A novel method for quantitative analysis on the post-necking behavior during uniaxial tension

In this study, a combined experimental–numerical method is proposed for quantitatively characterizing the post-necking behavior of cylindrical metal specimens merely through its experimental force–displacement curve during quasi-static tension. This method is based on a rational phenomenological analysis of the correspondence between the necking levels and the experimental variables (force and displacement) in plastic tension. Firstly, the definitions of the global and local inhomogeneity factors based on the statistical analysis of the radial change within the gauge section were introduced to assess the inhomogeneity degrees of post-necking specimens. In the proposed method, a number of tensile deformations with different necking levels are modeled through implanting different initial defects into specimen model in finite element analysis, respectively, outputting the corresponding simulated force–displacement curves. The inhomogeneity factors are calculated based on the intersected points between the experimental and simulated force–displacement curves. Through validation of optical measurement, it is proved that the proposed method has high accuracy and good reliability for investigating the inhomogeneous deformation with significant neck rather than those without significant neck and could exactly replace optical measurement, especially when the camera needs high resolution and acquisition frequency. This indicates it is feasible to utilize the force versus stroke curve in metal plastic forming to quantitatively analyze the localization behavior under general stress states besides uniaxial tension, concerning the contribution of initial defects.