ABSTRACT
The evolution of the number of sliding contacts is shown in Figure 2 for three different system sizes. In all the shown cases, the same kind of behavior is observed: The number of sliding contacts increases in time, but this evolution is interrupted from time to time by some events, in which the number of sliding contacts decays abruptly. The recurrence of this phenomenon has been checked for different time steps of the simulation and also for different functions f (t) (as described in Eq. 4). In some of these drop-offs, all the contacts stop sliding, whereas in others the number of sliding contacts is considerably reduced, but remains bigger than zero. In more detail, the sequence is the following: At the start, the number of sliding contacts grows steadily as the stress increases. Above a certain value, there is a sudden decrease on ns.After this change, the number of sliding contacts remains low for a while before starting a faster increase in time that will lead to a ns over the value reached previous to the collapse. Observe that the frequency with which these abrupt changes in ns occur increases as the experiment continues. The number of sliding contacts can grow after each dropoff beyond the value previous to the fall. Note also that the time at which the first event occurs is later for bigger systems. It is also observed that the cases in which there is a partial decay of ns, the value of sliding contacts remains low for a shorter period of time than in the drop-offs where ns decays to zero.
