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Defense

We have worked with the various DoD agencies to help them with preparedness (including vulnerability assessment), munitions research, and environmental clearances to perform large scale tests and disposal of energetic waste.  Our work over the years focused on munitions research, development and testing; Consequence analysis of military attacks on various targets (both with conventional weapons and emerging technologies such as High Energy Lasers and Reactive Material Payloads); and Chemical and Biological Agent Detection, Characterization and Defeat.

Morphology Characterization of Biological Agent Spores

We performed morphology characterization of biological simulants for Bacillus anthracis spores including Bacillus thuringiensis (Bt) spores and Bacillus subtilis (Bs) spores.  For Bt spores, we used Javelin Technical, a commercial pesticide, as the source.  Javelin contains various additives in addition to Bt spores.  We performed polarized light extinction measurements on Javelin Technical particles suspended in water.  Assuming an overall spherical shape for the particulates in Javelin, we inverted the extinction versus wavelength spectrum to determine the size distribution.  The resulting size distribution along with an SEM image of pure Bt spores are shown in the figure below.  The figure shows that in addition to the spores (size range of 500 – 1500 nm), there are several very fine particulates smaller than 200 nm in Javelin.  These could be the spore/cell fragments formed during the spray drying process used for Javelin manufacture, and various proteins and toxins secreted by Bt spores. 

We performed similar measurements on two types of Bs spores – (1) spores with DPA and (2) spores that have been genetically modified to remove DPA.  Assuming an overall ellipsoidal shape for these particulates, we determined their cross sectional area and aspect ratio distribution.  These results are shown in the figures below along with an SEM image of Bs spores.  These results show that the removal of DPA has almost no effect on the morphology of Bs spores.

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Material Property Toolkit for Spore Slurries

Through carefully controlled experiments and analysis, we measured the key material properties of Bacillus anthracis spore simulant slurries in water.  Based on these measurements, we developed a material property toolkit consisting of the following properties that are necessary to model processes such as hydrodynamic ram, tank failure, agent aerosolization and dispersion:

  1. Material EOS
  2. Acoustic speed
  3. Dynamic viscosity
  4. Dynamic Surface Tension
  5. Heat capacity
  6. Thermal conductivity
  7. Effect of combined shock and heat on agent viability

Shock Propagation in Spore Slurries
Using an instrumented shock tube, we performed shock propagation studies on Bacillus anthracis simulant slurries in water.  We found that at very low concentrations, the slurries behave like pure water.  However, at spore concentrations above 2% by weight, the slurries become compressible.  The shock waves undergo significant attenuation with travel distance in these slurries.  As a result, the shock pressure as well as the shock speed decrease significantly with travel distance.  Sample data from one of these tests are plotted in the figure below.  The pressure sensors P1 and P4 are 24” apart.

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Ignition of Aerosolized Spores

We performed ignition tests on aerosolized spores of pure Bacillus anthracis and its simulant Javelin Technical in an instrumented combustion tube shown below.  Photographs depicting the introduction of Javelin particulates into the combustion tube, their ignition and combustion are shown below. 

We moved our combustion tube into US Army ECBC’s BSL-2 facility where ignition tests were performed on pure Bacillus anthracis spores.  A photograph of the combustion tube inside a bio containment chamber at the BSL-2 facility is shown below.  Based on the measured time to ignition data at various temperatures, we developed an ignition kinetics model for Bacillus anthracis spores.  This is the first study of its kind.

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Dust Explosion of Spores

Biological agent spores can undergo a grain-silo type explosion in the presence of an ignition source if they are present at an appropriate concentration in a confined region.  To examine this further, we performed controlled tests in a 20-L Kuehner vessel shown below.  Simulant spores were introduced into the test chamber under turbulent conditions and ignited using a strong ignition source.  The chamber pressure was then measured versus time.  Based on the measured pressure-time histories at various concentrations, we determined the Minimum Explosible Concentration (MEC) of the spores and developed a model to predict the overpressure versus time from the explosion of spore ducts clouds. 

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Slow Cookoff of PBXN-109

We developed an engineering model for the Slow Cook Off (SCO) of explosive materials exposed to heat.  We applied this model to a relatively insensitive munition composition namely, PBXN-109.  We validated the model by comparing the predictions with small scale cookoff tests (Navy pipe bomb tests and Lawrence Livermore National Laboratory’s STEX) and Navy’s full scale tests (on a Heavy Wall Penetrator and a 500 lb GP Bomb).  The casing temperature at cookoff and the time to cookoff predicted by our model agree well with the test data.  Also, the strain data predicted by the model during the early stages of cookoff agree well with the measured strain gage data.  The strain gage data are not reliable during later stages of cookoff as the gages become debonded from the vessel wall. 

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Lethality Assessment and Target Defeat

For the US Department Of Defense, we participated in the design of two large scale test facilities – the first to evaluate the effectiveness of various non-energetic payload technologies for the defeat of control and command centers and WMD; and the second to test various advanced energetic materials (including nanoenergetic compositions).

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Interhalogens

The high reactivity of interhalogens makes them attractive for the defeat of various targets such as WMDs and electronic equipment at Command and Control Centers. 

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Reactive Materials

We developed an engineering model to predict the high-speed impact induced ignition of Aluminum-Teflon RM-4 reactive fragments.  We considered various hot spot mechanisms including void collapse, shear banding, frictional dissipation, and shock heating and their effect on reaction initiation.  Shown in the image below is a sequence of events that occur during the high speed impact of RM-4 reactive fragment with a metal target plate. 

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Large Scale Enclosed Detonation Tests

For the US Army DAC, we evaluated the emission data from full-scale enclosed detonation tests at the Nevada Test Site X-tunnel involving M107 HE loaded 155 mm projectiles.  In addition to examining the internal consistency of test measurements, we performed detailed mass and energy balance calculations and calculated the dynamics of cloud evolution and the composition accounting for both detonation and after-burn reactions.  These calculations showed that the effect of containment by the tunnel walls on the cloud evolution is significant.  Our predictions of major products and most minor products (such as VOCs and SVOCs) agreed well with the test data. 

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Munitions Disposal Through Open Burn and Open Detonation (OBOD)

For a DoD contractor, we performed OBOD calculations to determine the potential emissions from planned munition and energetic waste disposal operations.  Our results were used in the preparation of environmental site permitting applications.

Validation of Open Burn and Open Detonation Model Using BangBox Data

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