Experimental observations on the effect of strain rate on rock tensile fracturing

Abstract

Tensile fracturing was investigated in this study under a static (10−5) and quasi-static (10−3 and 10−2 S−1) strain rate in three different rock types (marlstone, marble, and hornfels). In addition, the effect of έ on the microscopic properties of the fracture such as the width and tortuosity was investigated by tracing the fracture path under the microscope. The results indicated that by increasing the έ from 10−5 to 10−2 S−1, the crack propagation speed in marlstone and marble increased from 4 to 22 m/s and in hornfels from 35 to 100 m/s. The improvement of the parameters associated with hydraulic fracturing is achieved by reducing the έ. By reducing the έ from 10−2 to 10−5 S−1, the (fracture toughness, and breakdown pressure) in marlstone, marble, and hornfels decreased by (37%, 22%), (42%, 30%), (46%, 39%), respectively. In addition, the width of the fracture was strongly affected by the έ, this parameter increased by 55%, 36%, and 51% in marlstone, marble, and hornfels, respectively, when the έ decreased from 10−2 to 10−5 S−1. In the very fine- and fine-grained rocks such as marlstone and hornfels; by decreasing the έ from 10−2 to 10−5 S−1, the tortuosity factor decreased only by about 0.4%, while in the medium-to coarse-grained rocks such as marble decreased by 4.6%. Keywords: Tensile fracture, Strain rate, Crack propagation speed, Tortuosity, Fracture width