Study of Stress and Displacement Wave Propagation in a Planetary Drilling Device

Percussive Dynamic Cone Penetrometer (PDCP) is a proposed lunar drilling instrument being developed by Honeybee Robotics Spacecraft Mechanisms Corporation that is a compact, low mass, high frequency, and low energy drilling device. It could be used to assess in-situ soil strength prior to landing of larger vehicles, deployment /construction of structures (habitats), evaluating stability of slopes and evaluating landing zones after soil/rocket plume interaction which may leave landed spacecraft unstable. This research investigates axial stress and displacement wave propagation in PDCP instrument subjected to various geometric and loading conditions by employing finite element method. Conditions of pre-stressed joints, presence of helical flutes along the surface of the drill bit length, placement of loading at various points along the length as well as cross-section, variation in geometry (such as abrupt change in cross section and presence of flange for loading), and rebounding versus non-rebounding impact of hammer were considered. ABAQUS software was utilized to draw, render as well as analyze PDCP models for each condition studied. A dynamic loading equivalent to 1 J of energy was applied as a rectangular pulse load to simulate one blow of hammer for all but one of the cases studied, and actual hammer drop was simulated in the last case studied. For each of those cases, elastic wave stress/displacement propagation along the length of the PDCP device and the stress/displacement time histories were compared amongst each other and the difference between them studied to identify cases of higher stress magnitude, duration and frequency