Shear cell experiments of snow and ice friction

Abstract

Snow and ice friction was investigated with a shear cell in which two surfaces of annular snow and/or ice samples were in contact and sheared by rotation. The temperature ranged from 0 to −25 °C, normal stress from 205 to 1292 Pa, and velocity from 0.9 to 25.3 m/s. The total friction coefficients measured by friction of two hard sintered snow plates ranged roughly from 0.2 to 0.8, which were separated into velocity-independent dry friction and linearly dependent viscous friction; only at velocities larger than 15 m/s did friction increase parabolically, evidence of turbulent friction. The dry friction coefficient (μD) was found to consist of Coulomb friction and adhesion, both of which were strongly dependent on temperature and hardness of snow; μD decreased linearly with lowering temperature from 0.47 at 0 °C to 0.22 at −25 °C. Viscosity was found to be dependent on snow type (grain characteristics) but independent of temperature; the average kinematic viscosity was roughly 5×10−5 m2/s for snow of density around 350 kg/m3. The total friction coefficient for ice-ice friction was an order of magnitude smaller than that of snow-snow friction, typically less than 0.04; its magnitude increased with velocity but at lower temperatures (e.g., −35 °C) it decreased exponentially with velocity. The minimum Coulomb friction coefficient as small as 0.008 was observed at −11 °C. All the friction coefficients for snow-snow, snow-ice, and ice-ice friction were summarized in temperature-velocity diagrams, which conveniently show the overall behaviors of snow and ice friction.