Modern bobsleigh tracks as the one at Pyeongchangs Alpensia Sliding Centre allow velocities up to 140 km/h. The main concern of track designers is to provide the spectators with a thrilling race and the athletes with a safe track. It is therefore extremely important for track designers to possess highly-reliable friction data as input to their track simulation programs [1
]. The measurement of steel–ice friction directly inside a track is an almost impossible undertaking, due to strong vibrations generated by the contact of runner and ice. The number of experiments in the past dealing with friction measurements for the system steel versus ice, especially for high sliding velocities is limited [2
]. Most of the data were obtained with tribometers (e.g., [4
]) or special devices (e.g., [2
]). Friction of steel on ice is dominated by the formation of a melt water film due to frictional heating. The basic mechanisms are well described in [7
]. Therefore, the main influencing parameters are temperature, speed and normal force as well as the thermal contact situation, defined by contact area, roughness and thermal conductivity. Marmo et al. measured steel–ice friction as a function of ice temperature at low velocities and received coefficients of friction between 0.15 and 0.06 with increasing temperature [8
]. Normal force was varied by Ovaska and Tuononen in the contact between a skate blade and an ice track resulting in friction values decreasing from 0.014 to 0.006 with increasing load [9
]. The influence of roughness on steel–ice friction was investigated by Spagni et al., showing that the resulting coefficient of friction is dependent on the friction regime and can have values between 0.08 and 0.02 in a broad temperature range [10
]. Because of the relation of our study to the sport of bobsleighing, we confine the review to experiments at high sliding velocities in the next paragraph.
De Koning et al. analyzed ice skates and measured mean coefficients of friction for straights and curves of 0.0046 and 0.0059, respectively [11
]. Similar results were obtained by Federolf and co-workers [12
]. Poirier published friction data for the bobsled derived on the base of precise speed measurements by radar [13
]. Averaging high and low speed data, a mean coefficient of friction of 0.0053 was obtained. A summary of all available friction data can be found in [1
] showing that, for sliding velocities up to 5 m/s, friction exhibits a drastic decrease from 0.06 for quasi-static conditions to 0.015 at 5 m/s. Higher sliding velocities change the friction behavior to an almost linear decrease down to 0.005 at 33 m/s. Sliding velocities higher than 33 m/s are not reported in literature, thus the question of a further friction decrease or an increase in friction due to the action of hydrodynamics cannot be answered yet. In an attempt to reduce the lack of experimental friction data at high velocities, we performed friction experiments under well-controlled conditions on a model system at three different temperatures. The work is supplemented by calculating coefficients of friction using the latest ice friction model.
The following section explains the experimental setup as well as steel sample and ice preparation. In addition to the experiments, the basics of ice friction calculations are given. The experimental section provides high-speed friction data and the numerical section shows computed friction data.