New constitutive equation for the Portevin-LeChatelier effect based on work-softening model

A new constitutive equation for the Portevin-LeChatelier effect has been proposed. A main feature of the equation is the introduction of an internal stress Yir which is supposed to be decreased with strain (work softening) and increased with time (age hardening). Yir is introduced in order to explain the negative rate sensitivity (n.r.s) of the flow stress. Another feature of the theory is that all the parameters used in the equation can be obtained by macroscopic experiments. The results of computer simulation based on the theory showed that the simulated values of the Luders strain, the strain rate, the stress drop and its rate agree quantitatively with the experimental data. Moreover, the simulation could explain the peculiar behavior of Luders deformation, namely, the fast and slow deformation, which was observed in the tensile test carried out at the moderate tensile speed of 3×10^-3 s^-1.