Experimental Study of Stick-Slip Failure Processes and Effect of Physical Properties on Stick-Slip Behavior

To investigate the process of stick-slip shear failure, small-scale poly methyl methacrylate samples with friction faults and a high-speed recording experiment system are used. The evolution of shear stress and slip displacement clearly shows both the propagation of stick-slip failures and the local slip-weakening behavior of the fault. The distribution of local stress ratio (yx)/sigma(y) along the fault is of great significance to determining the nucleation location. The interrelations among local shear stresses, slip displacements, slip velocities, and slip accelerations show the details of local deformations and motions of breakdown near the crack tip. Four distinctive phases of local breakdown process are found in both the nucleation zone and the dynamic rupture propagation zone. Experiments with three prefabricated roughnesses of the fault surfaces are conducted at normal stresses varying from 2MPa to 4MPa. The critical crack length decreases and the rupture velocity increases with increasing normal stress or decreasing the roughness. Both the local dynamic stress drop (d) and local breakdown stress drop (b) generally increase with increasing normal stresses and decrease with increasing the roughness. Although the critical slip-weakening displacement u(c) seems to be insensitive to normal stress, it decreases as the fault becomes smoother. The shear fracture energy G(c), which is determined by (b) and u(c), increases with an increase in the normal stress and increases with increasing the roughness. In addition, the linear relations of (d), (b), and u(c) to the static friction coefficient (s) are found, and a quadratic function relating G(c) and (s) is established.