How to run Progressive damage in Composite materials with Usermat ?
I would like to know if anyone here has experience writing a material model (Usermat) for stiffness degradation in composite materials. I have written a USERMAT material model that reduces the stiffness under cyclic loading, but 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.
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 am attaching the Fortran code and the input file for anyone to check if there is an error.
Thanks in advance.