Stress correction method for flow stress identification by tensile test using notched round bar

Abstract

In this paper, a stress correction method for flow stress identification using notched round bar tensile test is proposed. Flow stress is evaluated in uniform elongation and local elongation until final fracture in a tensile test with circumference notched round bar tensile test specimens. Tensile load and change in the shape of the notch are measured by image analysis. In order to correct the average tensile stress to the flow stress, inverse analysis is applied to the tensile test. For the validation of the inverse analysis, numerical tensile tests are performed by FEM. As a result of applying the inverse analysis for the numerical tensile tests, the corrected flow stress completely reproduces the two types of reference flow stress curves which are determined by Swift’s and Voce’s law. On the other hand, the flow stress corrected by Bridgman’s method, which is a conventional stress correction method, overestimated these reference flow stress curves. In the case of the actual tensile test of low carbon steel SS400 (in JIS), the flow stress corrected by inverse analysis corresponds to Swift’s law determined in uniform elongation. As well as numerical tensile test results, the flow stress corrected by Bridgman’s method is higher than that of obtained by the inverse analysis.