%0 Journal Article
%T High-Speed Ice Friction Experiments under Lab Conditions: On the Influence of Speed and Normal Force
%A Matthias Scherge
%A Roman B£¿ttcher
%A Mike Richter
%A Udo Gurgel
%J ISRN Tribology
%D 2013
%R 10.5402/2013/703202
%X Using a high-speed tribometer, coefficients of friction for bobsled runners were measured over a wide range of loads and speeds. Between 2.8£¿m/s and 28£¿m/s (equal to 10£¿km/h and 100£¿km/h), the measured coefficients of friction showed a linear decrease with increasing speed. The experiments revealed ultra-low friction coefficients of less than 0.01 after exceeding a sliding speed of about 20£¿m/s. At maximum speed of 28£¿m/s, the average coefficient of friction was 0.007. The experiments help to bridge the gap between numerous low-speed friction tests by other groups and tests performed with bobsleds on real tracks. It was shown that the friction data obtained by other groups and our measurements can be approximated by a single master curve. This curve exhibits the largest decrease in friction up to a sliding speed of about 3£¿m/s. The further increase in speed generates only a small decrease in friction. In addition, friction decreases with increasing load. The decrease stops when ice wear becomes effective. The load point of constant friction depends on the cross-sectional radius of the runner. The larger the radius is, the higher the load is, before the ice shows signs of fracture. It turned out that besides aerodynamic drag (not considered in this work), ice friction is one of the main speed-limiting factors. In terms of runner geometry, a flat contact of runner and ice ensures the lowest friction. The rocker radius of the runner is of greater importance for a low coefficient of friction than the cross-sectional radius. 1. Introduction The precise knowledge of the coefficient of friction is of crucial interest for people designing bobsled tracks, organizers, and technicians. The faster the sleds can travel on the run, the more thrilling the race. But the track must not be too fast: the crew still needs to be able to reach the bottom safely. So engineers have to calculate and simulate exactly how fast a sled can travel on specific sections of the track. The calculations are mainly based on the coefficient of friction between the runners and the ice. The second great impact on speed is aerodynamic drag, which was not investigated here. Generally, the number of experiments in the past dealing with friction measurements for the system steel versus ice is limited [1, 2]. Most of the data were obtained with tribometers (e.g., [3, 4]) or special devices (e.g., [1, 5]). In the following section, results closest to the system runner/ice will be reviewed. We concentrate on a temperature range between £¿2¡ãC and £¿12¡ãC. Evans et al. determined low-friction
%U http://www.hindawi.com/journals/isrn.tribology/2013/703202/