Magnetic Particle Velocity Measurements of Shocked Teflon

Abstract

A series of shock compression experiments have been undertaken on Teflon using single‐ and two‐stage gas‐guns. Peak pressures in these experiments range from a few kbars to over 10 kbars, as well as one shot completed at 117 kbar. Multiple particle velocity wave profiles, at a number of Langrangian positions, are obtained for each experiment using in‐situ magnetic gauges. Shock velocity is calculated from arrival times at both the particle velocity gauges and at embedded shock trackers. These direct measurements of particle and shock velocity are compared to previous shock compression results on Teflon. Particular attention is focused in the region below 10 kbar where evidence of a shock induced phase transition has been reported, based upon a cusp in the Hugoniot. The volume change for this transition is only ∼ 2.2 % making its observation difficult. A two‐wave structure on the shock front would be strong evidence of the shock‐induced transition, but has not been observed in these initial low‐pressure experiments. However, the Hugoniot data does show a subtle cusp between two of these shots at pressures of 6.4 and 7.9 kbar. The presence of the cusp is consistent with existing data, but appears at slightly higher pressure. Additionally, the in‐situ particle velocity gauges show an evolving wave front, which is likely associated with Teflon’s visco‐elastic properties. The wave front is initially steep, but rounds significantly after the wave has propagated several millimeters into the target.