Analytical approach for low and high cycle bending fatigue life prediction of carburized gear steel specimens

Bending fatigue is one of the most common failure modes in spur gears. In carburized spur gears, subsurface failure initiation is characteristic for the high cycle fatigue regime, which is rather hard to detect and may cause rapid crack growth and complete failure of the tooth. Experimental testing of specimens made of the same material under comparable loading conditions is often used to gain insight into actual fatigue behavior of the component. Furthermore, in the absence of definite fatigue data of the specimens, various methods are used for estimating fatigue parameters. In this paper, analytical model for bending fatigue life prediction of carburized gear steel specimens based on strain-life approach is proposed. Multilayer method and hardness method are used for estimating strain-life fatigue properties. Rule of mixture is employed to find average cyclic stress-strain curves of carburized specimens. An approach for conversion of axial to bending fatigue data by utilizing Neuber's rule and modifying factors is suggested. Initial validation of the analytical model is carried out against experimental results from the literature of two types of specimens with different carburizing depths. Good correlation between the predicted and experimental data is observed for both types of specimens, with nearly all data points falling within the scatter factor of three.