PSI - Issue 36

V.V. Kharchenko et al. / Procedia Structural Integrity 36 (2022) 59–65 V. V. Kharchenko et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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1. Introduction One of the key components of monitoring the current state of critical equipment materials during their service life is the determination of mechanical properties, in particular, strength properties. The use of standard destructive methods, in particular, uniaxial tensile tests, requires cutting out of material sample for the manufacture of specimens. In the case of the structures of working equipment this leads to a violation of the integrity and the need for further repairs. Therefore, indirect methods are developed to determine the mechanical properties, as well as to minimize the required volume of material for the specimens. These methods include hardness measurements and the instrumented indentation method. 2. Brinell hardness measurements At the moment, there is no national normative document for determining mechanical properties from the results of hardness measurements in Ukraine. There are only industry-specific regulatory documents, in particular, these are TPKM-10-01 (2001) and SOU-N NAEK 133 (2016) based on the Russian documents such as RD EO 0027 (2005), which have been replaced with the instruction I 1.2.1.02.019.1121 (2016). Due to the harmonization of national standards with European and international standards, DSTU EN ISO 6506-1 (2019) developed using the international standard, is the only document currently regulating the hardness measurement. According to this standard, the hardness is determined using only tungsten carbide balls, while all the correlations in the documents TPKM-10-01 (2001) and SOU-N NAEK 133 (2016) are developed using steel balls. In addition, this standard imposes more stringent requirements for the verification of hardness testers, in particular, in terms of accuracy and repeatability. The repeatability is determined only by the imprint diameter. Therefore, it is impossible to verify and use in practice devices with the measurement principle different from the Brinell method. This indicates the necessity to improve the methods for determining the mechanical properties using hardness, as well as to develop the regulations for the use of portable hardness testers. The analysis of mechanical properties determination based on the Brinell hardness performed by Kravchuk (2020) shows that the main attention is focused on the improvement of the correlations. At the same time, the intrinsic accuracy of the hardness measurement is important. As can be seen from Fig. 1, the error and repeatability of hardness values using portable hardness testers are significantly worse as compared with the stationary (TSh-2) ones.

Fig. 1. Dependence of error E rel on the repeatability r rel of the results of twenty Brinell hardness measurements of the reference block with a hardness of 182 HBW.

The Ukrainian standard imposes the requirements for hardness testing instruments in compliance with DSTU EN ISO 6506-2 (2019). It is used only for stationary and portable devices of static action based on the Brinell method.