Optical method to study post-necking material behaviour

Abstract

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.

Phase Transformation Crystallography in Pipeline HSLA Steel after TMCP

“…The separation of the samples for the investigation of mechanical property anisotropy was carried out along three directions: rolling direction (RD), transverse direction (TD) and at an angle of 45 • to RD. Strain at the stage of necking was measured according to the method described in [4,41].…”

Tensile Deformation and Fracture Behavior of API-5L X70 Line Pipe Steel

“…The specimen axis was parallel to RD, and the rolling plane was marked on a grip surface. Strain at the stage of necking was measured according to the method described in [32].…”

Application of the Method for Optical Measuring the Neck Profile to Determine the Hardening Curve of Aluminum from the Results of the Tensile Test

“…In [9], it is reported that the Nikon D7000 DSLR camera was used to capture images of the specimen with the neck and then to extract its geometry. For the same purposes in [10], the DSLR camera Canon 700D was used, while the video recording of the tests was carried out with a resolution of 1920×1080 pixels using the green chromakey. In the same work, using as an example the 09G2S steel specimens with different structural phase statement, it was proved that it is impossible to use various statistical models predicting the change in the neck shape, for example [11,12], but it is necessary to measure the neck when testing each specimen.…”

“…In [9,13], the material hardening curves were obtained using the Bridgman model, and in [10], using all three models mentioned above. Despite the results of the theoretical evaluation of the range of applicability of the Bridgman, Davidenkov-Spiridonova, and Ostsemin models presented in [6], the question of which model is more preferable to use requires experimental verification.…”

“…Despite the results of the theoretical evaluation of the range of applicability of the Bridgman, Davidenkov-Spiridonova, and Ostsemin models presented in [6], the question of which model is more preferable to use requires experimental verification. In this regard, the purpose of this study is to determine the hardening curve of a plastic material using the method for optical measuring the neck profile presented in [10,14] and to evaluate the accuracy of the hardening curves obtained using different stress distribution models. Pure aluminum was selected as a material for the study.…”