Friction of ice on ice

Abstract

New measurements have been made of the friction coefficient of freshwater polycrystalline ice sliding slowly (5 × 10−8 to 1 × 10−3 m s−1) upon itself at temperatures from 98 to 263 K under low normal stresses (≤98 kPa). Sliding obeys Coulomb’s law: the shear stress is directly proportional to the normal stress across the interface, while cohesion offers little contribution to frictional resistance. The coefficient of kinetic friction of smooth surfaces varies from μk = 0.15 to 0.76 and, at elevated temperatures (≥223 K), exhibits both velocity strengthening at lower velocities (<10−5 to 10−4 m s−1) and velocity weakening at higher velocities. Strengthening and weakening are attributed to creep deformation of asperities and localized melting, respectively. At intermediate temperatures of 173 and 133 K, the kinetic coefficient appears to not exhibit significant dependence upon velocity. However, at the low temperature of 98 K the coefficient of kinetic friction exhibits moderate velocity strengthening at both the lowest and the highest velocities but velocity independence over the range of intermediate velocities. No effect was detected of either grain size or texture. Over the range of roughness 0.4 × 10−6 m ≤ Ra ≤ 12 × 10−6 m, a moderate effect was detected, where μk ∝ Ra0.08. Slide‐hold‐slide experiments revealed that the coefficient of static friction increases by an amount that scales logarithmically with holding time. Implications of the results are discussed in relation to shearing across “tiger stripe” faults within the icy crust of Saturn's Enceladus, sliding of the arctic sea ice cover and brittle compressive failure of cold ice.