Hi,

I have a question regarding the use of local material coordinate systems in [I]Abaqus[/I] v6.9. Suppose I attach local coordinate systems to the integration points of a 3D nonlinear geometry, nonlinear material model using either *Orientation or the ORIENT user subroutine. [B] Does anyone know what the rotation is from the local coordinate systems in the reference state to the local coordinate systems in the deformed state?[/B] If the local coordinate systems are parallel to the global Cartesian system in the reference state, Ive found they DO NOT rotate to either the principal directions of strain relative to the reference state or the principal directions of strain relative to the deformed state. The [I]Abaqus[/I] documentation is unclear on how this rotation is calculated, but all components of stress and strain input to a UMAT are with respect to this system (see [I]Abaqus[/I] UMAT doc). I have tried passing T and DIRECT from USDFLD to UMAT, but these arrays are not the correct rotation when I have local coordinate systems. [B] I have reason to believe that if this rotation is not obtained, anisotropy or any phenomena coded in UMAT that depend on the use of local coordinate systems will yield incorrect stress and strain. [/B] Thanks for your help.

JY