Abstract
The concept of partial elastohydrodynamic (EHD) Hertzian contacts is defined between solids with real (rough) surfaces, using the film thickness/r.m.s. roughness ratio h/ σ as parameter. The influence of the partial EHD condition is described on EHD film thickness, normal load sharing between asperities and EHD film, frictional traction, mild and severe wear, surface fatigue and spalling fatigue. Kinematic effects of the traction vs. sliding rate relationship characteristic of partial EHD are identified in rolling bearings. Rough surfaces are treated as two-dimensional random processes, using height, slope, curvature and level-crossing statistics derived, for Gaussian height distributions, with the aid of statistics of the height and its first two derivatives. Scanning electron microscope observations of surfaces are used to visualize asperity geometry, lay and defect population. Normal load and traction force sharing between EHD film and asperities is analyzed for plastic and elastic asperities. Indentation hardness and h/ σ are parameters of plastic load sharing. Elastic load sharing depends on elastic modulus, h/ σ, and asperity slope and may depend weakly on the spectral distribution of asperity amplitudes. Traction force sharing depends on similar parameters and on the EHD traction/ sliding rate function. Stresses in elastic asperities and the size of asperity contact areas are expressed in terms of roughness height, its derivatives and h/ σ. Roughness parameters influencing wear, smearing (galling), and surface fatigue are identified from the asperity contact stresses obtained.
Published Version
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