Providing test data to define an isotropic hyperelastic material

From the menu bar in the Edit Material dialog box, select MechanicalElasticityHyperelastic.

(For information on displaying the Edit Material dialog box, see Creating and editing materials.)

Choose Isotropic as the material type.

Click the arrow to the right of the Strain energy potential field, and select the strain energy potential of your choice.

Arruda-Boyce

The Arruda-Boyce model is also known as the eight-chain model. For more information, see Arruda-Boyce form.

Marlow

For more information, see Marlow form.

Mooney-Rivlin

The Mooney-Rivlin model is equivalent to using the polynomial model with N=1. For more information, see Mooney-Rivlin form.

Neo Hooke

The Neo Hookean model is equivalent to using the reduced polynomial model with N=1. For more information, see Neo-Hookean form.

Ogden

For more information, see Ogden form.

Polynomial

For more information, see Polynomial form.

Reduced Polynomial

The reduced polynomial model is equivalent to using the polynomial model with $C_{ij}=0$ for $j\ne 0$. For more information, see Reduced polynomial form.

User-defined

You can define the derivatives of the strain energy potential with respect to the strain invariants in user subroutine UHYPER. This method is valid only for Abaqus/Standard analyses. For more information, see User subroutine specification in Abaqus/Standard.

Van der Waals

The Van der Waals model is also known as the Kilian model. For more information, see Van der Waals form.

Yeoh

The Yeoh model is equivalent to using the reduced polynomial model with N=3. For more information, see Yeoh form.

Unknown

If you define an isotropic hyperelastic material using experimental data, you also have the option of temporarily leaving the particular strain energy potential unspecified. You can use the Evaluate option to identify the optimal strain energy potential for the material data and then display the material editor again to complete the material definition; see Evaluating hyperelastic and viscoelastic material behavior, for more information.

Select Test data as the Input source to indicate that the material constants are to be computed from data taken from simple tests on a material specimen.

If you are defining the hyperelastic behavior of a viscoelastic material, click the arrow to the right of the Moduli time scale (for viscoelasticity) field to specify either long-term or instantaneous elastic response.

If you selected Marlow as the strain energy potential, select the Data to define deviatoric response and the Data to define volumetric response options of your choice.

• The deviatoric response is defined by the Uniaxial, Biaxial, or Planar test data specified as described in Step 8.

• The volumetric response is defined by one of the following methods:

  • Ignore test data: Abaqus/Standard assumes fully incompressible behavior, while Abaqus/Explicit assumes compressibility corresponding to a Poisson's ratio of 0.475.

  • Volumetric test data: The volumetric test data are specified directly, as described in Step 8.

  • Poisson's ratio: Specify a value for the Poisson's ratio of the isotropic hyperelastic material.

  • Lateral nominal strain: Lateral nominal strains are specified as part of the uniaxial, biaxial, or planar test data, as described in Step 8.

If you selected Ogden, Polynomial, or Reduced Polynomial as the strain energy potential, click the arrows to the left of the Strain energy potential order field to select a value.

If you selected Van der Waals as the strain energy potential, choose the method for specifying Beta:

• Select Fitted value to determine the value of $\beta$ from a nonlinear least-squares fit of the test data.

• Select Specify, and enter a value to specify $\beta$ directly. Allowable values are $0\le \beta \le 1$. It is recommended to set $\beta$=0 if only one type of test data is available.

You can specify the experimental stress-strain data for as many as four simple tests: uniaxial, equibiaxial, planar, and, if the material is compressible, a volumetric compression test. Use the Test Data menu to specify the experimental data. For details, see the following sections:

• Specifying uniaxial test data for an isotropic hyperelastic material model”

• Specifying biaxial test data for an isotropic hyperelastic material model”

• Specifying planar test data for an isotropic hyperelastic material model”

• Specifying volumetric test data for an isotropic hyperelastic material model”

If desired, select Hysteresis from the Suboptions menu to define hysteretic behavior. See Defining hysteretic behavior for an isotropic hyperelastic material model” for details.

Click OK to create the material and to close the Edit Material dialog box. Alternatively, you can select another material behavior to define from the menus in the Edit Material dialog box (see Browsing and modifying material behaviors, for more information).