REPRESENTATION OF CYCLIC HARDENING AND SOFTENING PROPERTIES USING CONTINUOUS-VARIABLES

Our aim is the modeling of cyclic hardening, cyclic softening, cyclic mean stress relaxation, and additional nonproportional cyclic hardenin g. We do so by means of hardening functionals for back stress and yiel d stress without employing additional memory surfaces. Rather, we supp ose all quantities to evolve simultaneously during elastic-plastic loa ding in a continuous manner. The basic idea is to formulate evolution equations for the hardening variables, which are of the ''hardening/dy namic recovery'' format with respect to a transformed are length. The corresponding transformation is influenced by continuously evolving pa rameters, measuring strain amplitude and nonproportionality during the recent process history. Although the resulting model has a very simpl e structure, it is capable of describing the basic phenomena under qui te general loading conditions.