Microcomputer simulation of stress wave energy transfer to rock in percussive drilling

Abstract An Apple II Plus microcomputer with high resolution graphics is used to simulate stress wave energy transfer to rock in percussive drilling. The drilling model is based on one-dimensional stress wave theory for the rod and bit, and on a nonlinear history-dependent force/penetration relationship for the bit/rock interaction. The programming language is Applesoft Basic. Input data are given for rod, bit, incident wave and bit/rock interaction. Also the position of a gauge is prescribed. During simulation the wave propagation in rod and bit is visualized. Also the normal force at the gauge station is plotted vs time on a simulated oscilloscope display. After simulation the drill-bit efficiency, defined as the ratio of work on rock to incident wave energy, and the maximum and minimum forces at the gauge station, are displayed. For the case of an integral drill steel and a rectangular incident wave, the computed efficiency differs from the known ideal efficiency by only a few tenths of a per cent. The use of the simulation program ‘Bit’ is illustrated by studying the influence of bit mass and shape on drill-bit effieiency. For the bits chosen mass is shown to be a far more important parameter than shape. The program has uses in research and development as well as in education.

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