Friction between skis and snow was studied in a variety of field and laboratory measurements. Whilst field tests have the drawback of changing conditions, in laboratory tests sport-specific sample sizes and speeds could not be measured up to now. Hence, a novel linear tribometer was developed allowing studies with whole skis at sportspecific speeds. The precision of the tribometer was better than 2.2 %. The dominant cause for the imprecision was the variability of the single snow tracks at lower speed, whilst at higher speeds also the determination of normal and friction force and speed became relevant. The precision is high enough for discriminating differences needed for the analysis of different ski and snow conditions and the study of friction processes.

In papermaking, the formation of bonds between single pulp fibers is influenced by the hardness of the fibers in their wet state. In this work, transversal hardness and modulus of pulp fibers have been studied via atomic force microscopy-based nanoindentation in dependence on relative humidity (RH). Additionally, the change in hardness of cellulose and xylan/cellulose model films was also investigated as a function of swelling in the presence of water and calcium chloride (CaCl 2 ) solution. The hardness of pulp fibers is decreasing slowly from 240 MPa at 5% RH to 90 MPa at 80% RH and exhibits a distinct decrease to 2.7 MPa at the fully wet state. The hardness in water is reduced by a factor of almost 100 compared with the dry state; therefore, a form change is easily possible and facilitates the formation of hydrogen bonds on the fiber surfaces. The investigations on the model films reveal that pure cellulose hardens in the CaCl 2 solution, compared with distilled water, whereas xylan on cellulose is becoming softer.

The purpose of this study was to analyze the effect of the surface structure on the friction between steel and snow. On a linear tribometer positioned inside a cold laboratory, four steel skis with different running surfaces were tested over a wide range of velocity, snow temperature and normal force. The surface roughness was measured with a focus variation microscope. The friction tests showed that the surface roughness had a major effect on friction between steel and snow, with higher friction for smooth surfaces than for rough ones. The effect was particularly strong for temperatures close to the melting point, where the friction strongly increased for smooth surfaces. The degree of dependence was affected by the gliding speed, leading to two different kinds of velocity-dependent friction curves. Increased adhesion and wet friction due to an increase in contact area were interpreted as cause for the higher friction of smooth surfaces.

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The purpose of this study was to analyze the effect of surfaces with different bearing ratios, but similar roughness heights, on the friction between ultrahigh molecular weight polyethylene (UHMWPE) and snow. On a linear tribometer positioned inside a cold chamber, the different samples were tested over a wide range of velocities and snow temperatures. The surface roughness was measured with a focus variation microscope and analyzed using the bearing ratio curve and its parameters. The surface energy was investigated by measuring the contact angles of a polar (water) and nonpolar (diiodmethane) liquid. The friction tests showed that the bearing ratio had a major effect on the friction between UHMWPE and snow. For temperatures close to the melting point a surface with wide grooves and narrow plateaus (nonbearing surface) performed well. For cold conditions, the friction was less for a surface with narrow grooves and wide plateaus (bearing surface). Interpretations of the results are given on the basis of mixed friction, with lubricated friction being dominant at higher snow temperatures and solid-solid interaction at lower ones.

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After falls, skiers or snowboarders often slide on the slope and may collide with obstacles. Thus, the skier's friction on snow is an important factor to reduce incidence and severity of impact injuries. The purpose of this study was to measure snow friction of different fabrics of ski garments with respect to roughness, speed, and contact pressure. Three types of fabrics were investigated: a commercially available ski overall, a smooth downhill racing suit, and a dimpled downhill racing suit. Friction was measured for fabrics taped on a short ski using a linear tribometer. The fabrics' roughness was determined by focus variation microscopy. Friction coefficients were between 0.19 and 0.48. Roughness, friction coefficient, and friction force were highest for the dimpled race suit. The friction force of the fabrics was higher for the higher contact pressure than for the lower one at all speeds. It was concluded that the main friction mechanism for the fabrics was dry friction. Only the fabric with the roughest surface showed friction coefficients, which were high enough to sufficiently decelerate a sliding skier on beginner and intermediate slopes.