Cross-country skiing holds a significant place in Norway's cultural history as the national sport. It plays a crucial role both in public health as a recreational activity and as a highly competitive sport. A decisive factor for performance in cross-country skiing is the friction between the ski and snow. As a consequence, a lot of effort is put into developing fast skis and glide products. In this development process, glide testing is essential to distinguish small differences between the products. However, a significant influence of changing weather, snow conditions and skier position make this task challenging in the field. This has made researchers develop laboratory setups to better control external factors. However, to obtain stable measurements, simplifications have been made by substituting snow with ice, and reducing both the sample size and speed. Therefore, the primary objective of this thesis has been to examine the friction between skis and snow within a controlled environment, under conditions that apply to crosscountry skiing. The first part of this work consisted of the development of a ski-snow tribometer (an instrument for measuring friction). This tribometer comprises a 6.5-meter-long snow track situated inside a freezing chamber. A ski is mounted to a carriage, which is driven across the track while the normal- and frictional forces are measured. Additionally, laboratory-grown dendritic snow has been produced by a custom-built snow machine as part of this setup. The results from the precision investigation showed that the setup could measure the friction coefficient of skis on new dendritic snow with a precision good enough to distinguish skis or glide products with very similar performance (?µ = 0.001). Based on the insights from the first study a new method to test skis has been developed. This method reduces the impact of a constantly changing snow surface with repeated runs, on the measured coefficient of friction. By assuming a linear polishing/friction trend of the measured coefficients of friction, the data can be modified to remove the effect of a falling or rising trend. This approach has proven effective in mitigating the impact of a changing coefficient of friction on the average between the skis and has been used in subsequent experimental studies. The second study investigated how loading conditions such as the normal load and placement of load (binding position) affected the macroscopic contact parameters and friction on a crosscountry ski. To quantify the changes in macroscopic contact parameters we developed a rig for measuring the pressure profiles of the contact zones on cross-country skis. This was achieved by pressing the ski onto loadcells to get the force measurement at every centimeter along the ski base. The results showed that increasing the normal load on the ski led to an increase in the contact length (apparent contact area), an increase in the average contact pressure, a larger load split towards the rear, and shorter spacing between the front and rear zones. The friction tests revealed that the coefficient of friction exhibited minimal variation with increased normal loads across three different snow conditions. Additionally, adjusting the ski binding to a more rearward position resulted in decreased friction levels under both cold (-10 °C) and warm (+5°C) air temperatures. Due to the interconnected parameters of the modern cross-country ski, it was difficult to explain how the different contact parameters contributed to the measured change in the coefficient of friction. Building on the knowledge from the second study, we developed an adjustable ski designed to isolate and manipulate the macroscopic contact parameters. This enabled the third study to focus on investigating the contact parameters isolated effect on the coefficient of friction. The adjustable ski decoupled the contact zones from the effect of the normal load, meaning that the apparent contact area was constant for different normal loads. In addition, the binding could be moved over the entire length of the ski, and the distance between the zones could be independently adjusted. These parameters were tested under settings relevant to cross-country skiing, meaning slider/contact zone configuration, speed, and snow conditions were in a range where the frictional trends have high validity to real-world skiing. The results showed that an increase in the average contact pressure was strongly connected to a reduction in the coefficient of friction at cold temperatures of -10 °C. At intermediate, (-2 °C) and warm (+5 °C) air temperatures the apparent contact area had a stronger effect on the friction than the normal load. The result of the load split between the contact zones at cold temperatures provided experimental evidence for the hypothesis that moving frictional power toward the front slider could create a thicker liquid-like layer earlier along the sliding ski, which consequently would result in a reduction in friction. Lastly, the effect of spacing showed a small, but consistent decreasing trend in friction for shorter spacing across the three temperatures tested.
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