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Failure modes of silicon nitride rolling elements with ring crack defects.

Wang, Y., 2001. Failure modes of silicon nitride rolling elements with ring crack defects. Doctoral Thesis (Doctoral). Bournemouth University.

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High quality silicon nitride ceramics have shown some advantages for rolling element bearing applications. In particular hybrid bearings (silicon nitride rolling elements and steel races) have the ability to withstand high loads, severe environments and high speeds. However, the difficulties of both sintering and machining the material may result in surfacedefects,such as surface ring cracks. It is difficult to detect surface ring cracks during high volume production processes and hence it is crucially important to understand their influence and the fundamental mechanism of the failures they cause. The purpose of this study is to examine the contact fatigue failure modes of silicon nitride rolling elements with surface ring crack defects. In this study, new experimental and computational techniques are developed to measure and model the interaction of the surface with pre-existing crack defects. A rolling contact fatigue test method is devised for positioning the ring crack in the contact path. Rolling contact fatigue tests are conducted using a modified four-ball machine in a hybrid ceramic/steel combination. A three-dimensional boundary element model is used to determine the stress intensity factors and to carry out the crack face contact analysis. Research shows that the RCF life performance of silicon nitride bearing elements is dependent upon the crack location and fatigue spall happens only at a few crack orientations. The spalling fatigue failure is not only influenced by the original ring crack propagation but also strongly influenced by the subsequent crack face contact. Secondary surface cracks play an important role in the forination of a fatigue spall. The crack gap and crack face friction coefficients significantly affect the formation of secondary surface cracks. Numerical calculation results are consistent with the experimental observations. A quantitative three-dimensional boundary element model has been developed, which can be used to determine the geometry of acceptable surfacering cracks.

Item Type:Thesis (Doctoral)
Additional Information:A thesis submitted in partial fulfilment of the requirements of Bournemouth University for the degree of Doctor of Philosophy. If you feel this work infringes your copyright please contact the BURO manager.
Group:Faculty of Science & Technology
ID Code:427
Deposited On:08 Nov 2006
Last Modified:09 Aug 2022 16:02


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