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Difficulty in analyzing automotive tire in workbench

  1. Nov 7, 2012 #1
    Hi,
    I am trying to analyze the effects of pressure on the automotive t=ire by modeling and simulating the same in ANSYS workbench. However, I am having trouble applying material conditions to the model.
    I wish to use mooney rivlin material but when I apply that based on the guidance given by the following link, my solution does not converge.

    video link:

    My boundary conditions are fine because if I use a material such as steel, I get a solution.

    Kindly help me and let me know where I could go wrong.
     
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Nov 8, 2012 #2
    The material behaves non linearly and you are using a linear solver.
     
  4. Nov 8, 2012 #3
    Chris,
    Can you please tell me what changes to make in order to run the analysis.
    Thanks
     
  5. Nov 8, 2012 #4

    Mech_Engineer

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    You need to use a non-linear solver (selecting "program controlled" is probably fine too), and you need to split a largely nonlinear problem into a lot of substeps. Depending on the amount of deflection you're seeing, it could be on the order of hundreds of substeps.
     
  6. Nov 8, 2012 #5
    Mech_Engineer,

    I used program controlled but that failed
    So I used substeps as
    Initial - 100
    Minimum - 10
    Maximum - 1000

    Using this too the solver ran for a long time but it didn't solve.

    I increased the newton raphson residuals to 4 to see where the force convergence was a problem and it appeared to be along the sidewall.
    I increased the no. of elements by refining the mesh but that too has not solved the problem.

    Is there anything else that can possibly be wrong with the solution?

    Thanks
     
  7. Nov 8, 2012 #6
    Following are the error messages that I obtained:
    substeps:
    initial: 20
    minimum: 10
    maximum: 100
     

    Attached Files:

  8. Nov 8, 2012 #7
    two more errors continued.
     

    Attached Files:

  9. Nov 8, 2012 #8

    Mech_Engineer

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    • What does the force convergence chart look like, was it slowly converging or bouncing all over the place?
    • Are you sure that your model is fully constrained? Does the deflection look something like you're expecting or is it mainly solid body movement?
    • Are you applying a contact condition on the bottom of the tire? What properties are you applying to that boundary?
     
  10. Nov 8, 2012 #9
    Mech_Engineer,

    The convergence curve begins from below, oscillates about the main line. I do get points in the run where there is convergence but the last two or three points don't converge leading to no solution.

    The boundary conditions are alright because if I apply steel as the material to the same model, I get results without any problems.

    I am currently analyzing the stresses developed in the tire only due to the inflation pressure. So there are no contact conditions needed to be developed.

    Please help.
    Thanks for your reply once again!
     
  11. Nov 8, 2012 #10

    Mech_Engineer

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    It sounds to me like the model isn't converging because you don't have enough substeps. You should consider increasing the number of substeps, and applying your pressure gradually through load steps.

    Ideally, the force convergence graph should start above the line and converge to below the goal line. If it oscillates about the goal line a lot I'm thinking it means the perturbed system is oscillating; a gradually applied and solved-for load may help with this.
     
  12. Nov 8, 2012 #11
    Mech_Engineer

    Thank you for your reply. I will try what you suggested and get back to you after that.
     
  13. Nov 12, 2012 #12
    Mech_Engineer,

    I tried the simulation changes that you had recommended but I am still facing the same problem.
     
  14. Nov 12, 2012 #13

    Mech_Engineer

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    I think you're going to have to try some simplification and see what it takes to get it to converge, either through a simpler geometry and/or simpler material model. Once you're able to get a solution, you can slowly add complexity and see at what point the model is no longer converging. My guess is the pressure load needs to be applied slowly with load steps; how much pressure are you applying? Have you tried a lower pressure to see at what point you can get a solution?
     
  15. Nov 12, 2012 #14
    I am applying a pressure of 0.7 Mpa.
    No, I have not tried to apply a lower value of pressure on the tire yet to see if that works ok.
    I will be doing that now to see if I get some convergence.
    Thanks
     
  16. Nov 12, 2012 #15

    Mech_Engineer

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    Try applying something much lower for a start and see how it goes. A pressure of 0.07 MPa might be a good starting point, and could provide you with the structure of load-stepping up from there.

    It seems possible your tire is not able to hold 0.7 MPa and is failing to converge because it is structurally failing. A lower starting point might help you visualize this.
     
  17. Nov 12, 2012 #16
    That makes sense.
    However, the pressure that I applied is the recommended maximum pressure for the tire. But I see what you mean. I'll decrease the load.
     
  18. Nov 12, 2012 #17

    Mech_Engineer

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    When you say you're modeling a tire, do you mean the steel belts and everything? Tires are a pretty complex composite design of rubbers, polymer bands, and layered steel mesh belts; it seems to me they would be a complex analytical challenge.
     
  19. Nov 12, 2012 #18
    For now I am just modeling it as a single rubber entity. I have not yet considered the steel reinforcements that go into it.
     
  20. Nov 12, 2012 #19

    AlephZero

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    The "recmmmended maximum pressure" will be for the real tire including the steel reinforcements, not for a rubber ring with no reinforcement.
     
  21. Nov 12, 2012 #20

    Mech_Engineer

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    Exactly what I was getting at. The model isn't converging because just rubber can't hold that much pressure. I'm guessing your modeling efforts will start to converge when you apply less pressure, but the deformations won't really match those of a "real" reinforced tire.
     
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