Showing papers by "Naval Surface Warfare Center published in 2008"

High‐Temperature Chemistry and Oxidation of ZrB2 Ceramics Containing SiC, Si3N4, Ta5Si3, and TaSi2

Abstract: The effect of Si 3 N 4 , Ta 5 Si 3 , and TaSi 2 additions on the oxidation behavior of ZrB 2 was characterized at 1200°-1500°C and compared with both ZrB 2 and ZrB 2 /SiC. Significantly improved oxidation resistance of all Si-containing compositions relative to ZrB 2 was a result of the formation of a protective layer of borosilicate glass during exposure to the oxidizing environment. Oxidation resistance of the Si 3 N 4 -modified ceramics increased with increasing Si 3 N 4 content and was further improved by the addition of Cr and Ta diborides. Chromium and tantalum oxides induced phase separation in the borosilicate glass, which lead to an increase in liquidus temperature and viscosity and to a decrease in oxygen diffusivity and of boria evaporation from the glass. All tantalum silicide-containing compositions demonstrated phase separation in the borosilicate glass and higher oxidation resistance than pure ZrB 2 , with the effect increasing with temperature. The most oxidation-resistant ceramics contained 15 vol% Ta 5 Si 3 , 30 vol% TaSi 2 , 35 vol% Si 3 N 4 , or 20 vol% Si 3 N 4 with 10 mol% CrB 2 . These materials exceeded the oxidation resistance of the ZrB 2 /SiC ceramics below 1300°-1400°C. However, the ZrB 2 /SiC ceramics showed slightly superior oxidation resistance at 1500°C.

Relationship Between RDX Properties and Sensitivity

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.

The resistance of metallic plates to localized impulse

Abstract: The responses of metallic plates and sandwich panels to localized impulse are examined by using a dynamic plate test protocol supported by simulations. The fidelity of the simulation approach is assessed by comparing predictions of the deformations of a strong-honeycomb-core panel with measurements. The response is interpreted by comparing and contrasting the deformations with those experienced by the same sandwich panel (and an equivalent solid plate) subjected to a planar impulse. Comparisons based on the center point displacement reveal the following paradox. The honeycomb panel is superior to a solid plate when subjected to a planar impulse, but inferior when localized. The insights gained from an interpretation of these results are used to demonstrate that a new design with a doubly-corrugated soft core outperforms solid plates both for planar and localized impulses.

Barnacle reattachment: a tool for studying barnacle adhesion

Abstract: Standard approaches for measuring adhesion strength of fouling organisms use barnacles, tubeworms or oysters settled and grown in the field or laboratory, to a measurable size. These approaches suffer from the vagaries of larval supply, settlement behavior, predation, disturbance and environmental stress. Procedures for reattaching barnacles to experimental surfaces are reported. When procedures are followed, adhesion strength measurements on silicone substrata after 2 weeks are comparable to those obtained using standard methods. Hydrophilic surfaces require reattachment for 2-4 weeks. The adhesion strength of barnacles in reattachment assays was positively correlated to results obtained from field testing a series of experimental polysiloxane fouling-release coatings (r = 0.89). The reattachment method allows for precise barnacle orientation, enabling the use of small surfaces and the potential for automation. The method enables down-selection of coatings from combinatorial approaches to manageable levels for definitive field testing. Reattachment can be used with coatings that combine antifouling and fouling-release technologies.

Microstructure and mechanical characterization of ZrC–Mo cermets produced by hot isostatic pressing

Abstract: Microstructure analysis and mechanical characterization were performed on ZrC–Mo composites with 20, 30, and 40 vol% Mo produced by hot isostatic pressing. The composites reached >98% relative density after processing at 1800 °C and 200 MPa for 1 h. The ZrC grain size was ∼1–2 μm after densification. The Mo appeared to form clusters that increased in size from 15 to 54 μm with increasing Mo content. Analysis of mechanical property data indicated that the Mo clusters acted as the critical flaws during fracture. Hardness decreased from ∼17 to ∼8 GPa with increasing Mo content, and was related to the effective hardness of each of the constituent materials. The elastic moduli also decreased with Mo additions from 392 GPa (corrected for porosity) to ∼380 GPa. Flexure strength and fracture toughness increased with increasing Mo content from 320 to 480 MPa and 1.0 to 6.6 MPa √ m , respectively. The elastic moduli, flexure strength, and fracture toughness were all found to follow a volumetric rule of mixtures.

Reduction of a ship's magnetic field signatures

Abstract: Decreasing the magnetic field signature of a naval vessel will reduce its susceptibility to detonating naval influence mines and the probability of a submarine being detected by underwater barriers and maritime patrol aircraft. Both passive and active techniques for reducing the magnetic signatures produced by a vessel's ferromagnetism, roll-induced eddy currents, corrosion-related sources, and stray fields are presented. Mathematical models of simple hull shapes are used to predict the levels of signature reduction that might be achieved through the use of alternate construction materials. Also, the process of demagnetizing a steel-hulled ship is presented, along with the operation of shaft-grounding systems, paints, and alternate configurations for power distribution cables. In addition, active signature reduction technologies are described, such as degaussing and deamping, which attempt to cancel the fields surrounding a surface ship or submarine rather than eliminate its source. Table of Contents: Introduction / Passive Magnetic Silencing Techniques / Active Signature Compensation / Summary

Flexural Creep Deformation of ZrB2/SiC Ceramics in Oxidizing Atmosphere

Abstract: Flexural creep of ZrB 2 /0-50 vol% SiC ceramics was characterized in oxidizing atmosphere as a function of temperature (1200°-1500°C), stress (30-180 MPa), and SiC particle size (2 and 10 μm). Creep behavior showed strong dependence on SiC content and particle size, temperature and stress. The rate of creep increased with increasing SiC content, temperature, and stress and with decreasing SiC particle size, especially, at temperatures above 1300°C. The activation energy of creep showed linear dependence on the SiC content increasing from about 130 to 511 kJ/mol for ceramics containing 0 and 50 vol% 2-μm SiC, respectively. The stress exponent was about 2 for ZrB 2 containing 50 vol% SiC regardless of SiC particle size, which is an indication that the leading mechanism of creep for this composition is sliding of grain boundaries. Compared with that, the stress exponent is about 1 for ZrB 2 containing 0-25vol% SiC, which is an indication that diffusional creep has a significant contribution to the mechanism of creep for these compositions. Cracking and grain shifting were observed on the tensile side of the samples containing 25 and 50 vol% SiC. Cracks propagate through the SiC phase confirming the assumption that grain-boundary sliding of the SiC grains is the controlling creep mechanism in the ceramics containing 50 vol% SiC. The presence of stress, both compressive and tensile, in the samples enhanced oxidation.

Review Article: Thermoelectric Technology Assessment: Application to Air Conditioning and Refrigeration

Abstract: A combination of factors—notably environmental concerns about global warming and ozone depletion due to refrigerants and the increasing demand for electronics and optoelectronic cooling—led to renewed activity in alternative cooling technologies. Currently, thermoelectric cooling is considered a popular cooling technology. This paper provides a critical review of thermoelectric technology and assesses its potential applications in air conditioning and refrigeration. The first part of this paper is devoted to the basic concept of thermoelectrics, with an overview of current thermoelectric materials and devices. The second part is a general overview of the applications of thermoelectric technology, with an emphasis on those related to air conditioning and refrigeration.

Analysis of broth‐cultured Bacillus atrophaeus and Bacillus cereus spores

Abstract: Aims: To compare physical properties of spores that were produced in broth sporulation media at greater than 108 spores ml−1. Methods and Results: Bacillus atrophaeus reproducibly sporulated in nutrient broth (NB) and sporulation salts. Microscopy measurements showed that the spores were 0·68 ± 0·11 μm wide and 1·21 ± 0·18 μm long. Coulter Multisizer (CM3) measurements revealed the spore volumes and volume-equivalent spherical diameters, which were 0·48 ± 0·38 μm3 and 0·97 ± 0·07 μm, respectively. Bacillus cereus reproducibly sporulated in NB, sporulation salts, 200 mmol l−1 glutamate and antifoam. Spores were 0·95 ± 0·11 μm wide and 1·31 ± 0·17 μm long. Spore volumes were 0·78 ± 0·61 μm3 and volume-equivalent spherical diameters were 1·14 ± 0·11 μm. Bacillus atrophaeus spores were hydrophilic and B. cereus spores were hydrophobic. However, spore hydrophobicity was significantly altered after treatment with pH-adjusted bleach. Conclusions: The utility of a CM3 for both quantifying Bacillus spores and measuring spore sizes was demonstrated, although the volume between spore exosporium and spore coat was not measured. This study showed fundamental differences between spores from a Bacillus subtilis- and B. cereus-group species. Significance and Impact of the Study: This is useful for developing standard methods for broth spore production and physical characterization of both living and decontaminated spores.

Micro-magnetostrictive vibrator using iron–gallium alloy

Abstract: A micro-magnetostrictive vibrator using an iron–gallium alloy (Galfenol) drive element was investigated. Galfenol is an iron-based magnetostrictive material with magnetostrictions greater than 200 ppm, a high relative permeability μ r > 70 and a Young’s modulus of ∼70 GPa. This material is machinable by conventional cutting techniques, and can operate under tensile, bending, and impact loads without degradation in performance. A micro-actuator using Galfenol, therefore, has advantages over a PZT type actuator in design simplicity, low drive voltage requirements, high robustness, and a wide temperature operating range. This paper describes the design, fabrication process, and performance of a micro-vibrator which utilizes either an un-annealed or stress-annealed Galfenol pin as the drive element. A displacement of 1.2 μm was observed with a high bandwidth of 30 kHz and a high tensile robustness withstanding a suspended weight of 500 g (6 MPa). The vibrator was also verified to be useful as a speaker which can generate clear sound from the power of a portable music player.

Predicting CH/π Interactions with Nonlocal Density Functional Theory

Abstract: We examine the performance of a recently developed nonlocal density functional in predicting a model noncovalent interaction, namely the weak bond between an aromatic pi system and an aliphatic C--H group. The new functional is a significant improvement over traditional density functionals, providing results which compare favorably to high-level quantum-chemistry techniques, but at considerably lower computational cost. Interaction energies in several model C--H/pi systems are in good general agreement with coupled-cluster calculations, though equilibrium distances are consistently overpredicted when using the revPBE functional for exchange. The new functional predicts changes in energy upon addition of halogen substituents correctly.

Processing of ZrC–Mo Cermets for High Temperature Applications, Part II: Pressureless Sintering and Mechanical Properties

Abstract: Pressureless sintering of ZrC-Mo cermets was investigated in a He/H 2 atmosphere and under vacuum. A large density increase was observed for specimens with > 20 vol% Mo after heating at 2150°C for 60 min in a He/H 2 atmosphere. The increase in density was attributed to the formation of Mo 2 C during heating and its subsequent eutectic reaction with Mo, which produced rounded ZrC grains in a Mo-Mo 2 C matrix. Sintering in vacuum did not produce the same increase in density, due to the lack of Mo 2 C formation and subsequent lack of liquid formation, which resulted in a microstructure with irregular ZrC grains with isolated areas of Mo. Mechanical properties testing showed a decrease in Young's modulus with increasing Mo content that was consistent with the models presented. Flexure strength of ZrC-Mo cermets sintered in He/H 2 atmosphere materials increased with increasing Mo content from 320 MPa at 20 vol% Mo to 410 MPa at 40 vol% Mo. Strength was predicted by adapting theories developed previously for WC-Co cermets.

A Model for Transitions in Oxidation Regimes of ZrB2

Abstract: A mechanistic model that interprets the transition in oxidation behavior of zirconium diboride as the temperature is varied from 600°C to 2500°C is presented. Available thermodynamic data and literature data for vapor pressures, oxygen permeability in boria, and viscosity of boria were used to evaluate the model. Three regimes and the temperatures of transition between them were identified. In the intermediate temperature regime, viz., 1000°C to 1800°C, good correspondence was obtained between theory and experiments for weight gain, recession, and scale thickness as functions of temperature and oxygen partial pressure. In this regime, the rate-limiting step is the diffusion of dissolved oxygen through a film of liquid boria in capillaries at the base of the oxidation product. At lower temperatures, an external boria scale forms, but it was not found to contribute significantly to oxidation resistance. Comparison with literature data on recession is very good, but weight gain is predicted to be higher than experimentally observed unless flow of viscous boria is included. At higher temperatures, the boria is lost by evaporation, and the oxidation rate is limited by diffusion of molecular oxygen through the capillaries between nearly columnar blocks of the oxide MO2.; this regime is soon followed by a rapid acceleration of recession due to vaporization of the oxide MO2 itself.

Guidance Algorithm for Range Maximization and Time-of-Flight Control of a Guided Projectile

Abstract: The availability of gun-hardened guidance and control systems has made highly accurate gun-launched rocket-assisted guided projectiles feasible. A composite guidance algorithm is presented for such vehicles. The algorithm is capable of extending range and cross-range capability of the projectile, and allows it to be retargeted after launch. The algorithm also employs model predictive control to control time of flight to allow a salvo of projectiles to arrive simultaneously. The time-of-flight control achieves its objective by trajectory shaping and corrects for winds, off-nominal launch conditions, and rocket motor variations.

Electromagnetic environment characterization of below-deck spaces in ships

Abstract: With wireless systems currently being introduced into confined, reflective spaces that were not originally intended for radio frequency emissions, it becomes necessary to assess the resultant electromagnetic environment of these spaces, especially where potential hazards may exist. In this work, we present experimental data to demonstrate that the below-deck compartments aboard Navy ships can be characterized as complex reverberant cavities. For general reverberant spaces, a cavity calibration factor can be used to predict maximum diffuse electric fields as a function of frequency and total radiated power.

Network-centric military system architecture assessment methodology

Abstract: Recent paradigm shift from considering software as a product to treating software as a service has produced capabilities for engineering complex Network-Centric Military Systems (NCMSs). As the industry works on building a cyber-infrastructure and the Department of Defence moves towards network-centric operations and warfare, military systems are becoming increasingly more network-centric. Assessment of the architecture of such a NCMS is a very complex process, involves the measurement and evaluation of hundreds of qualitative and quantitative elements, mandates subject matter expert evaluation, and requires the integration of disparate evaluations obtained by experimentation, demonstration, trial, testing, direct measurement, analysis and examination. Planning and managing such measurements and evaluations require a unifying methodology and should not be performed in an ad hoc manner. This paper presents such a methodology named Military System Architecture Assessment Methodology (MSAAM). MSAAM advocates mission-oriented risk-driven architecture assessment based on four assessment perspectives: product, process, people and project. It enables the decomposition of architecture assessment into small pieces corresponding to leaf indicators and provides a structured framework for overcoming the complexity of architecture assessment.

Beating of a circular cylinder mounted as an inverted pendulum

Abstract: This paper contains temporally and spatially resolved flow visualization and DPIV measurements characterizing the frequency-amplitude response and three-dimensional vortex structure of a circular cylinder mounted like an inverted pendulum. Two circular cylinders were examined in this investigation. Both were 2.54 cm in diameter and ∼140cm long with low mass ratios, m* = 0.65 and 1.90, and mass-damping ratios, m*ζ ( = 0.038 and 0.103, respectively. Frequency-amplitude response analysis was done with the lighter cylinder while detailed wake structure visualization and measurements were done using the slightly higher-mass-ratio cylinder. Experiments were conducted over the Reynolds number range 1900 ≤ Re ≤ 6800 corresponding to a reduced velocity range of 3.7 ≤U* ≤ 9.6. Detailed examination of the upper branch of the synchronization regime permitted, for the first time, the identification of short-time deviations in cylinder oscillation and vortex-shedding frequencies that give rise to beating behaviour. That is, while long-time averages of cylinder oscillation and vortex-shedding frequencies are identical, i.e. synchronized, it is shown that there is a slight mismatch between these frequencies over much shorter periods when the cylinder exhibits quasi-periodic beating. Data are also presented which show that vortex strength is also modulated from one cylinder oscillation to the next. Physical arguments are presented to explain both the origins of beating as well as why the quasi-periodicity of the beating envelopes becomes irregular; it is believed that this result may be generalized to a broader class of fluid-structure interactions. In addition, observations of strong vertical flows associated with the Karman vortices developing 2-3 diameters downstream of the cylinder are presented. It is hypothesized that these three-dimensionalities result from both the inverted pendulum motion as well as free-surface effects.

Nonlinear Meissner effect in a high-temperature superconductor: Local versus nonlocal electrodynamics

Abstract: Measured intermodulation distortion (IMD) power at 1.5 GHz in a series of ${\text{YBa}}_{2}{\text{Y}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ stripline resonators of varying strip widths is compared to the predictions of two qualitatively distinct theories of the nonlinear Meissner effect. The stripline resonators are patterned from a single wafer to ensure uniformity of the material properties. According to the first theory [T. Dahm and D. J. Scalapino, Phys. Rev. B 60, 13125 (1999)], the IMD power is dominated by contributions from the strip edges, while according to the second theory [D. Agassi and D. E. Oates, Phys. Rev. B 72, 014538 (2005)] it is dominated by contributions from the body of the strip. The parameter-free comparison of the measured data with the theoretical predictions clearly favors the latter theory. We conclude that the nonlinear component of the penetration depth must be treated with nonlocal electrodynamics. The origins of this outcome are discussed briefly in the framework of a Green's-function approach.

Nonlinear Meissner effect in a high-temperature superconductor: Local versus nonlocal electrodynamics

Abstract: Measured intermodulation distortion IMD power at 1.5 GHz in a series of YBa2Y3O7� stripline resonators of varying strip widths is compared to the predictions of two qualitatively distinct theories of the nonlinear Meissner effect. The stripline resonators are patterned from a single wafer to ensure uniformity of the material properties. According to the first theory T. Dahm and D. J. Scalapino, Phys. Rev. B 60, 13125 1999, the IMD power is dominated by contributions from the strip edges, while according to the second theory D. Agassi and D. E. Oates, Phys. Rev. B 72, 014538 2005 it is dominated by contributions from the body of the strip. The parameter-free comparison of the measured data with the theoretical predictions clearly favors the latter theory. We conclude that the nonlinear component of the penetration depth must be treated with nonlocal electrodynamics. The origins of this outcome are discussed briefly in the framework of a Green’s-function approach.

Comparison between Three Spiraling Ballistic Missile State Estimators

Abstract: During the reentry to the atmosphere, certain ballistic missiles are known to undergo violent spiraling motions induced by aerodynamic resonance between roll and yaw/pitch modes. Successful interception of such a spiraling target is critically dependent on the performance of the target state estimator. Strong nonlinearities involved in the system dynamics and measurement equations together with sensor noise make this a challenging estimation task. The performance of the Extended Kalman Filter, the Unscented Kalman Filter, and the Particle Filter designed for this estimation problem is compared in this paper. Additionally, a hybrid Rao-Blackwellized Particle Filter approach combining the Extended Kalman Filter and the Particle Filter is also considered. Simulation results are provided to support the conclusions from the present study. Nomenclature T X = North position of the target T Y = East position of the target T Z = Down position of the target m X = North position of the missile m Y = East position of the missile m Z = Down position of the missile z , y , x G = Gravitational acceleration components of the target z , y , x A = Aerodynamic acceleration components of the target ω = Spiraling frequency of the target ϕ = Aerodynamic roll angle of the target 1