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Five automotive oils, with different viscosity grades, were tested under different loads and speeds in a reciprocating test using piston rings and cylinder liners. Starved and fully-flooded conditions were also considered in order to analyze the influence of lubricant supplier in the lubrication regimes, especially in boundary-mixed transition. The expected Stribeck curve behavior was observed, and more interesting visualization appeared when the viscosity value was extracted from the Stribeck abscissa axis. The higher viscosity oils showed lower friction coefficient at low speed/load ratios. Such behavior is usually neglected and may be significant to understand the triblogical behaviour of engineering components. Computer simulation showed similar results, including the “cross-over” speed/load when the lower viscosity oils start to show lower friction.

Numerical characterization of surfaces with deep dimples, e.g. Laser Textured Surfaces, poses questions relative to the standard filtering techniques used to separate roughness, waviness and form effects. Usual roughness filters would produce a reference plane several micrometers “below” the surface. If this surface plane will be used as reference for mixed lubrication modeling, no hydro dynamic pressures and excessive high contact pressures may be calculated. The conventional roughness filters, Gaussian and Rk, and 4 other filters were applied in an artificially dimpled surface in order to demonstrate and especially to discuss how the Greenwood contact parameters were affected. Depending on the filter used, the estimation of the minimum surface separation for asperity contact varied two magnitude orders.