A Methodology for Post-Necking Analysis in Isotropic Metals

Metallic materials are commonly characterized through tensile tests. For ductile metals, a consistent part of the test occurs after the necking onset. A first estimate of the post-necking behavior could be obtained by extrapolating the mathematical model that fits the pre-necking law. However, as well known, the accuracy of the predictions would not be guaranteed. Therefore, over the past decades many efforts have been devoted to dealing with the necking phenomenon. The most popular correction formula proposed by Bridgman is an analytical method based on the neck geometry. Despite being widely used, it may not be accurate at large strains due to the assumption of uniform distribution of the equivalent stress and equivalent strain in the specimen minimum cross-section. Starting from Bridgman's idea and in order to overcome its limitations, the present paper develops an efficient method to calibrate the hardening law of isotropic metallic materials at large strains. The proposed method requires to record the outer contour of the necking zone during the test and to build a dataset of necking deformed shapes. Experimental quasi-static tensile tests were analyzed with the proposed approach, which appears promising when critically compared with other methods.