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Hello dear all,
for my master's thesis I'd like to write a simple VUMAT for a material with nearly zero compression stiffness.
So for a better understanding of VUMAT subroutines I did the ABQ tutorial for a VUMAT with isotropic, isothermal elastic material behaviour and compared the results with the built-in material definition.
There is a discrepancy of almost 35% of the S11 stress. ABQ Manual says that both times the Green-Naghdi stress-rate formulation is used.
Why are the results not the same? After hours of trying I still could not find the solution!