<CRITERION>

Description

The criterion object is used for specifying the calculation of an equivalent stress to be used in plasticity and viscoplasticity behavior models (for each potential in a gen_evp material). The criterion may also be used for determining the flow direction and in hardening evolution models depending on the application.

Syntax

The syntax to specify a criterion object will consist of giving the keyword for a particular criterion desired, followed by a list of appropriate coefficients which are dependent on the model chosen. The possible criterion types are:

CODE	DESCRIPTION
mises	classical von Mises criterion
2M1C	criterion 2M1C (only for potential mises_2m1c)
hill	Hill criterion
ratio	classical criterion useful as viscoplastic overstress function
karafillis_boyce	Karafillis Boyce criterion
full_hill	Hill criterion
tensile_mises	acts as von Mises criterion
nouailhas	macroscopic model developed by ONERA
modified_nouailhas	modified nouailhas model
linear_drucker_prager	non-associated drucker-prager criterion
anisotropic	classical energy equivalent form due to von Mises
cast_iron	criterion which provides asymmetric tension/compression
bron	modes anisotropic behavior in the criterion and flow direction
unsym	non-symmetric deviatoric / hydrostatic criterion
tresca	Tresca criterion

Some expressions which will be used are:

(344)\[J_2(\hat{\ten \sigma})=\sqrt{\frac{3}{2}{\bf \hat{s}}:{\bf \hat{s}}}~~~~~~~~~~~~ s_{ij} = \sigma_{ij} - \frac{1}{3}\enspace \sigma_{ii}\delta_{ij}\]

where \(\hat{\ten \sigma}\) is the effective stress which may be displaced by a kinematic back stress:

(345)\[\hat{\ten \sigma}= \ten \sigma - \sum \ten X\]

The true form of this stress will be determined by the potential.

Stored Variables

Criterion objects are not allowed to have any variables.