Real-time Measurement of Projectile Velocity in a Ballistic Fabric with a High-frequency Doppler Radar
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RESEARCH PAPER
Real-time Measurement of Projectile Velocity in a Ballistic Fabric with a High-frequency Doppler Radar L. Gilson 1,2 & A. Imad 2 & L. Rabet 1 & J. Van Roey 1 & J. Gallant 1 Received: 5 March 2020 / Accepted: 19 October 2020 # Society for Experimental Mechanics 2020
Abstract Background Because of technical limitations, most experimental studies on the energy-absorbing properties of ballistic fabrics are limited to discrete evaluations based on impact and residual velocities. Consequently, the continuous interaction between a projectile and a target material is still commonly assessed with analytical models or numerical simulations, the validation of which is based on the aforementioned discrete values. Objective The present document aims at describing and validating a new experimental method to make it possible to evaluate the continuous evolution of the projectile velocity during penetration into a fabric material. The method is based on the Doppler effect and a specific and complex nonstationary signal treatment. Methods A high-frequency continuous-wave Doppler radar was adapted to assess the continuous evolution of the velocity of a projectile penetrating a fabric material. Based on two ballistic-grade fabric configurations, a perforating and a nonperforating case were described and evaluated. The instantaneous Doppler frequency was extracted based on the Hilbert-Huang transform. A validation of the proposed method was performed based on high-speed camera images, giving the displacement of the apex of the deformation pyramid of the fabric with time. Additionally, a Weibel® Doppler radar was used to measure the impact velocity. Results Based on instantaneous frequencies deduced from the high-frequency radar signal analysis, Doppler theory and highspeed camera images, velocity–time and displacement–time plots were obtained. Additionally, the evolution of the fabric deformation (pyramid morphology) was recorded from the high-speed camera images. Conclusions Comparisons between the data assessed with the high-frequency Doppler radar and those deduced from the highspeed camera indicated that good agreement exists between the two methods. The new Doppler radar method seems to be a promising complementary tool for measuring the continuous interaction between a projectile and a fabric target material. Keywords Continuous measurement . Projectile velocity . Doppler radar . High-speed camera . Ballistic impact . Nonstationary signal analysis . Instantaneous frequency . Method validation
Introduction Since the development of polymeric fibers, much research has been conducted on the deformation and damage of ballistic fabrics. The literature on ballistic impact is very extensive. Indeed, it implicates a large number of parameters, both for the threat and for the protective material. Experimental and
* A. Imad [email protected] 1
Royal Military Academy (RMA), 1000 Brussels, Belgium
2
Univ. Lille, ULR 7512 - Unité de Mécanique de Lille, Joseph Boussinesq, (UML), 59000 Lille, France
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