Stress evolution of rock breakages by a disc cutter assisted by pre-cuts

To study the rock breakage mechanism by constant cross-section cutters assisted by pre-cuts, the present study first performed small-scaled linear cutting tests on sandstone specimens containing pre-cuts. The laboratory tests indicate that the sufficiently large penetration, causing successful internal and surface crack incisions, is essential for large chip formation. In addition, the small pre-cut depth may fail to form large chips. The numerical results agree well with laboratory tests in fracture patterns. More importantly, the numerical analysis indicates that the increases in rolling force frequently result in stress concentrations. When the stresses concentrate to critical values, fracture propagation occurs. The fracture propagation causes stress dissipation and the decrease in rolling force. Thus, the relation between cutting load fluctuations and crack propagation is revealed. Moreover, the influence of penetration on crack propagation is analyzed. By analyzing the stress fields at typical peak points of the rolling force, the crack propagation direction is predicted, and the influence of pre-cut depth on fracture propagation is studied.