Fatigue and fracture mechanisms in large rolling element bearings

Fatigue in rolling bearings generally results in failure by pitting (spalling). However, large bearings. most particularly those subjected to significant tensile hoop stress, sometimes fail due to more or less radial cracking, which may lead to fracture of the contacting raceways or of the rolling elements. Examples of this type of failure have been reported from a wide range of applications, suggesting that current understanding is imperfect. In the present paper, an analysis of crack initiation and propagation is presented and used to examine the conditions necessary to cause radial cracking and fracture in large bearing components, including rollers. The analysis includes the effects of hoop tensile stress and of fluid entrapment. Results of the analysis are used to demonstrate the significance of Hertz pressure, roller diameter and hoop stress, whether applied or residual. The results provide a reasonable explanation of the difference in the observed behavior bem,een small and large roller bearings. A simple map is proposed in order to predict the failure mode to be expected in roller bearings operating at mod est contact pressures.