Nonlinear possibilities
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The nonlinear behaviors for GRILLE models correspond to particular incremental behaviors in STAT_NON_LINE:


* GRILLE_ISOT_LINE for isotropic work hardening plasticity,


* GRILLE_ISOT_CINE for bi-linear kinematic work hardening plasticity,


* GRILLE_PINTO_MEN for Pinto Menegotto's behavior.

For nonlinear MEMBRANE modeling, we'll use the GROT_GDEP behavior in STAT_NON_LINE.