Stress Wave Propagation in Rods during Percussive Drilling Available to Purchase

Percussive drilling with a rock drill is a prevailing modern technique for blasthole drilling and rock bolting. In a rock drill, force and energy for rock fragmentation are generated by repeated collisions between a piston and a shank rod, and then transmitted to a drill bit through extension rods in the form of stress waves. Due to the reason that stress waves play a crucial role in conversion of the kinetic energy of impact into drilling work, understanding stress wave propagation in rods is important in optimizing the design of rock drills. Lundberg deeply studied the stress wave propagation by experiments and built its numerical models based on the one- and three-dimensional theories of elastic waves. Okubo et al. proposed two kinds of sleeve-type joint models according to the result of percussive drilling tests for stress wave propagation and dissipation with a hammer and rods. However since many factors are involved in percussive drilling, both the Lundberg's and Okubo's models of a piston and rods were simplified and far from the actual products. In this study, stress waves during percussive drilling were analyzed and a new numerical model was examined for accurately simulating stress wave propagation in rods based on the one-dimensional finite element method. We adopted actual shape models for a piston and rods, instead of treating them as simple uniform cylinders in Lundberg's and Okubo's studies. In addition, the spring model of a sleeve-type joint proposed by Okubo et al. was employed for simulating the stress wave propagation from one rod to another. Finally, the calculated results were compared with the experimental data of percussive drilling tests. The new model can effectively simulate the stress waveform and even the oscillation in the waveform caused by the complex shape of a piston and a shank rod.