Using Test Data for Mooney and Ogden Material Models

When defining Mooney Rivlin and Ogden hyper elastic models for nonlinear studies, you have two options:
  • Define constants directly in the Properties tab of the Material dialog.
  • Provide test data for the program to evaluate the constants internally.

Defining Hyperelastic Material Using Test Data

You can provide test data to define Mooney Rivlin and Ogden hyperelastic material properties.

To define the material using test data:

  1. Create a nonlinear study.
  2. When defining a hyper elastic material, click the Properties tab in the Material dialog.
  3. In the Select material source, click Custom defined.
  4. From Model type, select HyperElastic - Mooney Rivlin or HyperElastic - Ogden.
  5. Click Use curve data to compute material constants.
    The Tables and Curves tab is activated.
  6. From the Type menu, select Simple Tension, Planar Tension or Pure Shear, or Biaxial Tension depending on the data available.
  7. In the Table data, select the units and define the curve manually or click File to import the curve from a .dat file.
    If you have more than one test data file, repeat steps 6 and 7. You can define up to 3 curves (for Simple tension, Planar tension or pure shear, and Biaxial tension). Each curve can contain up to 200 data points. The data points of the curve must represent the stretch-ratio (deformed length / undeformed length) versus nominal stress, also known as engineering stress (force divided by the initial area).
  8. Click OK.
    The material constants are saved in a text file with the extension .log in the active result's folder for the study.
    The solver calculates the material constants as follows:
    1. Performs a curve-fitting to get the material constants.
      For Hyperelastic – Ogden material model, Simulation computes the four power material coefficients from these default ranges:
      Power Coefficients

      (Ogden material model)

      		 Default range (Min - Max)
      First 1.0 to 2.0
      Second 4.5 to 5.5
      Third -2.5 to -1.5
      Fourth 17.5 to 18.5
    2. Based on the calculated material constants, the strain energy density function and the stress function (derived from the energy density function) are defined.
    3. Back-calculates the stress, so called theoretical stress, from the user-defined strain.
    4. Calculates the stress error defined by the differences between the user-input and theoretical values.

Defining Mooney-Rivlin and Ogden Material Constants

To define the Mooney-Rivlin and Ogden constants directly:

  1. Create a nonlinear study.
  2. When defining a hyper elastic material, click the Properties tab in the Material dialog.
  3. In the Select material source, click Custom defined.
  4. From Model type, select HyperElastic - Mooney Rivlin or HyperElastic - Ogden.
  5. Set the units and number of constants and define the relevant constants and coefficients directly in the table based on the selected model.
  6. Click OK.