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Strategies for understanding the deflagration-to-detonation transition

Description: The deflagration-to-detonation (DDT) phenomenon has been studied for many years. However, no comprehensive model of the DDT process is available. It is important to understand the mechanism by which an explosive will detonate when the source of ignition is a weak shock or flame, and to able to predict this response. We have identified several key areas of the DDT problem which need to be understood before any such prediction can be made, and have established a modest program to obtain a more fundamental understanding of the behavior of explosive under the conditions that can lead to DDT.
Date: January 1, 1992
Creator: Asay, B.W.
Partner: UNT Libraries Government Documents Department

Strategies for understanding the deflagration-to-detonation transition

Description: The deflagration-to-detonation (DDT) phenomenon has been studied for many years. However, no comprehensive model of the DDT process is available. It is important to understand the mechanism by which an explosive will detonate when the source of ignition is a weak shock or flame, and to able to predict this response. We have identified several key areas of the DDT problem which need to be understood before any such prediction can be made, and have established a modest program to obtain a more fundamental understanding of the behavior of explosive under the conditions that can lead to DDT.
Date: May 1, 1992
Creator: Asay, B. W.
Partner: UNT Libraries Government Documents Department

Deflagration to detonation in HMX under high confinement. [HMX confined in steel tubes]

Description: The deflagration-to-detonation behavior of HMX confined in steel tubes was studied by means of x radiography, light emission, and various pin techniques. Unlike most reported experiments, the HMX bed was ignited by driving a piston (initially at rest and in contact with the HMX) into the bed with the pressure generated from burning, low-density HMX on the opposite side of the piston. Because a gasless igniter is used to start the burning of the low-density HMX, the piston has a relatively smooth initial motion. Analysis of the data from these experiments gives a rather detailed picture of the DDT process under these conditions. 2 refs., 19 figs.
Date: January 1, 1987
Creator: McAfee, J.M.; Campbell, A.W. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Response of propellant to hypervelocity attack

Description: This study was undertaken to examine the behavior of heterogeneous gun propellants when they are impacted by shaped-charge jets. In the immediate area surrounding the impact point, the pressure is believed to be above the detonation pressure of the full-density propellant. However, a detonation does not necessarily occur, and if it does, the detonation does not necessarily propagate. This is a function of grain size, web, perf pattern, jet diameter, propellant failure diameter, and composition. The investigators hope to eventually understand the mechanism and physics of the failure of detonation in these systems. This report summarizes the initial work performed in support of the study. The results presented here formed the groundwork for a more specific effort, which is continuing. 18 figs., 1 tab.
Date: January 1, 1987
Creator: Asay, B.W.; Ramsay, J.B. & Campbell, A.W.
Partner: UNT Libraries Government Documents Department

Temperature effects on failure thickness and deflagration-to-detonation transition in PBX 9502 and TATB

Description: The deflagration-to-detonation (DDT) behavior of TATB has been investigated at high temperatures and severe confinement. comparison is made to other common explosives under similar confinement. TATB did not DDT under these conditions. The failure thickness of PBX 9502 at 250[degrees]C has also been determined. Two mm appears to be the limiting value at this temperature.
Date: January 1, 1993
Creator: Asay, B.W. & McAfee, J.B.
Partner: UNT Libraries Government Documents Department

Temperature effects on failure thickness and deflagration-to-detonation transition in PBX 9502 and TATB

Description: The deflagration-to-detonation (DDT) behavior of TATB has been investigated at high temperatures and severe confinement. comparison is made to other common explosives under similar confinement. TATB did not DDT under these conditions. The failure thickness of PBX 9502 at 250{degrees}C has also been determined. Two mm appears to be the limiting value at this temperature.
Date: April 1, 1993
Creator: Asay, B. W. & McAfee, J. B.
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

Dynamic temperature and velocity measurements using neutron resonance spectroscopy

Description: The use of Doppler broadening in neutron resonances as a quantitative way to measure temperatures has been proposed and investigated for cases of static or quasi-static temperature measurements. Neutrons are temperature probes that can penetrate a sample to view its interior. At the same time products that may shield a sample optically are not opaque to neutrons so that temperature measurements can be made in their presence. When neutrons are attenuated by a sample material, the time-of-flight (TOF) spectrum of the transmitted neutrons exhibits a series of characteristic dips or resonances. These resonances appear when neutrons are captured from the beam in the formation of excited states in the A + 1 nucleus (n + A {ge} (A + 1){sup *}). Subsequent de-excitation of these states, by gamma emission or particle emission into 4{pi} steradians, effectively eliminates the captured neutrons from the transmitted beam. The resonance locations and lineshapes which appear in the TOF spectrum are unique to each isotopic element, and temperature determinations can be localized through the positioning of resonant tags.
Date: August 1, 1997
Creator: Yuan, V.W.; Asay, B.W. & Boat, R.
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

Measurement of the stress/strain response of energetic materials as a function of strain rate and temperature: PBX 9501 and Mock 9501

Description: We have measured the stress/strain behavior of PBX 9501, Mock 900-21 and two new mocks consisting of monoclinic granular sugar embedded in (1) a BDNPA-F/estane binder (a 9501 material mock; a hard organic crystal embedded in a plastic) and (2) neat estane (an LX-14 mock) at strain rates from 10{sup -3} to 10{sup -1}, at two L/D`s and at two temperatures (25 and 60 C). We find that the compressive strength falls with increasing temperature and rises with increasing strain rate. We also find that the new 9501 sugar mock most closely resembles the behavior of the 9501 explosive and differences may be attributable to the different ages of the estane binder used.
Date: September 1, 1995
Creator: Funk, D.J.; Laabs, G.W.; Peterson, P.D. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Deflagration-to-detonation in granular HMX: Ignition, kinetics, and shock formation

Description: Experimental studies and analysis of the deflagration-to detonation transition (DDT) in granular HMX are continued. Experiments performed using a direct-gasless igniter exhibit the same phenomenology as those ignited with a piston. Simple kinetics and mechanics describe the formation of the {approximately}100% TMD plug in terms of competing pressurization processes. A mass-conservation analysis of the experimentally observed structures shows how the low velocities characteristic of convective burning are amplified to shock-wave velocities through non-convective processes.
Date: June 1, 1993
Creator: McAfee, J. M.; Asay, B. W. & Bdzil, J. B.
Partner: UNT Libraries Government Documents Department

Experimental investigation of the representative volume element size.

Description: In this investigation, the minimum size of the representative volume element (RVE) of a heterogeneous material is determined experimentally using the digital image correlation (DIC) technique. The uniaxial compression experiment was conducted on the PBS 9501, a high explosive simulant material. The minimum size of the representative volume element (RVE) of the PBS 9501 heterogeneous material, where the average crystal diameter of the material is around 100{micro}m, was determined experimentally to be 1.5mm. This result is consistent with those numerical calculations on polycrystalline materials and some other composites.
Date: January 1, 2002
Creator: Liu, C. (Cheng); Stout, M. G. (Michael G.) & Asay, B. W. (Blaine W.)
Partner: UNT Libraries Government Documents Department

Dynamic measurement of the influence of projectile radius and velocity on strain localization during impact of an energetic material

Description: A new technique for measuring the dynamic displacement fields during deformation has been developed. The method uses high speed laser-induced fluorescence speckle photography. The authors report the effect of projectile velocity and radius on the strain fields in a quasi-two dimensional confined sample of PBX 9501.
Date: December 31, 1998
Creator: Asay, B.W.; Dickson, P.M.; Henson, B.; Fugard, C.; Funk, D.J. & Idar, D.J.
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

Direct measurement of strain field evolution during dynamic deformation of an energetic material

Description: The authors previously reported results showing displacement fields (at a single instant in time) on the unconfined surface of an explosive during deformation using white light speckle photography. They have now successfully obtained similar data in confined samples showing the evolution in time of the strain field using laser-induced fluorescence speckle photography. A modified data analysis technique using methods borrowed from particle image velocimetry was used in conjunction with an eight frame electronic CCD camera. For these tests, projectiles of varying shape were fired into an explosive sample. Localization of strain was observed in all cases and was found to be a strong function of the projectile shape, with ignition occurring in those cases where shear appears to play a dominant role. Results from this and continuing studies provide experimental evidence for strain localization, and for the first time allow the direct comparison to computer model predictions. The data are also being used in the design of more realistic and reliable constitutive models.
Date: September 1, 1997
Creator: Asay, B.W.; Henson, B.F.; Dickson, P.M.; Fugard, C.S. & Funk, D.J.
Partner: UNT Libraries Government Documents Department

Measurement of explosion time as a function of impact pressure for PBX 9501 subject to weak planar shocks

Description: At low pressures, the mechanical heating of the material is insufficient to generate ignition. At high pressures, prompt ignition is observed. At intermediate pressures, between {approximately} 0.75 to 2.0 GPa, mechanical heating is calculated to achieve sufficient heating to generate ignition after a variable induction time, equivalent to the induction time observed in purely thermal ignition experiments. These calculations depend on the calculation of at least two complex physical mechanisms in the material, mechanical heating and thermal decomposition. The authors present measurements of the surface temperature of confined PBX 9501 subject to weak planar shock with pressures spanning the range from moderate heating to prompt ignition.
Date: October 1, 1997
Creator: Henson, B.; Asay, B.W.; Dickson, P.M.; Fugard, C. & Funk, D.J.
Partner: UNT Libraries Government Documents Department