Tyre database, mechanical properties in TGM files

Discussion in 'Bug Reports' started by Martin Dyrlund, Mar 28, 2020.

  1. Martin Dyrlund

    Martin Dyrlund Registered

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    Downloading rear tyres for the GTE cars here:

    https://docs.studio-397.com/developers-guide/cars/car-physics/tyre-database

    and analyzing the material properties of the pliers and steel beads etc. seems to vary alot compared to what S397 are supplying in the following spreadsheet under material properties:

    https://docs.studio-397.com/developers-guide/cars/car-physics/tgm-spreadsheets/tgm-generator

    Lets take node 1 as an example. Here is a picture of material properties in the M_31-71-18x13_Slick_S7M_2017.tgm file that is downloaded from the tyre database.

    M_31-71-18x13_Slick_S7M_2017_Node_1.png
    Now for comparison lets take the two first lines under "PlyMaterial". This has the same sort of properties as steel so must be the steel bead near the rim and want to compare that with the material properties S397 have in their own TGM generator:

    TGM_Gen_Steel-Soft_used_for_bead.png

    The most values fit perfect, except for value nr. 3, Young's Modulus [Pa]. Normally steel has a modulus of elasticity of 200-210 GPa = 200-210*10^9 Pa. In the TGM generator they say 136 GPa (Soft steel) and in the actual tyres if you count all the zeroes its only at 17 GPa.

    Why is that?

    This is the same issue for almost all the other materials in this tyre.
     
  2. Martin Dyrlund

    Martin Dyrlund Registered

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    Thats constructive... I am perfectly fine, thanks. This is a bug report forum so if you have nothing informative to say then dont say anything.
     
    McFlex and Bjørn like this.
  3. davehenrie

    davehenrie Registered

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    I think what he was saying, is that your inquiry was waaaaay over the heads of most of the users here. I'm pretty sure somebody here knows the tire guy, Michael Borda is the only name I can dredge up. I would suggest finding the discord thread and trying to Contact the devs there.
     
  4. Lazza

    Lazza Registered

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    In the spreadsheet you'll see there's a modulus multiplier in AH7 (Construction sheet) which is why the raw material property is different to the output. I haven't looked into tyres much so can't comment on what that multiplication represents.

    The example Brabham BT44 tyre spreadsheet here has this multiplier set to 0.11 for the bead (the spreadsheet itself is an earlier version, but you can see it's equivalent) which gives 18.7GPa output from 170GPa input, similar to the figures you've shown.

    @davehenrie No, I think the post was pointless, just being funny. Nothing to do with the audience, any post can remain unanswered if people don't feel up to it. Deleted now anyway.
     
  5. Martin Dyrlund

    Martin Dyrlund Registered

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    Yeah can see they have a multiplier in the spreadsheets, but why? The idea behind the rF2 tyre model is you build up the tyre with the correct material properties of each part in the tyre and i guess ISI intended it to be used like that. Making a multiplier for something as critical as stiffness properties of a material and basicly dividing it with 10 doesnt make sense to me. Yes, you can make small corrections fine by me, but its not only the steel properties that is wierd...

    The reason why i discovered this was because i wanted to make my own GTE tyres. It takes roughly 30 hours to compile each tyre when you change these stiffness settings so its pretty time consuming. Reading through the quick start guide for the tyre tool, they dont mention Youngs Modulus has to be divided by 10.
     
  6. Lazza

    Lazza Registered

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    Ok, you didn't say so, so I was assuming you were only comparing the raw material properties to what was in the file.

    I don't know why, as I said. I'm sure there's a reason for it, maybe Michael can come and explain it at some point. I did some searching but couldn't find anything regarding it, unfortunately a number of development blog entries had comments at the time but they no longer exist on the S397 site (maybe one of those archive sites can see them, I don't know). I think quite a bit of extra explanation and questions got lost there.

    Care to share what else is weird? Might as well try and cover as much as possible.
     
  7. Corti

    Corti Registered

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  8. lagg

    lagg Registered

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    I don't know if what i'm going to say is useless, but the Young's Modulus of the die casting steel is 17 N/m2 and the carbon steel ≈ 20 N/m2.
    Could be that your 17 value is in N/m2 instead of GPa?
     
  9. Martin Dyrlund

    Martin Dyrlund Registered

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    Sorry, but that is pretty useless :D Everywhere in their spreadsheets the units are Pa (Pascal). 1 Pa = 1 N/m^2, so what you are saying is plain wrong. As i wrote earlier normal steel has a Youngs Modulus of around 200-210 * 10^9 Pa or 200-210 GPa.
     
  10. Kevin van Dooren

    Kevin van Dooren Registered

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    Bump.The low modulus of 136 GPa for steel could be that its for stranded steel wire. That multiplier could account for volume fraction. I assume ply orientation is a seperate input so I guess its not that.
     

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