The process of the interaction of a percussive drill and a target and the associated target response is investigated. In particular, three important topics involving rock targets are examined:​ a force-indentation model for brittle rocks, a computer simulation of bit motion in a percussive system, and a crushed zone and crack zone prediction during loading on rocks. These processes are validated by test results.

The force-indentation curve during quasi-static loading consists of cycles of crushing and chipping, with both upper and lower bounds. The crushing processes are shown to be linear and quadratic with indentation for the wedge and conical indenters, respectively. The chipping phase is linear with negative slope, and the force at the lower bound of chipping is kept at a finite level. The curves of the upper bound of chipping are modified by strength reduction factors in the form of Weibull parameters.

A computer program is developed that permits the determination of the motion and the force along the drill to the bit in a percussive system by assuming a one-dimensional longitudinal wave, whenever either the force-indentation relation of the target or the force history at the tip is provided. The program incorporates arbitrary piston and bit shapes, the pressures on the top and bottom of the piston and the applied thrust on the tool, and then evaluates the energy transfer. Correlation between the experimental data and the output of the program is satisfactory. A simpler model, which assumes a rigid piston and bit was found to be inadequate for a percussive system.

Linear elasticity is used to obtain the principal stress and strain distributions of a homogeneous and isotropic target, loaded by conical, wedge, and hemispherical indenters. The failure criterion expressed in terms of these variables is obtained for each indenter. Failure occurs both in a crushed zone and in a crack network region. The shape of the crushed zone is proposed to be bounded by the contour which satisfies the Coulomb-Mohr criterion. The crack network which results from extensional strain is described in terms of (a) the place and direction at which the crack is initiated, and (b) the prediction of the failure region.