Apply constraints to material model's parameters in MCalibration
I wonder if there is a way to apply inequality constraints to material model's parameters in MCalibration during data fitting. For example, considering the Mooney-Rivin model, the Drucker stability condition requires that
C10 + C01 > 0.
I looked up the forum and only found this page for applying Parameter Connections (equality constraints).
There are 2 ways to do that. The first is to use an equation-based constrains on the parameters. In this case I used a "penalty" value of 10 and the step-function to impose the inequality constraint. This approach is similar to a Lagrange multiplier.
Another approach is to set a fitness weight for the Drucker stability. That can be specified for each load case.