Experimental Determination of the Optimal Hardness Testing Method Depending on the Material’s Physical and Mechanical Properties

Abstract

The results of experimental studies on the optimal method of testing materials for hardness depending on physical and mechanical properties are presented. The possibility of evaluating the structural parameters, i.e., the homogeneity coefficients and the variation of the reliability of various devices for obtaining the hardness values of rolled metal products, is considered. The results obtained experimentally have shown the effectiveness of such evaluations. The reliability of the methods for testing the hardness of materials of different plasticities was controlled by determining the degree of dispersion of the obtained results by the LM-hardness method. The influence of the material’s physical and mechanical characteristics on the hardness test’s accuracy is analyzed. The possibility of choosing the most reliable Brinell, Vickers, or Rockwell method for determining hardness characteristics depending on the level of plastic properties of the sheet material was determined. Following Fisher’s theory of small samples in terms of the general population, a statistical assessment of the reliability of measurement methods was performed on a sample of a limited size, which makes it possible to assess the reliability of the results of hardness determination by various methods and determine the optimal variant of testing materials, including high-strength ones, for hardness. According to the methodology for analyzing variance to select the optimal variant for conducting studies of material hardness, the statistical assessment of the reliability of hardness measurements was carried out using a random sample from the general population in its central part in the number of five measurements following each other. The variance check is applied using the Cochrane criterion to determine the uncertain members of the variation series. Based on the research results, the predominant expediency of one or another Brinell, Vickers, or Rockwell method of conducting hardness tests depending on the level of plasticity of materials, especially high-strength ones, given their structural state as assessed by the parameters of hardness characteristics scattering – homogeneity coefficients m and variation v. The availability of this information will make it possible to determine the mechanical characteristics of materials by hardness values more reliably.