Computer simulation of the yield point phenomena based on the work-softening model

The yield point phenomena in low carbon steel have been explained by the Cottrell or the Johnston-Gilman theory in terms of microscopic variables such as dislocation density, dislocation velocity and the interaction energy between dislocation and solute atom. However, the lower yield stress and the amount of the Luders strain (stretcher strain) seems not to have been predicted by the above theories. In the present work we tried to explain the phenomena quantitatively by a phenomenological rheological model using macroscopic variables such as work-hardening rate and the strain rate sensitivity of flow stress which we can be measured by tensile test. In the model a new internal stress was introduced which is supposed to be work (strain)-softened and age-hardened. Numerical calculation showed that the model can predict the values of the upper and lower yield stress and the amount of the Luders strain, and the effect of strain rate on these characteristics.