On the Pivotal Role of the Cutter/Rock Interfacial Friction in Rock Cutting

Summary Our focus in this paper is on the role of the cutter-rock interfacial friction at the cutter front attacking zone. First, we use the cutting characteristic of a blunt cutter to build an analysis method for calculating the cutter front interfacial friction angle (IFA), which avoids the “intrinsic” specific energy concept and allows the wearflat coefficient of friction (COF) to be independent. Second, we show the existence of the cutter tip forces for sharp cutters. Much more consistent cutter front IFAs result when the cutter tip forces are considered. Third, we show both analytically and numerically the existence of a threshold stress at large depth of cut (DOC), which interestingly can then be used to derive an analytical solution for the “intrinsic” specific energy, thus providing a theoretical support for the rock scratch test (RST). Fourth, we provide the analytical solution of the cutter front stress, which highlights the pivotal role of the cutter front IFA. Finally, we derive for the first time the analytical solution for the wearflat contact stress. Extensive references are also provided to prove the miscellaneous formula and phenomena. In this paper, using analytical solutions and results, we explain many messy experimental observations on the cutter front IFA, on the cutter front stress, on the intrinsic specific energy, and on the wearflat contact stress. The cutter front IFA is shown to significantly affect the cutter front stress and, hence, the cutter front forces and the cutting efficiency. The cutting process is viewed as a united system in which the external factors, such as the DOC, back/side rake angles, and cutting velocity, work against the rock internal system via the hub of the cutter front IFA. However, the cutter/rock IFA is the major uncertainty, the significance of which has been commonly underestimated in the drilling industry and, hence, is worth promoting.