A preprint of this work is available at the preprint server xxx.lanl.gov: cond-mat/9909330.
To answer this question a shear stress is applied to the plate at the top of the granular layer by running the motor until the spring bends and stopping before the plate starts to slide (the experimental setup is shown here) . After a waiting time, the motor is started again. In the stick-slip regime we find that the first slip after the waiting is longer than previous and following slips and that the yield stress (the maximum displacement of the spring before a slip) is larger for the first slip.
This figure shows the spring displacement (~ applied shear stress) vs time after the granular layer was kept under shear stress for 51,400 seconds. The motor is started at ~ 1 second.
We also investigate the effect of humidity and the applied stress on the waiting time strengthening.
Send comments to wlosert@haverford.edu. Last updated 2/10/99
