we have performed recently a static non linear FE analysis of quite a simply shaped rubber component.
Predicted strains are in the order of 50% for a typical load case, say load case 1.
Deflections for this load case are predicted within 1% accuracy.
Then the task was to predict the failure location should the load be increased.
This was not easy. I have used three criteria, the maximum principal stretch (allegedly Kawabatas criterion), maximum true stress and maximum strain energy.
Following a test it was realized the failure does not happen close to the locations indicated by the mentioned criteria.
It seems to happen instead in an area where none of the three peaks, but on the other hand there is a very significant strain gradient.
I am thinking there must be a mistake in the FE modelling, unless this behaviour has a sense for a Nitrile rubber, i.e. failing where the stress gradient is at a maximum (and the principal stretch is maybe above a threshold?)
Is this possibility familiar to any of you? Or is there simply something wrong with the model / test?
Thank you very much for your help