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High-speed main shaft ball bearings applied in new aircraft propulsion systems experience the most critical operating conditions ever in rolling bearing history. Rotational speeds, loads, temperatures, and demands on reliability have increased continuously over the last few years. The frequency of classical subsurface material fatigue in high-speed ball bearings is low due to designs with Hertzian stresses far below the fatigue stress limit. Corresponding to increasing speeds and temperatures, surface initiated fatigue became the most important failure mode of high-speed ball bearings. This article shows an approach to describe the phenomenon of micro-spalling in high-speed ball bearings supporting jet engine main shafts by using a thermal, Newtonian, fully flooded elastohydrodynamic model. The basic failure mode, kinematics, loads, and the results obtained within the contact zones of the ball bearing for various operating conditions are presented.

Operating conditions in high speed mainshaft ball bearings applied in new aircraft propulsion systems require enhanced bearing designs and materials. Rotational speeds, loads, demands on higher thrust capability, and reliability have increased continuously over the last years. A consequence of these increasing operating conditions are increased bearing temperatures. A state of the art jet engine high speed ball bearing has been modified with an oil channel in the outer diameter of the bearing. This oil channel provides direct cooling of the outer ring. Rig testing under typical flight conditions has been performed to investigate the cooling efficiency of the outer ring oil channel. In this paper, the experimental results including bearing temperature distribution, power dissipation, and bearing oil pumping and the impact on oil mass and parasitic power loss reduction are presented.

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