U.S. Army Combat Capabilities Development Command Armaments Center

Graphene oxide nanosheets, stably dispersed in water at 0.2 wt.%, were inkjet-printed onto Ti foils and thermally reduced at 200 °C in N2, as a new method of fabricating inkjet printed graphene electrodes (IPGEs) for supercapacitors. The specific capacitance of IPGE ranged from 48 to 132 F/g, depending on the potential scan rate from 0.5 to 0.01 V/s using 1M H2SO4 as the electrolyte. The initial performance of IPGEs compares favorably to that reported for graphene electrodes prepared by other fabrication methods. This new finding is expected to be particularly useful for designing and fabricating inter-digitized electrode arrays with a lateral spatial resolution of ~ 50 μm for flexible micro-supercapacitors.

A partial-shape-recognition technique utilizing local features described by Fourier descriptors is introduced. A dynamic programming formulation for shape matching is developed, and a method for comparison of match quality is discussed. This technique is shown to recognize unknown contours that may be occluded or that may overlap other objects. Precise scale information is not required, and the unknown objects may appear at any orientation with respect to the camera. The segment-matching dynamic programming method is contrasted with other sequence-comparison techniques that utilize dynamic programming. Experimental results are discussed that indicate that partial contours can be recognized with reasonable accuracy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Abstract Unlike the vast majority of transition metal dichalcogenides which are semiconductors, vanadium disulfide is metallic and conductive. This makes it particularly promising as an electrode material in lithium-ion batteries. However, vanadium disulfide exhibits poor stability due to large Peierls distortion during cycling. Here we report that vanadium disulfide flakes can be rendered stable in the electrochemical environment of a lithium-ion battery by conformally coating them with a ~2.5 nm thick titanium disulfide layer. Density functional theory calculations indicate that the titanium disulfide coating is far less susceptible to Peierls distortion during the lithiation-delithiation process, enabling it to stabilize the underlying vanadium disulfide material. The titanium disulfide coated vanadium disulfide cathode exhibits an operating voltage of ~2 V, high specific capacity (~180 mAh g −1 @200 mA g −1 current density) and rate capability (~70 mAh g −1 @1000 mA g −1 ), while achieving capacity retention close to 100% after 400 charge−discharge steps.

Most of the earlier solutions for residual stresses were based on the assumption of elastic unloading and only a few considered reverse yielding. In this paper a new theoretical model for a high strength steel is proposed and a closed-form solution of residual stresses in autofrettaged tubes has been obtained. The new results indicate that the influence of the combined Bauschinger and hardening effect on the residual stress distribution is significant.

Accurate values of thermophysical properties of toxic chemical compounds over a range of temperatures are essential for understanding their environmental distribution, biotransformation, and development of potential water treatment processes. In this study, the aqueous solubility (sw), octanol–water partition coefficient (Kow), and Henry's law constant (kH) were measured for an insensitive munitions compound, 2,4-dinitroanisole (DNAN), at the temperatures of (298.15, 308.15, and 318.15) K. The effect of ionic environment on solubility, using electrolytes such as NaCl and CaCl2, was also studied. The data on the thermophysical parameters were correlated using the standard van't Hoff equation. All three properties exhibited a linear relationship with reciprocal temperature. The enthalpy and entropy of phase transfer were derived from the experimental data.

Highly reactive nanothermites prepared by mixing bismuth trioxide or cupric oxide nanoparticles with aluminum nanoparticles were evaluated as solid propellants for small-scale propulsion applications. Miniaturized engines were fabricated from steel in three-piece configurations without a converging/diverging nozzle. Bismuth trioxide-aluminum generated 46.1 N average thrusts for 1.7 ms durations with a specific impulse of 41.4 s. Cupric oxide-aluminum generated 4.6 N thrusts for 5.1 ms durations with a specific impulse of 20.2 s. Convective and conductive reaction regimes were identified as functions of bulk packing density and confinement geometry. Average thrusts and burning durations differed by greater than an order of magnitude for equivalent nanothermites dependent on the reaction regime. Adding small amounts of nitrocellulose to the nanothermites increased specific and volumetric impulses to maximum values of 59.4 s and while controllably reducing average thrusts and prolonging burning durations. The energy-conversion efficiencies of the thrusters were evaluated using a rotary-arm measurement, and a maximum efficiency of 0.19% was observed. Last, a miniaturized four-engine array was fabricated with micromachined initiators and sequentially fired. The high specific and volumetric impulses, fast combustion, and tailored reactions of nanothermites are appealing for many small-scale propulsion applications.

The subject of this paper involves tracking the present position of a maneuvering aircraft as well as predicting its future position. A tracking filter is developed that uses aircraft attitude angles (yaw, pitch, roll) in addition to the usual radar measurements. Computer simulation of tracker performance when tracking violently maneuvering aircraft indicates that a dramatic improvement is obtained by using attitude information. The approach taken is to develop a 12-or 15-state extended Kalman filter that models both translational and rotational degrees of freedom. By measuring and estimating attitude it is possible to approximately determine the magnitude and direction of the force system acting on the vehicle and therefore determine vehicle linear acceleration. Knowledge of acceleration is then used to improve the estimate of present and future position of the vehicle being tracked. Simulation of a T-38 aircraft performing a 5 g turn indicates that the new tracker produces maximum trajectory prediction errors that are 36 percent of the errors experienced by more conventional trackers.

Nanoscale cocrystal of CL-20 and HMX with a rounded morphology was prepared by bead milling an aqueous suspension of the coformers.

Irreversible and reversible chromatic transitions during heating and cooling cycles were investigated in polydiacetylene poly-PCDA (poly-10,12-pentacosadiynoic acid) composites with nanocrystalline zinc oxide (ZnO), titanium oxide (TiO2), zirconium oxide (ZrO2) and ZnO and ZrO2 alloys. In contrast to pure poly-PCDA, poly-PCDA composites with nanocrystalline ZnO displayed rapid reversibility on thermal cycling, whereas the corresponding composites with nanocrystalline TiO2 and ZrO2 were irreversible, and poly-PCDA composites with thermally prepared ZnO and ZrO2 alloys displayed slower reversibility. The mechanism of reversible and irreversible thermochromism in these materials was explored using Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and X-ray absorption fine structure (XAFS) spectroscopy. In pure poly-PCDA, heating leads to an irreversible strain on the polymer backbone to form a red phase, which is not released on cooling. In the presence of ZnO evidence is provided for chelation involving the side chain head groups which can release strain on cooling to rapidly form the blue phase. Chemical interaction coupled with reversible behavior was however observed only when the composites were prepared with ZnO having an average crystallite size of 300 nm and below with a fraction of an amorphous grain boundary phase. Poly-PCDA composites with ZnO/ZrO2 alloys showing slower thermochromic reversibility can be used both as temperature and elapsed time-temperature sensors.

Depth profiles of 300-keV protons implanted in n-type GaAs at room temperature have been obtained using secondary ion mass spectrometry and correlated with optical effects determined by infrared reflectance measurements. The profiles of the implanted hydrogen (1H) have been measured as a function of annealing for temperatures up to 600 °C. These profiles display a major redistribution of the hydrogen atoms with movement beginning at 200 °C and terminating by 700 °C. The hydrogen diffusion into the substrate can be approximated by an Arrhenius process with an activation energy of 0.62 eV and a diffusion constant of 1.54×10−5 cm2/s. The reflectance spectra indicate that while an optically uniform layer is present in the as-implanted specimen, more complicated optical profiles exist in the annealed samples. Annealing at 300 °C causes the layer to nearly double in thickness but higher temperature annealing produces optical profiles similar to the as-implanted state. Qualitatively, these optical changes follow the behavior of the hydrogen depth profiles.

We report the results of a multi-day diurnal study in which polarimetric and conventional thermal imagery is recorded in the mid- and long-wave IR to identify and compare the respective time periods in which minimum target contrast is achieved. The data shows that the chief factors affecting polarimetric contrast in both wavebands are the amount of thermal emission from the objects in the scene and the abundance of MWIR and LWIR sources in the optical background. In particular, it has been observed that the MWIR polarimetric contrast was positively correlated to the presence of MWIR sources in the optical background, while the LWIR polarimetric contrast was negatively correlated to the presence of LWIR sources in the optical background.

The US Department of Defense (DoD) realizes the many uses of additive manufacturing (AM) as it has become a common fabrication technique for an extensive range of engineering components in several industrial sectors. 3D Printed (3DP) sensor technology offers high-performance features as a way to track individual warfighters on the battlefield, offering protection from threats such as weaponized toxins, bacteria or virus, with real-time monitoring of physiological events, advanced diagnostics, and connected feedback. Maximum protection of the warfighter gives a distinct advantage over adversaries by providing an enhanced awareness of situational threats on the battle field. There is a need to further explore aspects of AM such as higher printing resolution and efficiency, with faster print times and higher performance, sensitivity and optimized fabrication to ensure that soldiers are more safe and lethal to win our nation's wars and come home safely. A review and comparison of various 3DP techniques for sensor fabrication is presented.

Abstract Nanothermites are promising propellants for miniaturized thruster applications, but in their pure state can be very sensitive to ignition stimuli and prone to phase separation. Consequentially, a need exists for desensitizing binders that do not inhibit nanothermite thrust performance. We investigate the effects of incorporating small weight concentrations of nitrocellulose as a gasifying binder in bismuth trioxide‐aluminum nanothermites. Thrust measurements revealed improvements in specific impulse up to 63.2 s using nitrocellulose. The launch tolerance of the nanothermites in response to high‐g acceleration was also explored and substantial improvements were realized for nanothermites prepared with nitrocellulose. As small as 5 % nitrocellulose content suppressed the sensitivity of the nanothermites to less than 1 % ignition probability after exposure to 30 kg acceleration events. Some nanothermite charges experimentally survived up to 90 kg loads. Most importantly, nitrocellulose predictably modulated the thrust performance and ignition sensitivity of the nanothermites as a function of weight content. Employing nitrocellulose as a binder, high performance nanothermite propellants can be synthesized for miniaturized thruster applications with tailored impulse generation and ignition sensitivity.

This paper compares two methods of measuring the finish of precision machined optical surfaces: the older, well-established mechanical stylus gauge and a recently developed optical gauge using interference microscopy. Results are found to be in good quantitative agreement for both random and periodic surface features, provided that appropriate filtering procedures are included in the data analysis to account for the differing transfer functions and bandwidths of the two measurement techniques. These results affirm the use of these techniques for the quantitative measurement and specification of machined optical surfaces.

Abstract Compact, three-dimensional cage compounds containing optimum numbers of nitro groups as determined in theory by thermohydrodynamic calculations, constitute a class of explosive compounds more powerful than HMX. This is a direct result of high crystal densities, particularly in combination with high strain energies built into certain of the cage systems. The synthesis of polynitro cage compounds has progressed on several fronts, and is currently in the second stage of a three-stage effort. The first stage has seen the synthesis of forerunners of more highly nitrated cage compounds, as part of a broad strategy to develop the methodology for achieving the polynitration of cage molecules. The nitro cage compounds whose syntheses are in progress (second stage) and will be completed in the near future are expected to be energetic. These compounds, in turn, are expected to lead, in the third stage, to stil more highly nitrated cage compounds including those which will be signifficantly more powerful than HMX. The results of the synthesis effort to date are outlined, and achievements highlighted. In adition, the results of the calculations identifying the optium polynitro cage compounds are discussed. The future direction of the program of synthesis is indicated.

Anisotropic Mg nanowires have been successfully prepared by electrocrystallization of Grignard's reagents thought to proceed via a modified faces, steps, and kinks (FSK) mechanism. Mg nanoparticles with roughly hexagonal shapes have also been obtained via chemical reduction of the same Grignard's reagents.

Extended-Kalman-filter-based trackers are discussed for maneuvering helicopters that use body angle and rotor tip-path-plane angle measurements in addition to the usual radar position measurements. Improvements were found in tracker performance when the body rotation and rotor tip-path-plane degrees of freedom were modeled within the extended Kalman filter. Tracker performance was further improved when measurements of body angles and rotor tip-path-plane angles were made available to the tracker.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Primary explosives are ubiquitous and essential components of a host of military munitions as well as commercial mining, construction, and demolition applications. Since their inception, the most widely used primary explosives have been based on either lead or mercury, with lead azide and lead styphnate now making up the bulk of practical use. The high toxicity of lead compounds, along with the ever increasing environmental regulations associated with them, has led to an urgent need for environmental and cost-effective replacements that meet performance requirements. This chapter will provide an up-to-date overview of the most viable primary explosive candidates for both detonator and primer applications, including discussions of their properties, chemical syntheses, and practicality. An overview of the development of primary explosives over the last century will be provided, putting the newer compounds in historical perspective and allowing for more effectively weighing their advantages and disadvantages compared to the legacy lead-based explosive compounds.

Abstract Electronic components are subject to high strain, during shock and vibration in many applications such as the automobile and aerospace. In many cases, this kind of electronic components will also be exposed to harsh temperatures of –65 °C to 200 °C. Electronic devices in harsh environments are often subject to strain rates of 1–100 per second. A large number of doped SAC solder alloys have emerged including SAC-Q, SAC-R, Innolot for electronic component interconnection. SAC-Q consists of inclusion of the Bi composition in Sn–Ag–Cu. For maximizing electronic package stability and high temperature storage and strain rates, the mechanical characteristic results and data for lead-free solder alloys are extremely significant. Thermal aging has been previously shown to cause modification of the mechanical properties at low strain rates. High strain-rate SAC-Q solder alloy data are not available for high temperature aging and testing at very low to high operating temperatures. For this analysis, the SAC-Q solder material was measured and analyzed at operating temperatures between –65 °C and 200 °C, at strain rates of up to 75 per second. Comparison with solder material SAC305, which has been tested under similar conditions, has also been made. When tensile experiments were carried out at various working temperatures, specimens for isothermal aging were preserved at 100 °C for up to 90 days after production and reflowing. The stress–strain curves are developed and described in this paper for a wide range of strain rates and test temperatures. Furthermore, the test results and data measured have been matched to the Anand viscoplasticity model and Anand constants have been determined by estimation of the high strain rate behavior measured in the broad range of working temperatures and stress levels.

ABSTRACT The mechanical properties of composite explosives are being studied as a function of mechanical confinement. Although other techniques for confinement were used, most of the results presented here were obtained by the use of a constant confining pressure obtained by oil immersion. While many energetic materials fail by crack processes when unconfined, with all of the forms of confinement used here they appear to fail by plastic flow. For crystalline explosives, for example, TNT and composition B, the yield strength and the modulus are independent of confining pressure. However, for materials containing polymer binders such as plastic-bonded explosives, these properties are found to significantly increase with pressure.