fedoo.weakform.StressEquilibrium.kinematic_form

property StressEquilibrium.kinematic_form

Finite-strain formulation of the constitutive update, set by nlgeom.

• “rate” (nlgeom="UL"): the law is integrated with the objective rate corate. It works on the spatial logarithmic strain ln V and on the Kirchhoff stress.

• “total” (nlgeom="TL"): the strain-space framework of Miehe, Apel and Lambrecht (2002). The law works on the material logarithmic strain ln U = 1/2 ln C, a state function of F on the reference frame (nothing is rotated: DR = I), and on the stress T dual to ln U. No rate is involved, and the stored “Strain” is ln U.

The two run the same law on the same strain under corate="log_r" and coincide whenever the stress is coaxial with the stretch; otherwise they are different constitutive statements (a yield criterion holds on T under “total”, on the Kirchhoff stress under “rate”).

A law that does not declare supports_total_formulation (the native laws, a modular Simcoon material…), and any law under the 2D plane-stress assumption, keep the “log_r” rate update under nlgeom="TL".

Before the problem is initialized, and without nlgeom, the value is “rate”.