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Using gas-gun-driven plate impact techniques, we have measured the Hugoniot of the filled silicone elastomer DC745U cooled to -60°C. DC745U consists of approximately 62 weight% poly-dimethyl-siloxane rubber and 38 wt% silicon dioxide filler. At ~ -50°C, the poly-dimethyl-siloxane rubber in DC745U crystallizes with ~ 40% crystallinity. This is accompanied by a density change from 1.31 g/cm³ at 23°C to 1.45 g/cm³ at -60°C. Below the crystallization transition temperature, a measurable increase in the shock velocity was observed. This is coincident with a decrease in compressibility due to crystallization of the polydimethylsiloxane repeat units. The linear US - up Hugoniot also significantly changes from US = 1:62 + 1:74up mm/µs at 23°C to US = 2:00 ± 0:05 + (2:06 ± 0:06)up mm/µs at -60°C. Cooling to -60°C and the associated crystalline phase transition therefore results in considerable stiffening. This is the first time, to our knowledge, that a polymer crystallization transition has been shown to affect shockwave properties in this way. [ABSTRACT FROM AUTHOR]

Several shock studies have been made on polyurethane materials, both fully dense and distended in the form of foams. However, there is a lack of shock data between the densities of 0.321 and 1.264 g/cm³ (fully dense).We present here data obtained from two different types of shock experiments at densities of 0.35, 0.5, 0.68, 0.78, and 0.9g/cm³ in order to fill in the density deficiencies and make it easier to develop an unreacted equation of state (EOS) for polyurethane as a function of density. A thermodynamically consistent EOS was developed, based on the Helmholtz free energy, and was used to predict the shock properties of polyurethane materials at densities from 1.264 to 0.348 g/cm³ . These estimates are compared to the available data. The data match quite close to the predictions and provide a basis for calculating polyurethane foam shock processes. Chemical reaction has been observed at relatively high pressure (21.7GPa) in fully dense polyurethane in an earlier study, and the equation of state presented here is representative of the unreacted polyurethane foam. Lowering the density is expected to drop the shock pressure for chemical reaction, yet there is not enough data to address the low density shock reaction thresholds in this study. [ABSTRACT FROM AUTHOR]

The dynamic (shock) responses of two carbon fiber-filled polymer composites have been quantified using gas gun-driven plate impact experimentation. The first composite is a filament-wound, highly unidirectional carbon fiber-filled epoxy with a high degree of porosity. The second composite is a chopped carbon fiber- and graphite-filled phenolic resin with little- to-no porosity. Hugoniot data are presented for the carbon fiber-epoxy (CE) composite to 18.6GPa in the through-thickness direction, in which the shock propagates normal to the fibers. The data are best represented by a linear Rankine-Hugoniot fit: Us = 2.87 + 1.17 × up(ρ0 = 1.536 g/cm³). The shock wave structures were found to be highly heterogeneous, both due to the anisotropic nature of the fiber-epoxy microstructure, and the high degree of void volume. Plate impact experiments were also performed on a carbon fiber-filled phenolic (CP) composite to much higher shock input pressures, exceeding the reactants-to- products transition common to polymers. The CP was found to be stiffer than the filament-wound CE in the unreacted Hugoniot regime, and transformed to products near the shock-driven reaction threshold on the principal Hugoniot previously shown for the phenolic binder itself. [19] On-going research is focused on interrogating the direction-dependent dyanamic response and dynamic failure strength (spall) for the CE composite in the TT and 0° (fiber) directions. [ABSTRACT FROM AUTHOR]

One of the more common ammonium nitrate(AN)-based explosives is ANFO, which is a mixture of AN prills and diesel fuel oil (FO) in a 94:6 ratio by weight. Since there are no available shock data on FO, a series of shock compression experiments have been completed using a two-stage light gas gun with a sealed liquid target cell. The FO studied was diesel #2 which has been used in a number of ANFO explosive shots. Density and sound speed data were measured and used to predict and compare the data to a universal liquid Hugoniot (ULH). In-situ magnetic gauges in the target cell were used to measure the particle velocity, shock velocity, and shock wave profiles. Projectile impact velocities ranged from 1.5 to 3.2 km/s, generating input pressures to the FO between 3 and 17 GPa (depending on the impactor material being used). No shock-induced reaction was observed in the FO in any of the experiments. Since the ULH was found to slightly under predict the FO Hugoniot states, a linear Hugoniot was fit to the data - Us = 1.775 + 1.725 up - in mm/μs. A Helmholtz EOS based on the Murnaghan isotherm was developed so the temperature on the Hugoniot could be estimated. At 12 GPa the shock temperature is expected to be 1500K. [ABSTRACT FROM AUTHOR]

FEFO is a liquid explosive with a density of 1.60 g/cm³ and an energy output similar to that of trinitrotoluene (TNT), making it one of the more energetic liquid explosives. Here we describe shock initiation experiments that were conducted using a two-stage gas gun using magnetic gauges to measure the wave profiles during a shock-to-detonation transition. Unreacted Hugoniot data, time-to detonation (overtake) measurements, and reactive wave profiles were obtained from each experiment. FEFO was found to initiate by the homogeneous initiation model, similar to all other liquid explosives we have studied (nitromethane, isopropyl nitrate, hydrogen peroxide). The new unreacted Hugoniot points agree well with other published data. A universal liquid Hugoniot estimation slightly under predicts the measured Hugoniot data. FEFO is very insensitive, with about the same shock sensitivity as the triamino-trinitro-benzene (TATB)-based explosive PBX9502 and cast TNT. [ABSTRACT FROM AUTHOR]

Simple molecules such as formic acid, HCOOH, have been suggested to play important roles in the origin of life due to their high pressure and temperature chemistry. The hydrogen bonding characteristics and polymerization of HCOOH under static high pressure have been recently investigated using both molecular dynamics calculations and experimental work. These works suggest that symmetric hydrogen bonding of HCOOH (forming a linear chain polymer where all C-O bonds are equivalent) occurs at 16 - 21 GPa at room temperature. In order to examine the shock compression behavior of this simple carboxylic acid, we present a series of gas gun-driven plate impact experiments on formic acid with shock inputs in the range of 5.5 - 23.0 GPa. Using in-situ electromagnetic gauges, shock wave profiles (particle velocities) were measured at multiple positions as a function of shock input pressure, providing valuable information about its unreacted equation of state. No easily recognizable shock-induced reactions were observed in any of the four experiments, and the four points lie close to a universal liquid Hugoniot based only on the sound speed of formic acid. [ABSTRACT FROM AUTHOR]

A Remote Liquid Loading System (RLLS) was designed and tested for the application of loading high-hazard liquid materials into instrumented target cells for gas gun-driven plate impact experiments. These high hazard liquids tend to react with confining materials in a short period of time, degrading target assemblies and potentially building up pressure through the evolution of gas in the reactions. Therefore, the ability to load a gas gun target immediately prior to gun firing provides the most stable and reliable target fielding approach. We present the design and evaluation of an RLLS built for the LANL two-stage gas gun. The system has been used successfully to interrogate the shock initiation behavior of ∼98 wt% percent hydrogen peroxide (H2O2) solutions, using embedded electromagnetic gauges for measurement of shock wave profiles in-situ. [ABSTRACT FROM AUTHOR]

Understanding of the chemistry that occurs under extreme, high-pressure, high-temperature shock environments poses both a significant scientific challenge, due to the difficulty of direct experimental observations, and an opportunity for discovery of new materials and bonding constructs. The combined high pressure, high temperature conditions induced by shock loading results in prompt reactions that may include dynamic bond breaking, dimerization and polymerization, and dissociation to small molecules. Understanding of the evolution of different reaction pathways as a function of shock input remains a significant challenge, due to both the very short shock timescales, and difficulty in measurement of reaction intermediates and products. We have used in-situ multiple magnetic gauges to measure changes in mechanical variables (such as particle velocity waveforms) resulting from the shock-induced chemistry. This allows us to gain some understanding of the shock input conditions necessary to start chemical reaction. Seven experiments have been completed on a set of related organic liquids; 1-3 cyclohexadiene was found to react at 4.9 GPa, 1-4 cyclohexadiene at 7 GPa, cyclohexene between 10 and 12 GPa, and cyclopentene results were inconclusive. Since 1-3 cyclohexadiene could dimerize by a Diels-Alder reaction, it was expected to react at the lowest pressure. [ABSTRACT FROM AUTHOR]

Shock-induced chemical reactions remain an area in shock physics that needs further investigation, particularly for determining the influence of pressure, temperature, and chemical structure on reactivity. Several studies have been done in the past that indicate dimerization, polymerization, and decomposition take place in different shock-produced pressure and temperature regimes depending on chemical functionality. We present results obtained from single-shock experiments in which liquids were studied using embedded multiple magnetic gauges to make in-situ measurements of the particle velocity profiles at up to ten Lagrangian positions in the liquid. One of the liquids was organic (tert-butylacetylene) and the other was a closely related silicon-based material (ethynyltrimethylsilane). Multiple wave structures were measured in each liquid when the input pressure was above a certain threshold. Here, the reactivity of these materials are compared. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report here on a collection of shock compression experiments on a silicon polymer foam with varying degrees of distension from low (∼0.4 g/cm3) to the near fully dense material (∼ 1 g/cm3). These experiments are being carried out on a two-stage gas-gun (50 mm bore) with a Kel-F 81 impactor at velocities between 1.5 and 3.1 km/s. Particle and shock velocity measurements are made with magnetic gauges by inserting the gauge package (0.001 inches thick) between layers of 2.3 mm thick foam. Special attention is required for assembly of these targets due to the foam’s low strength. To minimize compression and gaps at interfaces, the foams are positioned between support rings, which are machined to match the foam’s thickness. The Hugoniot data from these experiments is compared to unpublished data obtained with explosively driven flyers at Los Alamos National Laboratory in the early 1980’s. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Single-stage and two-stage gas gun experiments have been completed to measure the unreacted Hugoniot of PBX9501 high explosive (HE). Two types of experiments were done: 1) PBX9501 was impacted with a higher impedance projectile and the interface particle velocity history was measured using a magnetic gauge glued to the HE front; 2) a PBX9501 disc was mounted in the front of a projectile that impacted a LiF window and velocity interferometers (VISAR) were used to measure the impact interface particle velocity history. Inputs to the PBX9501 ranged from 3 to 15 GPa in these experiments. Particle velocity waveforms show an induction time followed by a particle velocity change (the nature of the change depends on the type of experiment) corresponding to shock-induced reaction in the PBX9501. The induction part of the waveform provided unreacted Hugoniot information so several new high-pressure Hugoniot points were generated. These data do not indicate a softening in the unreacted Hugoniot at high pressures; more experiments will be necessary to determine this. By using an estimate for the reaction product EOS, it was possible to estimate the average PBX9501 initial reaction rate for each experiment. The induction time decreases with pressure and the reaction rate increases with pressure. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A line optically-recording velocity interferometer system (ORVIS) was used to measure laser-driven flyer plates impacting windows of various materials. Since the particle velocity can be measured along a line, half the line measured the acceleration of the flyer plate as well as the effect of the impact on the window. The other half of the line measured the jump in particle velocity upon impact with the window because the window was mirrored on that half. This provided information about the flyer velocity and two independent measurements of the interface particle velocity resulting from the flyer impact. Hugoniot data for copper flyers were obtained. In addition, the flatness of the flyer plate during its acceleration and the effect of this flatness on the Hugoniot data obtained are discussed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have studied the effects of damage caused by compressive loading on the shock sensitivity of the plastic bonded explosive PBX 9501. PBX 9501 consists of 95 wt. % HMX and 5 wt. % nitroplasticized Estane binder. The binder is a mixture of 49 wt. % Estane® 5703 (BF Goodrich), 49 wt. % Nitroplasticizer (a eutectic mixture of bis(2,2-dinitropropyl)formal and bis(2,2 dinitropropyl)acetal), and 2 wt. % Irganox® 1010 stabilizer. PBX 9501 cubes, 25.4 mm on a side, were compressed to various uniaxial loads in an Instron machine. After loading, 10×10 mm cross-sections, 3.5 mm thick, were taken from the center of each cube. These slices were then subjected to nearly identical 35 kbar shocks. Transmitted shock wave profiles were measured using interface velocimetry (VISAR). Comparison of shock wave growth is a measure of shock sensitivity. Results on four samples indicate little change in sensitivity caused by compressive loading. [ABSTRACT FROM AUTHOR]