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Due to their cost-effectiveness, pulsator tests are widely adopted as a testing methodology for the investigation of the effects of material and heat and surface treatment on the gear strength with respect to tooth root fatigue fracture. However, since no meshing contact is present in pulsator tests, there are differences between the test case and the real-world application scenario where gears are rotating under load. Those differences are related to both statistical and fatigue phenomena. Over the years, several methodologies have been developed in order to handle this problem. This article summarizes them and proposes a first comparison. However, no complete comparison between the different estimation methodologies has been conducted so far. This article aims to partially cover this gap, first by presenting and comparing the methodologies proposed in the literature and then via a deeper comparison between two different elaboration methodologies. Those two methodologies, which have been developed by examined to the same test rig configuration, are also discussed in detail. The comparison is performed based on an actual database composed of 1643 data points from case-hardened gears, divided into 76 experimental campaigns. Good agreement between the estimated gear strengths was found. The database is also adopted in order to make further considerations about one methodology, providing additional validation and defining the specimen numerosity required. [ABSTRACT FROM AUTHOR]

Nitriding can significantly increase the load carrying properties of gears. While the diffusion layer is primarily responsible for improving the tooth root and flank load carrying capacity, the compound layer mainly determines the tribological properties of the gear surface. In the present work, the influence of the compound layer on the tribological load carrying capacity of nitrided gears in the N/N pairing was investigated. For this purpose, compound layers with different thickness, porosity and phase composition were produced and their micro-pitting and wear behavior were investigated in load stage and speed stage tests. The test results confirm that the properties of the compound layer are decisive for the micro-pitting and wear resistance of nitrided gears. For a high micro-pitting resistance, the presence of pores in the near-surface area of the compound layer is of high importance, since no micro-pitting occurred as long as pores were present. With regard to the wear behavior, no dependence on the compound layer thickness or the porous zone thickness was found while the phase composition of the compound layer shows a decisive influence. [ABSTRACT FROM AUTHOR]