The percussive process and energy transfer efficiency of percussive drilling with consideration of rock damage

Considering the strong nonlinearity of the percussive process, this paper used the finite element method to establish a three-dimensional percussive system model to study the energy transfer efficiency of percussive drilling. The model consists of 12-button bit model, damage-plasticity model for the rock, bit-rock interaction model, etc. The explicit dynamics solver in ABAQUS was adopted to solve the above model. In order to study different impactors, the percussive system was loaded by the prescribed pulse load that can be generated by ultrasonic impactor or electro-magnetic impactor, and by impact hammer with initial velocity that can be driven by high-pressure fluid or compressed gas, respectively. The simulation results are as follows. Increasing load duration and dynamic amplitude of the pulse load can improve the input energy, output energy and energy transfer efficiency. With the increase of the load duration or dynamic amplitude, the energy transfer efficiency first increases rapidly in the low input energy phase and then increases slowly in the high input energy phase. For the three pulse shapes-sine, triangle, square in this paper, the input energy, output energy and energy transfer efficiency under the condition of square pulse are the largest when the load duration and dynamic amplitude of the pulse force are fixed. While, the energy transfer efficiency under the condition of square pulse are the smallest and that of sinusoidal pulse are the largest when the input energy of the pulse force is fixed. Both the output energy and the energy transfer efficiency under dynamic loading increase first and then decrease with the static load. For the impact hammer, the energy transfer efficiency increases with the impact velocity of impact hammer.