International audienceThe mechanism of surface rolling contact fatigue (SRCF) in rolling bearings is investigated by means of dedicated experiments and numerical simulations of the damage progression. Pre-indented inner ring raceways in roller and ball bearings were extensively endurance tested. It is observed that spalls originated from indentations in ball bearings develop initially at the trailing edge of a pre-indented raceway with a typical V-shaped spall. In this location, the raceway material first detaches at the edge of the dent, forming a V-shaped damaged area, before growing at fast rate along the raceway. Roller bearings, however, follow the well-known behavior of slowly growing the spall directly across the raceway, before continuing along the rolling path. An existing physically based rolling contact fatigue model able to predict (1) material particle detachment by surface rolling contact fatigue and (2) the effect of the elastohydrodynamic lubrication (EHL) in such a process is adapted and used to simulate the surface damage growth in the two rolling bearing configurations. It is found that the model is able to describe well the experimental results, shedding some light on the developing mechanism of the two SRCF configurations. The difference between ball and roller bearing damage inception and progression is explained and discussed in detail
International audienceUntil now the estimation of rolling bearing life has been based on engineering models that consider an equivalent stress, originated beneath the contact surface, that is applied to the stressed volume of the rolling contact. Through the years, fatigue surface–originated failures, resulting from reduced lubrication or contamination, have been incorporated into the estimation of the bearing life by applying a penalty to the overall equivalent stress of the rolling contact. Due to this simplification, the accounting of some specific failure modes originated directly at the surface of the rolling contact can be challenging. In the present article, this issue is addressed by developing a general approach for rolling contact life in which the surface-originated damage is explicitly formulated into the basic fatigue equations of the rolling contact. This is achieved by introducing a function to describe surface-originated failures and coupling it with the traditional subsurface-originated fatigue risk of the rolling contact. The article presents the fundamental theory of the new model and its general behavior. The ability of the present general method to provide an account for the surface–subsurface competing fatigue mechanisms taking place in rolling bearings is discussed with reference to endurance testing data
The lubricant film developed in rotary lip seals is a vital element in achieving long-lasting seals with low friction. In this paper the basic principles controlling the development of a lubricant film in lip seals are studied using a micro-hydrodynamic model. This model takes into account the visco-elastic effects of the rubber on the development of the sealing pressure. Central to the model’s hypothesis is the assumption of the predominant action of the surface micro-geometry in the formation of the lubricant film. Optical observations of the contact area of a lip seal, using blue light induced fluorescence, supported this concept. Using this basic lubrication model, the minimum and average film thickness and shear stress are calculated for different loading conditions, material stiffnesses and statistical parameters characterizing the micro-geometry of the sealing surfaces. In the model the effect of the viscoelastic properties of the rubber on the dynamic response of the seal and resulting pressure is also considered. To support the predictions of the theory, a new experimental method for the determination of the film thickness in elastomeric contacts is applied. Comparison between experimental and theoretical results indicates the ability of the model to deal with effects previously excluded from the analysis. The correlation between measured film thicknesses and thicknesses predicted using the present model was found to be good for the full range of speeds tested.
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