Contact Stress

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  • cesarleonelflores83
    Junior Member
    • Jun 2010
    • 10

    Contact Stress

    I've run a simulation with sliding contacts and am looking for a contact stress output under stress but can't find any. Is the contact stress output hidden somewhere else in Postview?
  • maas
    Lead Code Developer
    • Nov 2007
    • 3400

    #2
    Yes, in general it is written under the velocity or acceleration field. You can check your logfile. It should say at the top of the file where and what data is stored to the plotfile.

    Cheers,

    Steve.
    Department of Bioengineering, University of Utah
    Scientific Computing and Imaging institute, University of Utah

    Comment

    • cesarleonelflores83
      Junior Member
      • Jun 2010
      • 10

      #3
      Hi Steve,

      I Checked my logfile

      OUTPUT DATA
      ================================================== =========================
      plot level ................................ : major iterations
      shell strains included .................... : No
      plot file field data:
      displacement ...................... : displacement
      velocity .......................... : none
      acceleration ...................... : contact traction
      temperature........................ : contact gap


      It says contact traction is under the acceleration field but that shows up as all zero. There's nothing under velocity, is this where contact stress should be?

      I've attached an example plot file.

      I'm looking for a good measure of the contact stress and contact patch area so I can assess the potential for wear.

      Best Regards,

      Cesar

      Comment

      • maas
        Lead Code Developer
        • Nov 2007
        • 3400

        #4
        Hi Cesar,

        Would you mind sending me the FEBio input file as well. I need to know what contact formulation you are using to determine where the problem might be.

        Thanks,

        Steve.
        Department of Bioengineering, University of Utah
        Scientific Computing and Imaging institute, University of Utah

        Comment

        • cesarleonelflores83
          Junior Member
          • Jun 2010
          • 10

          #5
          I've attached both the plot file and the input file. Thanks for your replies, Steve.

          Comment

          • maas
            Lead Code Developer
            • Nov 2007
            • 3400

            #6
            Ok, it seems that FEBio is not outputting the contact traction for the facet-to-facet sliding method. I'll have that fixed the next time I upload an FEBio executable. In the mean time, you can try the "sliding_with_gaps" contact method which does store the contact tractions. Just change the contact definition in the xml input file to

            <contact type="sliding_with_gaps">

            That should do the trick for now.

            Cheers,

            Steve.
            Department of Bioengineering, University of Utah
            Scientific Computing and Imaging institute, University of Utah

            Comment

            • cesarleonelflores83
              Junior Member
              • Jun 2010
              • 10

              #7
              Awesome!

              Thanks Steve.

              Is there a reason why the "sliding with gaps" method is not an option in the Preview contact type pull down menu?

              -Cesar

              Comment

              • maas
                Lead Code Developer
                • Nov 2007
                • 3400

                #8
                The sliding_with_gaps is called the node-on-facet method in PreView.

                Steve.
                Department of Bioengineering, University of Utah
                Scientific Computing and Imaging institute, University of Utah

                Comment

                • cesarleonelflores83
                  Junior Member
                  • Jun 2010
                  • 10

                  #9
                  I've also noticed that the contact traction data is not saved if the node on facet type is used AND the augmented lagrangian method option is not used.

                  Comment

                  • maas
                    Lead Code Developer
                    • Nov 2007
                    • 3400

                    #10
                    Good catch. The reason is because FEBio stores the Lagrange multipliers that enforce contact which are zero when the augmented Lagrangian is off. This should be an easy fix though, so consider it fixed.

                    Cheers,

                    Steve.
                    Department of Bioengineering, University of Utah
                    Scientific Computing and Imaging institute, University of Utah

                    Comment

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