PEER REVIEW
20
th
Australian International Aerospace Congress, 27-28 November 2023, Melbourne
ISBN number: 978-1-925627-66-4
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Normal Paper
Student Paper
Young Engineer Paper
Meaningful Prognostics of Degraded Rolling Element
Bearings
Andrew J. Becker
1
1
Prognostics & Health Management Group, Platforms Division, Defence Science and Technology, 506 Lorimer Street, Fishermans Bend,
Victoria, 3001, Australia
Abstract
While rolling element bearing life is considered to have expired at the first visible sign of rolling
contact fatigue, many hours of potentially useful service remain before the bearing approaches
functional failure. Estimating the remaining life after spall initiation (i.e. providing a prognosis)
has not received significant attention in the literature. However, the invention of the inductive
wear debris sensor (IWDS) not only improved the detection of deteriorating rolling element
bearings and gears but can also enable genuine prognostics. The ability to observe in real time
the liberated debris in lubrication systems via an IWDS has been a significant leap forward
compared to traditional oil analysis techniques. To achieve a meaningful prognosis the IWDS
must have metrics for reliably estimating the rolling contact fatigue spall size and the point at
which true rolling contact fatigue commences. Additionally, for variable load machines the
average rate of debris generation must be monitored as it will vary with load and alter the
predicted end of life. This paper describes a method of applying meaningful prognostics to
bearings within a machine installed with an IWDS.
Keywords: bearings, monitoring, prognostics, inductive sensor.
Introduction
Rolling element bearings are inherently limited by rolling contact fatigue (RCF) due to the
cyclical nature of loading and highly localised contact stresses between rolling element and
raceway. RCF can also be initiated prematurely by surface or sub-surface stress raisers such
as hard particle indentations or non-metallic inclusions. Typically, for high quality bearings it
is surface-initiated RCF that is responsible for reducing service life bearings since sub-surface
non-metallic inclusions are rare in precision bearings. Surface stress raisers can result from
causes such as:
1. Hard particle over-run (indentation),
2. True brinelling,
3. False brinelling,
4. Adhesive wear from incorrect lubrication, or
5. Electric discharge damage (EDD) of the running surfaces.
