Ice friction: the role of frictional heating and ice premelting
Dr. Bo Persson, PGI-1, Forschungszentrum Jülich
At low temperature (say below -30°C) the friction between ice and most materials is very high, unless the sliding speed is so high as to result in a very high frictional heating. In this presentation I will discuss the influence of frictional heating on ice friction focusing, in particular, on ice in contact with ice and ice in contact with rubber (e.g. tire applications). Like for many solids, the surface of ice undergoes a disordering or melting-like transition before reaching the ice bulk melting temperature. For the ice-vapour interface this premelting starts ∼ -20°C below the ice bulk melting temperaure, and results in softening of the ice surface. If premelting occurs also when ice is in contact with another solid (which depends on the nature of the other solid), it will result in a friction coefficient which drops continuously as the ice surface temperature approaches the ice bulk melting temperature. As the sliding speed increases the frictional heating increases too, but not as fast as intuitively expected because of the drop of the friction with increasing sliding speed. The influence of ice premelting will be illustrated with ice in contact with ice. Rubber friction on ice is a special case which requires a special treatment. Most ice surfaces have roughness on many length scales. Rubber is a viscoelastic material with internal damping. When rubber is sliding on ice, the ice asperities exert pulsating deformations of the rubber surface which result in energy dissipation in the bulk of the rubber, which gives the dominant contribution to rubber friction on ice at high enough sliding speeds. I will present results of rubber friction on ice for summer and winter tires illustrating this effect of the internal damping on the friction force.