Showing papers by "Naval Surface Warfare Center published in 1999"

Mechanical, Thermal, and Oxidation Properties of Refractory Hafnium and zirconium Compounds

Abstract: The thermal conductivity, thermal expansion, Youngs Modulus, flexural strength, and brittle–plastic deformation transition temperature were determined for HfB2, HfC0·98, HfC0·67, and HfN0·92 ceramics. The oxidation resistance of ceramics in the ZrB2–ZrC–SiC system was characterized as a function of composition and processing technique. The thermal conductivity of HfB2 exceeded that of the other materials by a factor of 5 at room temperature and by a factor of 2·5 at 820°C. The transition temperature of HfC exhibited a strong stoichiometry dependence, decreasing from 2200°C for HfC0·98 to 1100°C for HfC0·67 ceramics. The transition temperature of HfB2 was 1100°C. The ZrB2/ZrC/SiC ceramics were prepared from mixtures of Zr (or ZrC), SiB4, and C using displacement reactions. The ceramics with ZrB2 as a predominant phase had high oxidation resistance up to 1500°C compared to pure ZrB2 and ZrC ceramics. The ceramics with ZrB2/SiC molar ratio of 2 (25 vol% SiC), containing little or no ZrC, were the most oxidation resistant.

A Statistical Method for Profiling Network Traffic

Abstract: Two clustering methods are described and applied to network data. These allow the clustering of machines into "activity groups", which consist of machines which tend to have similar activity profiles. In addition, these methods allow the user to determine whether current activity matches these profiles, and hence to determine when there is "abnormal" activity on the network. A method for visualizing the clusters is described, and the approaches are applied to a data set consisting of a months worth of data from 993 machines.

A Weibull stress model to predict cleavage fracture in plates containing surface cracks

Abstract: This study applies recent advances in probabilistic modelling of cleavage fracture to predict the measured fracture behaviour of surface crack plates fabricated from an A515-70 pressure vessel steel. Modifications of the conventional, two-parameter Weibull stress model introduce a non-zero, threshold parameter (σ w-min ). The introduction of σ w-min brings numerical predictions of scatter in toughness data into better agreement with experimental measurements, and calibration of this new parameter requires no additional experimental data. The Weibull modulus (m) and scaling parameter (σ u ) are calibrated using a new strategy based on the toughness transferability model, which eliminates the non-uniqueness that arises in calibrations using only small-scale yielding toughness data. Here, the Weibull stress model is calibrated using toughness data from deep-notch C(T) and shallow-notch SE(B) specimens, and is then applied to predict the measured response of surface crack plates loaded in different combinations of tension and bending. The model predictions accurately capture the measured distributions of fracture toughness values.

An In Situ X‐Ray Absorption Spectroscopic Study of Charged Li ( 1 − z ) Ni ( 1 + z ) O 2 Cathode Material

Abstract: The authors have measured in situ the Ni K-edge X-ray absorption spectra of Li{sub (1{minus}z)}Ni{sub (1+z)}O{sub 2} cathode material charged in a nonaqueous cell The material was charged to various states of charge (ie, Li content) which corresponded to x = 00, 012, 024, 037, 049, and 086 in Li{sub (1{minus}x{minus}z)}Ni{sub (1+z)}O{sub 2} The authors have determined variations in the Ni-O and Ni-Ni coordination numbers, bond lengths, and local disorders as well as the Ni K-edge energies as a function of Li content They show that in the pristine state, the composition of the material can be described by the formula Li{sub 086}N{sub 114}O{sub 2} (ie, x = 0 and z = 014) That is, the material consists of Ni{sup 2+} (25%) and Ni{sup 3+} (75%) with half the Ni{sup 2+} atoms residing in Li sites and the other half in the NiO{sub 2} slabs Upon charging, initially Ni{sup 2+} is oxidized to Ni{sup 3} up to a state of charge which corresponds to x = 2z Upon further charging to states corresponding to 2z < x {le} 1 {minus} z, Ni{sup 3} is oxidized to Ni{sup 4+} with fractions being dependent on the values of x and z Analysismore » of the edge energies for NiO, stoichiometric LiNiO{sub 2}, and KNiIO{sub 6} as reference compounds for Ni{sup 2+}, Ni{sup 3}, and Ni{sup 4}, respectively, shows a quadratic dependence for edge energy vs oxidation state This type of correlation is consistent with variations observed in earlier studies for some Mn reference compounds in the same range of oxidation states Oxidation-state determination of Ni in Li{sub (1{minus}x{minus}z)}Ni{sub (1+z)}O{sub 2} as a function of state of charge (ie, Li content or x) on the basis of edge energies yielded results which are in excellent agreement with oxidation state determinations made on the basis of the mole fractions for Ni{sup 2+}, Ni{sup 3}, and Ni{sup 4} extracted from extended X-ray absorption fine structure spectra« less

The influence of tensile stress states on the failure of HY-100 steel

Abstract: The failure of an HY-100 steel plate has been examined as a function of stress state using notched and un-notched axisymmetric tensile specimens. The results show that increasing stress triaxiality leads to a rapid decrease in failure strains in a manner that is exponentially dependent on the degree of triaxiality. Two ductile failure mechanisms are identified: a void coalescence process, in which relatively equiaxed voids grow to impingement, and a void-sheet process, which links by a shear instability process large, elongated inclusion-initiated voids. The void-sheet mechanism intervenes and limits ductility at high-stress triaxialities in transversely oriented HY steel plate material, whereas the former process controls failure in longitudinally oriented material. These orientation effects are related to the morphology and alignment of the nonmetallic inclusion stringers that act as the primary void nucleation sites. Calcium treatments for inclusion-shape control improve ductility, especially at intermediate-stress triaxialities, primarily by suppressing the local conditions which give rise to the void-sheet instability process.

Asymmetric Hydrodynamic Impact and Dynamic Response of Vessels

Abstract: Theoretical simulations are compared with drop test experiments of vessel free-fall impact on calm water, with zero and nonzero initial heel angles. The impact force and moment are predicted by using a theory described in Xu et al. (1998). The resulting motions of vessels at asymmetric impact include vertical water entry and transverse rolling. The downward deceleration equation combines the hydrostatic and hydrodynamic forces and the weight of hull, while the rolling equation takes into account the restoring moments due to asymmetry. Another simplified approach of a water entry dynamics and injury model (Gollwitzer and Peterson, 1996) is also applied to evaluate the impact acceleration for symmetric cases. The experiments were conducted at the Coastal Systems Station, Panama City, Florida, using a 2 ft × 8 ft (0.61 m × 2.44 m) prismatic hull model with 20 deg deadrise. The comparisons between the asymmetric impact theory and experiment shows varying degrees of qualitative and quantitative agreement.

Limits of optical transmission measurements with application to particle sizing techniques

Abstract: Considerable confusion exists regarding the applicability limits of the Bouguer-Lambert-Beer law of optical transmission. We review the derivation of the law and discuss its application to the optical thickness of the light-scattering medium. We demonstrate the range of applicability by presenting a method for determining particle size by measuring optical transmission at two wavelengths.

Enhanced low dose rate sensitivity (ELDRS) of linear circuits in a space environment

Abstract: To investigate the ELDRS effect in a real space environment, an experiment was designed, launched, and placed in a highly elliptical orbit in November 1997. After its deployment, the electrical responses of several bipolar transistors and linear circuits have been and continue to be recorded once during every 12-hour orbit. System dosimeters are monitored to establish an average accumulated dose per orbit. With this information, the electrical parameter data are correlated with the dosimetry data to determine the total dose response of each device. This paper updates information on the ELDRS experiment through May 14, 1999. As of this date, the experiment has been in flight for a period of 18 months and has accumulated an approximate dose of 18 krd(Si). For comparison, devices, specifically linear circuits with the same date code, were irradiated using Co-60 sources, herein defined as ground-based tests. The ground-based tests are used to evaluate two hardness assurance tests, a room temperature irradiation at 10 mrd(Si)/s and an elevated temperature irradiation at 100/spl deg/C and 10 rd(Si)/s and to evaluate the ELDRS response. To that end, irradiations were performed at room temperature, approximately 22/spl deg/C, at fixed dose rates of 100, 1, and 0.01 rd(Si)/s and at elevated temperature, approximately 100/spl deg/C, at a fixed dose rate of 10 rd(Si)/s. Currently, irradiations are being performed at room temperature at a fixed dose rate of 0.001 rd(Si)/s. Comparing the ground-based data to the flight data clearly demonstrates that enhanced parametric degradation has occurred in the flight parts. The two hardness assurance screens predicted ELDRS but the design margin for the elevated temperature test may not be adequate.

Magnetostriction of Terfenol-D heat treated under compressive stress

Abstract: Heat treatment at temperatures >835/spl deg/C and compressive stresses >80 MPa substantially increased the magnetostrictive performance of Terfenol-D (Tb/sub 0.3/Dy/sub 0.7/Fe/sub 1.92/) under the condition of zero loading. This heat treatment created a built-in prestress which significantly increased the low stress magnetostriction and substantially altered the magnetization curve by reducing its initial susceptibility. For measurements at compressive stresses >15 MPa the effect of the built-in stress was minimal and the magnetostrictive performance was not appreciably altered.

Plastic deformation, energy dissipation, and initiation of crystalline explosives

Abstract: 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.

Fire safety of composites in the US Navy

Abstract: Composite materials for marine applications offer the benefit of weight savings, corrosion resistance, and reduced life-cycle costs. The composite structures used in marine applications tend to be large, complex, and thick. As such, the use of low-temperature non-autoclave cure resins is desirable. The US Navy is presently using fire-retardant (brominated) vinyl-ester resin for some topside composite structures. These composites are produced by the vacuum-assisted resin transfer method. Brominated vinyl-ester resin generates dense heavy smoke with high yields of carbon monoxide. Acid gases such as hydrogen bromide are also produced. Several alternative resins with and without non-halogenated fire retardants have recently been evaluated by the Naval Surface Warfare Center, Carderock Division in small-scale fire test methods. These included cone calorimeter testing at three different fluxes of 25, 50, and 75 kW m−2. The summary of results, including smoke production rate and carbon monoxide yield, is presented for various vinyl-ester resins with and without additives. Brominated epoxy vinyl ester marked #1168 exhibited lower heat release rates but significantly higher smoke generation and CO yield than non-brominated vinyl esters. Of the additives studied, aluminum trihydrate (15 phr, #1196) shows a 20 and 25% decrease in peak heat release rates, 24 and 13% decrease in average heat release rates, and 27 and 24% decrease in average mass loss rates at radiant heat fluxes of 50 and 75 kW m−2, respectively.

Neutron yields from 155 MeV/nucleon carbon and helium stopping in aluminum.

Abstract: Neutron fluences have been measured from 155 MeV/nucleon 4He and 12C ions stopping in an Al target at laboratory angles between 10 and 160 deg. The resultant spectra were integrated over angle and energy above 10 MeV to produce total neutron yields. Comparison of the two systems shows that approximately two times as many neutrons are produced from 155 MeV/nucleon 4He stopping in Al and 155 MeV/nucleon 12C stopping in Al. Using an energy-dependent geometric cross-section formula to calculate the expected number of primary nuclear interactions shows that the 12C + Al system has, within uncertainties, the same number of neutrons per interaction (0.99 +/- 0.03) as does the 4He + Al system (1.02 +/- 0.04), despite the fact that 12C has three times as many neutrons as does 4He. Energy and angular distributions for both systems are also reported. No major differences can be seen between the two systems in those distributions, except for the overall magnitude. Where possible, the 4He + Al spectra are compared with previously measured spectra from 160 and 177.5 MeV/nucleon 4He interactions in a variety of stopping targets. The reported spectra are consistent with previously measured spectra. The data were acquired to provide data applicable to problems dealing with the determination of the radiation risk to humans engaged in long-term missions in space; however, the data are also of interest for issues related to the determination of the radiation environment in high-altitude flight, with shielding at high-energy heavy-ion accelerators and with doses delivered outside tumor sites treated with high-energy hadronic beams.

Prediction of early lethal SEGR failures of VDMOSFETs for commercial space systems

Abstract: Quantitative risk assessments are presented for two radiation-hardened MOSFETs (Harris FSL11A0 and FRL11A0) using an extracted expression, integral flux curves representing different conditions, and experimentally-determined signature curves taken at different ion impact angles. The effectiveness of certain parameters including the selected orbit, spacecraft shielding thickness, drain and gate biases, device hardness, and time of exposure are discussed. Failures are studied using normalized Monte Carlo simulations validated by statistical methods. These validated Monte Carlo simulations are then used to extract and present an extracted expression. The concept of a lethal ion rate is discussed. Single event gate rupture (SEGR) failure thresholds at different ion impact angles are measured and reported on the Harris FSL11A0 and FRL11A0 (radiation-hardened vertical MOSFETs having similar layouts but with different SEGR sensitivities). Integral flux curves are presented for various orbits and conditions. Predictions of very early failures are performed using the extracted expression, the integral flux curves, and the new signature curves. Based upon these predictions, the influence of selected parameters are evaluated.

Analysis Techniques for Detecting Coordinated Attacks and Probes

Abstract: Coordinated attacks and probes have been observed against several networks that we protect. We describe some of these attacks and provide insight into how and why they are carried out. We also suggest hypotheses for some of the more puzzling probes. Methods for detecting these coordinated attacks are provided.

Hardness assurance implications of bimodal total dose response in a bipolar linear voltage comparator

Abstract: The total dose response of transistors and circuits from a single wafer lot has been measured for high and low dose rate and elevated temperature irradiations. A bimodal irradiation response is observed in the circuit response that is shown to be a result of the input transistors. Hardness assurance sampling plans are examined for their adequacy to deal with the bimodal response distributions.

Software Tools for Nonlinear Missile Autopilot Design

Abstract: A computer-aided design software package for nonlinear control synthesis is discussed. The software incorporates five different modern nonlinear control methods. The versatility of the software lies in its ability to develop nonlinear controllers using a simulation model. As a result, models of arbitrary complexity can be used in the control law development. The use of the design software is illustrated through the design of nonlinear regulators for a longitudinal missile model.

Enhanced low dose rate sensitivity (ELDRS) in a voltage comparator which only utilizes complementary vertical NPN and PNP transistors

Abstract: For the first time, enhanced low dose rate sensitivity (ELDRS) is reported in a vertical bipolar process. A radiation hardness assurance (RHA) test method was successfully demonstrated on a linear circuit, the HS139RH quad comparator, and its discrete transistor elements. This circuit only uses vertical NPN and PNP transistors. Radiation tests on the HS139RH were performed at 25/spl deg/C using dose rates of 50 rd(Si)/s, 100 mrd(Si)/s and 10 mrd(Si)/s, and at 100/spl deg/C using a dose rate of 10 rd(Si)/s. Tests at dose rates of 50 rd(Si)/s at 25/spl deg/C and 10 rd(Si)/s at 100/spl deg/C were performed on discrete vertical NPN and PNP transistor elements which comprise the HS139RH. Transistor and circuit responses were evaluated. The die's passivation overcoat layers were varied to examine the effect of removing a nitride layer and thinning a deposited SiO/sub 2/ (silox) layer.

Application of the 1998 Version of the Aeroprediction Code

Abstract: The U.S. Naval SurfaceWarfare Center aeroprediction code has been extended to the roll position of 45 deg (Ž ns in “ £ ” or cross-roll orientation) in addition to the roll position of 0 deg (Ž ns in “ ” or plus-roll orientation). It has also been extended to compute aerodynamics of nonaxisymmetricbodies based on an equivalent axisymmetric body. In addition, the nonlinear aerodynamic loads have been distributed over the body and lifting surfaces to provideamoreuseful tool forpreliminary structural analysis.Finally,new technologywas developed to improvethe predictionof axialforceat angleof attack.These new technologieshavebeen integrated into the1995Aeroprediction Code (AP95) and will be transitioned to legitimate users as the 1998 Aeroprediction Code (AP98). To make the AP98 more user friendly, an upgraded preand postprocessing, personal-computer interface was also developed. The theoretical methods of the AP98 are summarized, and a sample is shown of the comparisons of the AP98 predictions of static aerodynamics for several missile conŽ gurations to experimental data. Comparisons of theory andexperiment show that theAP98,on average, is at least as goodas theAP95and, in general,maybe slightlybetter.

Multisensor-multisite composite tracking in the presence of sensor residual bias

Abstract: The integration of multiple sensors for target tracking is complex but has the potential to provide very accurate state estimates. For most applications, each sensor provides its information to a central location where the integration is performed and the resulting composite track can be very accurate when compared to the individual sensortracks. This composite track has the potential to provide enhanced system decisions and targeting informationnot otherwise available. However, sensor bias can severely degrade composite tracking performance when it is not properly considered. This paper presents algorithms and simulation results for the composite tracking of maneuvering targets through the use of multisensor-multisite integration in the presence of sensor residual bias.Keywords: Composite 'Iacking, Sensor Integration, Sensor Residual Bias 1. INTRODUCTION The integration of multiple sensors located on different platforms for tracking maneuvering targets has beenintensely investigated in recent years. Situational awareness has become very important due to the increasingcomplexity of the battlespace and can be greatly enhanced with effective sensor integration. For most techniques, acentral track is updated with the information (i.e., measurements, estimates, etc.) provided by the sensor suite and

Thermodynamics energy for both supervised and unsupervised learning neural nets at a constant temperature.

Abstract: Unified Lyaponov function is given for the first time to prove the learning methodologies convergence of artificial neural network (ANN), both supervised and unsupervised, from the viewpoint of the minimization of the Helmholtz free energy at the constant temperature. Early in 1982, Hopfield has proven the supervised learning by the energy minimization principle. Recently in 1996, Bell & Sejnowski has algorithmically demonstrated Independent Component Analyses (ICA) generalizing the Principal Component Analyses (PCA) that the continuing reduction of early vision redundancy happens towards the "sparse edge maps" by maximization of the ANN output entropy. We explore the combination of both as Lyaponov function of which the proven convergence gives both learning methodologies. The unification is possible because of the thermodynamics Helmholtz free energy at a constant temperature. The blind de-mixing condition for more than two objects using two sensor measurement. We design two smart cameras with short term working memory to do better image de-mixing of more than two objects. We consider channel communication application that we can efficiently mix four images using matrices [AO] and [Al] to send through two channels.