A MECHANICAL MODEL FOR THE PREDICTION OF THE TIRE/ROAD FRICTION
The viscoelastic deformation of tire rubber by road surface asperities was modeled by the rolling contact between a Kelvin solid and a surface motif, which is the part of surface profiles between two peaks. Stress and strain calculations showed that contact losses might occur locally, depending on the rolling speed, the viscoelastic properties of the Kelvin solid and the geometry of the motif. Mean vertical and horizontal forces were calculated, from which a coefficient of friction was derived. The model was successfully coupled with a profile analysis method to predict tire/road friction at low speed from road surface microtexture. The contribution of various texture scales to friction was emphasized. For the covering abstract see ITRD E118503.
A NEW THEORY OF HYSTERETIC SLIDING FRICTION
Abstract This paper supports the concept that the damping properties of rubber contribute the greater proportion of frictional resistance when rubber slides on an irregular lubricated surface. The author presents and largely validates his rigorous mathematical mechano-lattice analogy analysis for calculating the hysteretic sliding friction of, and stresses in rubber sliding on, variously shaped asperities. The analysis allows large deformations and any Poisson's ratio, rigidity or damping factor of the rubber. A method of applying the results of this analysis to the problem of predicting the coefficient of lubricated friction of rubber sliding on roadstones is shown to be reasonably accurate. An explanation of the area dependence and the load dependence of the coefficient of sliding friction in terms of hysteresis is given. The effect of the shape and smoothness of asperities and the value of Poisson's ratio of the rubber on the critical stresses in and the coefficient of friction of the rubber, as discovered by the new stress analysis, are reported. A possible source of abrasion of rubber due to heating by the fine texture is discussed.
Friction and frictional rise of wedge sliders on rubber
Abstract The friction of wedge sliders on rubber depends surprisingly little on the angle between their leading faces and the rubber surface. Friction remains moderate even when this angle is 90°. A simple theory is put forward which accounts qualitatively for the observed limitation of the frictional force and which also predicts an experimentally verified lift of the sliders. In agreement with these findings, a photoelastic investigation of the stress distribution around the sliders reveals that no ramming pressure precedes them in the rubber. The absence of a ramming pressure is attributed to a forward tilt of the rubber which originates from the couple of the frictional force with respect to the undeformed rubber underneath.