Strength of silicon nitride bearing balls with respect to Hertzian contact and tensile loading

Description

Hybrid bearings are essential components for electro-mechanical systems requiring insulation. Silicon nitride is favored for this application due to its superior properties. However, premature failure of ceramic bearing balls often occurs due to crack initiation and propagation under contact stresses. Therefore, it is mandatory to assess relevant mechanical strength properties.
In general, the tensile strength of ceramic parts depend on the testing method, governed by the effective volume subjected to stress. Following the Weibull approach, the effective volume is essential to correlate different strength tests.
A Hertzian contact test, simulating bearing ball interactions, is thus a relevant method for characterizing bearing ball strength, by defining the contact stress at crack initiation as Hertzian contact strength. But as observed in experiments, the Weibullian strength scaling does not represent this critical stress. This means it cannot be directly obtained from conventional strength tests, such as the notched ball test, even when accounting for the effective volume.
This study experimentally investigates the load at initial crack formation under a Hertzian contact. For this, a ball-on-ball setup is realized to avoid friction. The notched ball test is used to determine the tensile strength and defect size distribution of the bearing balls. Based on these results, different approaches are used to correlate the tensile strength to Hertzian contact strength.

Period	2 Sept 2025
Event title	XIXth Conference of the European Ceramic Society
Event type	Conference
Location	Dresden, GermanyShow on map
Degree of Recognition	International