The resistance to sliding along Coulombic shear faults in ice

Sliding experiments were performed along Coulombic shear faults in laboratory-grown freshwater ice over a range of sliding velocities (4 × 10−3–8 × 10−7 m s−1) and temperatures (−3, −10 and −40 °C). The Coulombic failure criterion was used to describe the observed linear relationship between the shear stress along and the normal stress across the fault. From this relationship the coefficient of friction was determined. At each temperature the coefficient of friction peaks at a transitional velocity (∼8 × 10−6 m s−1). For a given velocity the coefficient of friction increases with decreasing temperature. We propose that the peaked shape of the coefficient of friction vs. sliding velocity graphs are a consequence of a change in sliding behavior from “ductile-like” at low velocities to “brittle-like” at higher velocities. The velocity-strengthening and velocity-weakening friction regimes are attributed to creep and to frictional melting, respectively.