The kinetic friction of polyethylen on snow, comparison between laboratory and field measurements

Experiments were done in the freezing chamber with polyethylen specimens sliding on ice using a tribometer. The coefficient of friction was measured as a function of the surrounding temperature (varyied between -25 degrees C and 0 degrees C) and the pressure on the slider (varyied between 50 MPa and 300 Mpa). The coefficient of friction is strongly depending on the temperature of the ice surface. It is on its minimum around -3 degrees C. In the temperature range between -3 degrees C and 0 degrees C the coefficient of friction is increasing with increasing temperature. In the temperature range between -3 degrees C and -25 degrees C the coefficient of friction is increasing with decreasing temperature. In the low temperature range the coefficient of friction is depending on the pressure on the slider. The higher the pressure, the lower is the coefficient of friction. The influence of the pressure is decreasing for an increasing temperature and above -6 degrees C there is no difference visible between different loads anymore. The temperature of the ice surface is higher than the surrounding temperature. Especially for low temperatures the temperature of the ice surface is significantly increased by frictional heating. The results correspond well to the idea of three different components forming the overall kinetic friction. At low temperatures dry friction dominates, whereas with increasing temperature a more lubricated friction decreases the coefficient of friction and for even higher temperatures capillary drag effects increase the friction again. The results are confirmed by extended field measurements of gliding with skis on snow under racing conditions.