Tribological Aspects of Rolling Bearing Failures

Rolling (element) bearings are referred to as anti-friction bearings due to the low friction and hence only slight energy loss they cause in service, especially compared to sliding or friction bearings.The minor wear occurring in proper operation superficially seems to suggest the question how rolling contact tribology should be of relevance to bearing failures.Satisfactorily proven throughout the 20 th century primarily on small highly loaded ball bearings, the life prediction is actually based on material fatigue theories.Nonetheless, resulting subsurface spalling is usually called fatigue wear and therefore included in the discussion below.The influence of friction on the damage of rolling bearings, at first, is strikingly reflected, for instance, in foreign particle abrasion and smearing adhesion wear under improper running or lubrication conditions.On far less affected, visually intact raceways, however, temporary frictional forces can also initiate failure for common overall friction coefficients below 0.1.Larger size roller bearings with extended line contacts operating typically at low to moderate Hertzian pressure, generally speaking, are most susceptible to this surface loading.As large roller bearings are increasingly applied in the 21 st century, e.g. in industrial gears, an attempt is made in the following to incorporate the rolling-sliding nature of the tribological contact into an extended bearing life model.By holding the established assumption that the stage of crack initiation still dominates the total lifetime, the consideration of the proposed competing normal stress hypothesis is deemed appropriate.The present chapter opens with a general introduction of the subsurface and (near-) surface failure mode of rolling bearings.Due to its particular importance to the identification of the damage mechanisms, the measuring procedure and the evaluation method of the material response analysis, which is based on an X-ray diffraction residual stress determination, are described in detail.In section 4, a metal physics model of classical subsurface rolling contact fatigue is outlined.Recent experimental findings are reported that support this mechanistic approach.The accelerating effect of absorbed hydrogen on rolling contact fatigue is also in agreement with the new model and verified by applying tools of material response analysis.It uncovers a remarkable impact of serious high-frequency electric current passage through bearings in operation, previously unnoticed in the literature.Section 5 provides an overview of state-of-the-art research on mechanical and chemical damage mechanisms by tribological www.intechopen.comTribology -Lubricants and Lubrication 34 stressing in rolling-sliding contact.The combined action of mixed friction and corrosion in the complex loading regime is demonstrated.Mechanical vibrations in bearing service, e.g. from adjacent machines, increase sliding in the contact area.Typical depth distributions of residual stress and X-ray diffraction peak width, which indicate microplastic deformation and (low-cycle) fatigue, are reproduced on a special rolling bearing test rig.The effect of vibrationally increased sliding friction on near-surface mechanical loading is described by a tribological contact model.Temperature rise and chemical lubricant aging are observed as well.Gray staining is interpreted as corrosion rolling contact fatigue.Material weakening by operational surface embrittlement is proven.Three mechanisms of tribocracking on raceways are discussed: tribochemical dissolution of nonmetallic inclusions and crack initiation by either frictional tensile stresses or shear stresses.Deep branching crack growth is driven by another variant of corrosion fatigue in rolling contact.