Momentum and energy processes during jackhammer operation: Fid-Bau Portal

Momentum and energy processes during jackhammer operation

Pang, S. S. / Goldsmith, W.

Summary An analytical model has been developed that describes the motion of the bit of a pneumatic jackhammer and the forces exerted at its tip during penetration of a target. This model assumes that the energy is transmitted in the form of a one-dimensional longitudinal wave without inclusion of the effect of lateral inertia. The piston and the bit can be of arbitrary shape, but are approximated here by uniform stepped sections. A computer program was developed to provide numerical results for the operation of the jackhammer/target system. The analysis includes the pressures that act on both the top and bottom of the piston and additional thrusts that are applied by the operator, an external thrust device, due to the weight of the jackhammer, or as the result of a combination of these effects. The program includes (1) the incident wave for an arbitrarily shaped piston/bit system, (2) the force history at any position of this unit, (3) the force profile along the bit at any instant, (4) the indentation history of the jackhammer bit when the force-indentation relation for the bit/target combination is knowna priori, (5) the rebound velocity of the piston, and (6) the energy transfer from the piston to the target. Numerical examples indicating the results of the calculations are presented and compared with data from corresponding experiments that involved the penetration of an Ingersoll-Rand jackhammer with five different tip shapes into Sierra granite. Both the force histories and indentation histories at the bit tip were measured; correspondence with predicted values was very good. The effects of variations in air pressure and applied thrust as well as the character of the force-indentation relation on the energy transferred to the target are also discussed.