Modeling of the connection road surface microtexture/water depth/friction

The paper deals with the variation of tire/road friction with thin water depths and the effect of road surface microtexture. Tests are performed in laboratory on slabs made of coarse aggregates mosaics embedded in a resin matrix. Microtexture levels are simulated by sandblasting the mosaic surfaces. Aggregate profiles are measured by means of high resolution sensor. Friction is measured at water depths ranging from 0 to 1 mm. Stribeck curves are plotted from which a critical water depth is defined at the transition between boundary and mixed lubrication regimes. Modeling of a rubber slider moving over a conical asperity is performed to better understand experimental observations. Masking effect due to water is modeled simply by cutting profiles at successive heights equal to the water depths. The slider is supported partly by emerging asperities, which generate friction forces, and partly by the masking water film. Friction forces are composed of three components: adhesion, hysteresis and hydrodynamic. The model is applied to aggregate profiles; results are expressed in terms of friction coefficient/water depth plots. Comparisons to experimental measurements are made and results are discussed.