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1

Durability assessment of railway car axles taking into account the character of the stress spectrum

Kibakov Oleksandr, Khomiak Yuriy, Jaremenko Volodymyr, Zheglova Victoria

Diagnostyka

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2024

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Vol. 25, No. 3

art. no. 2024311

EN

In many countries, railway cars with axles that have operated for over 50 years are still in use, which significantly exceeds their normative service life. This can be explained by the fact that design calculations are based on overestimated loads, as evidenced by published information on diagnostics of railway axles, which is performed under real operating conditions. In this work proposes a method for calculating the durability of axles of railway cars under real operating conditions, which is based on fatigue tests of samples made of axle material, the statistical theory of similarity of fatigue failure, analysis of the stress state and known models of fatigue curves. The calculations performed showed that, under real operating conditions, the durability of the axles exceeds N=1010 cycles, which indicates their operation in the field of gigacycle fatigue. These values N correspond to a service life of over 30 years. Recommendations are given for assessing the durability of railway axles, taking into account actual operating conditions.

2

The lifetime forecasting of machine elements by fatigue strength criterion

Khomiak Yuriy, Kibakov Oleksandr, Medvedev Stanislav, Nikolenko Ilya, Zheglova Victoria

Diagnostyka

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2021

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Vol. 22, No. 4

39--49

EN

The method for assessing the lifetime of structural elements by the criterion of fatigue strength is improved. It includes tests of laboratory material samples, the positions of the statistical theory of similarity of fatigue failure, calculation of the stress state by the finite elements method and takes into account the nature of cyclic loading with variable amplitude. A way for calculating the equivalence coefficient by the cycles μm is proposed, which takes into account the characteristics of fatigue strength and the cyclogram of the loading of the machine elements. Mathematical descriptions of integral distribution functions for typical loading modes (heavy, medium equiprobable, medium normal, light and especially light) are given and on their basis the corresponding loading cyclograms are obtained. The technique is implemented on the example of one of the main parts of an axial piston hydraulic machine (APHM) - a cylinder block (CB) made of tin bronze CuSn12. The possibilities of increasing the working pressure in the APHM by constructive and technological methods are analyzed. It is shown that in the manufacture of CВ from high-strength antifriction brass Zn28Mn3Co2, it is possible to increase the operating pressure in the APHM to 40 MPa, which for heavy duty operation will provide a CВ lifetime more than nine thousand hours.

3

Endurance limit of the axial-piston hydraulic machine cylinder block

Khomiak Yuriy, Kibakov Oleksandr, Medvedev Stanislav, Nikolenko Ilya, Zheglova Victoria

Diagnostyka

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2020

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Vol. 21, No. 1

71--79

EN

The fatigue resistance of the cylinder block (CB) of an axial-piston hydraulic machine (APHM) made of tin bronze CuSn12 has been investigated. Fatigue tests of smooth and notched standard samples were performed and fatigue curves were constructed. The stress state of the CB is investigated by the finite element method. It is established that the maximum stresses are localized on a small part of the partition between axial cylinders holes loaded by internal pressure. A method for recalculating the established length of this zone of partition with an uneven distribution of dangerous stresses by an equivalent length with a constant stress equal to the maximum is proposed. The use of the statistical theory of the similarity of the fatigue failure of Serensen-Kogayev, the results of the fatigue tests of the samples and the calculation of the equivalent length made it possible to determine the endurance limit of the CB considered. The acceptability of the proposed method estimating the endurance limit by the known results of resource tests of the CB APHM 210.25 is confirmed.