Analysis of shock pulses from a small velocity amplifier

The theme of this paper is a velocity amplification machine for high-g shock testing of micro-scale devices. The machine uses multiple sequential impacts to amplify velocity through a system of progressively smaller masses constrained to move in the vertical axis. Shock pulses are created through the finite collinear metal rod impact between the penultimate and ultimate masses, imparting shock pulses in excess of 20.000G for an impact velocity of approximately 4.2m/s. For stand-alone application or as an attachment to a drop table, the machine represents a small-scale and inexpensive alternative to conventional Hopkinson Bars or ballistic techniques. The objective of this paper is to investigate the interaction between the penultimate and ultimate masses in order to generate controlled shock pulses. The influence of the following parameters was examined: the geometry and material of the test rods enclosed in the penultimate and ultimate masses; mitigator use; and isolation of the test rods. A Hopkinson pressure bar was used as an ideal input to the pulse shaping test rods as a direct comparison to the velocity amplifier data. The primary outcome of the research is design details of the penultimate and ultimate masses of a velocity amplifier in order to achieve clean shock pulses of controlled amplitude and duration.