Showing papers by "Naval Surface Warfare Center published in 2007"

Refractory Diborides of Zirconium and Hafnium

Abstract: This paper reviews the crystal chemistry, synthesis, densification, microstructure, mechanical properties, and oxidation behavior of zirconium diboride (ZrB2) and hafnium diboride (HfB2) ceramics. The refractory diborides exhibit partial or complete solid solution with other transition metal diborides, which allows compositional tailoring of properties such as thermal expansion coefficient and hardness. Carbothermal reduction is the typical synthesis route, but reactive processes, solution methods, and pre-ceramic polymers can also be used. Typically, diborides are densified by hot pressing, but recently solid state and liquid phase sintering routes have been developed. Fine-grained ZrB2 and HfB2 have strengths of a few hundred MPa, which can increase to over 1 GPa with the addition of SiC. Pure diborides exhibit parabolic oxidation kinetics at temperatures below 1100°C, but B2O3 volatility leads to rapid, linear oxidation kinetics above that temperature. The addition of silica scale formers such as SiC or MoSi2 improves the oxidation behavior above 1100°C. Based on their unique combination of properties, ZrB2 and HfB2 ceramics are candidates for use in the extreme environments associated with hypersonic flight, atmospheric re-entry, and rocket propulsion.

UHTCs: Ultra-High Temperature Ceramic Materials for Extreme Environment Applications

Abstract: 3000°C. That's not just hot ... it's EXTREMELY hot. It is above the melting or decomposition temperatures for most of the materials known to man. But in the world of extreme environment engineering, it is just a baseline.

Magnetostriction of binary and ternary Fe–Ga alloys

Abstract: This article will review the development of the Fe–Ga (Galfenol) alloy system for magnetostriction applications including work on substitutional ternary alloying additions for magnetic property enhancement. A majority of the alloying addition research has focused on substitutional ternary elements in Bridgman grown single crystals with the intent of improving the magnetostrictive capability of the Galfenol system. Single crystals provide the ideal vehicle to assess the effectiveness of the addition on the magnetostrictive properties by eliminating grain boundary effects, orientation variations, and grain-to-grain interactions that occur when polycrystals respond to applied magnetic fields. In almost all cases, ternary additions of transition metal elements have decreased the magnetostriction values from the binary Fe–Ga alloy. Most of the ternary additions are known to stabilize the D03 chemical order and could be a primary contribution to the observed reduction in magnetostriction. In contrast, both Sn and Al are found to substitute chemically for Ga. For Sn additions, whose solubility is limited, no reduction in magnetostriction strains are observed when compared to the equivalent binary alloy composition. Aluminum additions, whose effect on the magnetoelastic coupling on Fe is similar to Ga, result in a rule of mixture relationship. The reviewed research suggests that phase stabilization of the disordered bcc structure is a key component to increase the magnetostriction of Fe–Ga alloys.

Towards the development of a virtual environment-based training system for mechanical assembly operations

Abstract: In this paper, we discuss the development of Virtual Training Studio (VTS), a virtual environment-based training system that allows training supervisors to create training instructions and allows trainees to learn assembly operations in a virtual environment. Our system is mainly focused on the cognitive side of training so that trainees can learn to recognize parts, remember assembly sequences, and correctly orient the parts during assembly operations. Our system enables users to train using the following three training modes: (1) Interactive Simulation, (2) 3D Animation, and (3) Video. Implementing these training modes required us to develop several new system features. This paper presents an overview of the VTS system and describes a few main features of the system. We also report user test results that show how people train using our system. The user test results indicate that the system is able to support a wide variety of training preferences and works well to support training for assembly operations.

Flammability properties and mechanical performance of epoxy modified phenolic foams

Abstract: This work has been mainly focused on the development and optimization of the processing methodology to produce epoxy modified phenolic foams. This study analyzes the relation between the composition and the structure as well as the mechanical and flammability performance of epoxy-phenolic (E-P)-based foams. Phenolic foams modified with different types and compositions of epoxy resin were successfully synthesized and characterized, showing uniform pore structure. Two epoxy resins were used for this approach. One is regular diglycidyl ether of bisphenol A (Epon 826) type and the other is a brominated bisphenol A (DER 542), which has halogen groups in the structure to improve the flammability properties of the resulting foams. Cone calorimeter (ASTM E 1354) was used to measure the heat release rate, the time to ignition, and other flammability properties of the E-P foams with different types of epoxy resins, under well-controlled combustion conditions. The mechanical performance of the system was studied and compared with competing foams, such us phenolic, epoxy, and polyurethanes, in aspects of compression, friability, and shear performances. Compared with conventional phenolic foams, E-P foams exhibit significant improvement in mechanical performance, lower friability and similar resistance to flame. These results demonstrate the potential of the E-P foam as a flame resistant and high performance core material for sandwich structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1399–1407, 2007

Dislocation Mechanics of Shock-Induced Plasticity

Abstract: The constitutive deformation behavior of copper, Armco iron, and tantalum materials is described over a range of strain rates from conventional compressive/tensile testing, through split Hopkinson pressure bar (SHPB) test results, to shock-determined Hugoniot elastic limit (HEL) stresses and the follow-on shock-induced plasticity. A mismatch between the so-called Zerilli–Armstrong (Z-A) constitutive equation description of pioneering SHPB measurements for copper provided initial evidence of a transition from the plastic strain rate being controlled by movement of the resident dislocation population to the strain rate being controlled by dislocation generation at the shock front, not by a retarding effect of dislocation drag. The transition is experimentally confirmed by connection with Swegle–Grady-type shock vs plastic strain rate measurements reported for all three materials but with an important role for twinning in the case of Armco iron and tantalum. A model description of the shock-induced plasticity results leads to a pronounced linear dependence of effective stress on the logarithm of the plastic strain rate. Taking into account the Hall–Petch grain size dependence is important in specifying the slip vs twinning transition for Armco iron at increasing strain rates.

Characterization of Gaseous Helium Flow Cryogen in a Flexible Cryostat for Naval Applications of High Temperature Superconductors

Abstract: A fifty meter proof of concept demonstrator was developed utilizing gaseous helium as a cryogen for the use in a high temperature superconductor (HTS) based degaussing system for use on Navy ships. Increased signature requirements as Navy future missions move into littoral waters have resulted in a new copper degaussing system. This system has an increased weight and installation cost because of the additional copper cable required. High temperature superconductors have been suggested as a replacement to the copper based cable to reduce system weight while maintaining the desired ship's magnetic signature. A feasibility study was conducted in 2004 that showed that a superconductive system provided the same performance at a lower cost and at a lower system weight. Many terrestrial superconducting cable projects use liquid nitrogen as the cryogen to keep the cable cold. However, an inert, gaseous cryogen would be preferred for naval applications, but such a cooling system has never been demonstrated in a power cable. This paper describes the experimental setup and preliminary results of testing a helium cooled loop for use in a HTS based degaussing system.

Conceptual modelling for designing large-scale simulations

Abstract: Large-scale complex simulations take many years to develop and cost millions of dollars.Development of such simulations requires many areas of expertise and poses significant technical and managerial challenges.Some of the challenges can be met with the development and use of a conceptual model (CM).This paper describes a life cycle for the development of a simulation CM.The role of the CM in large-scale complex simulation model design is explained. The objectives under which a simulation CM should be created and used are enunciated.The life cycle presented provides a structured blueprint of simulation CM development and specifies the work products to be created under the designated processes together with the integrated verification and validation activities.

Production planning for remanufactured products

Abstract: This paper presents a methodology for production planning within facilities involved in the remanufacture of products Remanufacturing refers to the process of accepting inoperable units, salvaging good and repairable components from those units, and then re-assembling good units to be re-issued into service These types of facilities are common, yet many suffer from the unpredictability of good and repairable component yields, as well as processing time variation These problems combine to make it extremely difficult to predict whether overall production output will be sufficient to meet demand Low yields of key components can lead to shortages which require the facility to purchase new components for legacy systems, often with long lead times, thus causing overall delays The approach developed here is a probabilistic form of standard material requirements planning (MRP), which considers variable yield rates of good, bad, and repairable components that are harvested from incoming units, and probabilist

Ab initio equation of state of an organic molecular crystal: 1,1-diamino-2,2-dinitroethylene.

Abstract: A complete equation of state for the molecular crystal 1,1 -diamino-2,2-dinitroethylene has been calculated from first principles for temperatures between 0 and 400 K, and for specific volumes from 61 to 83 cm 3 /mol, corresponding to relative volumes from 0.78 to 1.06. The calculated 300 K isotherm agrees very well with the experimentally measured pressure-volume relation reported by Peiris et al. (Peiris, S. M.; Wong, C. P.; Zerilli, F. J. J. Chem. Phys. 2004, 120, 8060). The volumetric thermal expansion coefficient is calculated to be 140 ppm/K at 300 K and atmospheric pressure and varies considerably with specific volume as well as temperature. The Gruneisen parameter varies significantly with temperature, but its variation with specific volume is small. The calculated specific heat (160 J/mol/K at 300 K and atmospheric pressure) has only a very small dependence on specific volume.

Investigation of the Decomposition Mechanism and Thermal Stability of Nitrocellulose/Nitroglycerine Based Propellants by Electron Spin Resonance

Abstract: Nitrocellulose based (NC) and nitroglycerin based (NG) propellants often have a fixed acid and water content during the manufacturing time. After manufacture, the quantity and ratio of acid/water will continue to vary depending upon the conditions of storage and operation. The level of variation depends on many factors such as loading density, temperature, volume of ullage and sealing condition of the containing cartridge, just to name a few. As described in this paper and other literature, the degradation mechanisms and aging processes of NC/NG based propellants are extremely complicated. This paper describes the details of the application of Electron Spin Resonance (ESR) to study if the free-radical mechanism is involved in the decomposition of nitrocellulose and nitroglycerin. Due to the high free-radical intensity possessed by the propellant composition, we believe that a π complex intermediate may be formed between DPA and NG and/or NC. The formation of a π complex intermediate is not preferred because it may enhance the rate of decomposition of nitrate esters.

Modeling a Ship's Ferromagnetic Signatures

Abstract: Ferromagnetic models of ships and submarines that predict or reproduce their magnetic signatures have found applications in the development of both offensive and defensive military systems from World War II to the present. The mathematical basis of generalized coordinate systems will be presented and demonstrated with example applications to analytic spherical and prolate spheroidal magnetic ship models. In addition, the advantages and pitfalls of using complex finite-element- and boundary-element numerical techniques to predict high-order near-field ship signatures will be discussed, followed by a short description of the design and testing of complementary physical scale models. Extrapolation of measured magnetic signatures from testing environments to threat areas using semi-empirical math models will be presented, along with an explanation of their inherent instabilities and methods for regularizing them. These magnetic ship signature modeling techniques are used today in designing optimized signature reduction systems that have a minimum impact on ships and their systems. The discussion will be closed with an important discussion of the verification and validation of magnetic models of surface ships and submarines.

The Effects of Hydrogen in Hermetically Sealed Packages on the Total Dose and Dose Rate Response of Bipolar Linear Circuits

Abstract: It is demonstrated with test transistors and circuits that a small amount of hydrogen trapped in hermetically sealed packages can significantly degrade the total dose and dose rate response of bipolar linear microelectronics. In addition, we show that when exposed to an atmosphere of 100% molecular hydrogen dies with silicon nitride passivation are unaffected, whereas dies with silicon carbide or deposited oxides become very soft at high and low dose rate.

Processing of ZrC–Mo Cermets for High‐Temperature Applications, Part I: Chemical Interactions in the ZrC–Mo System

Abstract: The chemical compatibility of ZrC and Mo was investigated in carburizing and carbon-free environments at temperatures from 1700° to 2200°C. Heating in the carburizing atmosphere resulted in the complete reaction of Mo with C, while the carbon-free atmosphere resulted in retained metallic phase with a maximum of 13.8 mol% Mo2C formed. The presence of Mo2C was not detected at 2100°C in the carbon-free atmosphere, confirming the existing phase equilibria in the Zr–Mo–C system. Heat treatments in the carbon-free atmosphere also showed liquid formation at 2200°C, as evident from microstructure analysis. Liquid formation was consistent with the interaction between Mo and Mo2C. The liquid was found to comprise at least 7 vol% of the total component, based on a phase diagram for the Mo–C system. The formation of a liquid should allow for the processing of ZrC–Mo cermets by liquid-phase pressureless sintering.

Level Set Hyperspectral Image Classification Using Best Band Analysis

Abstract: We present a supervised hyperspectral classification procedure consisting of an initial distance-based segmentation method that uses best band analysis (BBA), followed by a level set enhancement that forces localized region homogeneity. The proposed method is tested on two hyperspectral images of an urban and rural nature. The proposed method is compared to the maximum likelihood (ML) method using BBA. Quantitative results are compared using segmentation and classification accuracies. Results show that both the initial classification using BBA features and the level set enhancement produced high-quality ground cover maps and outperformed the ML method, as well as previous studies by the authors. For example, with the compact airborne spectrographic imager image, the ML method resulted in accuracies les95.5%, whereas the level set segmentation approach resulted in accuracies as high as 99.7%.

Taxonomy for the modeling and simulation of emergent behavior systems

Abstract: Preliminary to the development of a theoretical framework for the specification, modeling, and design of emergent behavior systems is the construction of a consistent lexicon of emergent behavior terms and the development of an emergent behavior systems taxonomy. Without these two critical components of lexicon and taxonomy we will not be able to 1) understand what emergent behavior is, 2) establish axiomatic relationships, and 3) identify emergent behavior apart from other phenomena. This paper briefly presents a taxonomy based upon five orders of emergent behavior with four sub-orders and briefly summarizes the author's continuing research in this area.

Ab initio studies of crystalline nitromethane under high pressure.

Abstract: We have studied the mechanical compressibility and band structure of solid nitromethane both in equilibrium and compressed states using Hartree-Fock and density functional theory (DFT) with atom-centered all-electron linear combination of atomic orbitals basis sets. Hartree-Fock calculations with a 6-21G basis set, uncorrected for basis set superposition error, gave the best agreement with experimental compression studies. These results may be due to the cancellation of basis set superposition error with dispersion force errors. The equilibrium DFT band gap is comparable to the lowest-energy feature in electron-impact spectroscopy of nitromethane but underpredicts the optical absorption gap; we interpret these features in terms of the presence of tightly bound excitons. Only minor changes in the gap are observed under hydrostatic compression.

Demonstration of a Novel Man-Portable Magnetic STAR Technology for Real Time Localization of Unexploded Ordnance

Abstract: We report results of field tests of the first prototype of a novel man-portable Magnetic Scalar Triangulation and Ranging (STAR) technology. The new magnetic sensor system technology is being developed with support from the Strategic Environmental Research and Development Program (SERDP) to provide an easily deployable magnetic sensor system for real-time, point-by-point Detection, Localization and Classification (DLC) of magnetic targets such as Unexploded Ordnance (UXO) and buried mines. The STAR technology is based on a multi tensor gradiometer approach that uses magnetic gradient tensor magnitudes, i.e., "gradient- contraction-type" parameters to perform DLC of magnetic targets. The magnetic STAR sensor uses the scalar functions to triangulate a magnetic UXO-type target's position vector and to calculate the target's magnetic signature vector. The vector components of an object's magnetic signature provide a basis for real time classification of its type, i.e. UXO-like or not. In order to provide proof of principle of the STAR concept and demonstrate its advantages for high mobility magnetic sensing applications, we designed, constructed and field-tested a prototype man-portable STAR Gradiometer. The portable gradiometer's hardware and software are completely self- contained and provide a practical and user friendly capability for real time DLC of magnetic targets. Target DLC parameters: e.g., range, bearing, elevation and magnetic signature are correlated with Global Positioning System time and position data and displayed in near real time (total delay < 3 seconds) on a heads-up display that clips onto the operator's safety glasses. Interactive software controls data acquisition, performs signal processing to remove residual motion noise effects and runs the STAR Algorithm to generate and display the target's DLC parameters. Field tests have demonstrated proof-of-principle of the STAR concept and conclusively demonstrated that the technology has unique advantages for DLC by highly mobile sensing platforms. While being carried and operated by a single individual, the portable sensor has demonstrated very robust, motion noise resistant performance even while undergoing rotational motion of more than 40 degrees per second. The field test results very strongly indicate that the man-portable STAR technology can provide a wide variety of highly maneuverable sensing platforms (including Autonomous Underwater Vehicles) with uniquely effective, motion-noise-resistant magnetic sensing modalities for DLC of magnetic targets such as UXO and underwater mines.

Transient Resonance in Hypervelocity Launchers at Critical Velocities

Abstract: A projectile accelerating along launcher rails may cross a range of critical velocities and induce resonance. As a result, the rails and other components exhibit increased displacements and stress that may cause launcher failure. This work is focused on the computation of the critical velocity and investigation of the transient resonance in the assembly of a notional electromagnetic hypervelocity launcher. Several analytical and finite-element models were employed. Different models yielded a good correlation and aided in better understanding of the launcher dynamics. Analysis shows that various components of a launcher can have different critical velocities. The results of this work will further be used to develop a novel design approach based on the idea of controlling the intervals between the critical velocities to minimize the enhanced occurrence of induced resonance regimes in launcher assemblies

Reducing Crane Payload Swing Using A Rider Block Tagline Control System

Abstract: This paper considers payload swing control of large, marine cranes using an active rider block tagline system (ARBTS). The contribution is the control system development and simulation comparison of the ARBTS approach to standard luff cranes without ARBTS. It is shown that the ARBTS control system off-loads boom actuation (luff) for ship motion cancellation. Thus, the boom can be used for its intended purpose of moving the load radially per the operator's command. For the simulation case considered, the maximum luff power decreases from 150 kW to 4 kW and the luff rope speed decreases from 0.9 m/s to 0.02 m/s. Application of this approach to existing offshore crane designs could increase their operational envelope, without increased power requirements or necessitating costly mechanical changes, permitting operations in rough sea conditions.

The effect of covalent surface immobilization on the bactericidal efficacy of a quaternary ammonium compound

Abstract: This study investigates the effect of surface immobilization on the bactericidal function of a quaternary ammonium compound. Quaternary ammonium silane (QAS) coated planar surfaces did not produce any measurable mortality of Staphylococcus aureus, while 1 μm QAS-coated microparticles did produce S. aureus mortality. The experiments using QAS-coated microparticles indicate that the ability of QAS molecules to disrupt the cell wall is not hindered by covalent immobilization of QAS to a surface. These results provide evidence that S. aureus cells on a QAS-coated planar surface are not exposed to a sufficient number of QAS molecules to produce significant mortality. This result has important implications for the development of self-decontaminating coatings. Covalent immobilization is used to prevent leaching of the bactericidal compound. However, covalent immobilization may result in a significant tradeoff in bactericidal performance. Published in 2007 by John Wiley & Sons, Ltd.

A constitutive equation for the dynamic deformation behavior of polymers

Abstract: A constitutive equation based on the generalized concept of thermally activated flow units is developed to describe the stress–strain behavior of polymers as a function of temperature, strain-rate, and superposed hydrostatic pressure under conditions in which creep and long-term relaxation effects are negligible. The equation is shown to describe the principal features of the dynamic stress–strain behavior of polytetrafluoroethylene and, also, the yield stress of polymethylmethacrylate as a function of temperature and strain rate. A key feature of the model, not utilized in previous constitutive equation descriptions, is an inverse shear stress dependence of the shear activation volume. In contrast to metal deformation behavior, an enhanced strain hardening with increasing strain at higher strain rates and pressures is accounted for by an additional rate for immobilization of flow units. The influence of hydrostatic pressure enters through a pressure activation volume and also through the flow unit immobilization term. The thermal activation model is combined with a temperature dependent Maxwell–Weichert linear viscoelastic model that describes the initial small strain part of the stress strain curve.

Numerical SDRE Approach for Missile Integrated Guidance - Control

Abstract: ‡Numerical s tate -dependent Riccati equation based integrated guidance -control formulation is developed for an internally actuated missile. The dynamic system under consideration is of tenth order , making it tedious to algebraically manipulate the equations of motion into the state -dependent coeffic ient form central to the design methodology . A robust numerical approach based on previous research is developed to derive the state dependent parameterization of the system. The approach works directly with an input -state numerical simulation model of the system . The state -dependent Riccati equation is solved numerically at the instantaneous values of the state vector . The approach provides a fully numerical methodology for deriving state -dependent Riccati equation control lers for arbitrarily complex dynam ic systems. The proposed approach is applied for th e design of integrated guidance -controller of an internally actuated missile. Closed -loop simulation results for three -dimensional target intercept ions are presented .

Vacuum Electronics: Status and Trends

Abstract: The vast preponderance of U.S. radar transmitters today use vacuum electronic amplifiers, spanning the spectrum from UHF to EHF. Enhancements to performance, reliability, and cost of ownership are being applied continuously to these systems; routine in-service life extensions mandate continuing vacuum electronics research and development to support system needs for the foreseeable future. In addition, exciting advances in vacuum electronics will provide dramatic improvements in millimeter-wave radar resolution, broadband low-noise power at microwave frequencies, compact high power sources operating at lower voltages, and life-cycle cost improvement. Recent progress in key enabling technologies, e.g., advanced device modeling and micro-fabrication, is expected to continue. This paper reviews the status and trends of vacuum electronics, with selected applications emphasizing recent advances in device performance in the microwave regime: multiple-beam klystrons (MBKs), microwave power modules (MPMs), and gyro-amplifiers in the millimeter-wave regime.

Target State Estimation for Integrated Guidance-Control of Missiles

Abstract: An extended Kalman filter for estimating the states and parameters of a target undergoing spiraling motions is discussed. The research is motivated by the target state information requirements for implementing integrated guidance-control systems. Nonlinear point-mass model of the target including gravitational and aerodynamic forces is considered in the formulation. The spiraling target motions are modeled by a second-order oscillator dynamics modulating the aerodynamic normal force, together with aerodynamic drag and the acceleration due to gravity. Based on an error analysis, line-of-sight angles, line-of-sight rates, range and range rate measurements are then chosen for the implementation of the estimator. Target interception results with an integrated guidance-control law employing the filter estimates are given.