Bowhead Science and Technology

Anderson, MD, United States

Bowhead Science and Technology

Anderson, MD, United States

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Kellogg F.,Bowhead Science and Technology | Zhou L.,University of Central Florida | Hofmeister C.,University of Central Florida | Giri A.,TKC Global | And 2 more authors.
Advances in Powder Metallurgy and Particulate Materials - Proceedings of the 2015 International Conference on Powder Metallurgy and Particulate Materials, PowderMet 2015 | Year: 2015

Previous research has shown that nanostructuring tungsten grains can significantly lower the ductile-tobrittle transition temperature of tungsten, improving low (near room) temperature ductility. Cryogenic attrition of coarse grained tungsten powders is an attractive technique for nanostructuring due to its capabilities for preventing oxidation, easing scalability, and possibly introducing grain-stabilizing nanoscale dispersoids. In this work, the feasibility of applying cryogenic attrition to the nanostructuring of coarse grain tungsten powders was explored through the examination of the morphology and grain size of the powder via transmission electron microscopy, scanning electron microscopy, and powder x-ray diffraction. Gas fusion chemical analysis was used to determine if there were any increases in the oxygen, hydrogen, or nitrogen concentration of the powder after cryogenic attrition.


Zhou L.,University of Central Florida | Kellogg F.,Bowhead Science and Technology | Hofmeister C.,University of Central Florida | Giri A.,TKC Global | And 3 more authors.
International Journal of Refractory Metals and Hard Materials | Year: 2015

Nanostructured pure tungsten (W) powders have been fabricated through cryogenic attrition (i.e., cryomilling) in a liquid nitrogen medium for the first time. The microstructure and chemistry of W powders before and after 4 and 12 h of cryomilling were thoroughly examined by gas fusion chemical analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM). Cryomilling in liquid nitrogen protected the tungsten from oxygen and hydrogen contamination while introducing nitrogen. Results showed that the W grain size decreased with cryomilling time, and reached approximately 5 nm after 12 h of cryomilling. High resolution TEM suggested that nitrogen reacted with W to form tungsten nitride (WN). Additionally, amorphous W was identified in the 12 h cryomilled W powder. Tungsten carbide (WC) contamination from the milling media and minor Fe-Cr-Ni-containing impurities from the stainless steel vessel were also documented. The WC had grain size ranging from 20 nm to 150 nm, and was homogeneously dispersed in W matrix. © 2015 Elsevier Ltd. All rights reserved.


Zhang T.G.,Bowhead Science and Technology | Satapathy S.S.,U.S. Army | Dagro A.M.,U.S. Army | McKee P.J.,Dynamic Science Inc.
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2013

Recent wars have heightened the need to better protect dismounted soldiers against emerging blast and ballistic threats. Traumatic Brain Injury (TBI) due to blast and ballistic loading has been a subject of many recent studies. In this paper, we report a numerical study to understand the effects of load transmitted through a combat helmet and pad system to the head and eventually to the brain during a blast event. The ALE module in LS-DYNA was used to model the interactions between fluid (air) and the structure (helmet/head assembly). The geometry model for the head was generated from the MRI scan of a human head. For computational simplicity, four major components of the head are modeled: skin, bone, cerebrospinal fluid (CSF) and brain. A spherical shape blast wave was generated by using a spherical shell air zone surrounding the helmet/head structure. A numerical evaluation of boundary conditions and numerical algorithm to capture the wave transmission was carried out first in a simpler geometry. The ConWep function was used to apply blast pressure to the 3D model. The blast pressure amplitude was found to reduce as it propagated through the foam pads, indicating the latter's utility in mitigating blast effects. It is also shown that the blast loads are only partially transmitted to the head. In the calculation where foam pads were not used, the pressure in the skin was found to be higher due to the underwash effect in the gap between the helmet and skin, which amplified the blast pressure. Copyright © 2013 by ASME.


Kellogg F.,Bowhead Science and Technology | McWilliams B.,U.S. Army | Cho K.,U.S. Army
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2016

Spark plasma sintering has been a well-studied processing technique primarily for its very high cooling and heating rates. However, the underlying phenomenon driving the sintering behavior of powders under an electric field is still poorly understood. In this study, we look at the effect of changing current pathways through the powder bed by changing die materials, from conductive graphite to insulating boron nitride for sintering aluminum alloy 5083 powder. We found that the aluminum powder itself was insulating and that by changing the current paths, we had to find alternate processing methods to initiate sintering. Altering the current pathways led to faster temperature raises and faster melting (and potentially densification) of the aluminum powder. A flash sintering effect in metallic powders is observed in which the powder compact undergoes a rapid transition from electrically insulating to conducting at a temperature of 583 K (310 °C). © 2016 The Minerals, Metals & Materials Society and ASM International (outside the USA)


Wilber D.H.,Bowhead Science and Technology | Clarke D.G.,HDR | Gallo J.,U.S. Army | Alcoba C.J.,U.S. Army | And 2 more authors.
Estuaries and Coasts | Year: 2013

A long-term (2002-2011), spatially robust, ichthyoplankton sampling program conducted in the New York/New Jersey Harbor produced 3,033 epibenthic samples from which the relationships between winter flounder egg and larval distributions and environmental parameters were examined. Variations in water temperature, sediment characteristics, and tidal phase were all significantly associated with egg distributions. Inferences about spawning habitats were based on the presence of early-stage eggs (ES1 and ES2). In the Lower Bay (LB), these habitats were primarily non-channel and characterized by more sandy substrates, averaging 96.5 % sand, 2.3 % silt/clay, 0.2 % total organic carbon (TOC), and shallower water (average depths of 5.3 m) compared to LB non-channel stations without ES1 and ES2 eggs (50.2 % sand, 42.0 % silt/clay, 2.1 % TOC, and 7.9 m depths). Occurrences of all stages of eggs in channels were associated with strong tides and severe cold winter water temperatures. These conditions increase the probability of egg transport from shallow spawning sites through increased vertical mixing (strong tides) and delayed development that prolongs the risk of displacement (cold temperatures). Yolk-sac (YS) and Stage-2 larvae were smaller in 2010 when spring water temperatures were highest. Overall, YS larval size decreased with warmer winters (cumulative degree-days for the month preceding peak YS larval collections, r2 = 0.82, p < 0.05). In all years, YS larvae collected in LB were smaller and Stage-3 larvae collected in channels were larger and possibly older than those from non-channel habitat. Because estuarine winter flounder populations are highly localized, adverse effects experienced during egg and larval stages are likely to propagate resulting in detrimental consequences for the year class in the natal estuary. © 2013 Coastal and Estuarine Research Federation.


Sliozberg Y.R.,Bowhead Science and Technology | Sliozberg Y.R.,U.S. Army | Chantawansri T.L.,U.S. Army
Journal of Chemical Physics | Year: 2013

The structural and mechanical properties of imperfect entangled polymer networks with various fractions of elastically active chains are studied using a generic coarse-grained model. Network topology is analyzed at various degrees of cross-linking and correlated with the mechanical response under uniaxial deformation at various strain rates. We found excellent agreement between results obtained from the structural analysis and from fitting to stress relaxation data. The relaxation tensile modulus at various engineering strains was also calculated as a function of the fraction of active strands. Results indicate that the mechanical and viscoelastic properties of entangled polymer networks are susceptible to variation in the network structure, where defects can affect the mechanical response especially at low strain rates and the relaxation behavior at long times. © 2013 AIP Publishing LLC.


Emerson R.,U.S. Army | Lawrence B.,Bowhead Science and Technology | Montgomery A.,Science and Mathematics Academy | Safriet S.,Air Force Research Lab
28th Annual Technical Conference of the American Society for Composites 2013, ASC 2013 | Year: 2013

In the present investigation novel needle-processed S2-glass laminates are fabricated and several key failure modes are characterized. Double cantilever beam testing shows that mode I fracture toughness improves up to 270% compared to non-needled baseline material. In-plane compressive strength of needled material improves by up to 475%. In plane tensile strength shows mixed results, improving by 6% for moderate volume fractions of through-thickness reinforcement (TTR) and decreasing by 6% at larger volume fractions. Double lap shear tests show that interlaminar shear strength improves as much as 17% for TTR inserted at ±45°; relative to the laminate plane. X-ray micro-computed tomography (micro-CT) is used to investigate the unique 3D microstructure resulting from the needling process for 90° TTR samples. The micro-CT reconstructions show that the dimensions of the disturbances of the inplane fabric are significantly smaller than those imparted by the conventional tufting or stitching processes at each penetration site. Micro-CT reveals that some penetration sites are aggregates of closely spaced neighbors, resulting from the lack of precise spatial control with the needling process used in the present research. At these aggregate locations the in-plane disturbances are roughly equal in size to those from tufting/stitching. Modifications to the automated processing equipment are shown and discussed. The modifications allow better spatial control at the penetration sites and the ability to insert TTR at ±45° relative to the laminate plane.


Wilber D.H.,Bowhead Science and Technology | Davis D.,HDR | Clarke D.G.,HDR | Alcoba C.J.,U.S. Army | Gallo J.,U.S. Army
Estuarine, Coastal and Shelf Science | Year: 2013

Winter flounder habitat use in New York/New Jersey Harbor was examined through a long-term (2002-2010) bottom trawl sampling program (Aquatic Biological Survey) in which 5234 winter flounder were captured in 2069 samples collected at approximately 26 stations throughout the harbor. Interannual variability in catch-per-unit-effort (CPUE) primarily was attributable to fluctuations in Year-1 juvenile CPUE, which was positively correlated with total annual egg abundances from the previous year. Adult male CPUE during the spawning season was positively correlated with total egg abundances of the same year, whereas adult female CPUE was unrelated to annual egg abundances in the harbor. Annual variation in adult male densities in the harbor during the spawning season reflects the intensity of estuarine spawning activity, whereas adult female densities may include non-reproductive, foraging individuals. Seasonal fluctuations in condition indices reflected energy use during the spawning season, with relatively high condition in January, reduced levels in March and April, and elevated condition again in May. Adult CPUE peaked in April, coincident with the critical feeding period that follows spawning. Mean April water temperatures were positively correlated with egg abundances the following year and Year-1 juvenile CPUE two years later. A similar correlation between April temperatures and Year-1 juvenile abundances two years later was demonstrated using published data for winter flounder collected in Niantic Bay, CT. Higher April water temperatures may enhance benthic secondary production during the critical feeding period, and thus increase prey availability for foraging adults that need to restore energy reserves in order to reproduce the following year. A direct examination of benthic secondary production and variation in winter flounder estuarine foraging and subsequent spawning activity is needed to more fully understand this relationship. © 2013 Elsevier Ltd.


Sherrill W.M.,U.S. Army | Johnson E.C.,Bowhead Science and Technology | Paraskos A.J.,U.S. Army
Propellants, Explosives, Pyrotechnics | Year: 2014

Three 7,8-disubstitited glycolurils were synthesized and subjected to various nitration conditions yielding the corresponding mono-, di-, and tetranitro derivatives. Prior to their synthesis, these nitrated compounds were evaluated computationally to determine their densities and heats of formation, from which explosive performance was predicted. Details on the methods used for the synthesis as well as the results from their computational analysis are discussed. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wilber D.H.,Bowhead Science and Technology | Hadley N.H.,South Carolina Department of Natural Resources | Clarke D.G.,U.S. Army
North American Journal of Fisheries Management | Year: 2012

Benthic-pelagic coupling is an important habitat function provided by oyster reefs that is potentially affected by sedimentation impacts. In this study, the distributions of three resident crab species, the flat mud crab (also known as the flatback mud crab) Eurypanopeus depressus, the common mud crab (also known as the Atlantic mud crab) Panopeus herbstii, and the invasive green porcelain crab Petrolisthes armatus, were examined with respect to sedimentation on six restored intertidal eastern oyster Crassostrea virginica sites in South Carolina. Sedimentation among sites ranged from 4% to 60% cover and was composed of silty clay and sand. Crab associations with sedimentation differed among species. Common mud crabs and green porcelain crab densities were negatively correlated with percent sediment cover, whereas flat mud crab densities were not related to sediment cover. Flat mud crabs occupy the interstices of the reef, and their densities were positively correlated with scorched mussel Brachidontes exustus densities. Total crab biomass and individual body weight were converted to annual secondary production estimates, which ranged from 6.1 to 27.2 g/m2 (ash-free dry weight) among sites. Sedimentation on oyster habitat reduced crab annual secondary production beyond a prediction made by a proportional inverse relationship between percent sediment cover and crab secondary production. As an example, at 50% sediment cover, crab annual secondary production was reduced by 68%. The discrepancy between observed and predicted (proportional) reductions in crab secondary production estimates were most pronounced when sedimentation levels were less than 60% cover. These results suggest the use of proportional loss estimates tomitigate for sedimentation impacts on oyster habitat, when quantified as percent sediment cover, do not adequately compensate for impacts to resident crabs and consequential energy loss to crustacean and fish predators that include many important recreational and commercial species. © American Fisheries Society 2012.

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