Stress and Displacement Propagation in a Drilling Tube Due to Rebounding and Non-Rebounding Hammer Impact Mechanisms

This paper discusses results of finite element investigation of two different mechanisms to drive a drilling instrument designed for lunar exploration. The instrument consists of a hollow tubular rod, one end of which rests upon the substrate to be drilled and the other end is actuated upon by a powered mechanism. Two different mechanisms of driving the drill have been considered - (1) Impact hammer which can rebound after contact, and (2) Attached hammer which is actuated by, for example, piezoelectric mechanism, and there is no rebound of hammer. Deformable three dimensional finite element models were prepared in ABAQUS to investigate the above two cases. Three different models were studied, with two of them simulating a rebounding hammer while the third simulating an attached hammer. An initial velocity was assigned to the hammer for both cases to simulate impact. Propagation of axial stress and displacement waves resulting from the impact as well as their time histories were studied. It was observed that no rebound case has a higher stress magnitude as well as a larger frequency of stress fluctuation, which might translate to a higher drilling efficiency.