The load spectrum is a crucial factor for assessing the fatigue reliability of in-service rolling element bearings in transmission systems. For a bearing in a high-speed train gearbox, a measurement technique based on strain detection of bearing outer ring was used to instrument the bearing and determine the time histories of the distributed load in the bearing under different gear meshing conditions. Accordingly, the load spectrum of the total radial load carried by the bearing was compiled. The mean value and class interval of the obtained load spectrum were found to vary non-monotonously with the speed and torque of gear meshing, which was considered to be caused by the vibration of the shaft and the bearing cage. As the realistic service load input of bearing life assessment, the measured load spectrum under different gear meshing conditions can be used to predict gearbox bearing life realistically based on the damage-equivalent principle and actual operating conditions.
High‐strength steels are widely used in high‐performance bearings utilized in most mechanical systems. However, there has been little statistical analysis regarding the fatigue failure behaviour of the material, where surface peeling resulted from contact fatigue during rolling is a significant life‐limiting mechanism. In this study, we examine the statistical behaviour of surface‐crack nucleation, propagation, and peeling in a high‐speed train axle bearing made of GCr15 steel by using a laboratory rolling‐contact equipment. We reveal that cyclic rolling‐contact leads to the formation of a hardness gradient in the outer ring of the bearing. The gradient layer is of several millimetres. The peeling rate could be as high as 28 μm per million cycles when the contact pressure is close to that applied in real service. Peeling‐induced cracking is dominantly transgranular. The incipient angle is about 23.2°, and its depth could be hundreds of micrometres. The findings reported here could be employed to assess the lifetime of bearings made of GCr15 steel and possible other engineering metals.
The differences in the roller diameters within a roller bearing is unavoidable in practice, which is known as the off-sized effect. The off-sized effect results in the dynamic variation of the load distribution in bearings and further the abnormal vibration and premature failure of bearings. This paper experimentally investigates the effect of off-sized rollers on the dynamic load distribution in a cylindrical roller bearing. Different configurations of off-sized rollers are given considering the oversized and undersized roller conditions, and the number and position of off-sized rollers. The real-time roller-raceway contact loads distributed in the bearing are measured under these test cases. The results show that a single off-sized roller leads to the loading change directly on itself and further the load rebalances among the adjacent rollers. Under the conditions of multiple off-sized rollers, a stack effect of the competition rule of roller loading dominates the variation range of the dynamic load distribution. As results of the stack effect, among all roller configurations, the configuration of multiple off-sized rollers adjacent to each other leads to the minimum range of the dynamic load distribution, while the configuration of two off-sized rollers separated by a regular roller leads to the maximum one.
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