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Thread: Fiber in a transversely isotropic biphasic material

  1. #1
    Join Date
    Apr 2017
    Location
    Chelmsford
    Posts
    5

    Default Fiber in a transversely isotropic biphasic material

    Hello FEBio community,

    Following this post (Link), I've managed to find a way of setting different fiber orientations among the same object. I separated my object into three parts, assigned a material property for each part, and wrote in the FEBio script the fiber direction I wanted to create, as following:

    <material id="8" name="TibCartSuperficialZone" type="biphasic">
    <phi0>0.2</phi0>
    <fluid_density>1</fluid_density>
    <solid type="solid mixture">
    <solid type="spherical fiber distribution">
    <alpha>0</alpha>
    <beta>2.15</beta>
    <ksi>10</ksi>
    <fiber type="vector"> 1, 0, 0</fiber>
    </solid>
    <solid type="neo-Hookean">
    <density>1</density>
    <E>20</E>
    <v>0.45</v>
    </solid>
    </solid>
    <permeability type="perm-const-iso">
    <perm>0.001</perm>
    </permeability>
    </material>

    I obtained different results according to whether the fiber orientation has been implemented or not. But, as I'm not familiar with programming, I would like to know if this way of generating a fiber orientation is correct.

    Thanks a lot and best regards,

    Antoine

  2. #2
    Join Date
    Dec 2007
    Posts
    608

    Default

    Hi Antoine,

    It is acceptable to embed <fiber> or <mat_axis> tags within the individual <solid> components of a mixture. If you also have a global material axis orientation (e.g., defined in the <ElementData> section), FEBio will compound the transformations. In other words, the <fiber> or <mat_axis> orientation in the <solid> tag will be set relative to the global material axis orientation for that element.

    Please note that, as I was double-checking this feature in FEBio, I found a bug in the current code which needed to be fixed. We will be releasing a new version of the code shortly, so please use that latest version.

    For the material you define in your example, please note that a "spherical fiber distribution" is technically isotropic. In other words it shouldn't matter which way the material axes are pointing for this type of fiber material. If you do see a difference in your analyses, they should be small and due to the error inherent to numerically integrating the stress over all fiber directions.

    Best,

    Gerard

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