[Solved] Solution Dependent Variables (*DEPVAR) in VUMAT
Implementing a user material model VUMAT requires input on the *DEPVAR option in Abaqus. Failure to do so results in a warning via the .DAT file
"USER SUBROUTINE UMAT WILL BE USED WITH THE STAVEV ARRAY
DIMENSIONED TO ZERO SINCE THE *DEPVAR OPTION IS NOT USED WITH THIS
MATERIAL. CONSEQUENTLY, DEFINING STATEV ENTRIES IN SUBROUTINE UMAT
WILL CAUSE CODE EXECUTION ERRORS"
I yearn to understand these SDVs, when and when not to use them. Does it depend on the material model?
Specifically to the hyperelastic models such as Neo-Hookean or Mooney-Rivlin, what are the SDVs in these two cases?
Thank you very much.
The number and type of Solution Dependent Variables (SDV) depends on the material model. They are typically used to "remember" the state a material point is in between calls to the VUMAT. For viscoplastic material models there are typically the components of the viscoplastic deformation gradient. For hyperelastic materials the stress can be directly calculated from the provided deformation gradient (or stretch tensor), and it is therefore not necessary to use ANY state variables when you code a VUMAT for a hyperelastic material model.
Another use of state variables is to save other values that you are interested in. For example, you can save the first invariant I1, if you like. You can then create history or contour graphs of those state variables.