Identification of Work Hardening Behavior under Large Strain by Uniaxial Tensile Test Using Digital Image Correlation

In this study, a new method of identifying the postnecking strain hardening behavior of sheet metal was proposed. The local in-plane stresses and tensile load after diffuse necking in a uniaxial tensile test can be theoretically calculated using the in-plane strains measured with a digital image correlation (DIC) system and applying a mixed law composed of a power law and a Voce law with a weight coefficient. The tensile load calculated using the mixed law coincided with the experimental load without depending on strain, and the weight coefficients of four steel sheets were identified. The evaluable strain ranges of the proposed method were 3-5 times larger than the uniform elongation of the materials. The stress state in the defuse necking zone was between uniaxial tension and plane strain. On the basis of the stress state, it was found that the effect of stress anisotropy on the result of stress calculation was insignificant. The proposed method enables the identification of the postnecking strain hardening behavior easily and stably by only the uniaxial tensile test with DIC strain measurement.