THE ZERO-NORMAL-STRESS CONDITION IN PLANE-STRESS AND SHELL ELASTOPLASTICITY

The use of elastoplastic models in calculations of shell and plate structures, or more generally in stress situations in which one normal stress component is forced to be zero, usually leads to complicated algorithms. This leads to cumbersome programming, which in turn may easily entail errors in the code. Moreover, the fraction model for cyclic plasticity cannot be used within most algorithms since the normal stress perpendicular to the plane of the element is not necessarily zero for each of the fractions. In this contribution an algorithm will be presented that enforces a zero-stress condition at integration point level, while obviating the need to develop special subroutines for plane-stress or shell plasticity. The algorithm is based upon an implicit integration of the stress-strain law and can be combined with the newly developed technique of consistent tangent operators.