I am running nonlinear static analyses on shells + members structures. I am using the 'Plasticity - von Mises' material model, and use the large deformations formulation.
In my material I am entering the yield strength (325MPa), and the tangent modulus (0MPa).
In most of the cases I have run, there are areas in the model that give a higher stress than yield. For example, I may have a max Von mises stress of 355MPa or 330Mpa while the yield stress is 325. Why does this happen? I am expecting the maximum stress to be the yield stress. In one of my tests I made sure that max Von mises stress = max P1 stress = max Z stress so it does not seem that the software is tracking another stress to determine plasticity threshold.
Please note that even by using a positive tangent modulus (say 210000MPa), the stress is still much higher than the strain would indicate. Also, by entering a stress-strain curve manually results are the same.
Any insight appreciated.