Abstract
Ice friction is affected by various system and surface-related parameters such as ice temperature, ambient air temperature and humidity, relative sliding velocity, specific surface pressures and surface texture (waviness, roughness) as well as the macroscopic geometry of the samples. The influences of these parameters cannot be easily separated from each other. Therefore, ice friction is a very complex tribological system and it is challenging to draw sound conclusions from the experiments. In this work, ice friction experiments with stainless steel samples that have different isotropic surface roughness values were carried out. Two tribological experimental setups were used: (i) an inclined ice track where the sliding velocity of the freely sliding steel samples was determined and (ii) an oscillating tribometer, where the coefficient of friction was assessed. For both experimental setups, the environmental parameters such as air temperature, relative humidity and ice surface temperature as well as the test parameters such as normal load and surface pressure were kept as constant as possible. The results of the experiments are discussed in relation to the ice friction mechanisms and the friction regimes.
Highlights
Depending on ice and ambient temperatures, sliding velocity and surface contact pressure, different mechanisms prevail that divide ice friction into different friction regimes
Mixed friction occurs when the surface temperature at some points within the contact zone rises above the melting point of ice and the thickness of the liquid-like layer is still lower than the characteristic roughness of the mating surfaces—friction coefficient decreases with the thickness of the liquid-like layer
Analyses of sliding velocitiy and coefficient of friction of stainless steel samples having different isotropic surface roughness were conducted for ice contact on two different experimental setups and test parameter sets
Summary
Depending on ice and ambient temperatures, sliding velocity and surface contact pressure, different mechanisms prevail that divide ice friction into different friction regimes. With regard to the thickness of the liquid-like layer, three different friction regimes are typically distinguished: dry, mixed and hydrodynamic friction. In ice tribology, such conditions are extremely rare because a thin liquid-like layer is always present on the ice surface when ice temperature is above around −35 ◦ C (depending on the contact pressure) [3]. Mixed friction occurs when the surface temperature at some points within the contact zone rises above the melting point of ice and the thickness of the liquid-like layer is still lower than the characteristic roughness of the mating surfaces—friction coefficient decreases with the thickness of the liquid-like layer. If in the contact zone the temperature is higher than the melting point of the ice and the thickness of the Lubricants 2019, 7, 106; doi:10.3390/lubricants7120106 www.mdpi.com/journal/lubricants
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