Hello all!

I am struggling to reproduce the results of Abaqus built-in Neo-Hookean model with my own VUMAT. To be clear I get the exact same results for uniaxial tension tests with both a single element as well as a 4x4 mesh. Shearing or rotations does not seem to be captured in the same manner however and for these cases I only get correspondence for some components of the stress tensor. I've tried varying mass-scaling, hourglass stiffness and using double precision but to no success. Any insight into what could be the source of error would be helpful.

I've included the example I'm currently struggling with as well as the VUMAT which is the one produced by Mr Hohenberger with some slight adjustments. For this particular case using the VUMAT even results in some "wierd" element modes which are not seen with the built-in model. Is there some extra stability in the built-in model that I'm missing perhaps?

All the best
J