Hyperelastic material models can be used for modeling rubber-like materials where solutions involve large deformations. The material is assumed nonlinear elastic, isotropic, and incompressible.
The finite element formulation for such materials has numerical difficulties due to incompressibility. A penalty method, based on the introduction of compressibility to the strain energy density function, is used to assemble the additional degrees of freedom into the global stiffness matrix. The introduction of the penalty function modifies the strain energy function from incompressible to nearly incompressible.
Higher order elements (high quality) provide higher numerical stability than lower order elements (draft quality).
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.
All the skills needed to run a nonlinear analysis apply to the hyperelastic models as well. The load step and mesh size require careful considerations. In some cases, especially when no experience with the problem at hand is available, a trial and error approach is recommended.