A procedure for determining the true stress–strain curve over a large range of strains using digital image correlation and finite element analysis

Abstract

A procedure for determining the stress–strain curve including post-necking strain is proposed. Hourglass type specimens were used for tensile tests, and the stress–strain curves were identified through an iteration process using finite element analysis. The strain at the position of minimum diameter was measured by digital image correlation. This procedure was applied to carbon steel of various degrees of cold work. The radius of the minimum section of the hourglass type specimen was changed in order to investigate the effect of stress triaxiality on the failure strain. The procedure could derive the stress–strain curve including the post-necking strain. From the obtained curve, it was shown that the stress–strain curves for different degrees of cold work were almost identical when the plastic strain by the cold working was added to the strain. Furthermore, it was revealed that the true stress–strain curve could be approximated well by the power law equation and the curve could be estimated by using the stress–strain relation for before-necking strain.