General Mechanical

General Mechanical

Curve fit – Hyperelasticity

    • Lovisa Svanborg


      I have done curve fit for hyperelastic material models. My question are.

      • If a model is unstable will it work for a lower strain where the slope not is negative, i.e. if the simulation results just get lower strains or will it not work?
      • The relative error is showned in engineering data, but I think this is sum of relative error for 3 test. Can I see error contribution for each uniaxial, planar and biaxial and then they will sum it which is showing in Ansys? 
      • If a only use uniaxial test data, will it make a curve fit based on uniaxial, planar and biaxial and approx planar and biaxial data? Because in Ansys they plot all tests even if I have only uniaxial.

      Regards Lovisa


    • SaiD
      Ansys Employee



      Here are the answers to questions 1 and 3:


      1. The model should work in the strain range where the slope of the material data is not negative. But if the strains in the model go higher and reach the unstable region, the model will most likely fail. If you are sure that strains in the model are limited to the stable region, you can even ignore the data points in the unstable region and fit your material model using only data in the stable region.
      2. If only uniaxial data is provided, Ansys plots the data for biaxial and planar. But the model response only in uniaxial mode is reliable. If you need to simulate other deformation modes, you need to provide material data for those modes too. See this video (at around 3:15): How to Perform Curve-fitting for Hyperelastic Material Models — Lesson 1 – ANSYS Innovation Courses


      Hope this helps.


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