SYMPOSIA PAPER Published: 01 January 1998

A New Type of Flaking Failure in Bearings for Electrical Instruments of Automotive Engines


The higher transmission efficiency of engine accessory drive belts has resulted in a new type of bearing damage, called “brittle flaking”. The type of grease used in the bearing was found to have a significant effect on the occurrence of brittle flaking. Thus, brittle flaking can be avoided by using specific greases. The amount of hydrogen measured in the inner rings, outer rings and balls of bearings run under acceleration-deceleration tests, was highest in the stationary ring, where brittle flaking was likely to occur. Brittle flaking was reproduced in rolling contact fatigue tests when the test specimens were charged with a sufficient amount of hydrogen prior to testing. The test results concluded that brittle flaking is caused by the diffusion of hydrogen into the steel due to the decomposition of the grease by a tribochemical reaction.

Author Information

Tamada, K
NTN Corporation, Kuwana, Japan
Tanaka, H
NTN Corporation, Kuwana, Japan
Tsushima, N
NTN Corporation, Kuwana, Japan
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Developed by Committee: A01
Pages: 167–185
DOI: 10.1520/STP12127S
ISBN-EB: 978-0-8031-5381-3
ISBN-13: 978-0-8031-2421-9