Reliability Analysis of the Static Bending Strength of Cylindrical Hardened Gears

The target of this study is to investigate the static bending strength of teeth in cylindrical hardened gears based on reliability analysis. The effect of hardness on the static bending strength of the tooth of the cylindrical gear was investigated in the static loading conditions. The gears were carburized with low-pressure in a 4 mbar acetylene atmosphere and cooled with gas. In order to obtain different hardness values, different cooling rates were applied using different gases and gas-pressures. For this objective, shot-peened and unshot-peened gears having different core and surface hardness values are tested on a pulsator test machine providing a quasi-static loading condition. Shot peening treatment was performed according to Atmen A and Atmen N method. Material used for gear samples is 20MnCr5 steel and samples have the same geometry. The quasi-static load for tooth fracture is monitored and measured. The bending stresses for applied load which causes fracture is calculated. Tooth-root failures starting from the surface are experimentally observed. The shot-peening treatment is found to have no positive effect on the bending strength of the tooth under static loading conditions, although the shot peening treatment is effective in improving the dynamic bending strength of the gears. The increase in the hardness value results in an increase in the static bending strength of the gears. A high static bending strength value was obtained for high-rigidity gears heat-treated in a 20 bar Helium (He) atmosphere. The hardness of the core has been shown to have no significant effect on the determination of the static bending strength of the gears since the damage occurred from the surface. The appearance of the damage surfaces for gears is typical static loading damage from the surface, depending on the maximum tensile stress of the crack. Reliability involves the damage behavior of a product and is therefore an important criterion for product assessment. Gears are the most important machine elements in many mechanical power transmission systems and therefore the reliability of the gears is very important. Reliability analysis is required to determine the possible strength values of the gears to meet the strength values foreseen in the literature. Reliability analyses of the static bending strength of the tooth in cylindrical hardened gears are conducted. The mean values, standard deviations and standard variables of the static bending strength are calculated. It is concluded that the reliability levels of the static bending strength satisfy the required