Investigation on the Tool-Rock Interaction Using an Extended Grain-Based Model

The poor drill-ability of rock in deep hard formation leads to the problems of low rate of penetration (ROP) and high drilling cost. A detailed understanding of the rock-tool interaction is of great significance for improving the rock breaking efficiency and optimizing the cutting parameters. For this purpose, this paper establishes a numerical model of heterogeneous granite which considers the influence of mineral distribution and real grain structure. The fracture behaviors of granite under tool cutting and indentation are investigated subsequently. It is found that there are always four kinds of microcracks in granite, intragranular tensile crack, intragranular shear crack, intergranular tensile crack and intergranular shear crack, among those four crack types, the intergranular tensile crack and intragranular shear crack are dominated, almost no intergranular shear cracks occur. Lateral pressure has no great influence on the volume of cutting chips in rock cutting, but is the direct factor that affects the rock-breaking efficiency in rock indentation. The initiation and propagation of radial cracks will be obviously inhibited in large lateral pressure, and the number of radial cracks will decrease sharply, resulting in low rock-breaking efficiency. Lateral pressure seems to have little effect on the indentation force, the possible reason for this lateral pressure insensitivity is because the far-field lateral pressure has less influence on the indenter tip around field than the existence of free surface. The research results can provide the basis for improving granite rock-breaking efficiency and optimizing rock-breaking tools to a certain extent.