Friction Impact on the Accuracy of the Dependence of Micro-Hardness on Plastic Deformation in Testing Metals under Uniaxial Compression

Abstract

Two sets of cylinder specimens with a height to diameter ratio of 1.5 made of annealed technical copper and AK12pch silumin were tested for uniaxial compression to different degrees of plastic deformation. At the first stage of the experiments, the ends of the specimen were ground on skins of different grain sizes and polished. Then the micro-hardness of the ends of each sample was measured. Micro-hardness measurements were carried out by the Vickers method at three loads on the indenter: 0.196, 0.490, and 0.980 N. At the second stage, the samples were cut along the meridional section, each sample was poured with a compound based on epoxy resin into an individual mold so that the meridional section of the cut sample came out onto the surface of the mold. After the process of grinding and polishing the meridional section, the micro-hardness of the center of the section was measured under the same loads that were used for measurements at the ends. At the third stage, the dependences of the micro-hardness on the intensity of plastic deformation were made. A comparative analysis of the indicated dependences, made from the results of measurements at the ends of the specimen and the surface of their meridional sections, showed that friction at the ends of the specimen during compression has a significant effect on the position of the dependence “micro-hardness - plastic deformation”. The evaluation of hardening based on the micro-hardness of the ends leads to significant errors.