2:30 PM - 2:45 PM
[SCG48-30] Dramatic velocity weakening of dry quartz friction at relatively slow slip velocities
Keywords:high-velicity friction, velocity weakening, gel lubrication
Three types of friction experiments were performed using a rotary-type testing machine on a pair of hollow-cylindrical specimens of quartz with outer and inner diameter of 25 and 5 mm, respectively, at a constant normal stress of 1.5 MPa. Constant velocity tests and velocity stepping tests were conducted under a range of slip velocities from 0.005 to 105 mm/s. In slide-hold-slide (SHS) tests, samples were first slid at v = 105 mm/s, by which sliding friction coefficient f decreases to attain a steady-state value of about f = 0.2. Then, rotation of the sample was stopped for periods of 1 to 10000s, after which rotation of the sample at the same rate was restarted.
In room humidity conditions, steady state friction shows velocity weakening at v > 0.01 mm/s, which is consistent to the previous studies. We find that steady-state friction values measured at the dry condition are almost constant at f = 0.2 for slip velocities v from 0.1 to 100 mm/s. SHS tests show that time-dependent frictional healing is observed for hold time duration t > 10s in room humidity condition. On the contrary, the time-dependent frictional healing is negligible when tested in the dry condition.
Our results imply that the moisture-absorption strengthening, which has been proposed to be an effective mechanism for time-dependent healing of high-velocity friction of gabbro (Mizoguchi et al. 2006) is an important underlying mechanism of the frictional weakening of quartz rocks observed in ambient humidity conditions.