Percussive Drilling: Experimental and Numerical Investigations

This paper focuses on experimental and numerical investigations on percussive drilling. An experimental setup, using a single bit button, was developed to carry out dynamic indentation tests on hard rocks under different confining pressures. The influences of multiple factors on the percussive drilling process such as the weight on bit, the confining pressure, and the impact energy have been studied. An experimental campaign consisting of multiple test series was carried out on the Red Bohus granite using a conical insert, under weight on bit of 0–8.64 kN, confining pressures of 0–30 MPa and impact energies of 30–114 J. The drilled rock volumes were measured by a 3D laser scanner. For the numerical part, a virtual laboratory has been developed to explain the experimental observations and to clearly identify the effects on the different fragmentation mechanisms. An empirical law for the drilled volume as function of the three studied factors has been also established. A finite-element-based modeling approach and a contact mechanism were used in the simulations of the dynamic bit–rock interaction process. A damage-viscoplastic model which takes into account the confining pressure and the strain-rate effects as well as the main fracture types in a dynamic indentation: damage in tension and crushing in compression, was used. The investigations showed the following valuable findings: the increase of the weight on bit favors the insert penetration, but it does not influence the chipping process, the increase of the confining pressure reduces the insert penetration and prevents the chips creation, and the increasing of the impact energy leads to deeper craters and more chips.