> > In both cases the code had problems converging and when it did, I ended up > with negative plastic strain. This is not possible and I don’t know how it > happens because I explicitly only increment the plastic strain when the > increment is positive. > > This sounds like a logic bug. You are updating the auxilary variable for plastic strain with all positive numbers but as the system evolves you get negative numbers? PETSc does does not change these number other than computing the gradients for you.
> I am sure there is an easy solution to how I can update the internal > variables and determine the correct stress for the residual but I just > cannot figure it out. I’d be thankful for any hints. > > Thanks, > Max
