Evaluation of True Stress-True Strain Relationship after Local Necking by Stepwise Tensile Test

Abstract

The goal in this research is to evaluate the correct true stress-true strain curve after local necking up to a true strain of 1.0. To achieve this goal, a smooth round tension test was carried out by a stepwise method. Yield stresses of the materials tested ranged from 251 to 1182MPa. The tensile load-neck section diameter curve was measured in the stepwise test and was transformed into an average stress-true strain curve in the neck. The necking ratio-true strain relationship was determined by an optical microscope observation. The necking ratio was defined as the radius of the neck section divided by the radius of the neck curvature. The true stress-true strain curve after local necking can be evaluated from the average stress-true strain curve and the necking ratio-true strain relationship using an empirical equation up to a true strain of 1.0 regardless of the yield stress of the materials tested. In addition, circumferentially notched tension tests with different notch radii were carried out in a stepwise manner to evaluate the true stress-true strain curves in the neck.Regardless of the initial notch shape, the true stress-true strain relationship after local necking was similar in the notched tension test and in the smooth round tension test.