Search

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]

In previous work involving firing flat nosed steel rods into the 60/40 RDX/TNT explosive Composition B-3, we found an apparently anomalous "hump" in particle velocity wave profiles. The "hump" occurred on the center-line established by the rod, and at relatively late times, > 1 ms, after detonation onset. Several explanations, including that of a late time reaction, were postulated. This report will present evidence that the anomalous late time "hump" is due to the arrival of rarefaction waves from the rod's periphery. Simple analytic calculations and reactive-burn hydro-code calculations will be presented supporting this hypothesis. [ABSTRACT FROM AUTHOR]

We present gas-gun driven plate impact shock initiation experiments on the explosive PBX 9502 (95 weight percent triaminotrinitrobenzene, 5 weight percent Kel-F 800 binder) heated to ∼ 76°C. PBX 9502 samples were heated by flowing hot air through a sample mounting plate and surrounding coil. Temperatures were monitored using embedded and surface mounted type-E thermocouples. The shock to detonation transition was recorded using embedded electromagnetic particle velocity gauges. Results show increased shock sensitivity; time and distance to detonation onset vs. initial shock pressure are shorter than when the sample is initially at ambient temperature. Our results are consistent with those reported by Dallman and Wackerle: the "Pop-plot," or distance to detonation, xD, vs. impact pressure, P, is log10(xD) = 3.41-2.47log10(P). [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]

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]

Gas-gun driven plate impact experiments were performed on High Performance Propellant (HPP) to measure the shock compression behavior and Hugoniot. HPP is a proprietary blend of ammonium-perchlorate (AP), aluminum, and plastic binder. A small amount of FeO2 gives the propellant a rust color. The primary diagnostic was embedded magnetic particle velocity gauges. The Hugoniot was determined by performing multiple experiments using different impactors and a range of impact velocities. Impact stresses ranged from 0.3 GPa to 15 GPa. Even at the highest stress no reaction was observed; none was expected. At low stress HPP exhibits viscoelastic behavior with rounded wave profiles. Hugoniot data can be described using a model based on a Murnaghan isotherm with a small amount of porosity. [ABSTRACT FROM AUTHOR]

The shock to detonation transition was evaluated in the HMX based explosive PBXN-9 by a series of light-gas gun experiments. PBXN-9 consists of 92 wt% HMX, 2wt% Hycar 4054 & 6 wt% dioctyl adipate with a density of 1.75 g/cm3 and 0.8&% voids. The experiments were designed to understand the specifics of wave evolution and the run distance to detonation as a function of input shock pressure. These experiments were conducted on gas guns in order to vary the input shock pressure accurately. The primary diagnostics were embedded magnetic gauges, which are based on Faraday’s law of induction, and Photon Doppler Velocimetry (PDV). The run distance to detonation vs. shock pressure, or “Pop plot,” was redefined as log(X) = 2.14–1.82 log (P), which is substantially different than previous data. The Hugoniot was refined as Us = 2.32+2.211 Up. This data will be useful for the development of predictive models for the safety and performance of PBXN-9 along with providing increased understanding of HMX based explosives in varying formulations. [ABSTRACT FROM AUTHOR]

Several HMX-based explosive samples were subjected to shockless compression using Sandia’s Z magnetic compression accelerator. A multi-panel ICE configuration containing various thicknesses of energetic composites PBX9501, PBXN9, LX-10 was subjected to ramp loading up to 320 Kbar over 500 ns. A Velocity Interferometer System for Any Reflector (VISAR) was used to measure transmitted wave profile data of particle velocity and forward and backward procedures were used with an optimization method to determine appropriate EOS data. [ABSTRACT FROM AUTHOR]

We have completed a series of shock initiation experiments on two lots of PBX 9502 (95 weight % TATB, 5 weight % Kel-F 800 binder). One PBX 9502 lot contained few fine particles (10 weight % <20 microns) while the second lot contained many fines (38 weight % <20 microns). Large, 71 mm diameter PBX 9502 samples were used and input pressures were 7.5–8.5 GPa, resulting in run distances of 25–35 mm. Buildup to detonation was measured using embedded magnetic particle velocity gauges. An unusual feature of the work was the use of metallic impactors (316 stainless steel) in combination with magnetic gauges. It has previously been assumed that conducting impactors would badly perturb the magnetic gauge measurements. However, we observed only a baseline voltage shift of ≈10% which increased linearly with time. Results include detonation coordinates (x*, t*) vs. initial shock pressure. No lot to lot differences in initiation behavior were observed. [ABSTRACT FROM AUTHOR]

The temperature control system for gas gun targets was originally designed to heat or cool a sample to a final temperature between -75 °C and +120 °C. The system has now been used for 14 experiments, 13 of which were on the high explosive PBX 9502 cooled to a final temperature of -55 °C. These experiments have stimulated us to make many improvements, including redesigned plumbing and an extension of the heating range to +250 °C. In addition, rise time data from the magnetic gauges indicates that sample/projectile tilt is on the order of 10 milliradians. An optical system was built to measure changes in the sample surface position and orientation. Measurements made on a Teflon test sample will be presented. [ABSTRACT FROM AUTHOR]

A series of quasi-isentropic magnetic pulse compression experiments using the Sandia Z accelerator and DICE small pulser have provided new insights to the material behavior of various constituents typically used in energetic composites. In this study, a combination of forward and backward procedures with optimization methods is used to determine appropriate constitutive and EOS property data. Sensitivity analysis is performed to assess the uncertainties of the experimental measurements and the subsequent influences in determining material response. The data interrogation technique has been applied to a series of tests with ramp loading condition to 50 Kbar over duration of ∼500 ns for panel configurations containing explosive crystals (HMX and RDX), binders (Estane, C7-Teflon, Kel-F and THV) and composites (PBS9501, PBX9502, and Al/Teflon). [ABSTRACT FROM AUTHOR]

Nitroplasticized Estane (hereafter NP-Estane) is the plastic binder used to hold HMX grains together in the plastic bonded explosive PBX 9501. It is a mixture of 49 wt. % Estane®5703 (BF Goodrich), 49 wt. % Nitroplasticizer (a 50/50 eutectic mixture of bis(2,2-dinitropropyl)formal and bis(2,2 dinitropropyl)acetal), and 2 wt. % Irganox® 1010 stabilizer. NP-Estane samples 0.1 – 2 mm thick were prepared by compression molding at 110°C. Hydrostatic compression to 2 kbar was measured at 34, 43, and 53°C. CP was measured at ambient conditions. NP-Estane was also isentropically compressed to ≈ 35 kbar in experiment Z1251 on the Sandia Z-Machine. Profiles of ramp waves transmitted through NP-Estane were measured and compared with a free surface reference profile using Hayes’s “Backward” analysis and repeated forward analysis with the CTH hydrocode. The following thermodynamic quantities have been obtained; volume coefficient of thermal expansion α = 7.2(10-4)/C, CP = 1.76 J/g C, CV = 1.41 J/g C, isentropic and isothermal bulk moduli, BS = 36.4 kbar, BT = 29.3 kbar, Grüneisen constant Γ = 1.45. The Z1251 experiment is well fit using a Mie-Grüneisen equation of state with the quadratic US - uP relation, US = 1.69 + 2.7uP - (0.7/1.69)uP2 km/s. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

New experimental diagnostics and computational modeling provide an unprecedented means for improving the understanding of energetic material behavior at the mesoscale (grain or crystal ensemble levels). This study focuses on the determination of appropriate constitutive and EOS property data of the constituents of an energetic composite at high stress and moderate strain-rate states. The Sandia Z accelerator is used to determine the mechanical response of energetic composites via isentropic ramp wave compression loading. In this paper we describe an energy source method in CTH that models ramp loading for the analysis of ICE experiments. This approach is applied to design experimental configurations to probe the constituent response of PBX 9501 subjected to ∼40 Kbar ramp load over 300 ns duration. Multiple VISAR are used to determine the averaged response of the composite material in comparison to the individual constituents including the effects of anisotropy of HMX crystals and the interactions of fine crystallites with binder material. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This work applies a ramped, quasi-isentropic compression loading technique (ICE) to investigate the mechanical behavior of polymers that are often used in energetic composites. The focus of this effort is the determination of appropriate constitutive and EOS property data at high stress states and moderate strain rates that is needed for detailed mesoscale modeling. Several thicknesses of samples were subjected to a ramp load of ∼45 Kbar over 500 ns duration using the Sandia Z-machine. Profiles of transmitted ramp waves were measured at window interfaces using conventional VISAR. Shock physics analysis is then used to determine the nonlinear material response of the binder materials. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Fluoropolymers are widely used in a variety of applications due to their favorable properties that include chemical inertness, low coefficient of friction, and ability to withstand high-temperature operating conditions. Additionally, their high densities also make them desirable materials for use as high explosive binders in plastic bonded explosives. Here, we present the first investigation of the dynamic (shock) and static compression behavior of the fluorinated binder poly(chlorotrifluoroethylene-co-vinylidene fluoride) (Kel-F 800). Kel-F 800 samples prepared by both compression molding and melt-processing methods were studied. We observed little difference in the dynamic behavior of the two materials, despite a difference in crystallinity of 10–15%. A linear Rankine-Hugoniot fit to the Hugoniot loci in the Us-up plane gives Us = 1.838 + 1.824 up. Langrangian sound velocities at pressure were also measured at 3.0 (cL = 4.7 mm/μs) and 4.9 (cL = 5.8 mm/μs) GPa. © 2006 American Institute of Physics [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]

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]

Measuring techniques, including magnetic gauges, quartz gauges, manganin gauges, PVDF gauges, velocity interferometry, piezoelectric pins, shorting pins, flash gaps, etc., have been used over the years in shock experiments in condensed phase materials. The use of a particular technique depends on the measured parameter and the sample material properties. This paper concentrates on in-situ magnetic gauging which is particularly useful in high explosive (HE) shock initiation experiments. A short history of this technique will be given but the main discussion will concentrate on the multiple magnetic gauge technique developed at Los Alamos National Lab.(LANL). Vorthman and Wackerle[SUP1,2] started the technique development in 1980, concentrating on particle velocity and "impulse" gauges so that Lagrange analysis could be used to map the entire reactive field. Over the years, changes to the gauge design, fabrication, and experimental focus have led to the present LANL technique. During the past two years measurements have tracked the reactive wave evolution resulting from a shock-to-detonation transition in several high explosive materials. Analysis of the data from a single experiment provides: 1) an unreacted Hugoniot point in which both the shock velocity and particle velocity are measured, 2) shock front tracking, 3) ten particle velocity profiles which measure the reactive wave evolution, 4) a "Pop-plot" distance-(time-)to-detonation point, and 5) a 3% measurement of the detonation velocity. Details of the experimental setup and information from several experiments will be discussed. [ABSTRACT FROM AUTHOR]

Planar shock wave initiation of the explosive EDC-37 was studied using multiple embedded magnetic particle velocity gauges. EDC-37 consists of (by weight) 91% HMX, 1% nitrocellulose, and 8% K10, a liquid eutectic mixture of di- nitro-ethyl-benzene and tri-nitro-ethyl-benzene. Its nominal density is 1.841 ± 0.002 g/cm[SUP3]. The Hugoniot for EDC-37 was measured as U[SUBS] = 2.4+2.4μ[SUBP], similar to other explosives of this density containing at least 90% HMX. The run distance to detonation, X[SUP*], vs. shock pressure P, was measured as log(X[SUP*])= 2.0-1.5 log(P). This curve is shifted to a few GPa higher pressure compared to that of other plastic bonded explosives containing 90 - 95 % HMX. This shift is most likely due to the low void content of EDC-37. Like other high density HMX based explosives, EDC-37 initiates with wave profiles having a little increase in particle velocity at the shock front (heterogeneous initiation), and also a second wave which starts small at the impact surface, grows as it travels, and reaches a large amplitude when it overtakes the shock front (homogeneous initiation). This latter characteristic indicates a time delay between formation of hot spots and release of hot spot energy. [ABSTRACT FROM AUTHOR]