Identification of a percussive drill rod joint from its response to stress wave loading

Abstract

In percussive drilling of rock, elastic stress waves are generated in a drill string through repeated axial impacts by the hammer of a rock drill. For holes deeper than a few meters, several drill rods are commonly joined by means of cylindrical coupling sleeves with internal threads which connect drill rods with external threads at their ends. Each coupling sleeve (CS) joint serves to transfer stress wave energy from one drill rod to the next with minimum loss of energy due to reflection and dissipation. This paper deals with the development of an identification procedure for the nonlinear dissipative spring mass (NDSM) model of a CS joint developed by Lundberg et al. Stiffness, friction and mass parameters were determined by minimizing the diffence between simulated and measured responses of the joint, in reflection or transmission, to the same incident stress wave loading. Similar results were obtained as with an existing mixed static and dynamic identification procedure, but with considerably less expenditure of equipment and time. The most reliable results and the smallest deviation between simulated and measured responses were achieved in transmission.