The main difference between modeling the piece of rubber and using separate springs at every node is that the modeled component is all connected together, whereas the individual springs are all individual. If you the analysis could somehow magically compress only some of the springs but not all of the springs, then
- using a part with a load on a fraction of the surface still compresses most of the surface.
- using individual springs would compress only the springs with the load.
Of course, most situations that I can think of are not like the individual springs example because the real rubber pad is a continuous block (or however you model it). The real pad is not individual volumes at each node and unrelated to the neighbors.
Of course, you have a known stiffness, so you need to adjust the material properties of the modeled pad to duplicate that stiffness. Otherwise, choose the material that best fits the behavior of your support. (In other words, isotropic material type because like a regular material, hyperelastic material type allows for large stretch, and so on.)
John Holtz, P.E. Global Product Support
Autodesk, Inc. If not provided, indicate the version of Inventor Nastran you are using.If the issue is related to a model, attach the model! See What files to provide when the model is needed.