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Incremental (visco)plasticity: additive decomposition

The implementation of incremental plasticity for linear geometrical
calculations in CalculiX follows the algorithms in [18], section
5.3 and is based on an additive decomposition of the strain tensor into an
elastic and a plastic part. In CalculiX, it is used in the absence of the
NLGEOM parameter on the *STEP card. The internal variables are
the same as for the multiplicative decomposition (cf. previous section) in
their infinitesimal limit. It seems that the additive decomposition exhibits
less convergence issues than the multiplicative decomposition (although this
may also be attributable to the general nonlinear geometrical setup).

guido dhondt
2018-12-15