Time-resolved measurements of near infrared emission spectra from explosions: Pure pentaerythritol tetranitrate and its mixtures containing silver and aluminum particles J. Appl. Phys. 108, 036101 (2010); 10.1063/1.3437056 Time-resolved optical measurements of the post-detonation combustion of aluminized explosives Rev. Sci. Instrum. 77, 063103 (2006);
Articles you may be interested inUsing time-frequency analysis to determine time-resolved detonation velocity with microwave interferometry Rev. Sci. Instrum. 86, 044705 (2015); 10.1063/1.4916733Influence of explosive density on mechanical properties of high manganese steel explosion hardened Time-resolved measurements of near infrared emission spectra from explosions: Pure pentaerythritol tetranitrate and its mixtures containing silver and aluminum particles Time-resolved emission spectroscopy and high-speed photography were used to study the chemical dynamics and thermal history of aluminized hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) charges following detonation. The aluminized RDX charges contained 20 wt. % of either 30-70 nm or 16-26 lm Al particles. Non-aluminized RDX charges were also studied for comparison. Spectra collected from the aluminized charges exhibited Al and AlO emissions during the first 60 ls, followed by a broadband emission that evolved over two time scales: one in the early time, 0-200 lsec, and another on late time, 0.5-10 ms. The apparent temperatures of the early-time fireballs were obtained using barium atom thermometry and were found to be 2900 K for the RDX-only charges, 3600 K for the RDX-micron Al charges, and 4000 K for the RDX-nano Al charges. In both types of aluminized samples, once Al and AlO emissions ceased, the fireballs began to cool and approached the temperature obtained for the non-aluminized RDX charges. For aluminized charges, a late-time luminescence was also observed, with the intensity and duration dependent upon the size of the Al particles. Aluminum nanoparticles yielded a higher early-time temperature, but a less intense and shorter duration late-time emission, while micron-sized particles produced a lower early-time temperature, but a longer-lived and more intense late-time energy release. These results indicate that post-detonation Al combustion occurs in multiple stages during the evolution of the fireball.
Aluminum nanoparticles and explosive formulations that incorporate them have been a subject of ongoing interest due to the potential of aluminum particles to dramatically increase energy content relative to conventional organic explosives. We have used time-resolved atomic and molecular emission spectroscopy to monitor the combustion of aluminum nanoparticles within the overall chemical dynamics of post-detonation fireballs. We have studied the energy release dynamics of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) charges incorporating three types of aluminum nanoparticles: commercial oxide-passivated nanoparticles, oleic acid-capped aluminum nanoparticles (AlOA), and nanoparticles in which the oxide shell of the particle has been functionalized with an acrylic monomer and copolymerized into a fluorinated acrylic matrix (AlFA). The results indicate that the commercial nanoparticles and the AlFA nanoparticles are oxidized at a similar rate, while the AlOA nanoparticles combust more quickly. This is most likely due to the fact that the commercial nano-Al and the AlFA particles are both oxide-passivated, while the AlOA particles are protected by an organic shell that is more easily compromised than an oxide layer. The peak fireball temperatures for RDX charges containing 20 wt. % of commercial nano-Al, AlFA, or AlOA were ∼3900 K, ∼3400 K, and ∼4500 K, respectively.
We report the development of a new methodology for analyzing CYLEX tests streak images. In these tests, the displacement of the wall of an explosive filled cylinder is obtained by backlighting the cylinder. The profile is imaged through a slit and streaked across a film record as the cylinder is detonated. A critical step in processing this data is the spatial calibration of the film and extraction of the profile of the cylinder from the image. Historically this has been a tedious task as it was performed by eye with the assistance of an optical comparator. Recently we developed an algorithm which automates the data calibration and extraction process of digitized streak records utilizing the Shen‐Castan edge detection algorithm and the image processing capabilities found in the IGOR PRO software. The new processing methodology greatly increases the resolution of the data, removes human subjectivity, and reduces analysis time from hours to seconds. The higher resolution of the new method has enabled much greater accuracy in measuring early‐time (<15 µs) expansion. With the aid of CTH hydrocode calculations, new fitting functions were developed to model both the early and late‐time expansion data. These functions contain physically meaningful fitting parameters and include terms which mimic the intensity and time scales of the shock and gas induced expansion of the cylinder independently. We demonstrate the methodology and hydrocode calculations on a recent CYLEX test series aimed at examining the effects of a plastic liner on high‐purity oxygen‐free copper cylinders filled with a high explosive.
In recent years, emission spectroscopy has been applied to the study of post-detonation combustion in explosives, often yielding valuable information on temperatures and chemical dynamics. The post-detonation fireballs that form as under-oxidized detonation products burn in the surrounding air are optically dense and the corresponding emission spectra sample only the material at or near the surface of the fireball. In the present study, we exploit the large optical density in order to probe the dynamics occurring in the interior of the fireball. Emission spectra are collected following detonation of 20 g aluminized Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) charges using fiber optics located behind the flame front and then compared with the corresponding spectra of the surface layer collected from outside the fireball. We find that in the early evolution of the fireball (t ≤ 60 μs and r ≤ 10 cm in the current study), combustion and light emission are predominantly confined to the surface, while the interior is dark. Later, after the fireball expands and mixes with the surrounding air (t ≥ 120 μs or r ≥ 30 cm), combustion and emission occur throughout, and we find no significant differences between the spectra collected from the interior of the fireball versus those from its surface.
Abstract. The cylinder test (aka cylinder expansion or Cylex test) is a standard way to measure the Gurney velocity and determine the JWL coefficients of an explosive and has been utilized by the explosives community for many years. More recently, early time shock information has been found to be useful in examining the early pressure-time history during the expansion of the cylinder. Work in the area of nanoenergetics has prompted Air Force researchers to develop a miniaturized version of the Cylex test, for materials with a sufficiently small critical diameter, to reduce the cost and quantity of material required for the test. This paper discusses the development of a half-inch diameter version of the Cylex test. A measurement systems analysis of the new miniaturized and the standard one-inch test has been performed using the liquid explosive PLX (nitromethane sensitized with ethylene diamine). The resulting velocity and displacement profiles obtained from the streak records were compared to Photo Doppler Velocimetry (PDV) measurements as well as CTH hydrocode simulations. Measurements of the Gurney value for both diameter tests were in agreement and yielded a similar level of variability of 1%-4%.
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