In this paper, researches on wear and contact fatigue in rolling contact from a tribological viewpoint are introduced. The detailed mechanisms of wear are put aside, and a quantitative theory of wear at rolling contact is first introduced. Then a theory of contact fatigue accompanied by certain plastic flow is described featuring the effect of tangential traction. Three major modes of wear due to different mechanisms are known, i.e. abrasive wear, corrosive wear and adhesive wear. The advantage to the analysis of contact fatigue is that the contact geometry is macroscopically well defined, mostly Hertzian, and the process generally terminates in the removal of fragments. In a wear process, on the other hand, the removal is accompanied with microscopic geometrical changes in the surfaces, so that a feedback loop is provided as shown. Thereafter, the real contact points are formed at the asperities of the modified microirregularities, which makes the phenomena much more complicated. The life due to rolling contact fatigue has been studied with different machine elements like rolling-contact bearings, gears, cams etc. and different names like flaking, pitting or spalling have been given to the fatigue damage on their contact surfaces. Typically with involute gears, difference in the contact fatigue life between the driver and the folIower region was empirically known, i.e. the life is much shorter with the follower. In meshing of involute gears, only the points on their pitch circle make pure rolling contact. With the distance from it, slip of opposite sign increases in addendum and dedendum, and the addendum becomes the driver and the dedendum becomes the follower in the exact terminology given above. Then, contact fatigue or pitting first appeared always on the dedendum. A classic explanation was given by War. It was postulated that cracks which led to eventual detachment of flakes started at the contact surface, not in the subsurface layer, and the role of hydrostatic pressure in their growth was noted. It may be interesting to note that wear is heavier on the driver surfaces while fatigue life is shorter with the follower surfaces. It is reasoned, that damage is concentrated in thin subsurface layer with the driver while rather thick layer is damaged in the follower. This might serve to a unified understanding of the two major modes of tribological failure in the wheel/rail systems.
Wear and fatigue in rolling contact
Verschleiß und Materialermüdung beim Rollkontakt
2002
8 Seiten, 14 Bilder, 9 Quellen
Aufsatz (Konferenz)
Englisch
Wear and fatigue in rolling contact
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