Quasi-static fracturing in double-flawed specimens under uniaxial loading: the role of strain rate

Mechanical properties and cracking behaviors of flaw-weakened rock mass are distinguishably influenced by the quasi-static strain rate. Such advanced knowledge is mainly obtained through the numerical simulations, which are rarely verified experimentally. This paper carries out a coupled experimental-numerical investigation on double-flawed rock-like specimens at different quasi-static strain rates, with consideration given to the macro-mechanical properties, the quasi-static cracking behaviors and the underlying fracture mechanism. Three ordinary arrays of double pre-existing flaws, namely, the coplanar array, the vertical non-overlapping array and the vertical aligning array, are analyzed experimentally. The obtained results show that the crack initiation stress and the peak stress of double flaw-contained specimens generally increase with increasing the strain rate. The extension length of the first macroscopic crack, the crack initiation mode, the amount of far-field cracks, and the degree of ultimate fragmentation in double flaw-contained specimens are closely related to the strain rate. Furthermore, the vertical non-overlapping array of double pre-existing flaws is studied numerically by using peridynamics. The quasi-static fracture behaviors obtained by peridynamics are in good agreement with the experimental observations. The stress concentrates around the tips of flaws when the strain rate is relatively low, while apart from around the tips of flaws, the stress concentration also occurs in the interior of specimens when the strain rate is relatively high. This study provides the better understanding of the quasi-static strain rate effects on mechanical properties and fracture behaviors of rock mass, in particular those containing natural flaws that appear in sets or groups with similar orientation and characteristics.