Figure 2

Propagation length l vs. shear force F_x.

The propagation length l of the precursors, normalized by the slider length L, is shown as a function of the shear force F_x, which is normalized by the loading force W, for various magnitudes of (a) the driving velocity V, (b) the height h at which the shear force is applied and (c) the applied normal force F_z. In (a), F_z = 400 N and h = 0 mm; in (b), F_z = 400 N and V = 0.4 mm/s; and in (c), V = 0.4 mm/s and h = 0 mm. The two solid straight lines show the results of fitting the data in the ranges of small and large values of F_x/W, respectively, for all conditions in (a) and (b) because the behaviors do not depend on V and h. In (c) the two solid straight lines in the same color show the results of the fitting the data in the small and large values of F_x/W, respectively, for every magnitude of F_z because the behaviors depends on F_z. The broken lines show the critical length l_c normalized by L determined by the intersection of the two solid straight lines.