I'm new in this forum.
I am writing a VUMAT subroutine for ABAQUS in order to implement a consitutive law under large deformation. I used the command *ORIENTATION for the material directions.
But how could I get the initial cosines in the subroutine ? How is the deformation gradient computed in VUMAT when there is initial material orientation ? Is it purely F or is it multiplied by another matrix rotation accounting for the initial orientation ? Same for the stretch U ?
Thank you for your help.