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In the present paper a research programme aimed at investigating both the bending and contact fatigue properties of an austempered ductile iron applied to gears is presented, in order to determine reliable values of the limits, which take into account the influence of the production process, to be applied in the design of gearboxes. The bending fatigue tests are performed according to the single tooth fatigue approach and the pitting tests are performed with a back-to-back rig. Metallurgical analysis is performed on the failed specimens, in order to understand the origin and the propagation of the failures and to appreciate the influence of the micro-structure on the performances obtained.

In this work, experimental and theoretical analyses of the power losses in an industrial planetary speed reducer were performed in order to define the weight of the different types of power losses in the global efficiency as well as to understand the appropriateness and the effectiveness of the models and tools available in the literature for the prediction of these power losses. From this investigation, it has emerged that even if for all the kinds of power losses improvements are in principle possible, those for which, at the same time, more improvements seem possible and effective models are lacking are the load-independent power losses. For this reason, a computational fluid dynamics methodology able to evaluate load-independent gear power losses in planetary gearboxes is proposed. The other types of power losses were determined by means of analytical models available in the literature and, together with the calculated load-independent gear power losses, compared with the experimentally determined power losses showing the effectiveness of the adopted calculation models.

Large gears for wind turbine gearboxes require high performances and cost-effective manufacturing processes. Heat distortion in the heat treatment phase and the consequent large grinding stock are responsible for high manufacturing costs due to reduced productivity. A research project aimed at the identification of new materials, manufacturing and heat treatment processes has been performed. Air quenchable alloy steels, combined with a specifically developed case hardening and heat treatment process, have been identified as an interesting solution, both from the point of view of cost effectiveness, thanks to reduced distortions and grinding stock, and for the environmental sustainability. The research project has been completed by the manufacturing of a full-scale gear, on which the whole process has been validated. Nevertheless, in order to judge the applicability of these steels to large gears, data from specific tests on the performances against typical gear failure modes, like bending and contact fatigue, are necessary as well. Single tooth fatigue bending tests and disc-on-disc contact fatigue tests have therefore been performed on two innovative materials, respectively, a high hardenability steel and a bainitic structure steel, and on a reference traditional case hardening steel. The results of these tests, which provide useful data for gear designers, are presented and discussed in this paper.

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