Almost all polymer have a Young’s modulus that is almost the same in tension and compression. There are some materials, however, that have quite different responses in tension and compression. Once example is certain soft polymer foams. The figure to the right shows the stress-strain response of one such material. The reason for the difference in this case is due to the deformation mechanisms of the microstructure, for example cell wall bending and buckling.
The obvious question in a case like this is what material model can predict that type of response?
In a difficult problem like this it can be useful to use a heavy hammer, such as the PolyUMod Parallel Network (PN) model. This model runs a bit slow, but it contains some really awesome features. In this case the elastic element type ETYPE=18 is exactly what is needed. Here is a screenshot from the PolyUMod User’s Manual. More details of the model are giving that Manual.
Once we have selected this model it is very quick and easy to calibrate an accurate material model (see image below).
All the details of the calibration, and more, are shown in this video.