13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- 3. Result We conducted nucleation simulations with the total 15 sets of the revised RSF parameters (a/b, c) and found systematic changes in the results. Figure 4 shows the results with variation of c=0.0, 2.0, 4.0 under a fixed a/b=0.95, the snap shots of slip and slip rate evolution. When c=0.0 (the aging law) was adopted, a crack-like expansion occurred similar to Fig. 1a. Contrasting to this, when c=2.0, 4.0 were adopted, the crack-like propagation was completely disappeared. A narrow zone of peak slip velocity appears at the edge of the nucleation front propagating outwards like in the slip-law case, but the wide (and growing) region behind the front remains slipping at a velocity more than the 1/3 of the peak velocity, resulting in a slip distribution similar to that of an expanding crack as in the aging law case. Namely, the nucleation regime with the revised RSF was found to have both pulse feature in the spatial propagation and the crack feature in the slip rate distribution. The result may be understandable by comparing the revised law and the slip law. The revised law, as in the slip law favoring pulse, yields a slip-weakening distance nearly independent of the amount of strength reduction (Fig. 3), but it differs from the slip law in that it involves a time-dependent healing term, which should contribute significantly where the slip is proceeding near steady state. Crack-like extension would be no longer incompatible with the energy balance for instantaneous nucleation length l as pointed out in the section 1.2. Figure 4. Snapshots of normalized slip (left panels) and slip rate (right panels) simulated by using the revised RSF for a/b=0.95 with three variations in the c parameter: (top) case with c=0.0, (middle) case with c=2.0, and (bottom) case with c=4.0. Figure 5 shows the results with variation of a/b=0.90, 0.85, 0.80, 0.75 under fixed c=2.0 (the optimum) and c=4.0. Only snap shots of the slip rate are shown for brevity. For both c, transition from a pulse regime to a patch regime was observed as a/b was decreased. The transition was around a/b=0.80 for c=2.0 and a/b=0.85 for c=4.0, which are much larger than a/b=0.5 in the previous studies as schematically summarized in Fig. 6. The condition for the patch regime widens
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