Necking phenomenon based on the Aramis system

Abstract

In this study, the necking three-dimensional strain on minimum cross-section at room temperature was performed experimentally and analytically. A modified strain assumption was applied to overcome significant errors in calculating necking strain by Bridgman assumption. Then, one relatively simple strain distribution function was deduced based on equilibrium equation of necking element. To obtain the parameters in this function, the monotonic tensile tests in two kinds of carbon structure steels Q235 and Q345 were carried out. Meanwhile, the Aramis system based on digital image correlation method was adopted to measure the surface axial strain and deformation parameters during the loading process. The experimental and numerical results were compared with the traditional Bridgman strain assumption. The maximum axial strain calculation error the strain distribution function and experiment value was less than 8%, which was obviously less than that calculated by Bridgman assumption. Additionally, the variation law of the three-dimensional strain calculated by this function was consistent with that obtained by the macroscopic analysis of fracture surface. The application of traditional Bridgman formula can be expanded by this study. Meanwhile, it can provide a new idea to study the stress distribution characteristics and better understanding of ductile materials’ deformation properties.

Inverse determination of the flow curve in large range of strains for cylindrical tensile specimen

“…pointed that such considerable errors mainly caused by the assumption that the strains distribute uniformly on the necking cross-section in the derivation of Bridgman-based methods. 18 Recently, taking geometrical configuration of necking and material properties into consideration, Chen et al. 19 has modified the original Bridgman model to improve the prediction accuracy of the flow curve after necking.…”