NSWC Indian Head

Abstract An interlaboratory comparison of seven lots of commercially available RDX was conducted to determine what properties of the nitramine particles can be used to assess whether the RDX has relatively high or relatively low sensitivity. The materials chosen for the study were selected to give a range of HMX content, manufacturing process and reported shock sensitivity. The results of two different shock sensitivity tests conducted on a PBX made with the RDX lots in the study showed that there are measurable differences in the shock sensitivity of the PBXs, but the impact sensitivity for all of the lots is essentially the same. Impact sensitivity is not a good predictor of shock sensitivity for these types of RDX. Although most RDX that exhibits RS has low HMX content, that characteristic alone is not sufficient to guarantee low sensitivity. A range of additional analytical chemistry tests were conducted on the material; two of these (HPLC and DSC) are discussed within.

Abstract Efforts directed towards creating new environmentally friendly replacements for existing primary explosives have resulted in development of copper(I) 5‐nitrotetrazolate (DBX‐1). The chemical and physical properties of this material have been extensively investigated and it appears that DBX‐1 is a suitable drop‐in replacement for lead azide in a variety of ordnance applications. DBX‐1 is easily prepared, has excellent thermal stability and has safety and performance properties which are equivalent to or exceed those for lead azide. A program to qualify DBX‐1 for military use per NAVSEAINST 8020.5C has recently been completed and data has been forwarded to NSWC‐IH for submission to Naval Sea Systems Command.

Abstract In this work we investigate the potential application of nano‐aluminum/nitrocellulose mesoparticles as an ingredient for solid composite rocket propellants. The basic strategy is to incorporate nanoaluminum in the form of a micrometer scale particle containing a gas‐generator, to enable easier processing, and potential benefits resulting from reduced sintering prior to combustion. The mesoparticles were made by electrospray and comprised aluminum nanoparticles (50 nm) and nitrocellulose to form micrometer scale particles. In this study, 80 % solids loaded composite propellants (AP/HTPB based) were made with the addition of micrometer sized (2–3 μm) aluminum (10 wt‐%), and compared directly to propellants made by directly substituting aluminum mesoparticles for traditional micrometer sized particles. Propellant burning rate was relatively insensitive for mesoparticles containing between 5–15 wt‐% nitrocellulose. However, direct comparison between a mesoparticle based propellant, to a propellant containing micrometer scale aluminum particles showed burning rates approximately 35 % higher while having a nearly identical burning rate exponent. High speed imaging indicate that propellants using mesoparticles have less agglomeration of particles on the propellant surface.

An experimental study was conducted to understand the combustion behavior of polytetrafluoroethylene (PTFE)/boron–based solid fuels for future hybrid rocket motor applications. Fuels were loaded with 10–40% boron powder (w/w). Two different types of PTFE were examined in this study, while a single type of boron powder was considered. No significant differences in the decomposition mechanisms for PTFE and a candidate solid fuel mixture were observed by differential scanning calorimetry (DSC) and temperature-jump (T-jump)/Fourier transform infrared (FTIR) experiments. Diffusion flame studies between solid fuels and gaseous oxygen were carried out to measure regression rates and to develop a fundamental understanding of the combustion behavior. The fuels with the lowest boron content readily extinguished upon removal of the supplemental oxygen flow. The fuels with the highest loadings of boron self-propagated after ignition. X-ray diffraction on postcombustion residue of the self-propagating material revealed graphite and boron carbide as the remaining products, while particles captured leaving the surface of the fuel under normal burning conditions were found to be mostly boric acid. Boron oxidation and magnesium fluorination were observed in the flame zone of the diffusion flame by UV-Vis emission spectroscopy (magnesium is the major impurity in the elemental boron powder used). The results of this study suggest that solid fuels comprising PTFE and boron show promise for improving the energy density of hybrid rockets.

Abstract Efforts directed towards creating new environmentally friendly replacements for existing primary explosives have resulted in development of potassium 5,7‐dinitro‐[2,1,3]‐benzoxadiazol‐4‐olate 3‐oxide (KDNP). The chemical and physical properties of this material have been investigated and it appears that KDNP is a suitable drop‐in replacement for lead styphnate in a variety of ordnance applications. KDNP is easily prepared, has excellent thermal stability and has safety and performance properties, which are equivalent to or exceed those for lead styphnate. KDNP has been qualified for military use per NAVSEAINST 8020.5C.

The phase stability of epsilon hexanitrohexaazaisowurtzitane at high pressure and temperature was investigated using synchrotron angle-dispersive x-ray diffraction experiments. The samples were compressed at room temperature using a Merrill–Bassett diamond anvil cell. For high-temperature compression experiments a hydrothermal diamond anvil cell developed by Bassett was used. Pressures and temperatures of around 5 GPa and 175 °C, respectively, were achieved. The epsilon phase was determined to be stable under ambient pressure to a temperature of 120 °C. A phase transition to the gamma phase was seen at 125 °C and the gamma phase remained stable until thermal decomposition above 150 °C. Pressure-volume data for the epsilon phase at ambient and 75 °C were fitted to the Birch–Murnaghan formalism to obtain isothermal equations of state.

An experimental investigation on the ignition behavior of α-Aluminum Hydride (α-AlH3) has been conducted. The ignition characteristics were determined through the use of two separate modified T-jump experiments. In each experiment, a small amount of material was placed onto a platinum wire, which was heated rapidly through resistive heating. As a result both ignition and hydrogen release temperatures were studied for heating rates ranging from 104 to 105 K/s. The hydrogen release temperature was determined in vacuum, and ignition was studied at ambient pressure in air, CO2, and mixtures of argon with oxygen. Both the hydrogen release and ignition temperature increased as the heating rate increased. Hydrogen release temperatures ranged from approximately 650 to 1200 K, whereas ignition was observed to range from below the melting temperature of aluminum (933 K) to approximately 1500 K. Activation energies for hydrogen release were ∼27 kJ/mol, and are well below those reported by others at much lower heating rates. This result is consistent with the affects of higher heating rates transitioning the rate-limiting step from one of chemical kinetics to intraparticle hydrogen diffusion. For conditions in which the particles would ignite it was found that the environment did not play a significant role in the ignition temperature, beyond a critical oxygen mole fraction of XO2 > 0.05. Ensemble average burning times were found to decrease by a factor of about 3 when the oxygen mole fraction was increased from 0.1 to 0.5.

In this study the combustion behavior of solid fuels loaded with micron-sized aluminum, nanoaluminum, and aluminum hydride with loadings of 10, 20, and 40 mass % are compared directly using pure oxygen as the oxidizer. An opposed flow burner was used to screen the various fuels at various oxidizer flow rates. Regression rates were gathered over oxidizer impingement velocities ranging from approximately 40 to 160 cm/s (strain rates of 80-320 s−1). Fuels loaded with aluminum hydride were found to have regression rates comparable to or better than that of the baseline hydroxyl terminated polybutadiene (HTPB) fuel. In addition, the regression rate increased with increasing aluminum hydride content. Conversely, the regression rates of fuels loaded with micron-sized aluminum were found to decrease with increasing aluminum content. Emission spectroscopy revealed that under most conditions the aluminum in the fuels loaded with micron-sized aluminum did not ignite within the immediate vicinity of the solid fuel sample. Temperature measurements determined from thermal emission support this conclusion as well. Finally, a lab-scale hybrid rocket motor was used to compare the combustion performance of the fuels relative to each other. It was found for the same oxidizer mass flow rate, pressure and thrust were highest for alanized fuels. Data included were thrust, pressure, regression rate, and mass burning rate.

This is an effort to understand plastic deformation and energy dissipation in crystalline solids during shock or impact. It builds on recent atomic force microscope observations that plastic flow creates localized distortions in the lattice and molecules of at least some classes of molecular crystals. A distorted lattice potential is developed through which the dislocations responsible for plastic flow move by quantum tunneling. Plastic strain and energy dissipation rates are determined and related to crystal size and damage. These account for plastic flow in crystalline solids and the initiation of chemical reactions in crystalline explosives subjected to shock or impact. The predictions are compared with experiments.

Multiphase flows are present in many important fields ranging from multiphase explosions to chemical processing. An important subset of multiphase flow applications involves dispersed materials, such as particles, droplets, and bubbles. This work presents an Eulerian–Eulerian model for multiphase flows containing dispersed particles surrounded by a continuous media such as air or water. Following a large body of multiphase literature, the driving force for particle acceleration is modeled as a direct function of both the continuous-phase pressure gradient and the gradient of intergranular stress existing within the particle phase. While the application of these two components of driving force is well accepted in much of the literature, other models exist in which the particle-phase pressure gradient itself drives particle motion. The multiphase model treats all phases as compressible and is derived to ensure adherence to the 2nd Law of Thermodynamics. The governing equations are presented and discussed, and a characteristic analysis shows the model to be hyperbolic, with a degeneracy in the case that the intergranular stress, which is modeled as a configuration pressure, is zero. Finally, results from a two sample problems involving shock-induced particle dispersion are presented. The results agree well with experimental measurements, providing initial confidence in the proposed model.

A constitutive equation applicable to HCP metals and certain high strength alloy steels is applied to commercial purity titanium and the alloy Ti-6Al-4V. Deformation twinning and strain aging influence the deformation behavior of titanium, but are less significant in the alloy. Adiabatic heating is significant in the alloy at strain rates greater than 102 s−1.

A series of low stress shock impact experiments were performed on water to examine the dynamic response under tension and establish a lower bound for water rupture or cavitation threshold. The experimental cell configuration permitted particle velocity measurements at the water-air free surface separated by a 5-μm-thick aluminized Mylar diaphragm. Water samples were triply distilled, de-ionized, and degassed prior to experiments. The average tensile strength for shock-induced cavitation in the water was found to be 8.7±0.2MPa. Experiments are compared with hydrocode simulations using a simple fracture criterion and published experimental data.

Abstract An experimental investigation of the combustion characteristics of HTPB‐based solid fuels containing aluminum and aluminum hydride has been conducted. Aluminum is commonly used as a fuel supplement in solid rocket propellants because of its ability to increase the specific impulse of a propellant. Similarly, aluminum hydride, or alane, is another attractive fuel supplement because it can significantly (∼7–8 %) increase specific impulse even beyond that of aluminum. In this study, the regression rates of a baseline fuel (pure HTPB) were compared with that of fuels containing either aluminum or alane as additives using a counterflow combustion experiment with nitrous oxide (N 2 O) as the oxidizer. The additives were investigated in concentrations of 10, 20, and 40 % by weight of the fuels. The addition of aluminum at all loadings resullted in a decrease in the regression rate relative to the baseline, whereas the addition of alane resulted in at worst similar regression rates and at best (highest loading) approximately a 20 % increase in regression rate. The decomposition behavior of selected fuels was analyzed using traditional thermal analysis techniques; thermal gravimetric analysis and differential scanning calorimetry

Abstract The detonation of a metalized explosive generates a fireball that has a spatially non‐uniform distribution of particle concentration and gas temperature. The transient gas temperature field must be probed with ruggedized spatially‐ and temporally‐resolved diagnostics. The use of in‐situ thermocouples for temperature measurements within multiphase fireballs is demonstrated. Although the thermocouple temperature lags behind the local gas temperature, the transient gas temperature is assessed by modeling the sensor assuming first‐order response and using two analysis methods: (1) when the thermocouple temperature trace reaches a local extrema, the thermocouple temperature is instantaneously equal to the local gas temperature, and (2) reconstructing the gas temperature trace using multiple co‐located thermocouples of different lag responses. The temperature history within the fireball at various distances is presented for charges consisting of packed beds of particles saturated with liquid nitromethane. The results for reactive particles (Al, Ti, Zr) are compared with non‐reactive particles (Fe), as well as homogeneous NM charges. For NM charges, a maximum gas temperature of about 1100 K occurs at times on the order of 100’s of milliseconds, less than the temperature of the burning soot in the fireball (∼1900 K). With Al particles, the gas temperature is spatially non‐uniform due to particle jetting and non‐uniform particle combustion, but gas temperatures up to about 1800 K are recorded for times up to 0.5 s, less than the temperature of the burning particles (∼2700 K). Inert particles act as a heat sink and the thermocouple temperatures recorded did not exceed 400 K.

The ab initio calculation of the 0 K isotherm of the organic molecular crystal 1,1-diamino-2,2-dinitroethylene (C2H4N4O4), also known as FOX-7, is accomplished by means of solutions of the many-body Schrödinger equation in a periodic crystal lattice. It was found that the Hartree–Fock method is adequate to represent the behavior of the material and that, in general, density functional methods give inferior results. Initially, calculations were done assuming rigid molecules under compression. In further calculations the internal molecular bond lengths were optimized for each value of compression. Finally, calculations were performed in which all the molecular coordinates were optimized. The results are compared with experimental x-ray diffraction data obtained by compressing samples in diamond anvil cells. Excellent agreement is obtained when the molecular coordinates are completely optimized. In addition, FOX-7 is highly anisotropic and this anisotropy must be taken into account to obtain good agreement with hydrostatic compression data.

The neutral homoleptic tris-bpy aluminum complexes Al((R)bpy)3, where R = tBu (1) or Me (2), have been synthesized from reactions between AlX precursors (X = Cl, Br) and neutral (R)bpy ligands through an aluminum disproportion process. The crystalline compounds have been characterized by single-crystal X-ray diffraction, electrochemical experiments, EPR, magnetic susceptibility, and density functional theory (DFT) studies. The collective data show that 1 and 2 contain Al(3+) metal centers coordinated by three bipyridine (bpy(•))(1-) monoanion radicals. Electrochemical studies show that six redox states are accessible from the neutral complexes, three oxidative and three reductive, that involve oxidation or reduction of the coordinated bpy ligands to give neutral (R)bpy or (R)bpy(2-) dianions, respectively. Magnetic susceptibility measurements (4-300 K) coupled with DFT studies show strong antiferromagnetic coupling of the three unpaired electrons located on the (R)bpy ligands to give S = (1)/2 ground states with low lying S = (3)/2 excited states that are populated above 110 K (1) and 80 K (2) in the solid-state. Complex 2 shows weak 3D magnetic interactions at 19 K, which is not observed in 1 or the related [Al(bpy)3] complex.

A closer look into the predicted large strain response and plastic shear instability behavior derived from the so-called Z-A equations, incorporating thermally activated yielding of bcc metals (due to their high Peierls stresses) and thermally activated strain hardening of fcc metals (produced by dislocation intersections), shows the need for including dynamic recovery effects in the strain hardening for both bcc and fcc cases. Recovery effects are observed in the stress/strain behavior of tantalum and the bcc-like Ti-6A1-4V titanium alloy. Critical strains for shear banding are computed for Ti-6Al-4V, copper, and ARMCO iron. In addition, a recent result on ductile fracture is reported.

The characteristics of the axial flow within the core of a concentrated line vortex are investigated using molecular tagging velocimetry (MTV). A well-defined array of isolated vortices of alternating sign is generated in the wake of a NACA-0012 airfoil pitching sinusoidally at small amplitude and high reduced frequencies. The circulation and peak vorticity of the vortices are varied by the choice of oscillation frequency. Interaction of these two-dimensional vortices with the walls of the test section generates an axial flow within the vortex cores. The magnitude of the axial flow and its spatial/temporal characteristics are quantified using the MTV technique. Results show that the peak axial flow speeds can be very high, of the order maximum swirl speed of the vortices. The maximum axial speed ratio (maximum axial speed normalized by maximum swirl speed) is found to vary in the range 0.6–1.0 for the parameters investigated here. Initially, the axial flow is spatially confined in isolated structures corresponding to the core of vortices. As the vortex convects downstream, however, the spatial structure of axial flow changes from isolated regions to a continuous region for the highest reduced frequency investigated here. This change in structure is correlated with a significant decrease in the peak axial flow speed.

Robots can be used to mitigate risks in unsafe and austere settings. In recent years, explosive ordnance disposal robots have reduced the technician's time-on-target, and thus, reduce the direct risk of exposure. This article focuses on the study and development of innovative techniques as the foundational work for a new robot platform. The proposed system includes an organic electrochemical transistor device to detect the existence of explosive residues, and lead to decisions for safe-removal progress. Taurus' surgical gripper facilitates object tactile exploration, and manipulation with control precision to the millimeter range. The highly sensitive triboelectric tactile sensor could reduce intrusiveness during contact, and mitigate the risk of detonation. Haptic devices and visual displays are used to convey important signals, in order to improve the situational awareness of the teleoperator. A machine learning classifier can be used to assist the user to identify objects from tactile sampling. The integration of these methodologies allows for a sensitive approach to concealed objects that are only accessible through tactile sensing.

A widely recognized limitation in mammalian olfactory research is the lack of current methods for measuring odor availability (i.e., the quantifiable amount of odor presented and thus available for olfaction) of training or testing materials during behavioral or operational testing. This research utilized an existing technology known as Controlled Odor Mimic Permeation Systems (COMPS) to produce a reproducible, field-appropriate odor delivery method that can be analytically validated and quantified, akin to laboratory-based research methods, such as permeation devices that deliver a stable concentration of a specific chemical vapor for instrumental testing purposes. COMPS were created for 12 compounds across a range of carbon chain lengths and functional groups in such a way to produce similar permeation rates for all compounds. Using detection canines as a model, field-testing was performed to assess the efficacy of the method. Additionally headspace concentrations over time were measured as confirmation of odor availability using either externally sampled internal standard-solid phase microextraction-gas chromatography-mass spectrometry (ESIS-SPME-GC-MS) or collection onto a programmable temperature vaporizing (PTV) GC inlet with MS detection. Finally, lifetime usage was considered. An efficient method for producing and measuring reliable odor availabilities across various chemical functional groups was developed, addressing a noted gap in existing literature that will advance canine and other nonhuman mammal research testing.