Bay 12 Games Forum

Hi all.

I'm working on a set of real-world physics numbers for my own use and for anyone else who would see fit to use them, possibly even for submission to Toady.

But I'm not in the science department.  I'm in the history department.  Yes, Martha, I'm not the history department, I'm in the history department.  And I need someone in the math biology department.

(10 points to anyone who gets that reference...  )

But actually, sort of the crossroads of material science/physics and biology departments.

So, being something of a SIMP, I'm going to need help.  Can you people literate in the appropriate areas give me a bit of advice?

First problem:

I want to come up with real-world Yield, Fracture and Strain at Yield values for bone, skin, and other keratinous, collagenous and bone-based biomaterials.  Unfortunately, the viscoelastics are nowhere near as straightforward to read as inorganics.  And if I use the "yield" value most papers give, it'll distort the results such that organics are brittle.

So, the question is, how do you read an appropriate, relevant Yield value from the stress/strain diagram of a viscoelastic material?

Note that, since in DF we're talking about axe surgery and not plastic surgery, we're really not concerned about the lower yield-to-viscoelastic deformation "yield" that most of the literature talks about, but rather to the yield-to-beginning-of-failure that is more like inorganic yield (i.e., where the material is strained past the point of its ability to elastically deform, therefore straining plastically and damaging it).

But the stress/strain diagrams and the literature really don't give clear guidance on this.  At all.  So, as a matter of the question applied to concrete example, what Yield values should be estimated from visually reading the stress/strain diagram below?

Eyeballing it, here's what I got, but I'm really not very confident at all with my understanding of what we should treat as the Yield point for collagenous/viscoelastic stuff:

Tendon: 16.5 MPa or so (from where I see the 'crook' in the curve before it goes linear up until failure)
Rhinoceros Skin: about 25 MPa?  (from about where the direction of the curve changes from concave to convex)
Cat Skin: about 8 MPa

Am I totally off on these?






This is a sort of repost of the question from the modding forum.  And as I said there, I will be obscenely grateful for your help.  And as I clarified there, I mean grateful to an obscene degree, not in an obscene way.  (!)

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Update June 17, 2015

So, due to some RL unpleasantness, this got put aside for a couple of years, with enough research completed to come up with some preliminary numbers.  I'm sort of eyeing it again.  At bare minimum, I'm going to link the research notes and spreadsheet in a Google spreadsheet here in the OP for others to use.  More ideally, I'd like to realize this and get it usable, but I need to get up to speed and see how things have changed since 40.xx.

Overall, the project is still in mid-WIP stage.  I have done quite a bit of research, and came up with workable material templates for almost all relevant materials back in the days of 34.11.

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LINK: Materials Spreadsheet (Google spreadsheet -- open to commenting)
LINK: Notes and References on Material Physical Characteristics (Google doc -- open to commenting)

The purpose of this project is to create a mod that achieves the following:

• Introduces meaningful difference between the skins and hides of different animals, such that rhino hide or dragonskin are substantially more protective than, say, deer leather or elfskin.
• Does the same for bones, teeth, claws, nails, and horns.
• Where appropriate, makes it possible to choose to make either leather or fur.


• Sets up a unified and elegant system of tiered gradations of creature skins* and hard body parts** that:
• eliminates many redundant, less interesting, or inappropriate leathers;
• makes special leathers stand out more, whether because they are more protective or because they are unique or creepy;
• presents itself tightly in-game, with no immersion-breaking workaroundiness;
• and is content-neutral and vanilla-flavored, with as few subjective design decisions as possible, so as to be broadly useful and easily-integrated (relatively, anyway) into other more comprehensive mods.

• Introduces reworked biomechanical physics stats (density, torsion, impact, shear, etc. values) based on researched real-world data for all affected materials, adjusting as necessary for playability and for the game's own quirks (e.g., accurate specific heat values won't work right in DF).

What this first part means, essentially, is we should not see "cow leather" or "one-humped camel leather," and certainly not "blue jay leather" or "worm leather," because those just aren't that interesting (and in the latter cases don't make sense).

But we will still see specific names for almost everything that is more interesting for one reason or another: "elf skin," "cat skin," "tiger leather," "elephant hide," "beaver fur," "sharkskin," "dragonskin" and so on.  Likewise, carapace will be renderable into chitin, properly renamed in its body-part form, and only the more fantastical insects/athropods/crustaceans (think larger than man-sized) should have carapaces that can be turned into armorable chitin.


* Skins, hides, scales, and chitins, and their associated tanning products, including the possibility to make either fur and leather from any specific furred skin.

** Bones, teeth, claws, nails, horns and hooves.

My work here has drawn on Deon's Genesis, Meph's Masterwork DF, Veok's Standardized Leather Mod, Lofn's tanning mods, and a few other mods, but also relies to a great deal on some rather tedious research of my own into engineering, scientific and medical sources available online.




Concerns and Wrinkles to Consider

The proposed system departs from vanilla in a few important ways:

1) Physics values for organic materials are pretty radically changed, albeit in the same spirit as vanilla DF -- using real-world physics data as much as possible. I've done quite a bit of research (mostly medical and engineering sources you can find on the internets), and, along with the grateful use of Arkhometha's research, I've been able to find some respectable values for skin, bone, leather, chitin etc. to use as a basis for the corresponding game materials.

It's hard to find good data on how these numbers are reflected in actual gameplay, so they may be considered experimental.  Nonetheless, I think it's about time to put some more accurate real-world numbers into those fields, and if it works well, it should be that much more awesome.  I'll definitely need the help of !!SCIENTISTS!! with testing this part, and there should be some pretty entertaining results as they're fine-tuned.

This means that the tougher beasties may be a bit more Fun than they were before.  But it also means that the leather from those special beasties can make some considerably decent armor.

2) Body part and creature raws have to be changed to conform to the system (mainly because of the reason in (3) below).  Quite a bit of tedious work.  And, to be compatible, any creatures added will have to be adjusted accordingly.

3) There are quite a few categories ("body parts") of skin, bone, etc.  now, making for a extra complexity at the level of designing creatures , but it should be easily manageable with reference to the spreadsheet.



Development Plan and Progress

not updated since 2013 -- will updated once I've refamiliarized

• Research physical data on skin and leather; come up with plausible physics values and scheme for quality gradation to try out: Done. But refiguring some things now that we have a more sensible understanding of the physics values (particularly strain at yield).  Going a bit slow because redoing documentation extensively.
• Material templates for all grades of skin, tanned leather, scale and carapace materials: Done.
• Material templates for all grades of bone, tooth, nail/claw, and horn materials: 70% done, in progress.  (Refiguring some things since I got a better handle on what the different physics values mean, both real-world and in-game.)
• Tanning/cleaning reactions: Done.
• Body detail plans: Done.
• Tissue templates: Halted until material templates finished; then I'll get back to trying to determine differentiating features between selected body space and hole in ground.
• Misc. supporting stuff -- false creature entry, civ permissions list:  Not started yet.
• Updating all vanilla creatures to use appropriate skin, bone and tooth types: Not started yet.
• Documentation and instructions for making animals compliant: Not started yet.
• Test and refine physics values: Not started yet. Maybe you can help!

A preview of the overall scheme can be seen in the first 'reply' post below.




Whatever I produce is intended to be freely available for any use whatsoever without permission or credit.  Comments, criticism and advice toward meeting that goal are all very welcome.[/list]

Alright.  Searched the suggestions forum for all instances of the word "sanity" and haven't found any on-point, so I have one that might be a nice, procedural solution for dwarven mental health that is flexible and simpler than, say, a whole range of specific insanities/dysfunctions.

In the Unknown Armies pen-and-paper RPG rulebook, there is a gem of a sanity/insanity system that, supposedly, is similar to, but more powerful and flexible to Call of Cthulhu's (from what I've read of people's comments; I haven't read the CoC rulebook, myself).

This is how it runs down. I'm going to explain it in terms of Unknown Armies's game mechanics for simplicity, but obviously Toady could translate it any way he sees fit.

The system is based on five categories of mental stress: Violence, Unnatural (could also be called sense of reality), Helplessness, Isolation and Self.  In order to keep this post from becoming a multi-tile Wall of Text, I'm not going to go into definitions for these, but I'd be happy to explain if anyone's curious.

In each one of these you, have two meters: Hardened and Failed.

Hardened ranges from 0 to 10 "notches", while Failed ranges from 0 to 5.

Any given stressful experience affects one or more Stresses, and (in the Unknown Armies system) has a difficulty category of 1 to 10.  The idea is that the character, if he is not sufficiently hardened, has to make a sanity check against his Mind stat to see how he deals with it.  If he succeeds, he gains a rank of being Hardened toward that Stress.  If he fails, he puts a notch in the Failed meter toward that Stress.

Hardened means he coped, though at some cost to his humanity (dwarfity), and Failed means he did not cope, and is now psychologically damaged as a result.

Example: So, say, Urist McInnocent, who has only two ranks of Hardened in Violence, sees someone killed for the first time in his life.  Seeing someone killed is, say, a difficulty-3 Violence Stress check.  He has to make a check against his Mind stat.

If he succeeds, yay, he now has another rank in Hardened, for a total of 3, and now he'll shrug off difficulty-3 Stress checks without having to make a Mind check. If he fails, he puts a notch in the Failed meter, with consequences we'll examine shortly.

Now, though he now laughs at Violence stresses of difficulty 3 or below, a difficulty-4 or higher stress will still require a Mind check. We're upping the sanity ante. Once a character has reached 10 ranks of Hardened in a given Stress, he is now "so jaded and blase" about it that he is impervious to that Stress.

So, a dwarf becoming Hardened, just like a human becoming so, has very important and positive effects on his ability to survive in his environment. Of course, we are all probably aware of the negative effects of someone being Hardened to something: they become callous.

And, as a matter of fact, the UA system accounts for this. To quote the author:

This is not a good thing.  Mental stress makes us vulnerable.  But it also makes us human.  If you fill in too many hardened marks, you become so completely callous that you are unable to feel fear at all. That's because you are now cut off from a broad range of emotional experiences that everyone else shares. You're 'hardened' all right: hardened into an emotional fortress[], completely isolated, unable to make a fundamental connection with other human beings.  You're a sociopath.

If you get ten ranks of Hardened in two or more Stresses, or if your total of Hardened ranks exceeds 35, you become a sociopath. In UA game terms, you become disconnected from your passions (specific Noble, Rage and Fear passions), which within that system allow you to do extroardinary feats if the situation triggers them, and certain types of mages lose their empathic connection to the source of their magic.

Now, Failed marks are much worse. If a Stress check is failed, the unfortunate sot gets to choose one of three responses: panic (gibbering and freaking out), paralysis (freezing up like a well-lit deer, not literal paralysis), or frenzy (going batshit crazy and attacking the source of the stress).  The response lasts until the fear source is gone, but the character immune to other Stresses until it's gone as well, since he's too whacked to process them.

If a character acquires 5 notches in the Failed meter, he becomes insane with regard to that Stress, and a little bit in general.  He picks up a tic, some sort of mental aberration.  And any time he faces that Stress again, he gets no Mind check.  He just goes straight to panic, paralysis or frenzy.  Do not pass Go, do not collect your medication.

The tic/mental aberration can take the form of a phobia, a trauma bond (i.e., associating some incidental thing connected to the event with it, as in the classic case of a PTSD war veteran triggering at the sound of a wine cork popping), flashbacks, blackouts/fugue states, addictive behaviors, philia/obsession, delusions, and probably other things.  This stuff could be a lot of Fun.

The game also does allow for psychological first-aid and long-term mental health, so that counseling can eliminate notches from either meters.

The UA rulebook goes on in considerable (and enjoyable, well-written) detail about the different Stresses, with examples of different difficulty levels of checks and what they mean in real-world terms. It also gives descriptions of different levels in the Hardened and Failed meters in each Stress, likewise with real-world meanings.

Anyway, that's the basic rundown, drawn from pages 64-71 of the UA rulebook.

As you can see, it's a sanity system not dependent on a laundry list of pathologies, but rather on the source material -- the different areas of trauma handled by the brain.  This sort of system would allow for a procedural, more nuanced treatment of mental issues in DF (with lots of comical potential, I'm sure; Urist McInnocent sees his buddy raised as a zombie next to his pet cat, and trauma-bonds the Unnatural failed stress check he makes to the cat; now his pet cat is a trigger and he occasionally flees, eventually one day going berzerk and killing it).

It's really fascinating reading, actually.  Greg Stolze and John Tynes, the authors, either know their shit off-hand or did some serious research.  The chapter is great reading on its own, but I'm not here to pimp it.  I think, though, you definitely might find it a great source to check out, Toady.

[Note: This is serious fucking subject matter. As much as I've been humorous or casual with this, apologies and respect to people who are facing PTSD from war experiences or other serious life traumas. None of this is intended to make light of that or the people who genuinely suffer from them.]