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.
PREDICTION OF TIRE-ROAD FRICTION FROM TEXTURE MEASUREMENTS
A purely theoretical means for predicting tire-road friction has been the subject of research for the past two decades. It is based on a faithful simulation of a pneumatic tire sliding over the wet texture of the road surface. This involved the stress-gross strain analysis of the tread rubber, the effect of shear rate, heat, and lubrication. A device called the Yandell-Mee texture friction meter is described and is the end product of this research. When placed on a road surface, it samples a total texture profile 60 cm long to an accuracy of 0.05 mm and predicts side force and locked-wheel wet friction for three speeds in seconds. Because the result varies only with texture changes, this is an excellent control tool for pavement engineers.
Theory of Rolling Friction for Spheres
A theory of rolling friction featuring the importance of elastic hysteresis losses is presented. A simple model of retarded elasticity is chosen to represent the physical properties of the material. A prediction resulting from the theory is that the coefficient of friction for a relatively hard sphere rolling on a softer base material should vary with speed so as to go through a maximum. This relationship resembles closely the variation of mechanical loss with frequency.The results are not restricted to rolling but also apply to well‐lubricated sliding where shearing forces have been minimized. Although the theory is developed for a material with idealized physical properties, it nevertheless affords a basis for comparing real materials and for predicting their frictional properties in cases where deformation losses are predominant.