Current gear design guidelines and standards have given little or no consideration to the increase in strength that can be achieved by using ultra-clean steels. In order to fully exploit the potential of ultra-clean steels, it is therefore necessary to use higher-quality calculation methods that combine FEM stress calculations with local strength calculations. Therefore, the aim of this paper is to extend the inclusion-based model to allow for the calculation of the tooth root bending strength of gears with different steel cleanliness. For this purpose, a material analysis of 20MnCr5 with three different degrees of cleanliness is carried out and the respective material defect distribution is determined. In order to be able to represent the determined material defect distributions of the different cleanliness grades in the inclusion-based model, the model is extended accordingly, and a sensitivity analysis is carried out on the influence of the material defect distribution functions on the tooth root bending strength calculation. Finally, the model is applied to a pulsator test to verify the applicability of the model. The results of the verification show that the calculation of the mean bending strength of gears in pulsator investigations is generally possible with the extended inclusion-based model. The inclusion-based model thus offers the potential to improve the statistical significance of pulsator test results by supplementing the limited number of practical test points with the virtual test points of the inclusion-based model.

The demand for lighter and more powerful gearboxes is leading to an increase in power density. Planetary gearboxes are commonly used due to their high gear ratios with low space and weight requirements, making them suitable for various aerospace applications, including safety-critical ones. This necessitates high component safety validation requirements from aviation authorities, which typically involve both computational and experimental validation. Due to the high costs of traditional ring gear test rig investigations, this study develops an alternative method to determine the fatigue strength of spur ring gears, specifically focusing on flank bending fracture. To develop this method and understand the damage cause, the stress during operation is analysed using finite element methods, alongside analytical calculations examining how the macro-geometry influences flank bending fracture. The developed method uses a pulsator fixture to secure the spur ring gear accurately while considering the contact conditions. The robustness and repeatability of this method are assessed by simulating stress changes from manufacturing and assembly variations. Experimental tests validate the investigation method concerning the generated damage type. Results indicate that critical bending stress conditions can be achieved using the developed test method in a standard pulsator. Additionally, analytical findings suggest that the risk of bending fracture increases with higher negative addendum modification in ring gears.