Bay 12 Games Forum

Hi all.

I'm working on a fairly extensive slate of physics numbers to fill in placeholder data (partially for my skins/bones/teeth expansion mod, and partially just for general purposes in line with what Arkhometha was doing).  I have little scientific background, and math was kinda not my thing as much as I wanted it to be.  I am basically Layman Reaching Way Over His Head.  So, while I am researching and getting a handle on quite a bit, I still come up on terms and questions I kinda need help with.

So, I was hoping some of you more-scientifically-literate folks, engineers, biologists, what have you, could help me with some terms as I try to render this all layman-comprehensible, or at minimum come up with decent numbers. (Yes, I know the game doesn't handle proper physics numbers all that correctly yet.)

And I thought I'd do it in an ongoing thread so I don't have to pollute other threads or spam the forums with a new, narrow thread every time I have some obtuse question.

So, to start with:

Question: What is "work of fracture," and is it useful for finding shear values?  Is it useful for finding any other DF-relevant physics values -- yields, ultimate strengths, moduli, strain at yield, etc.?

Blah blah background: I'm feeling like I'm starting to be a boss with the tensile stuff, and even compressive to some degree, but I'm coming across this term/material property in a paper on rhinoceros skin that seems really promising, but I can't figure out how to use it.

Wikipedia mentions it in passing as a related concept on its fracture toughness page, but nothing else.  Other references are pretty arcane as far as it goes for me.

I don't necessarily need a full explanation -- my main concern is a very practical "what can this data be used for."  Not to sound like a philistine or anything -- I'm just not wanting to put anyone out by asking for an advanced material science lesson.

Thanks in advance for any and all help.


EDIT: Adjusted subject to be a bit more accurate.

Alright, thanks Grim.  I'll be a lot more intelligent about this stuff once I wade into it, and then I'm sure I'll be a lot better able to digest all of it.

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Spent the last four days trying to figure out just what the hell all these physical data like strain at yield really mean, so I'm now I'm going back through all my numbers and coming up with final numbers for bone, horn, tooth, etc.  Should be done with that in a few days, and then I'll be getting into the BDPs in earnest.

General body hair on furry creatures becomes kind of confusing. What I have done before, was to make sure the tissue was still called 'skin', and left the hair tissues where they are to prevent the headache of non-fur hair being weird, and having to remove all the tissues by hand. So far I have not found a way to prevent hair from showing up at all after butchery, or a way to keep cetain tissue layers together after butchery.

Yeah, I'm not quite sure what to do here.  My inclination thus far has been to go all the way and change the methodology to integrate fur and skin in the same layer, just getting rid of hair as a tissue layer except where it makes specific sense (manes, furry tails, etc.).

I'm not at all sure that it wouldn't be better to keep "fur" as a separate tissue layer, like it's already set up with hair by default, but that nonsensical butchering product is bothersome.  Doesn't make sense to have a butchered ermine yield both "ermine pelt" and "ermine fur"/"ermine hair."  On the other hand, something like a horse would technically look more like a human -- a creature with a normal skin that drops hair (mane and tail).

Looking at your experience, if I understand it all correctly, to do it this way will get away from that problem of "hair" showing up in butchering products, but it's going to involve a hell of a lot of manual removal of hair from creatures.  But it's the only non-awkward way to do it -- and nonsensical butchering products fit into that "workaroundiness" I'm trying so hard to get away from.  Hrm.  Lots of work.

I also notice you added a seperate material for the tissue layer fur. What you can do, is to simply use the tissue layer fur for the tanned items as well so that you only need to set one color per creature.

Wouldn't that mean that the pelt/furred skin wouldn't need to be tanned?

As for FBs, from what I know they are built basicaly the same as vanilla creatures. Standard mats+tissues, + whatever body detail plan their specific nature requires, like the hair body detail plan, humanoid relsizes, ribcages etc etc. The standard mats will allways load first, so if you modify another body detail plan to overwrite one of the materials it should remove the original. It is a somewhat sloppy way to do it, but right now also the only way and the end result should be good.

The question would be, then, which BDPs to modify...  But wait.  I think I'm seeing it...  So, for example, for hardcoded vermin birds, take a later BDP that the game will always apply to them -- say, one of the new feathered body part ones -- and use it to remove the "monstrous"-strength tissue layers and replace them hollow bones and weak skin and gizzards, etc.?  (Or remove all specific organs in favor of nonspecific bird viscera.)  If I've got what you mean right, AWESOME -- that would solve the bird/FB hard-coding BDP problem.

Note that all lines used by the random creatures generator can be found in the string dump. Maybe someone has made a specific article about it by now, im not sure. String dump link: http://dwarffortresswiki.org/index.php/String_dump

...  which also suggests I may want to relegate the CHITIN_MATERIALS and CHITIN_TISSUES to FB-only use like I did for the STANDARD ones...

Yeah, I was pleased as pie to remove leather from vermin.  I have actually been trying to figure out how much farther I can go to get vermin body parts out of the lists -- like removing all body parts and replacing them with "viscera" or "guts" or something that fulfills all proper functions. 

Not whales -- whale sharks.  Big, filter-feeding sharks.  Whales, though, yeah, would be probably fit in the HIDE_STRONG category.

For composite animals like merpeople, satyrs, nautili etc., I think I may be able to do both -- if the butchering glob trick Squishynoob mentioned here works as I hope it will, then you can get both skin and scaly skin in appropriate proportions.  Crossing fingers on that...

Working on body detail plans right now.  Not a lot of documentation on that, it seems.  So far every skin/scale/carapace type gets its own body detail plan, including vermin (to keep them from having leather, tallow and soap types on the stocks lists).

I'm not sure how to handle birds, though -- Grimlocke, you mentioned something about how the FBs use the standard materials body plan:

FB fur may prove annoying to add. I have in the past tried this using the hair body detail plan, but only found it that birds also use this, causing weird bird fur.

I've gathered that FBs are hard-coded to use the standard body detail plan, and was thinking of using it *only* for them.  But you've noticed birds seem to use that plan as well?  If so, that definitely throws a kink into giving FBs tougher skin, bones, etc., unless I want birds having monstrous skin and bones and teeth.  Hard-coded?

This actually looks very useful to me - I'm messing around with the idea of a borderlands mod, and I'd love to be able to make my leathers special for things like skags and alpha skags, but I can't imagine how - would you mind allowing me to borrow that spreadsheet of yours? You'd get full credit if this thing gets bigger than a personal mod.

Of course.  You can use any part of it you want.  This is totally built off the work of others.  Anyone can use any or all parts of it for any purpose without permission or credit (of course, I'd love to know if and when it proves useful, but nothing I'd insist on).

Ah there it is then. Will be watching the progress, and let me know if you need help with the testing.

Should also warn you that modifying all the vanilla creatures is... tedious. This game realy has an absurd amouth of creatures. Possibly you can use some of the vanilla body detail plans to cut down on some of that work.

That would be hugely appreciated, given that I'm still learning to swim and I'm well into the deep end here.

Yep, definitely intend to make as full use of body detail plans as possible.  This should explode the numbers of them pretty significantly, but it should be manageable.

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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]