Abstract: Based on the definitions of hardening,softening and ideal plastic behavior of elastic-plastic materials in th e true stress tensor space,the phenomena of simple shear oscillation are shown to be relative to the oscillatory occurrence of hardenin g and softening behavior of elastic-plastic materials,namely the oscillation of hardening behavior,by analyzin g a simple model of rigid-plastic materials with kinematical hardening under simple sh ear deformation.To make the models of elastic-plastic materials realistic,must be satisfied the followin g conditions:for any constitutive model,its response stresses to any continuous plastic deformation must be non-oscillatory,and there is no oscillation of hardening behavior durin g the plastic deformation.

Key words: objective rates, elastic-plastic constitutive relation, simple shear oscillation