Temperature

From the above discussion on the influence of the lubricating layer thickness on the friction coefficient and our general experience with ice, it is evident that temperature has a strong influence on the friction coefficient. Some researchers merely report a decrease in the friction coefficient with increasing temperature [2, 42-47], which is the case when friction is dominated by boundary friction conditions [42, 48]. However, with Fig. 9.3 in mind one can anticipate that across the whole range of friction regimes the friction coefficient on ice will eventually increase with temperature after passing through a minimum; this has been confirmed by several researchers as shown in Fig. 9.7 [2, 42-52]. The coefficient of friction decreases first with increasing temperature and rises again when the temperature approaches 0°C. A minimum coefficient of friction is seen between —2 and —7°C. Obviously, at lower temperatures the friction is dominated by solid-solid contact, typical for the ice friction curve to the left of the minimum, as illustrated in Fig. 9.3. At temperatures close to the melting point the thickness of the lubricating liquid-like layer becomes large enough to not only facilitate sliding but also add to the resistance through the build-up of capillary bridges, as is typical for the mixed friction regime. However, the location of the friction minimum and therewith the onset of this increase in friction depends largely on the slider material, the normal load, and the linear sliding velocity. Table 9.1 summarizes the differences in the operating parameters between the experiments and therewith provides explanations for the differences between the four sets of data. In the

Fig. 9.7 Temperature dependence of the friction coefficient; for experimental parameters refer to Table 9.1. (Reprinted with permission from [77]. Copyright 2010, American Institute of Physics)

Table 9.1 Experimental parameters for the data plotted in Fig. 9.7

Calabrese [51] Steel ring (AISI 1018) 889.6 <1 1,235

Slotfeldt-E et al. [50] HDPE slider block 100 0.3 15,000

de Koning et al. [41] Steel skate blade ("Viking special'') 700 8 &400

following sections it is discussed how sliding velocity, normal force, area of contact, and slider material influence the coefficient of friction.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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