INTRODUCTION: This contribution summarizes 10 years of research with respect to gliding phenomena of nordic skis. The focus was put on the interplay of ski sole preparation and friction. Commencing from a broad literature overview, issues like grinding, waxing, structuring, and brushing will be addressed. METHOD: By means of snow and ice tribometers, friction was measured under lab conditions as function of ice/snow temperature, load and sliding velocity. Prior to the tests, ski sole and snow were analyzed with respect to molecular structure of UHMWPE by transmission electron microscopy (TEM) and grain structure of the snow by optical microscopy. The ski sole samples were prepared following the procedures applied in competition. Using photoelectron spectroscopy (XPS) the depth of wax penetration into the sole was quantified. RESULTS: Figure 1 shows the distribution of fluor after waxing and brushing indicating that both grinding structure and mechanical treatment have a significant impact. XPS was used to follow traces of fluor from the very surface of the ski sole into the bulk of polyethylene showing a penetration depth of 100 nm. High resolution TEM images of the ski sole revealed that upon optimal preparation the C-H chains of UHMWPE can be directed by brushing accompanied by intermixing with wax. As a result, the gliding effect is generated in a nanometer-thin layer composed of wax with embedded polymer brushes. The tribometer tests showed that lowest friction can be achieved when this layer was prepared succesfully. Moreover, the formation of this layer sensitively responds to the quality of polyethylene, wax composition and the energy input by manual brushing. Fig. 1: Fluor distribution DISCUSSION: The results underline that the mechanisms of friction acting between ski sole and snow depend on many influences. The influences interact with each other, some act synergetically, some antagonistically. Ski tribology in combination with high resolution physical and chemical analytics is able to unravel the underlying mechanisms. As a general conclusion it has to be stated that ski technicians have to perform nanotechnological procedures in a field of multidimensional optimization. It can be shown that several mechanical treatments, like brushing, have their origin in practical considerations such as the removal of excessive wax. However, the tribological effects unfold their action at the nanometer scale. CONCLUSION: Since tribology of the interface between ski sole and snow is mainly dominated by nanometric influences, highly-sophisticated analysis tools are necessary to relate the mechanical treatment during ski preparation with the effects of gliding in competition. The fact that the test equipment as described above cannot be installed into a waxing container, requires the development of robust preparation procedures that can be applied under the conditions of competition. Of great value is the intensive collaboration of experienced ski technicians with tribologists familiar with surface science techniques and thin film lubrication. --- The hosting University of Jyväskylä is planning to publish conference proceedings "Science and Nordic Skiing III". In case you are interested in this publication please contact the editors (Anni Hakkarainen anni.s.j.hakkarainen@jyu.fi) to become registered for the book.
© Copyright 2015 3rd International Congress on Science and Nordic Skiing - ICSNS 2015. 5-8 June 2015, Vuokatti, Finland. Published by University of Jyväskylä; University of Salzburg. All rights reserved.