help with vumat
I trying to learn user subroutines in abaqus, particularly vumat. I have started with Neo-Hookean model as an example kindly posted by Jorgen (thank you!). I included some modifications to match the code with the current abaqus version (6.13). I tested it on one element model using C3D8R element. However the results of my vumat (attached) are not matching with the build-in model. Any help/suggestions is greatly appreciated!
I am also trying to learn subroutines using the neo-hookean model as a starting case. I have implemented the neo-hookean model for shell elements. However, I have also been unable to match the VUMAT and the builtin function. For shell elements I believe I have to calculate the stretch in the 33 direction, which is essentially the difference in the codes. did you manage to resolve your issue?
Not completely - I have some mesh distortion with the vumat in the cases of uniaxial tensile test with clamped faces or biaxial tensile. When faces are free to deform, results are matching exactly.
Enhanced hourglassing helps a little with the distortion and results look closer to the built-in model (but not exact). Do you have any problems with mesh distortion by any chance?