Effects of wedge angle on the ductile failure and the distribution of microcracks for indentation tests on rock-like material

To improve the safety and automation of mechanical excavation methods used in tunnels, this paper investigated the behavior of rock-like materials indented by a single cutter. The development of microcracks during the indentation process and the correlation between microcracks and macrocracks was investigated using the nondestructive technique of acoustic emission. The complete loading curves, including post peak stages, of the indentation tests were acquired by using crack opening displacement (COD) control as the feedback signal in a closed-loop, hydraulic loading system (MTS). The wedge angle of cutter was varied from 90° to 150° to study its effect on the ductile failure and brittle fracture behavior of indentation tests. Microseismic activity of the microcracks received by the acoustic emission technique was used to interpret and represent the evolution of elasto-plastic interface and the intrinsic width after crack initiation. As the wedge angle increased, the radius of the elasto-plastic interface decreased, from 9 mm for 90° to 4 mm for 150° of wedge angle. However, the intrinsic width after crack initiation remained almost constant (about 8 mm) in spite of the changing of wedge angle. The angle of cutter has obvious effects on the development of plastic zone very close to the cutter tip, but does not influence the intrinsic width of crack further away from the cutter tip.