Add a weak constraint to a governing equation for damage

Dear All:

I have a governing equation , where d is the damage variable, A and B are constant variables, and H_p is the maximum value of positive strain energy (calculated by the positive principal strain). I want to add a constraint that, when the "positive " strain energy is less than the "negative" strain energy, H_n (calculated by the negative principal strain), then the damage will be zero, i.e. for domain . How should I add this constraint to the governing equation? How to select the Lagrange multiplier?

Thank you for your help and time.