Implementing anisotropic plasticity in UMAT

[robidpra]

Hello,

I'm looking into implementing anistropic plasticity in ABAQUS.
I know the Hill criterion is implemented by default in ABAQUS (see abaqus docs), but I want to implement it in a UMAT, because I have to couple it with other features.

Regarding the STRESS variable that I can use in a UMAT, are these components according to the original reference system (i.e. XYZ), or are these with respect to the principal axis? In other words, does S22 mean the stress along the Y-direction and so can I use this in the calculation of the Hill anisotropy criterion for example.. Or do I have to rotate STRESS using DROT?

I could not find a UMAT example code with anisotropic plasticity.

 

[FEA way]

Stress components are stored according to general convention used in Abaqus - with respect to global directions. But you can use utility routines to get different variables for UMAT, such as principal stresses (SPRINC routine).