<CRITERION> unsym

Description

This criterion models the equivalent stress and deformation with deviatoric and hydrostatic terms. The criterion is written:

\[f_{cr} = (1-a)\sigma_{eq} + a\:\trace{\ten \sigma} - R\]

This criterion accepts a single coefficient a which must be input on a separate line from the unsym token. This criterion is also non-associated where the flow normal is written:

\[\ten n = \frac{3}{2} \frac{\ten \sigma ' - \ten X}{J_2(\ten \sigma-\ten X)}\]

with the \(\ten X\) term being the summation of back stresses. Often this criterion is used in conjunction with the ziegler kinematic hardening options [M11], but this is not necessarily so.