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Engineering models of deflagration-to-detonation transition

Description: For the past two years, Los Alamos has supported research into the deflagration-to-detonation transition (DDT) in damaged energetic materials as part of the explosives safety program. This program supported both a theory/modeling group and an experimentation group. The goal of the theory/modeling group was to examine the various modeling structures (one-phase models, two-phase models, etc.) and select from these a structure suitable to model accidental initiation of detonation in damaged explosives. The experimental data on low-velocity piston supported DDT in granular explosive was to serve as a test bed to help in the selection process. Three theoretical models have been examined in the course of this study: (1) the Baer-Nunziato (BN) model, (2) the Stewart-Prasad-Asay (SPA) model and (3) the Bdzil-Kapila-Stewart model. Here we describe these models, discuss their properties, and compare their features.
Date: July 1995
Creator: Bdzil, J. B. & Son, S. F.
Partner: UNT Libraries Government Documents Department

Characterization of HMX particles in PBX 9501

Description: The particle size distribution and morphology of HMX (cyclotetramethylene-tetranitramine) in the plastic-bonded explosive, PBX 9501 (95% HMX and 5% polymeric binder, by weight), are important to understanding the micromechanical behavior of this material. This paper shows that the size distribution of the {open_quotes}as-received{close_quotes} HMX powder, as measured by light scattering, is not preserved through the processing operations of formulation into molding powder and subsequent consolidation through hydrostatic pressing. Morphological features such as cracking and twinning are examined using reflected light microscopy. This technique helps confirm and interpret the results of the particle size analysis. These results suggest that use of the particle size distribution of the {open_quotes}as-received{close_quotes} powder could potentially yield significant errors in detailed simulations of formulated materials.
Date: September 1, 1997
Creator: Skidmore, C.B.; Phillips, D.S.; Son, S.F. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Remote plunger removal device for small-scale incremental pressing

Description: Small-scale pressing of high explosives (HE) at Los Alamos National Laboratory (LANL) and elsewhere is routinely performed using pneumatic presses. Blast shields provide protection to the operator during the pressing procedure, but safety of the operator is a concern during removal of the plunger, which is currently performed manually. To minimize this risk, very high tolerances between the plunger and the die are required. These tolerances are often very costly, especially in the case of long, relatively narrow dies. The safety issue is an even greater concern with incremental pressing in which cleaning the die between increments is difficult or impossible. To better protect press operators, a device has been designed and constructed to allow remote plunger removal in a standard HE press. In this report the authors describe this modified press that allows remote removal of the plunger.
Date: September 1, 1997
Creator: Burnside, N.J.; Son, S.F. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Modeling compaction-induced energy dissipation of granular HMX

Description: A thermodynamically consistent model is developed for the compaction of granular solids. The model is an extension of the single phase limit of two-phase continuum models used to describe Deflagration-to-Detonation Transition (DDT) experiments. The focus is on the energetics and dissipation of the compaction process. Changes in volume fraction are partitioned into reversible and irreversible components. Unlike conventional DDT models, the model is applicable from the quasi-static to dynamic compaction regimes for elastic, plastic, or brittle materials. When applied to the compaction of granular HMX (a brittle material), the model predicts results commensurate with experiments including stress relaxation, hysteresis, and energy dissipation. The model provides a suitable starting point for the development of thermal energy localization sub-scale models based on compaction-induced dissipation.
Date: December 31, 1998
Creator: Gonthier, K.A.; Menikoff, R.; Son, S.F. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Ignition dynamics of high explosives

Description: Mechanical insults of granular high explosives (HE) can result in localized areas of elevated temperature, or hot spots. The evolution of these hot spots is a central issue of HE science. Because of the complexity involved, it is worthwhile to study mechanical and reaction processes in isolation. Mechanical processes are isolated and studied using inert materials or weak insults where reaction may be minimal. Likewise, purely thermal processes can be considered to isolate HE reaction response. In this work the authors study the radiant ignition of various HEs of interest, including HMX (C{sub 4}H{sub 8}N{sub 8}O{sub 8}), PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF), RDX (C{sub 3}H{sub 6}N{sub 6}O{sub 6}), TATB (C{sub 6}H{sub 6}N{sub 6}O{sub 6}), and PBX 9502 (95% TATB, 5% Kel-F) and aged PBX 9502. Initial work has included unconfined samples at ambient pressure in air. Diagnostics have included photodiodes to record first light emission, high speed photography, microthermocouple and IR emission measurement to obtain surface temperature, IR emission of gases above the pellet, and a novel nonlinear optical technique to characterize the dynamic {beta}-{delta} solid phase transformation and the formation of a liquid layer. The authors find that ignition delays at various power levels is very similar for HMX and RDX; except that the minimum radiant flux needed for RDX ignition is higher. The addition of only 5% binder (PBX 9501) causes significantly longer ignition delays at lower heat fluxes compared with HMX alone. TATB and TATB-based explosives exhibit much longer ignition delays than HMX. In contrast to HMX, however, no measurable difference is observed in TATB by the addition of a binder (PBX 9502, aged or pristine).
Date: December 31, 1998
Creator: Ali, A.N.; Son, S.F.; Sander, R.K. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Modeling energy dissipation induced by quasi-static compaction of granular HMX

Description: A simple extension of a conventional two-phase (inert gas and reactive solid) continuum model of Deflagration-to-Detonation Transition (DDT) in energetic granular material is given to account for energy dissipation induced by quasi-static compaction. To this end, the conventional model equations,, valid in the limit of negligible gas phase effects, are supplemented by a relaxation equation governing irreversible changes in solid volume fraction due to intergranular friction, plastic deformation of granules, and granule fracture. The proposed model constitutes a non-strictly hyperbolic system of equations, and is consistent with the Second Law of Thermodynamics for a two-phase mixture. The model predicts stress relaxation and substantial dissipation induced by quasi-static compaction; such phenomena are commonly observed in quasi-static compaction experiments for granular HMX. Predicted intergranular stress histories compare well with experimental data.
Date: November 1, 1997
Creator: Gonthier, K.A.; Menikoff, R.; Son, S.F. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Deflagration to detonation experiments in granular HMX

Description: In this paper the authors report on continuing work involving a series of deflagration-to-detonation transition (DDT) experiments in which they study the piston-initiated DDT of heavily confined granular cyclotetramethylenetetranitramine (HMX). These experiments were designed to he useful in model development and evaluation. A main focus of these experiments is the effect of density on the DDT event. Particle size distribution and morphology are carefully characterized. In this paper they present recent surface area analysis. Earlier studies demonstrated extensive fracturing and agglomeration in samples at densities as low as 75% TMD as evidenced by dramatic decreases in particle size distribution due to mild stimulus. This is qualitatively confirmed with SEM images and quantitatively studied with gas absorption surface area analysis. Also, in this paper they present initial results using a microwave interferometer technique. Dynamic calibration of the technique was performed, a 35 GHz signal is used to increase resolution, and the system has been designed to be inexpensive for repeated experiments. The distance to where deformation of the inner wall begins for various densities is reported. This result is compared with the microwave interferometer measurements.
Date: March 1, 1998
Creator: Burnside, N.J.; Son, S.F.; Asay, B.W. & Dickson, P.M.
Partner: UNT Libraries Government Documents Department

Inert plug formation in the DDT of granular energetic materials

Description: A mechanism is proposed to explain the {open_quotes}plugs{close_quotes} that have been observed in deflagration-to-detonation transition (DDT) of granular explosives. Numerical simulations are performed that demonstrate the proposed mechanism. Observed trends are reproduced.
Date: September 1, 1995
Creator: Son, S.F.; Asay, B.W. & Bdzil, J.B.
Partner: UNT Libraries Government Documents Department

Modeling DDT in granular explosives with a multi-dimensional hydrocode

Description: We describe results obtained with the implementation of a new large drag limit, two-phase continuum mixture model of DDT into MESA2D. The kinetics scheme originally described by BN is used to simulate a suite of 1D and 2D experiments. The BN kinetics scheme is found to be inadequate.
Date: September 1, 1995
Creator: Kober, E.M.; Bdzil, J.B. & Son, S.F.
Partner: UNT Libraries Government Documents Department

Ignition dynamics of high explosives

Description: The laser ignition of the explosives HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, C{sub 4}H{sub 8}N{sub 8}O{sub 8}), {delta}-phase HMX, PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF), TATB (1,3,5-triamino-2,4,6-trinitrobenzene, C{sub 6}H{sub 6}N{sub 6}O{sub 6}), and PBX 9502 (95% TATB, 5% Kel-F) and aged PBX 9502 has been conducted with the intent to compare the relative sensitivities of those explosives and to investigate the effect of beam profile, binder addition, and porosity. It has been found that there was little difference between a gaussian beam and a top hat profile on the laser ignition of HMX. The authors observe that the addition of binder in the amounts present in PBX 9501 resulted in longer ignition delays than that of HMX. In contrast to HMX, the addition of binder to TATB in PBX 9502 shows no measurable effect. Porosity effects were considered by comparing the ignition of granular HMX and pressed HMX pellets. Porosity appears to increase ignition delay due to an increased effective absorption scale and increased convective heat loss. This porosity effect also resulted in longer ignition delays for {delta}-phase HMX than for {beta}-phase HMX. In order to simulate ignition in voids or cracks, the standard ignition experiment was modified to include a NaCl window placed at variable distances above the sample surface. When ignition experiments were performed at 29 W/cm{sup 2} and 38 W/cm{sup 2} a critical gap distance was observed of 6 {+-} 0.4 mm below which ignition was severely inhibited. This result underscores the importance of gas phase processes in ignition and illustrates that conditions can exist where simple ignition criteria such as surface temperature is inadequate.
Date: April 1, 1999
Creator: Ali, A.N.; Son, S.F.; Sander, R.K.; Asay, B.W. & Brewster, M.Q.
Partner: UNT Libraries Government Documents Department

Aging and PBX 9502

Description: Components made from PBX 9502, an insensitive high explosive formulated with triaminotrinitrobenzene (TATB) and Kel-F 800 binder, have been in service for nearly two decades. Since that time, samples have been destructively evaluated to determine if potential changes that might affect safety, reliability, or performance have occurred in the high explosive with time. Data from routine, historical testing is reported elsewhere. This paper focuses on specific tests conducted to evaluate the effects of natural aging on handling sensitivity (through the small-scale tests of Human Electrostatic Discharge, friction, and Drop Weight Impact), compressive strength, and thermal ignition. Also reported are the effects of a radiation environment on TATB. Small-scale sensitivity tests show no differences between aged and unaged material. Observed differences in compressive strength behavior are attributed to conditions of original material rather than aging effects. Thermal ignition by flame and laser methods showed no changes between aged and unaged material. Extreme levels of radiation are shown to have only minimal effects in explosive response tests. PBX 9502 is concluded, once again, to be a very stable material, aging gracefully.
Date: December 31, 1998
Creator: Skidmore, C.B.; Idar, D.J.; Buntain, G.A.; Son, S.F. & Sander, R.K.
Partner: UNT Libraries Government Documents Department

New paradigm for simplified combustion modeling of energetic solids: Branched chain gas reaction

Description: Two combustion models with simple but rational chemistry are compared: the classical high gas activation energy (E{sub g}/RT {much_gt} 1) Denison-Baum-Williams (DBW) model, and a new low gas activation energy (E{sub g}/RT {much_lt} 1) model recently proposed by Ward, Son, and Brewster (WSB). Both models make the same simplifying assumptions of constant properties, Lewis number unity, single-step, second order gas phase reaction, and single-step, zero order, high activation energy condensed phase decomposition. The only difference is in the gas reaction activation energy E{sub g} which is asymptotically large for DBW and vanishingly small for WSB. For realistic parameters the DBW model predicts a nearly constant temperature sensitivity {sigma}{sub p} and a pressure exponent n approaching 1. The WSB model predicts generally observed values of n = 0.7 to 0.9 and {sigma}{sub p}(T{sub o},P) with the generally observed variations with temperature (increasing) and pressure (decreasing). The WSB temperature profile also matches measured profiles better. Comparisons with experimental data are made using HMX as an illustrative example (for which WSB predictions for {sigma}{sub p}(T{sub o},P) are currently more accurate than even complex chemistry models). WSB has also shown good agreement with NC/NG double base propellant and HNF, suggesting that at the simplest level of combustion modeling, a vanishingly small gas activation energy is more realistic than an asymptotically large one. The authors conclude from this that the important (regression rate determining) gas reaction zone near the surface has more the character of chain branching than thermal decomposition.
Date: September 1, 1997
Creator: Brewster, M. Q.; Ward, M. J. & Son, S. F.
Partner: UNT Libraries Government Documents Department

A model for steady-state HNF combustion

Description: A simple model for the combustion of solid monopropellants is presented. The condensed phase is treated by high activation energy asymptotics. The gas phase is treated by two limit cases: high activation energy, and low activation energy. This results in simplification of the gas phase energy equation, making an (approximate) analytical solution possible. The results of the model are compared with experimental results of Hydrazinium Nitroformate (HNF) combustion.
Date: September 1, 1997
Creator: Louwers, J.; Gadiot, G.M.H.J.L.; Brewster, M.Q. & Son, S.F.
Partner: UNT Libraries Government Documents Department

Lead-free electric matches.

Description: Electric matches are used in pyrotechnics to initiate devices electrically rather than by burning fuses. Fuses have the disadvantage of burning with a long delay before igniting a pyrotechnic device, while electric matches can instantaneously fire a device at a user's command. In addition, electric matches can be fired remotely at a safe distance. Unfortunately, most current commercial electric match compositions contain lead as thiocyanate, nitroresorcinate or tetroxide, which when burned, produces lead-containing smoke. This lead pollutant presents environmental exposure problems to cast, crew, and audience. The reason that these lead containing compounds are used as electric match compositions is that these mixtures have the required thermal stability, yet are simultaneously able to be initiated reliably by a very small thermal stimulus. A possible alternative to lead-containing compounds is nanoscale thermite materials (metastable intermolecular composites or MIC). These superthermite materials can be formulated to be extremely spark sensitive with tunable reaction rate and yield high temperature products. We have formulated and manufactured lead-free electric matches based on nanoscale Al/MoO{sub 3} mixtures. We have determined that these matches fire reliably and to consistently ignite a sample of black powder. Initial safety, ageing and performance results are presented in this paper.
Date: January 1, 2002
Creator: Son, S. F. (Steven F.); Hiskey, M. A. (Michael A.); Naud, D. (Darren); Busse, J. R. (James R.) & Asay, B. W. (Blaine W.)
Partner: UNT Libraries Government Documents Department

Steady state HNG combustion modeling

Description: Two simplified modeling approaches are used to model the combustion of Hydrazinium Nitroformate (HNF, N{sub 2}H{sub 5}-C(NO{sub 2}){sub 3}). The condensed phase is treated by high activation energy asymptotics. The gas phase is treated by two limit cases: the classical high activation energy, and the recently introduced low activation energy approach. This results in simplification of the gas phase energy equation, making an (approximate) analytical solution possible. The results of both models are compared with experimental results of HNF combustion. It is shown that the low activation energy approach yields better agreement with experimental observations (e.g. regression rate and temperature sensitivity), than the high activation energy approach.
Date: April 1, 1998
Creator: Louwers, J.; Gadiot, G. M. H. J. L.; Brewster, M. Q.; Son, S. F.; Parr, T. & Hanson-Parr, D.
Partner: UNT Libraries Government Documents Department

Some Observations on the Structure of TATB

Description: The recent discovery of second-harmonic light generation (SHG) from 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has renewed interest in both the crystallography and the identification of defect structures in this material. The accepted crystal structure is triclinic but centrosymmetric (P-1); SHG is not expected from materials of this symmetry. A wide variety of syntheses have been shown to produce SHG-positive materials, including an emulsion technique, two different recrystallization methods, and a variety of combined reaction - precipitation processes. In addition, two standard commercial powders have shown the property after annealing in the 300 C range. We have examined the structures of several of these powders using polarized light microscopy (PLM), scanning electron microscopy (SEM), and powder X-ray diffraction (XRD). We find that SHG-positive materials typically contain crystals both more transparent and more strongly faceted (i.e. ''more perfect'') than weak-SHG ones and that the positive samples show stronger texture in their powder diffraction patterns. These results are compared with predictions from Cady's structure.
Date: June 28, 1999
Creator: D.S., Phillips; Schwarz, R.B.; Skidmore, C.B.; Hiskey, M.A. & Son, S.F.
Partner: UNT Libraries Government Documents Department

Propagation studies of metastable intermolecular composites (MIC).

Description: Thermite materials are attractive energetic materials because the reactions are highly exothermic, have high energy densities, and high temperatures of combustion. However, the application of thermite materials has been limited because of the relative slow release of energy compared to other energetic materials. Engineered nano-scale composite energetic materials, such as Al/MoO{sub 3}, show promise for additional energetic material applications because they can react very rapidly. The composite material studied in this work consists of tailored, ultra-fine grain (30-200 nm diameter) aluminum particles that dramatically increase energy release rates of these thermite materials. These reactant clusters of fuel and oxidizer particles are in nearly atomic scale proximity to each other but are constrained from reaction until triggered. Despite the growing importance of nano-scale energetic materials, even the most basic combustion characteristics of these materials have not been thoroughly studied. This paper reports initial studies of the ignition and combustion of metastable intermolecular composites (MIC) materials. The goals were lo obtain an improved understanding of flame propagation mechanisms and combustion behaviors associated with nano-structured energetic materials. Information on issues such as reaction rate and behavior as a function of composition (mixture ratio), initial static charge, and particle size are essential and will allow scientists to design applications incorporating the benefits of these compounds. The materials have been characterized, specifically focusing on particle size, shape, distribution and morphology.
Date: January 1, 2002
Creator: Son, S. F. (Steven F.); Busse, J. R. (James R.); Asay, B. W. (Blaine W.); Peterson, P. D. (Paul D.); Mang, J. T. (Joseph T.); Bockmon, B. (Bryan) et al.
Partner: UNT Libraries Government Documents Department

OPTICAL MICROSCOPY AND SMALL-ANGLE SCATTERING STUDY OF POROSITY IN THERMALLY TREATED PBX 9501

Description: Heat transfer and comlmstion properties of a high explosive (HE) are influenced by the HE microstructure. The development of voids and cracks in an HE system under the conditions of thermal loading can have a strong impact on the safety and reliability of a weapon system. The optical microscopy and small angle x-ray scattering (SAXS) techniques are useful tools for microstructural characterization. A combination of the tools allows lengthscales from hundreds of microns to tenths of nanometers to be probed, allowing a thorough description of a system's microstructure to be made. We present an optical microscopy and SAXS study of the effects of thermal loading on the microstructure of PBX 9501. Pressed pellets of PBX 9501, an HMX-based system, were heated in an oven at 180 'C for periods of 0, 15 and 30 minutes. Optical micrographs reveal the developmenit of large pores in the microstructure with increasing thermal treatment as well as increased cracking and morphological changes of crystal grains, associated with the beta to delta phase transition in HMX. SAXS measurements were performed in order to quantify the observed porosity,
Date: January 1, 2001
Creator: Mang, J. T. (Joseph T.); Skidmore, C. B. (Cary B.); Hjelm, R. P. (Rex P.); Ricker, T. P. (Thomas P.) & Son, S. F. (Steven F.)
Partner: UNT Libraries Government Documents Department

High-nitrogen explosives

Description: The syntheses and characterization of various tetrazine and furazan compounds offer a different approach to explosives development. Traditional explosives - such as TNT or RDX - rely on the oxidation of the carbon and hydrogen atoms by the oxygen carrying nitro group to produce the explosive energy. High-nitrogen compounds rely instead on large positive heats of formation for that energy. Some of these high-nitrogen compounds have been shown to be less sensitive to initiation (e.g. by impact) when compared to traditional nitro-containing explosives of similar performances. Using the precursor, 3,6-bis-(3,5-dimethylpyrazol-1-yl)-s-tetrazine (BDT), several useful energetic compounds based on the s-tetrazine system have been synthesized and studied. The compound, 3,3{prime}-azobis(6-amino-s-tetrazine) or DAAT, detonates as a half inch rate stick despite having no oxygen in the molecule. Using perfluoroacetic acid, DAAT can be oxidized to give mixtures of N-oxide isomers (DAAT03.5) with an average oxygen content of about 3.5. This energetic mixture burns at extremely high rates and with low dependency on pressure. Another tetrazine compound of interest is 3,6-diguanidino-s-tetrazine(DGT) and its dinitrate and diperchlorate salts. DGT is easily synthesized by reacting BDT with guanidine in methanol. Using Caro's acid, DGT can be further oxidized to give 3,6-diguanidino-s-tetrazine-1,4-di-N-oxide (DGT-DO). Like DGT, the di-N-oxide can react with nitric acid or perchloric acid to give the dinitrate and the diperchlorate salts. The compounds, 4,4{prime}-diamino-3,3{prime}-azoxyfurazan (DAAF) and 4,4{prime}-diamino-3,3{prime}-azofurazan (DAAzF), may have important future roles in insensitive explosive applications. Neither DAAF nor DAAzF can be initiated by laboratory impact drop tests, yet both have in some aspects better explosive performances than 1,3,5-triamino-2,4,6-trinitrobenzene TATB - the standard of insensitive high explosives. The thermal stability of DAAzF is equal to that of hexanitrostilbene (HNS), yet it has a greater CJ pressure and detonation velocity. In an effort to reduce the critical diameter of TATB without sacrificing its insensitivity, we ...
Date: January 1, 2002
Creator: Naud, D. (Darren); Hiskey, M. A. (Michael A.); Kramer, J. F. (John F.); Bishop, R. L. (Robert L.); Harry, H. H. (Herbert H.); Son, S. F. (Steven F.) et al.
Partner: UNT Libraries Government Documents Department