Impact cutting property of rock material using a point attack bit

Abstract

The objective of this research was to investigate the impact cutting properties of several rock and cement mortar materials using a point attack bit. To clarify the fundamental impact property of rock material, several impact shear and bending tests were conducted by means of a falling weight method. The fracture probability of rock material at various falling heights was found to depend on Weibull's distribution. The critical impact shear energy corresponding to the fracture probability of 99% was found to increase linearly with the unconfined compressive strength and the shear strength of rock material. The critical impact bending energy increased linearly with the radial compressive strength. To investigate the cutting capacity by a point attack bit, a new rotary impact cutting test machine was constructed. Several relationships between cutting torque, acceleration, cutting volume per unit work and cutting pitch were investigated. The cutting mechanism of rock material using the point attack bit was analysed theoretically from the fundamental impact properties of a cement mortar material, i.e. the critical impact shear energy. It is clarified, experimentally and theoretically, that the cutting torque, the acceleration, and the cutting volume per unit work increased almost linearly with the cutting pitch.