Calibration and Validation of Stress–Strain Curve in High-Strain Region of Mild Steel Sheet

Abstract

Stress–strain curve in the high-strain region is one of the most important models that must be taken into consideration for high-precision sheet metal forming simulation. In this study, using mild steel sheets, tensile tests were conducted with a necked shape specimen at the center in order to generate non-uniform elongation. Using image analysis, strain–load relationships were obtained using multiple gauge lengths, and stress–strain relationships were obtained by inverse analysis using FE simulation. With a sufficiently small gauge length it is possible to get stress–strain curve in the high-strain region. The advantage of this method is that the experiments can be implemented only with a uniaxial tensile test. For validation, the original hole expansion test model that is not affected by friction is proposed. The thickness strain distribution along the hole with large plastic strain is compared with the experimental and numerical results to indicate the validity of this method.