Development of a Shock and Detonation Velocity Measurement System Using Chirped Fiber Bragg Gratings

Abstract

Dynamic measurements of shock and detonation velocities are performed using long chirped fiber Bragg gratings (CFBGs). Such thin probes, with a diameter of typically 125 µm or even 80 µm can be directly inserted into high-explosive (HE) samples or simply glued laterally. During the detonation, the width of the optical spectrum is continuously reduced by the propagation of the wave-front, which physically shortens the CFBG. The light power reflected back shows a ramp-down type signal, from which the wave-front position is obtained as a function of time, thus yielding a detonation velocity profile. A calibration procedure was developed, with the support of optical simulations, to cancel out the optical spectrum distortions from the different optical components and to determine the wavelength-position transfer function of the CFBG. The fitted slopes of the X–T diagram give steady detonation velocity values which are in very good agreement with the classical measurements obtained from discrete electrical shorting pins (ESP). The main parameters influencing the uncertainties on the steady detonation velocity value measured by CFBG are discussed. To conclude, different HE experimental configurations tested at CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives) are presented: bare cylindrical sticks, wedges for shock-to-detonation transitions (SDT), spheres, a cast-cured stick around a CFBG, and a detonation wave-front profile configuration.

Multimode polymer chirped fiber Bragg grating for shock and detonation velocity

“…The measurement principle remains the same as with a silica CFBG [8]. A CFBG is either placed along or even inside a HE material.…”

“…It was demonstrated by many groups [1][2][3][4][5][6][7] since almost 20 years that CFBG offer, a continuous measurement with minimal disturbance, good signal-to-noise ratio and high flexibility in the integration of the sensor. We presented many results in 2020 [8] and discussed the limitations of the silica fiber. A silica CFBG is sometimes not sensitive over its entire length especially in shock-to-detonation transitions experiments [9].…”

Performance comparison of TOPAS chirped fiber Bragg grating sensor with Tanh and Gaussian apodization

“…The configuration in CFBG makes the Bragg wavelength vary linearly along the grating axis so that CFBG has a greater reflectance spectrum than uniform FBG in full-width half maximum (FWHM). Uniform FBG has a length of up to 50 mm with sensing distance limited to 10 mm, while CFBG has a typical length of 15-50 mm so that it has the potential to distinguish spatial events that occur, with this capability CFBG can be an alternative in temperature and strain sensing [13], [14], monitoring damage to hybrid composites [15] and measuring shock and detonation velocity [16], [17].…”

Application of Fiber Bragg Gratings as a Sensor of Pulsed Mechanical Action

“…The basic principles of FBG operations are summarized, in particular in the reviews [ 1 , 2 , 3 , 4 , 13 ]; possible applications in [ 1 , 2 , 3 , 4 , 5 , 6 , 8 , 15 , 16 , 17 ]; and manufacturing technology in [ 1 , 2 , 3 , 7 , 11 , 13 , 14 , 15 ]. In particular, the use of FBG in medicine is considered in the reviews [ 4 , 6 , 8 , 11 ]; in biochemistry and pharmacy in [ 4 , 5 , 14 ]; for environmental applications in [ 5 , 11 , 14 ]; as well as for other applications [ 16 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. An overview of works on the properties of chirped FBG and their application is given in [ 27 ].…”

“…Presumably, the only application for which pulsed mechanical action on FBG has been studied is the systems for shock wave and detonation diagnostics [ 17 , 22 , 24 , 31 , 32 , 33 , 34 ]. The basic concept [ 17 ] is that the change in the radiation reflection parameters (spectral and total power), which can be determined in real time during the physical destruction of FBG, occurs during the propagation of the detonation wave.…”