Stress-strain curves of metallic materials and post-necking strain hardening characterization: A review

For metallic materials, standard uniaxial tensile tests with round bar specimens or flat specimens only provide accurate equivalent stress-strain curve before diffuse necking. However, for numerical modelling of problems where very large strains occur, such as plastic forming and ductile damage and fracture, understanding the post-necking strain hardening behaviour is necessary. Also, welding is a highly complex metallurgical process, and therefore, weldments are susceptible to material discontinuities, flaws, and residual stresses. It becomes even more important to characterize the equivalent stress-strain curve in large strains of each material zone in weldments properly for structural integrity assessment. The aim of this paper is to provide a state-of-the-art review on quasi-static standard tensile test for stress-strain curves measurement of metallic materials. Meanwhile, methods available in literature for characterization of the equivalent stress-strain curve in the post-necking regime are introduced. Novel methods with axisymmetric notched round bar specimens for accurately capturing the equivalent stress-strain curve of each material zone in weldment are presented as well. Advantages and limitations of these methods are briefly discussed.