Jorgen,

just one more question: if you talking about the variation of Kirchhoff stress with respect to the rate of deformation tensor, its the so called Lie derivative. Is that right? But that differs from the Jauman rate..

For ANSYS I think the following is true: In the corotational approach, they use the Jauman rate (which is also the needed consistent tangent modulus). However, the corotational coordinate system is rotated by means of the rotation tensor. Therein, ANSYS expects all quantities (stresses, tangent). Up to my knowledge, this approach assumes small strains otherwise the corotated system differs more or less from the rotation tensor.

May be, we can discuss this a little further...

Armin