Velocity-dependent friction on Coulombic shear faults in ice

Previous experiments [Fortt AL, Schulson EM. Acta Mater 2007;55:2253] at -10 degrees C on sliding along Coulombic shear faults in ice at a constant-velocity revealed that the coefficient of friction exhibits velocity-strengthening at lower velocities and velocity-weakening at higher velocities. Here we present the results of new, variable-velocity sliding experiments. When velocity changes are confined solely within either the velocity-strengthening or the velocity-weakening regime, the difference parameter (A - B) that describes the sensitivity of the steady-state coefficient of friction to changes in velocity is independent of the sense of the velocity change and agrees with the values calculated from constant-velocity tests. When velocity changes straddle the two regimes, (A - B) is different from the values calculated from constant-velocity tests and the coefficient of friction exhibits a memory. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.