INTRODUCTION: Can friction form a thick, low-friction film in the contact between ski and snow? Is the melting rate sufficiently large for that? These are questions to be discussed in this paper. Lubrication theory can be applied to the ski friction problem, since proper lubrication of the ski requires that the melting rate must balance the amount of water pushed out from the contact between a ski base asperity and the snow. If we assume that the base of the skis is ground with longitudinal ridges and valleys and is placed in contact with a smooth snow surface, then the flow balance equation reads: (U+03B4 /U+03B4 y) * h^3 (U+03B4 p/U+03B4 y) = -12U+03B7 (U+03B4 hm/U+03B4 t) = -12 (U+03B7^2 * u^2 / hLU+03C1 (1) where p is water-film pressure, h is the thickness of the water film, u is the speed, and U+03C1, U+03B7, and L, are water density, viscosity, and latent heat, respectively. The RHS of (1) can be interpreted as a "melt squeeze effect" since U+03B4hm/ U+03B4t is the melting rate. METHOD: The flow balance equation (1) can be solved analytically for flat grinds and numerically for more complex grind textures. In both cases it is possible to determine the load-carrying capacity (LCC) of a single ridge, and the coefficient of friction (COF). RESULTS/DISCUSSION: The results show that there is an obvious difference between grind textures with different amplitude. The figure below shows non-dimensional heat maps of LCC and COF vs grind amplitude and water film thickness. It is also possible to determine the melting rate to be in the order of magnitude of 1 mm/s at high speeds. This implies that the snow surface will change during one passage of one skier. The implications of this will be discussed during the presentation. CONCLUSION: The friction melt lubrication theory may be valid if there is sufficient time of contact between the ski and snow. However, it is far from clear that there is time enough for the friction to generate a melt film that creates a hydrodynamically lubricated situation under situations with dry and/or cold snow surfaces.
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