SELECTION OF SLIM HOLE CORE RODS BY VIBRATORY ANALYSIS

This paper describes the axial, torsional, and transient buckling vibr atory models developed for the selection of optimum core rod size. The axial and torsional vibratory core rod simulator (VCRS) models are co upled by way of a transient buckling wave which propagates over the le ngth of the core rod. This paper reports the frequencies and magnitude s of the stresses in the 101 core rod now in use. In addition, four co re bit vibratory forcing functions for thrust and torque were develope d. The thrust and torque frequencies and magnitudes for the bit forcin g functions were extracted from full-size laboratory core bit tests wi th fast Fourier transforms. The natural frequencies of the core rod we re determined with closed-form solution models and were confirmed with a finite element model. Finally, a selection of core rod sizes were m odeled to determine the best size to minimize damaging stress which st ems from vibration.