Deep Contact Endurance Limit of Surface-Hardened Gears

Abstract

The reliability and durability of gears in most cases depend on the contact endurance of the material of the parts. Analysis of the stress state of surface-hardened gears has shown that under contact loading, the source of primary damage can be located both on the surface and in the depth of the hardened layer. The greatest danger is deep destruction. To prevent deep pitting, it is necessary to ensure a sufficient amount of the maximum allowable stresses in the depth of the layer, exceeding the effective equivalent stresses. The value of the allowable stresses is determined by the value of the contact endurance limit, depending on the mechanical properties of the material. The article discusses the results of experimental studies of the contact fatigue resistance of transmission gears of energy-saturated mobile machines made of cemented steel grades. It is established that the limit of contact endurance is related to the hardness of the material, determined by the Rockwell method, by a linear dependence. This dependence is taken as a basis for a comparative analysis of the calculated lifetime and experimentally established in the process of bench tests of gears. Taking into account the nonlinear nature of the ratio of hardness values determined by the Rockwell and Vickers scales, the relationship is obtained between the limit of deep contact endurance and the value of hardness measured by the Vickers scale with a load of 1.961 N. It is shown that the results of comparison of calculated and experimental data are greatly influenced by the limiting state of the deep contact pitting of the teeth of the tested gears. Statistical processing of calculated and experimental data was carried out. It is found that with the identity of the limiting state of the active surfaces of the gear teeth, the results of the lifetime calculation correspond to experimental data with a correlation coefficient of 0.964 and an average standard deviation of 13 %. The obtained expression for calculating the limit of deep contact endurance contributes to increasing the reliability of calculating the lifetime of gears provided by the resistance of deep contact fatigue.

Keywords

• gears
• bench tests
• contact deep pitting
• contact fatigue resistance
• lifetime calculation
• deep contact endurance limit