Selection of the suitable material model for the strength calculation of rubber and plastics (hyperelastic materials)
The selection of the correct material model for the FE analysis of rubber, plastics or similar hyper-elastic materials depends not only on the amount of the expected strains during the simulation, but also on the available material data. For high strains, the Mooney-Rivlin model is used if possible, since the Neo-Hooke model may not accurately represent them. Particularly in the course of preliminary investigations during prototype development, only a few test data are available that describe the material sufficiently accurately for the FEM calculation of the corresponding plastic or elastomer. Clues for the selection of the material model are among others:
- Magnitude of the expected strains
- Information from the material manufacturer (e.g. Shore hardness)
- available experimental data or material tests
FE analysis of rubber and plastics using the Mooney-Rivlin material model
The Mooney-Rivlin material model is a more complex nonlinear material model. It is defined with up to 9 parameters and also maps high strains well. It is used, among other things, for the FEM calculation of rubber parts such as seals, membranes, tyres, hoses, but also springs and rubber bearings. When using this material model, it must be ensured that the measurement data and measurement conditions for material characterization are similar to the later stress state of the component to be represented. We adapt customer-defined parameters by means of a curve fit with test results before they are used in the FE analysis of the respective plastic or rubber component.
FEM calculation of rubber and plastics using the Neo-Hooke material model
The much simpler Neo-Hooke material model allows the characterization of the hyperelastic material with only two parameters. These parameters can often be derived or converted from the manufacturers' data sheets, especially in the course of preliminary design. If, for example, a Shore hardness is specified for the material, the coefficients for describing the elastomer can easily be determined from this, at least roughly. However, the Neo-Hooke model for calculating the strength of rubber or plastic materials can only be used for smaller strains. For large strains > 200 %, the Mooney-Rivlin material model is recommended.