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Thread: strain units in postview

  1. #1
    Join Date
    Jan 2019
    Location
    Gold Coast, Australia
    Posts
    60

    Default strain units in postview

    Hi,

    What is unit for strain in postview: mm/mm or %

    Cheers,
    Nataliya

  2. #2
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    2,048

    Default

    Hi Nataliya,

    Strain is unitless since it is a ratio of two lengths. The unit of length does not matter since the strain value would be the same regardless of the length unit.

    Cheers,

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

  3. #3
    Join Date
    Jan 2019
    Location
    Gold Coast, Australia
    Posts
    60

    Default

    Hi Steve,

    My unit system is mm for geometries of objects, in Neo-Hookean model I used MPa for Young’s modulus and scalar value for poison ration (0.49). My intention was to use poisson ratio over 0.5 as ligament is almost incompressible but FEBio does not allow doing it.

    As results, I obtain max 50 MPa effective stress (von misses stress) and 0.6-0.8 for Lagrange strain (strains). If strain is unitless (mm/mm), I obtain very unrealistic strain of 60%-80% as physiological strain range is between 5-10%. Is it an indicator that I have to use different material model which will better describe material properties of ligament?

    Cheers,
    Nataliya
    Last edited by NataCalc; 09-28-2019 at 05:59 PM.

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