Erosion Wear Characteristics of Rock Eroded Using Abrasive Air Jet at 90° Impingement Angle

An abrasive air jet, which is sufficiently powerful to break rock, has significant potential in the field of assisted rock breaking, such as assistive tunnel excavation using a tunnel boring machine. To make its application more efficient and beneficial, a clear and definite erosion mechanism of an abrasive air jet is necessary. However, the present erosion mechanisms of an abrasive air jet have mostly neglected the secondary erosion of rebounding particles. The effect of rebounding particles on rock erosion was analyzed by numerical simulation and scanning electron microscopic images. We obtained a variety of stresses and the distribution when a perpendicular abrasive air jet erodes rock through smoothed particle hydrodynamics (SPH). In addition, the particle trajectory and a variety of velocities were also obtained, which provide the data necessary to analyze the formation and characteristics of the erosion pits. It can be concluded that the rebounding abrasive particles play an indispensable role in the stress formation and distribution of rock, and are also the primary cause of a particular erosion pit feature, that is, a semi sphere-like bottom, under an annular platform. The incident abrasive at the center of an air jet deepens the erosion pit with a large impact force and its energy propagates into the rock with a stress wave. Meanwhile, the rebounding abrasive enlarges the diameter of both the erosion pits and the semi sphere-like bottom. Because the diameter of an erosion pit is larger than that of a semi sphere-like bottom, an annular platform is formed. The incident abrasive at the jet boundary involves the formation of an annular platform. The incident and rebounding abrasives have different roles in the erosion wear of rock. The main wear characteristics of the rock are cutting and deformation wear. The incident abrasive with a high velocity induces the deformation and cutting wear at the semi sphere-like bottom. Only a cutting wear can be induced at an annular platform by an incident abrasive with a lower velocity. The rebounding abrasive induces the cutting wear of the rock only. However, the features of an erosion rock surface vary depending on the eroding angle of the rebounding abrasive.