LAUSR

To make comparison between classic necking stress solution Bridgman formula and ChenChi formula, the difference of necking surface profile assumptions in these two formulas were discussed theoretically. Then, the uniaxial tension experiment on 16 groups of carbon structural steels Q235 and Q345 were carried out at room temperature. Associate with the necking displacement measured by Aramis optical dynamic 3D strain measurement system, the parameter equation of necking surface profile was determined. The comparison results indicate that ChenChi formula is more accurate than Bridgman formula in calculating the necking stress distribution. Furthermore, to overcome the difficulty of measuring the radius curvature R in these formulas, an empirical formula of the geometric dimensions in the necking section was applied and the parameter was corrected based on the necking strain measured by Aramis system. As a result, the obtained equation in this study can provide an improved calculation method for the analysis of three-dimensional stress in necking and a reference for future research on the necking and ductile fracture of structural steels.