com/Flintknapping.htm

So shear may have a minor role in weapons and armor, though reasonably flexible ones, like those made of metal or wood, would mainly experience bending stress and localized compressive stress.  Significant shear would only happen in hard, brittle things that can't bend or compress much.  And impact strength really tells you all you really need to know about impacts involving those.  Above the impact energy required to shatter the thing, it shatters; below, it's more or less undamaged.

It is a really complex problem, though, especially impact strength.  Brittle impacts are more energy-dependent, while plastic impacts are a complete pain to model.

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Toady said that all of the material properties are used during wrestling, I think.

Do you know where?  The raws say:

Code: [Select]

Used for blunt-force combat, measured in KPa.  Data scattered around the net (used compressive strength).  All very spotty.
[IMPACT_YIELD:120000] used marble
[IMPACT_FRACTURE:120000]
[IMPACT_ELASTICITY:100]

Not used.
[COMPRESSIVE_YIELD:120000]
[COMPRESSIVE_FRACTURE:120000]
[COMPRESSIVE_ELASTICITY:100]
[TENSILE_YIELD:15000]
[TENSILE_FRACTURE:15000]
[TENSILE_ELASTICITY:100]
[TORSION_YIELD:15000]
[TORSION_FRACTURE:15000]
[TORSION_ELASTICITY:100]

Used for cutting calculations in combat, measured in KPa.  Data scattered around the net used tensile strength).  All very spotty.
[SHEAR_YIELD:15000] used marble
[SHEAR_FRACTURE:15000]
[SHEAR_ELASTICITY:100]

Not used.
[BENDING_YIELD:15000]
[BENDING_FRACTURE:15000]
[BENDING_ELASTICITY:100]

A unitless measure for how sharp the edge is for combat purposes.
[MAX_EDGE:1000]