The rolling contact fatigue is distinguished into subsurface initiated (spalling and case crushing) and surface initiated (pitting and micropitting). A characteristic depth was identified for each of these mechanism. The characteristic depth of the case crushing is the hardening depth, while for the spalling it is the maximum cyclic shear stress depth. The pitting depth is the size of the crack for which the mode I stress intensity factor range, due to the fluid pressurization, is higher than the threshold. This depth can be similar to the micropitting depth, in the order of 10 µm, for heavily loaded small radius contacts. Rolling contact fatigue cyclic shear stress indexes are then defined on the basis of the characteristic depths, and they identify the load intensity of each rolling contact fatigue mechanism. The characteristic depths and the stress index approach can be used to relate specific tests to component design, without any size effect misinterpretation

The paper proposes a brief overview of the commonly adopted approaches for the experimental study of scuffing on gears for advanced applications and suggests a new methodology for the design of an experimental campaign aimed at determining the scuffing resistance of an innovative aerospace gear material.\ud \ud The present study has been carried out by AM Testing srl in collaboration with Avio Aero within the VHLGM (Validation of High Load Capacity Gear Material) project of the Clean Sky Sustainable and Green Engines framework

This paper shows the results of an experimental study\ud carried out on spur gears for aerospace applications operating\ud in loss of lubrication. The aim of this work was to establish a\ud baseline for gear behavior under oil off conditions. A total\ud amount of 40 tests were performed with gears made from 2\ud materials operating at different levels of sliding speed and\ud contact pressure. In some cases the bulk temperature was\ud measured to evaluate the heating of the running gear. A more\ud relevant wear and heating of the gears was observed with the\ud increase of the contact pressure rather than with the increase of\ud the sliding speed. In all the tests the transmission was able to\ud transfer the required power. However some tests were stopped\ud before the required time because of the overcoming of the rig\ud safety threshold. The results showed a different oil off time\ud depending on the material