Thannk you very mych for the reply. I definetely see where you are coming from in terms of looking at this when the yield strength is the limiting factor. How do you suggest this be achieved when teh ultimate tensile strength is to be considered and as the failure critieria? I already have this model setup with the isotropic bilinear cureve for the material since i am intersted in the stresses and behavior AFTER it yields. 

Would a tri-linear or other curve work and set the values after the UTS to 0? I will conitnue to investigate but apprecaite any feedback that you woudl have.

Thank you again.