The amount of friction between tire and road is a combination of adhesion between rubber and ansphalt on the one hand and local ploughing of stones in the rubber tire due to local slip. The rolling resistance of a tire is mainly due to hysteresis losses (visco-elastic deforming tire). Modeling this friction behavior in the tire-road contact area is one of the research areas of the group Surface Technology and Tribology. As contact takes place at the surface, the material properties of rubber and asphalt need to be known at the surface layer. Due to deformation, aging and weather influences, these material properties can largely differ from the bulk material properties. The material properties of both tire and asphalt in the surface layer are therefore required to accurately model the friction and wear behavior in the contact.
The contribution of the adhesion and ploughing component on the friction can be investigated by experimental set-ups, like the pin-on disk friction tester. In this test, a stone sphere is pressed against a rotating rubber disc, or a rubber sphere is pressed against a rotating stone disc. Friction is measured for varying rotation velocities and pressures (deformation).
Next to friction modeling, research is being carried out on tire and road wear. In the Netherlands, passenger cars produce a staggering 6000 cubic meter of rubber particulate matter on an annual base. Besides, porous asphalt concrete shows high wear behavior in corners and highway exits due to elevated friction forces (acceleration, deceleration). The developed wear models are based on crack ignition and crack growth. The maximum stress will occur near the surface due to friction. Hence, cracks will initiate at the surface and grow inwards the material, which, in the end, will lead to raveling.
Rubber surface layer