Experimental studies of the resultant contact forces in drillbit-rock interaction

The understanding of drillbit-rock interaction is essential to the optimisation of the percussive drilling technology. It is obvious that rock fragments mainly as a result of the contact forces developed during impacts. In addition, the modelling of the dynamic response of a drilling module is possible if the contact law can be described in terms of the force and penetration. In this paper, the resultant contact force versus penetration is examined for a drillbit with conical and spherical inserts in contact with a rock. Quasi-static indentation and dynamic impact experiments are conducted on sandstone, granite and basalt. A power-law relationship is obtained between the measured resultant contact force and the penetration. The relationship is in good agreement with existing theoretical results for elastic-ideally plastic solids.