The friction of ice on ice at low sliding velocities

The kinetic coefficient of friction mu has been measured for both freshwater, granular ice and saltwater, columnar ice sliding against itself. The variables were ambient temperature (-3 degrees C to -40 degrees C), sliding velocity (5 x 10(-7)-5 x 10(-2) m s(-1)), normal pressure (0.007-1.0 MPa) and grain size (2.5-6.0 mm). Generally, mu decreased with increasing velocity and with increasing temperature, but was relatively insensitive to both pressure and grain size over the ranges investigated. At the lower temperatures (-30 degrees C and -40 degrees C) the friction velocity curve exhibited a peak at intermediate velocities. The friction coefficients for freshwater and saltwater ice were almost indistinguishable at higher temperatures (-3 degrees C and -10 degrees C), but saline ice had lower friction at lower temperatures. The results are explained in terms of frictional heating, creep and fracture.