Search

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.

The tensile test is widely used for identifying the material plastic flow curve: this is a fundamental step in the design and in material behavior analysis. However, during these tests on ductile metals the necking phenomenon occurs, and the stress and strain states become triaxial and non-uniform. In the scientific literature several characterization methods have been proposed to properly address these aspects.The present work proposes an alternative strategy for identifying the plastic flow curve, focusing on temperature and strain-rate insensitive elasto-plastic materials. This is a hybrid methodology whereby a FE-based inverse method is combined with the 1D description of necking proposed by Audoly and Hutchinson. Indeed, the inverse method employs as target function the specimen profile, but to properly define it a relationship between the original and the deformed configuration of the tensile sample is required, and it is provided by this 1D model.The accuracy and the validity of the proposed strategy was verified on benchmark cases with ad-hoc experimental profiles obtained via numerical simulations. Finally, this method was applied to real case studies and the identified plastic flow curve was compared with the one obtained using a traditional FE-based inverse method having as target the force-stroke curve.