Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session Y02: Characterization of Reactive and Energetic Materials IRecordings Available
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Chair: Alexandra Reinert, NSWC Crane Room: Anaheim Marriott Platinum 6 |
Friday, July 15, 2022 9:15AM - 9:30AM |
Y02.00001: Energy Accounting During and Following Impact of Reactive Metal and Metal-Composite Projectiles Kevin L McNesby, Richard A Benjamin, Steven W Dean, Jesse Grant, Tim Weihs Results from experiments designed to measure kinetic plus chemical energy during impact of reactive material projectiles and of steel projectiles are presented. The reactive material projectiles are fabricated to enable launch from a rifled barrel, achieving spin stabilization. Fabrication methods and reactive material composition to achieve maximum energy release are discussed. A vented chamber calorimeter (wall-mounted pressure gauges) equipped with a force gauge-mounted impact anvil and a suite of optical diagnostics is used to measure the tradeoff between impact kinetic energy and chemical energy during 1 km/second impact and reaction of the spin-stabilized reactive material projectiles and equal density steel projectiles. Imaging pyrometry is used to measure temperatures during and following impact of steel and of reactive material projectiles. Wavelength resolved emission spectroscopy is used to identify continuous and discrete emission in the visible spectral region. Fragment size distribution is measured using laser-illuminated Edgerton shadowgraphy. Total energy delivered on target for each projectile type is discussed. |
Friday, July 15, 2022 9:30AM - 9:45AM |
Y02.00002: Initiation of a metal/fluoropolymer reactive material subjected to dynamic shear–compression loading Bradley Miller, Steven G Thoma, Jamie Kimberley Structural Reactive Materials (RMs) are multi-material composites that provide adequate structural strength and large exothermic yield. Combining the thermal energy output with kinetic energy kinetic energy, RMs fulfill a role in increasing the overall performance and energetic release of military weapon systems. The goal of this current research is to enhance the understanding of the thermomechanical conditions that are responsible for Al/PTFE RM ignition under dynamic loading. Two mechanisms of initiation commonly reported in the literature are shear-induced and crack-induced. In order to investigate the propensity of shear-induced initiation a Shear Compression Specimen (SCS), combined with Kolsky Bar experimentation, was utilized to predominately load the RM specimen in dynamic shear. COMSOL Multiphysics simulations were conducted in conjunction with the experiments to obtain equivalent stress–strain response of the RM so that the work done on the gauge section of the SCS could be quantified. With the implementation of high-speed cameras, the gauge section of the SCS was monitored in order to observe if RM ignition occurred from the dynamic shear loading. The results of the experiments conducted here indicate that fracture precedes ignition despite severe shear-induced plastic deformation (and associated heating) occurring in the gauge section of the specimen, indicating that a crack-induced ignition mechanism is likely active in this materials system under the studied loading rates. |
Friday, July 15, 2022 9:45AM - 10:00AM |
Y02.00003: Measurements of Sparks inside HE Fireballs Nick Glumac, Samuel Brunkow, Allen L Kuhl, Vladimir Mozin We studied sparks inside HE fireballs, caused by triboelectric charge buildup on carbon particles in the detonation products gases. We studied spark emissions from fireballs created by the detonation of 25-g hemispherical charges. The charge was mounted on a 4-inch diameter steel rod to absorb the high detonation pressures and initiated by a RP-80 ignitor. The rod was flush mounted on a UV transparent PMMA plate. As the hemispherical fireball expanded, it could be photographed both from the side and from underneath. Fireball gases turbulently mix with air, forming a turbulent combustion layer near the outer edge of the fireball. This was visualized using framing-camera photography and 3-color pyrometry. The sparks were visualized using a UV photography system consisting of: (i) a UV lens, (ii) a high-speed image intensifier, and (iii) a booster and (iv) a relay lenses that feeds into a conventional high-speed camera. The sparks emit electromagnetic radiation. This was recorded by 4 different RF antennas covering different frequency ranges: |
Friday, July 15, 2022 10:00AM - 10:15AM |
Y02.00004: Influence of Air-Fuel Ratio on Turbulent Fireball Temperatures Allen L Kuhl, David Grote, Ann Almgren, John Bell We predict the explosion fields from the detonation of different spherical HE charges. Our high-order Godunov code is used for this purpose. Thermodynamics of the gaseous products are predicted by tabulated Cheetah code results. Initial conditions are provided by a similarity solution for a constant velocity Chapman-Jouguet detonation wave, which is mapped onto the Cartesian grid when the wave reaches the radius of the charge. Adaptive Mesh Refinement is used to follow the dynamics of the turbulent mixing structures on the computational mesh. Three different 1-kg charges are studied: TNT, Comp B and LX-14. These have very different Heats of Combustion (3473, 2667, 2292 cal/g) and Air-Fuel ratios (3.14, 2.37, 1.13 g/g) for TNT, Comp B and LX-14, respectively. The computed vorticity fields in the fireballs are similar—which means that the turbulent mixing rates are similar. But to reach stoichiometric conditions, it takes 1.1 units of time for LX-14, 2.4 units of time for Comp B, and 3.1 units of time for TNT. After achieving stoichiometric conditions, further turbulent entrainment of air simply cools the fireball. This is reflected in the mean fireball temperatures, for example: the LX-14 fireball cools to room temperature in 26 milliseconds, while the Comp B fireball remains at 1,500 K until 260 milliseconds. So, while the mean fireball temperatures at stoichiometric conditions are similar, the late-time fireball temperatures are strongly dependent on the air-fuel ratio. LLNL-ABS-832910 |
Friday, July 15, 2022 10:15AM - 10:30AM |
Y02.00005: Effect of pore morphology and multiple hotspot formation mechanisms in high energetic materials Chunyu Li, Alejandro H Strachan The detonation sensitivity of energetic materials depends strongly on the localization of energy in hotspots. Hotspots with temperatures above a critical value can form self-sustained deflagration waves, which subsequently can turn into a detonation. Shock-induced pore collapse is one of the most important hotspot formation mechanisms. Defects or pores in HE materials are complicated and usually have much different morphologies. Although numerous studies have reached the general conclusion of higher porosity results in higher shock sensitivity, the detailed hotspot formation mechanism or mechanisms for complex pore morphology has not been well understood. |
Friday, July 15, 2022 10:30AM - 10:45AM |
Y02.00006: Effect of combined pressure-shear loading on explosives John E Reaugh, Bradley W White The strength of highly filled composites such as plastic bonded explosives is affected by confining pressure as well as strain rate. This behavior is also observed for natural geologic materials and concretes. Mechanical property testing for explosives is typically uniaxial compression and tension. A few laboratories have included compression testing under confining pressure (triax tests). In these tests, two of the principal stresses are equal. |
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