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!