A fracture mechanics study of unassisted and water jet assisted rock disc cutting

Abstract

The work presented in the thesis introduces the use of the principles of fracture mechanics on the mechanism of rock breakage by disc cutters with and without water jet assistance. The work may be divided into five major parts: 1. Rock fracture tests; The values of fracture toughness are measured from three different directions of the rock blocks by three different testing methods: radially cracked ring specimens, three point bend specimens and short bar specimens. The effect of moisture on the fracture toughness was also investigated. 2. Indentation tests; A primary study of the use of a disc cutter as a type of indenter has been carried out. These tests provided a parameter, contact pressure, for predicting the disc cutting forces and understanding the fragmentation of the rock during cutting. 3. Water jet assisted disc cutting tests; The factors influenced the performance of water jet assisted disc cutting were investigated, including: a) The pressure of the water jet; b) The position of the water jet nozzle; c) The cutting speed; and d) The spacing distance and penetration depths. 4. Theoretical analysis of disc forces; Based on a widely accepted assumption, a simple mathematical model was developed for the relationships between the cutting forces. The indentation fracture theories were used to predict the performance of disc cutting. A further use of the predictor equations in the water jet assisted cutting was also investigated. 5. The analysis of stress distribution beneath the disc cutter; Boundary element method was used in the investigation of the stress distribution beneath the disc cutter. The effects of geometries of the disc cutters, spacing distance, penetration depth were also considered.