I am testing a nonlinear contact problem (i.e. nonlinear material) using two square blocks seperated by a very small distance. I already know from a non contact problem exactly what the plastic strain is when I unload the force at my last time step.
The contact problem is simple but the results I obtain make no sense at all. I have placed soft springs into the model and placed very small displacements with my initial time steps with no usable results. Any suggestions? I am running advanced simulation vs 7.5.3
It sounds like one block is fixed and the second unconstrained (depends on the contact to provide a path to ground). Whenever you have an initially unconstrained body like this, particularly when a load is applied in the unconstrained direction, you need either very small initial time steps (along with time dependent loading), or matrix stabilization, or both.
In this case you may be able to simply turn on matrix stabilization on the Analysis Options tab in the Strategy Parameters modeling object. It should be sufficient to prevent uncontrolled displacement until contact is established.