Non-invasive timing of gas gun-launched projectiles using external surface-mounted optical fiber-Bragg grating strain gauges

Abstract

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.

A Hypervelocity Impact Facilities Based on Double-Barreled Two-Stage Light Gas Gun

“…Because the energy of the impact is delivered faster than it can be dissipated, the impact causes extreme transient densities and temperatures at the impact site. The resulting pressure can reach almost 1 TPa and the temperature can be sufficient to cause vaporization of the materials involved [2]. So, hypervelocity impacts experiments are taking in so many disciplines, such as materials science, measure & control system, vehicle design and even military affairs [3,4,5].…”