Elastoplastic Contact Force Due to Repeated Longitudinal Impacts on a Novel Percussive Drill: Fid-Bau Portal

Elastoplastic Contact Force Due to Repeated Longitudinal Impacts on a Novel Percussive Drill

Vila, Luis J. / Malla, Ramesh B.

A series of special percussive drilling devices has been designed by the NASA Jet Propulsion Laboratory and Honeybee Robotics Spacecraft Mechanisms Corporation for exploration of planetary bodies (e.g., Mars). The percussive mechanism of these special drilling devices consists of three main components: ultrasonic horn, free mass, and drill bit/rod. This paper presents the analysis of the interaction between the free mass/striker and the drill rod including the coupled effects of structural vibration; plastic deformation of the rod; repeated impacts; and the support condition of the rod on the contact force, contact duration, and coefficient of restitution. The impact between the free mass and the drill rod is analyzed by means of a modified Hertz force-indentation relation coupled with the structural vibration obtained using the mode superposition method. The material of the striker is considered elastic, while the rod is considered as an elastic perfectly plastic material. A numerical integration scheme, with equilibrium iterations, is implemented to solve the system’s equations. It is observed that for both support conditions considered, i.e., fixed and elastic support, the first impact yields the largest plastic deformation, which then decreases as the number of impacts increases. The maximum contact force and the coefficient of restitution are observed to increase with the number of impacts while the duration of contact decreases. Additionally, the effect of the support condition of the rod on the contact force decreases as the number of impacts increases.