Material coordinates?

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  • Mack
    Junior Member
    • Mar 2009
    • 4

    Material coordinates?

    Dear Steve,

    For the linear orthotropic material, how are the material coordinates (1, 2, 3) defined for each element? For example, a sphere where the E1 direction is radial? Unfortunately, I'm trying to model a more complex geometry than a sphere.

    Thank you for your help.

    Mack
  • maas
    Lead Code Developer
    • Nov 2007
    • 3400

    #2
    Hi Mack,

    Currently, it is assumed that the material axes (i.e. symmetry axes) align with the global cartesian coordinate system. So it is not possible to align e.g. the E1 axis in the radial direction for a sphere. FEBio does have the capability to define a local element coordinate system, but this material does not make use of it. In principle I could add this capability but I have not done so simply because I have never been asked . If this is a feature you would like to see in FEBio, please make a feature request on the forum and I will look into adding it.

    Cheers,

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

    Comment

    • kostas
      Junior Member
      • Jul 2020
      • 13

      #3
      Hi Steve,

      I just wanted to make sure. Is the feature you describe above available now in FEBio ? I have a curved tube geometry and I want to apply a local coordinate system. Along with this action, will the material properties adjust to the new material axes (e.g. E1->radial, E2->circumferential, E3->longitudinal). I am using the Fung-orthotropic material.

      Thank you,
      Kostas

      Comment

      • maas
        Lead Code Developer
        • Nov 2007
        • 3400

        #4
        Hi Kostas,

        The Fung-Orthotropic material indeed uses the local material axes. In the latest development build of FEBio Studio, you can set the material axes property, by clicking the material in the model tree, and then setting the Axes option in the property panel under the model tree.

        Cheers,

        Steve
        Last edited by maas; 07-29-2020, 09:23 AM. Reason: fixed type
        Department of Bioengineering, University of Utah
        Scientific Computing and Imaging institute, University of Utah

        Comment

        • kostas
          Junior Member
          • Jul 2020
          • 13

          #5
          Hi Steve,

          Yes, I tried using the "Axes" ->"local" option but I was told that I would not get acceptable results because I have a tetrahedral element mesh (TET4). I have previously defined a local coordinate system by applying "Set axes from curvature", and now as I understand, the only way to apply these changes in the material is through the "Axes" option. However, since the "local" option does not work for me, will I be able to achieve the results I want by using any of the other settings of the "Axes" option (vector, angles or (none)) ? If so, would you be so kind as to elaborate ? Thank you for your time.

          Comment

          • maas
            Lead Code Developer
            • Nov 2007
            • 3400

            #6
            Hi Kostas,

            Indeed, for tet meshes, the "local" option is not very useful. It uses the local node numbering to generate the axes, which is quite random for tet meshes. You should still be able to use the "Set axes from curvature" option, though. Is that not working for you then?

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

            Comment

            • kostas
              Junior Member
              • Jul 2020
              • 13

              #7
              Hi Steve,

              Yes I am using the "Set axes from curvature" option but don't I, also, have to set the "Axes" option in the material properties ? If I run the case with value in the "Axes" option being "(none)", then it ends with an "ERROR TERMINATION" message. Thanks again.

              Kostas

              Comment

              • maas
                Lead Code Developer
                • Nov 2007
                • 3400

                #8
                Hi Kostas,

                If you set the axes from curvature, you do not need to set the Axes property. I suspect that the error termination may not be related to this, but double check the FEBio input file to make sure that the axes are defined properly. They should be specified in the MeshData section. If that doesn't help, feel free to send me the model and I'd be happy to take a closer look.

                Cheers,

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

                Comment

                • kostas
                  Junior Member
                  • Jul 2020
                  • 13

                  #9
                  Hi Steve,

                  The MeshData section does not seem to be working. I am posting a WeTransfer link if you want to download the project file and take a look. Thank you for your time!

                  Kostas

                  Comment

                  • maas
                    Lead Code Developer
                    • Nov 2007
                    • 3400

                    #10
                    Hi Kostas,

                    Can you please send me an updated link for this one as well? It has also expired.

                    Thanks,

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

                    Comment

                    • kostas
                      Junior Member
                      • Jul 2020
                      • 13

                      #11
                      Hi Steve,

                      I am posting the same link that I posted in the thread " Differences between data in PostView ". It's the same file. Thanks again!


                      Kostas

                      Comment

                      • maas
                        Lead Code Developer
                        • Nov 2007
                        • 3400

                        #12
                        Hi Kostas,

                        The file you send me does not contain a MeshData section. Did you send me the correct file?

                        Cheers,

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

                        Comment

                        • lancef
                          Member
                          • Jul 2016
                          • 31

                          #13
                          Hi Steve,

                          I came across this thread and have similar questions. I have a tet mesh that I'd like to add active contraction fibers to using the trans iso-mooney rivlin model. The local option for the fiber orientation doesn't do me any good, so I've been using the set axes from curvature option. My concern is that I'm not fully understanding how it's setting the axes. From element to element I can get a pretty big change in the coordinate system. In a practice file I made, I built a torus and applied local curvature axes to it. If I were to assign fibers to that model, my chosen axis would switch based on where I was on the torus. For some of the torus, I'd want my fibers in the x, some in the y, and some in the z. Is this expected?

                          Also, how do I assign my fibers to the local axes in a material like the trans iso-MR? Would I still choose local as the fiber type, and then reference the element data?

                          Thanks, Steve!

                          Comment

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