I have written a USERMAT material model that reduces the stiffness under cyclic loading. After I ran it for an open hole specimen, I got an error message of UY exceeding the limit of 10000, which means that the stiffness is decreasing a lot or the model is insufficiently constrained.

After that error, I ran my Fortran code in Code Blocks with a strain input and the material parameters but I got the same as the hand results, so there is no error of parenthesis or sign that affects the damage update.

Following the recommendations of running a 2d analysis with a single element (PLANE182), with the bottom nodes constrained in all directions and the nodes at the top with the cyclic loading in the Y direction, I still get strange results, for instance even though the strain in y-direction has the highest value the stress in the x-direction is the highest with a value of 0.2339E6 MPa. I also observed that the damage Df is extremely high (71) while it should be between zero and one.

I really don't know how to improve the situation, I am attaching the Fortran code and the input file. I will be so thankful if anyone could help me.

Thanks in advance.