Frottement et usure

Fretting fatigue and fretting wear

¹ Département matériaux mécanique physique, Ecole centrale de Lyon
² Laboratoire de mécanique des contacts, Institut national des sciences appliquées de Lyon

Abstract

Fretting fatigue and fretting wear are encountered in all quasi-static loaded assemblies such as splines, keys, cables, conduits, lugs, bearing races and shafts, orthopaedic implants, cranes, turbine blade roots, electrical contacts, nuclear reactor components, power plant machinery, etc. These two forms of damage have been identified as two of the plagues of modern machinery as they significantly reduce the life of machine elements. In steel assemblies, they are easily identified as they are accompanied with the production of red powder or oxides, which led many designers to use anticorrosion rather than anti-wear treatments. Fretting is however not limited to steel, it is found in all contacts subjected to vibrations.

Fretting is a very difficult phenomena to study as it is difficult to reproduce and control. As such it is useful to approach fretting in terms, not so much of overall displacement or amplitude, but in terms of velocity adaptation and attempt to identify the manner in which the amplitude imposed by the experiment is taken up by the contact. Visualizations have shown that amplitude can be taken up in different ways, by the rubbing solids themselves and the interface.

Clearly, fretting fatigue and wear depend on where the velocity is adapted and the interpretation of results is almost impossible unless that information is available. This explains why fretting results and trends are so contradictory. The authors have attempted to point our a certain number of errors or misconceptions which are often presented as truths throughout the literature. These are denounced rather firmly in the hope that the readers will be jolted into re-evaluating them. The misconceptions concern :

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  two and three-body contacts,

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  wear mechanisms,

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  critical amplitudes before damage,

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  corrosion in fretting,

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  the role of deris,

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  temperature in fretting,

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  accelerated fretting tests.

They also stress implicity, the necessity of attacking this multi-disciplinary subject by multi-disciplinary teams. Both surface and volume physicists and mechanical engineers are needed to avoid the short cuts taken by the ones in the field of the others and vice-versa. The lack of cross-fertilization is certainly largely responsable for the confusion that transpires form the literature and for the misconceptions noted above.