Optical method to study post-necking material behaviour

The article is devoted to the determination of equivalent stresses and strains in the minimum cross-section of the neck during tensile testing of cylindrical specimens. To correct the average tensile stresses, the Bridgman theory is used, based on the experimental measurement of the neck. The paper proposes an approach for calculating the radius of curvature of the neck based on the approximation equation that describes the entire profile of specimen. Its accuracy was estimated using the finite element method. A program has been developed that provides the measure of the diameter of specimen in the minimum cross-section of the neck and the calculation of the radius of its curvature from the video recording of the test process based on the proposed equation. Using this program, hardening curves for 09G2S steel were constructed at engineering, true and equivalent stresses.