Recommendations for Using Hyperelastic Materials

To improve your hyperelastic material model, follow these recommendations:

Obtain test data for the deformation modes that are likely to occur in your simulation. For example, if your component is loaded in compression, make sure that your test data include compressive, rather than tensile loading.
Both tension and compression data are allowed, with compressive stresses and strains entered as negative values. If possible, use compression or tension data depending on the application, since the fit of a single material model to both tensile and compressive data will normally be less accurate than for each individual test.
Try to include test data from the planar test. This test measures shear behavior, which can be very important.
Provide more data at the strain magnitudes that you expect the material will be subjected to during the simulation. For example, if the material will only have small tensile strains, say under 50%, do not provide much, if any, test data at high strain values (over 100%).

Note: Most solid rubber materials have very little compressibility compared to their shear flexibility and are modeled as incompressible in a FEA simulation. This behavior is not a problem with plane stress, shell, or membrane elements. However, it can be a problem when using other elements, such as plane strain, axisymmetric, and three-dimensional solid elements. For example, in applications where the material is not highly confined, it would be quite satisfactory to assume that the material is fully incompressible: the volume of the material cannot change except for thermal expansion.

In cases where the material is highly confined (such as an O-ring used as a seal), the compressibility must be modeled correctly to obtain accurate results.

Compressibility is defined as the ratio of the initial bulk modulus $K_{0}$ to the initial shear modulus $μ_{0}$ .

Poisson's ratio, $ν$ , also provides a measure of compressibility since it is defined as $ν = \frac{3 (K_{0} / μ_{0}) - 2}{6 (K_{0} / μ_{0}) + 2}$ .