While converting true-stress vs true-strain curve into effective stress vs effective plastic strain, the removal of elastic strains can be based on a constant or varying strain value. For relatively small hardening, both methods should yield identical plastic strains but significant hardening, using an instantaneous elastic strain as opposed to a constant elastic strain is highly recommended. The following figures demonstrates both approaches.

1. True Stress Strain Curve (Click image to enlarge)

2. Constant Elastic Strains based on the Initial Yield Stress (Click image to enlarge)

3. Varying Elastic Strains due to Hardening Effect based on Instantaneous True Stress (Click image to enlarge)

4. Resulting Effective Stress vs Effective Plastic Strain from both methods (Click image to enlarge)