Development of magnetic gauges for the measurement of particle velocities duringone-dimensional shock loading

Abstract

The measurement of particle velocity in shock-loaded materials (that is thevelocity of material flow behind the shock front) is an important parameter inthe understanding of a material’s response to shock loading. This canbe measured directly by the use of embedded sensors within the targetmaterial, which track the material flow. This takes advantage of Faraday’slaw, where a moving conductor within a magnetic field experiences animposed voltage, the magnitude of which is dependent upon the length ofthat conductor and the velocity through the magnetic field. However,such measurements are not as widespread as other techniques such asinterferometers or stress gauges. In this paper, the development of suchsensors is discussed, and the results from their use in a material whoseshock response is already known (polymethylmethacrylate) are presented.Much of the work by previous authors concerning particle velocity gaugeshas introduced them at an angle to the impact axis. This was done toprevent each gauge element interfering with those immediately behind it byimpeding material flow. Therefore we have investigated the role of gaugeplane angle on the resultant particle velocity gauge records. We have alsoincluded a separate castellated gauge element, the shock tracker, to measurethe shock position with respect to time, and thus use to determine theshock front velocity. The results from this gauge element are discussed,both in context with the results from the particle velocity gauges andwith measurements under known conditions from the work of others.