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Non‐destructive subsurface damage monitoring in bearings failure mode using fractal dimension analysis

Walter Holweger (Central Materials, Schaeffler Technologies GmbH & Co. KG, Herzogenaurach, Germany)
Frank Walther (Materials Test Engineering (WPT), TU Dortmund University, Dortmund, Germany)
Jörg Loos (Tribology/Fundamentals, Schaeffler Technologies GmbH & Co. KG, Herzogenaurach, Germany)
Marcus Wolf (Tribology/Fundamentals, Schaeffler Technologies GmbH & Co. KG, Herzogenaurach, Germany)
Jürgen Schreiber (Institute for Non‐destructive Testing, Fraunhofer‐Institut, Dresden, Germany)
Werner Dreher (Naturwissenschaftliches und Medizinisches Institut, Universität Tübingen, Reutlingen, Germany)
Norbert Kern (Naturwissenschaftliches und Medizinisches Institut, Universität Tübingen, Reutlingen, Germany)
Steffen Lutz (Naturwissenschaftliches und Medizinisches Institut, Universität Tübingen, Reutlingen, Germany)

Industrial Lubrication and Tribology

ISSN: 0036-8792

Article publication date: 20 April 2012

Abstract

Purpose

Bearings in field applications with high dynamic loading, e.g. wind energy plants, suffer from sudden failure initiated by subsurface material transformation, known as white etching cracks in a typical scale of μm, preferably around the maximum Hertzian stress zone. Despite many investigations in this field no precise knowledge about the root cause of those failures is available, due to the fact that failure under real service conditions of wind energy plants differs from what is known from test rig results in terms of contact loading, lubrication or dynamics. The purpose of this paper is to apply Barkhausen noise measurement to a full bearing test ring running under conditions of elastohydrodynamic lubrication (EHL) with high radial preload.

Design/methodology/approach

Full bearing tests are carried out by use of DGBB (Deep Grove Ball Bearings) with 6206 specification, material set constant as 100Cr6, martensitic hardening, 10‐12 percent maximum retained austenite and radial preload of 3500 MPa. Speed is set 9000 rpm, temperature is self setting at 80°C by test conditions. For tests, synthetic hydrocarbon base oil (Poly‐α‐Olefine) with a 1 percent amount of molydenum‐dithiophosphate (organic chain given as 2‐ethylhexyl) was used.

Findings

Non‐destructive fractal dimension analyses by use of Barkhausen noise measurements is of versatile value in terms of recording bearing manufacturing processes, but can also be part of non‐destructive condition monitoring of bearings in field applications, where predictive reactive maintenance is crucial for availability of the plant.

Research limitations/implications

Barkhausen noise signal recording may also be valuable for case studies related to microstructure changes of steel under operation conditions. Bearings are exposed in plenty of conditions to phenomena such as straying currents, subsequently straying magnetic fields. Hardly anything is known about how microstructure of bearing steel is susceptible to such conditions. This will be part of further studies.

Originality/value

Results given in the paper show that sudden bearing failure, according to formation of subsurface material property changes might be driven by activities of dislocations. Since those activities start with sequences of stress field‐induced formation of domains, later by formation of low‐angle subgrains, and at least phase transformation, recording of the Barkhausen signal would lead to real predictive condition monitoring in applications where a highly dynamic loading of the contact, even with low nominal contact pressure leads to sudden failure induced by white etching.

Keywords

Citation

Holweger, W., Walther, F., Loos, J., Wolf, M., Schreiber, J., Dreher, W., Kern, N. and Lutz, S. (2012), "Non‐destructive subsurface damage monitoring in bearings failure mode using fractal dimension analysis", Industrial Lubrication and Tribology, Vol. 64 No. 3, pp. 132-137. https://doi.org/10.1108/00368791211218650

Publisher

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Emerald Group Publishing Limited

Copyright © 2012, Emerald Group Publishing Limited