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NASA NTRS1988

An electrochemical study of corrosion protection by primer-topcoat systems on 4130 steel with ac impedance and dc methods

To investigate metal surface corrosion and the breakdown of metal protective coatings, the ac impedance method is applied to six systems of primer coated and primer topcoated 4130 steel. Two primers were used: a zinc-rich epoxy primer and a red lead oxide epoxy primer. The epoxy-polyamine topcoat was used in four of the systems. The EG and G-PARC Model 368 ac impedance measurement system, along with dc measurements with the same system using the polarization resistance method, were used to monitor changing properties of coated 4230 steel disks immersed in 3.5 percent NaCl solutions buffered at pH 5.4 over periods of 40 to 60 days. The corrosion system can be represented by an electronic analog called an equivalent circuit consisting of resistors and capacitors in specific arrangements. This equivalent circuit parallels the impedance behavior of the corrosion system during a frequency scan. Values for the resistors and capacitors, that can be assigned in the equivalent circuit following a least-squares analysis of the data, describe changes that occur on the corroding metal surface and in the protective coatings. Two equivalent circuits have been determined that predict the correct Bode phase and magnitude of the experimental sample at different immersion times. The dc corrosion current density data are related to equivalent circuit element parameters. Methods for determining corrosion rate with ac impedance parameters are verified by the dc method.

Mendrek, M. J.↗

NASA NTRS1988

Geochemical comparison of K-T boundaries from the Northern and Southern Hemispheres

Closely spaced (cm-scale) traverses through the K-T boundary at Stevns Klint (Denmark), Woodside Creek (New Zealand) and a new Southern Hemisphere site at Richards Bay (South Africa) were subjected to trace element and isotopic (C, O, Sr) investigation. Intercomparison between these data-sets, and correlation with the broad K-T database available in the literature, indicate that the chemistry of the boundary clays is not globally constant. Variations are more common than similarities, both of absolute concentrations, and interelement ratios. For example, the chondrite normalized platinum-group elements (PGE) patterns of Stevns Klint are not like those of Woodside Creek, with the Pt/Os ratios showing the biggest variation. These differences in PGE patterns are difficult to explain by secondary alteration of a layer that was originally chemically homogeneous, especially for elements of such dubious crustal mobility as Os and Ir. The data also show that enhanced PGE concentrations, with similar trends to those of the boundary layers, occur in the Cretaceous sediments below the actual boundary at Stevns Klint and all three the New Zealand localities. This confirms the observations of others that the geochemistry of the boundary layers apparently does not record a unique component. It is suggested that terrestrial processes, eg. an extended period of Late Cretaceous volcanism can offer a satisfactory explanation for the features of the K-T geochemical anomaly. Such models would probably be more consistent with the observed stepwise, or gradual, palaeontological changes across this boundary, than the instant catastrophe predicated by the impact theory.

Tredous, M.↗

NASA NTRS1990

Field-Induced-Gap Infrared Detectors

Semimetals become semiconductors under applied magnetic fields. New detectors require less cooling equipment because they operate at temperatures higher than liquid-helium temperatures required by extrinsic-semiconductor detectors. Magnetic fields for detectors provided by electromagnets based on recently-discovered high-transition-temperature superconducting materials. Detector material has to be semiconductor, in which photon absorbed by exciting electron/hole pair across gap Eg of forbidden energies between valence and conduction energy bands. Magnetic- and compositional-tuning effects combined to obtain two-absorber detector having narrow passband. By variation of applied magnetic field, passband swept through spectrum of interest.

Elliott, C. Thomas↗

NASA NTRS1990

Realtime multi-plot graphics system

The increased complexity of test operations and customer requirements at Langley Research Center's National Transonic Facility (NTF) surpassed the capabilities of the initial realtime graphics system. The analysis of existing hardware and software and the enhancements made to develop a new realtime graphics system are described. The result of this effort is a cost effective system, based on hardware already in place, that support high speed, high resolution, generation and display of multiple realtime plots. The enhanced graphics system (EGS) meets the current and foreseeable future realtime graphics requirements of the NTF. While this system was developed to support wind tunnel operations, the overall design and capability of the system is applicable to other realtime data acquisition systems that have realtime plot requirements.

Shipkowski, Michael S.↗

NASA NTRS1990

Optical and electrical properties of thin superconducting films

Infrared spectroscopic techniques can provide a vital probe of the superconducting energy gap which is one of the most fundamental physical properties of superconductors. Currently, the central questions regarding the optical properties of superconductors are how the energy gap can be measured by infrared techniques and at which frequency the gap exists. An effective infrared spectroscopic method to investigate the superconducting energy gap, Eg, was developed by using the Bomem DA 3.01 Fourier Transformation Spectrophotometer. The reflectivity of a superconducting thin film of YBaCuO deposited on SrTiO3 was measured. A shoulder was observed in the superconducting state reflectance R(sub S) at 480/cm. This gives a value of Eg/kT(sub c) = 7.83, where k is the Boltzmann constant and T(sub c) is the superconducting transition temperature, from which, it is suggested that YBaCuO is a very strong coupling superconductor.

Covington, Billy C.↗

NASA NTRS1990

On the interpretation of the Exosat photometry of two hot DA white dwarfs

Exosat photometric observations of the hot DA white dwarfs GD 2 and EG 70 are presented and analyzed using model atmosphere and synthetic spectrum calculations. The numerical accuracy of the calculations and their impact on the reliability of the results are addressed. The optimum atmospheric parameters that explain the complete spectral coverage are derived. The consequences of these conjectures for the spectral evolution theory of white dwarf stars are considered.

Vennes, Stephane↗

NASA NTRS1992

One Year of Rayleigh Lidar Measurements at Toronto

The Rayleigh lidar technique is being used at York University to study middle atmospheric thermal structure with particular emphasis on the properties and influence of internal gravity waves. These measurements are now carried out on a routine basis (every clear night) in order to determine seasonal variability and, eventually, long term trends. The transmitter consists of a doubled Nd:YAG laser with an output of 0.4 Joules per pulse at 20Hz (8 Watts) which is expanded to obtain a divergence of 0.4 milliradians. Backscattered photons are collected by a half meter cassegrain telescope, filtered to a bandwidth of 1nm, detected by a PMT, and counted with a multi-channel scaling averager. Strong backscatter from lower altitudes is blocked using a rotating chopper (25000rpm) which triggers the laser. The range gate and hardware averaging interval are variable but typically 300m and 5 minutes. Relative density profiles are obtained by simply normalizing to a model (eg. CIRA) at some altitude. Absolute temperature is derived using the hydrostatic equation, ideal gas law, and a model pressure value at the altitude where the photocount statistical uncertainty is about 15 percent - typically 90km for the entire night's average. The lower limit is currently about 30-35km due the presence aerosol from the volcanic eruption of Mt. Pinatubo.

Whiteway, James A.↗

NASA NTRS1991

Anomalous temperature and zonal wind in the tropical upper stratosphere, 1982/1983

Observed temperature and zonal wind anomalies during 1982-1983 are described in relation to the 20-yr rocketsonde data record. Temperature data from the Nimbus 7 SAMS indicate that in mid-1982, cooling occurred in the upper and middle tropical stratosphere, starting shortly after the eruption of El Chichon (April 1982). Rocketsonde data from Kwajalein gave additional evidence of cooling and revealed that zonal winds in the upper and middle stratosphere were anomalous in 1982 and also in 1983. Rocketsonde observations were consistent with balance winds derived from SAMS. Upper-level cooling was linked to anomalous easterlies near the equator and therefore could not be interpreted as a radiative (nondynamical) response to El Chichon. The structure of an expected 2D dynamical response to aerosol heating is examined with a numerical model and compared to the data. It is suggested that internal sources of atmospheric variability (eg., extratropical forcing and quasi-biennial oscillation) contributed to the equatorial cooling observed in 1982.

Dunkerton, Timothy J.↗

NASA NTRS1992

An evaluation of corrosion protection by two epoxy primers on 2219-T87 and 7075-T73 aluminum

A comparison of the corrosion protection provided by two amine epoxy primers was made using salt fog, alternate immersion, and total immersion as exposure media. The study is the result of a request to use an unqualified low volatile organic carbon (VOC) primer (AKZO 463-6-78) in place of the current primer (AKZO 463-6-3) because environmental regulations have eliminated use of the current primer in many states. Primed, scribed samples of 2219-T87 and 7075-T73 aluminum were exposed to 5-percent NaCl salt fog and 3.5-percent NaCl alternate immersion for a period of 90 days. In addition, electrode samples immersed in 3.5-percent NaCl were tested using electrochemical impedance spectroscopy (EIS). The EG&G model 368 ac impedance measurement system was used to monitor changing properties of AKZO 463-6-78 and AKZO 463-6-3 primed 2219-T87 aluminum for a period of 30 days. The response of the corroding system of a frequency scan can be modeled in terms of an equivalent circuit consisting of resistors and capacitors in a specific arrangement. Each resistor/capacitor combination represents physical processes taking place within the electrolyte, at the electrolyte/primer surface, within the coating, and at the coating/substrate surface. Values for the resistors and capacitors are assigned following a nonlinear least squares fit of the data to the equivalent circuit. Changes in the values of equivalent circuit parameters during the 30-day exposure allow assessment of the time to and mechanism of coating breakdown.

Mendrek, M. J.↗

NASA NTRS1992

Use of cyclic current reversal polarization voltammetry for investigating the relationship between corrosion resistance and heat-treatment induced variations in microstructures of 400 C martensitic stainless steels

Software for running a cyclic current reversal polarization voltammagram has been developed for use with a EG&G Princeton Applied Research Model 273 potentiostat/galvanostat system. The program, which controls the magnitude, direction and duration of an impressed galvanostatic current, will produce data in ASCII spreadsheets (Lotus, Quattro) for graphical representation of CCRPV voltammograms. The program was used to determine differences in corrosion resistance of 440 C martenstic stainless steel produced as a result of changes in microstructure effected by tempering. It was determined that tempering at all temperatures above 400 F resulted in increased polarizability of the material, with the increased likelihood that pitting would be initiated upon exposure to marine environments. These results will be used in development of remedial procedures for lowering the susceptibility of these alloys toward the stress corrosion cracking experienced in bearings used in high pressure oxygen turbopumps used in the main engines of space shuttle orbiters.

Ambrose, John R.↗

NASA NTRS1993

Development and testing of hermetic, laser-ignited pyrotechnic and explosive components

During the last decade there has been increasing interest in the use of lasers in place of electrical systems to ignite various pyrotechnic and explosive materials. The principal driving force for this work was the requirement for safer energetic components which would be insensitive to electrostatic and electromagnetic radiation. In the last few years this research has accelerated since the basic concepts have proven viable. At the present time it is appropriate to shift the research emphasis in laser initiation from the scientific arena--whether it can be done--to the engineering realm--how it can be put into actual practice in the field. Laser initiation research and development at EG&G Mound was in three principal areas: (1) laser/energetic material interactions; (2) development of novel processing techniques for fabricating hermetic (helium leak rate of less than 1 x 10(exp -8) cu cm/s) laser components; and (3) evaluation and testing of laser-ignited components. Research in these three areas has resulted in the development of high quality, hermetic, laser initiated components. Examples are presented which demonstrate the practicality of fabricating hermetic, laser initiated explosive or pyrotechnic components that can be used in the next generation of ignitors, actuators, and detonators.

Kramer, Daniel P.↗

NASA NTRS1991

Space Shuttle Program: Automatic rendezvous, proximity operations, and capture (category 3)

The NASA Johnson Space Center is actively pursuing the development and demonstration of capabilities for automatic rendezvous, proximity operations, and capture (AR&C) using the Space Shuttle as the active vehicle. This activity combines the technologies, expertise, tools, and facilities of the JSC Tracking and Communications Division (EE), Navigation, Control and Aeronautics Division (EG), Automation and Robotics Division (ER), and Structures and Mechanics Division (ES) of the Engineering Directorate and the Flight Design and Dynamics Division (DM) of the Mission Operations Directorate. Potential benefits of AR&C include more efficient and repeatable rendezvous, proximity operations, and capture operations; reduced impacts on the target vehicles (e.g., Orbiter RCS plume loads); reduced flight crew work loads; reduced ground support requirements; and reduced operational constraints. This paper documents the current JSC capabilities/tools/facilities for AR&C and describes a proposed plan for a progression of ground demonstrations and flight tests and demonstrations of AR&C capabilities. This plan involves the maturing of existing technologies in tracking and communications; guidance, navigation and control; mechanisms; manipulators; and systems management and integrating them into several evolutionary demonstration stages.

Jackson, William L.↗

NASA NTRS1991

Autonomous docking ground demonstration (category 3)

The NASA Johnson Space Center (JSC) is involved in the development of an autonomous docking ground demonstration. The demonstration combines the technologies, expertise and facilities of the JSC Tracking and Communications Division (EE), Structures and Mechanics Division (ES), and the Navigation, Guidance and Control Division (EG) and their supporting contractors. The autonomous docking ground demonstration is an evaluation of the capabilities of the laser sensor system to support the docking phase (12ft to contact) when operated in conjunction with the Guidance, Navigation and Control Software. The docking mechanism being used was developed for the Apollo Soyuz Test Program. This demonstration will be conducted using the Six-Degrees of Freedom (6-DOF) Dynamic Test System (DTS). The DTS environment simulates the Space Station Freedom as the stationary or target vehicle and the Orbiter as the active or chase vehicle. For this demonstration the laser sensor will be mounted on the target vehicle and the retroreflectors on the chase vehicle. This arrangement was used to prevent potential damage to the laser. The sensor system. GN&C and 6-DOF DTS will be operated closed-loop. Initial condition to simulate vehicle misalignments, translational and rotational, will be introduced within the constraints of the systems involved. Detailed description of each of the demonstration components (e.g., Sensor System, GN&C, 6-DOF DTS and supporting computer configuration) including their capabilities and limitations will be discussed. A demonstration architecture drawing and photographs of the test configuration will be presented.

Lamkin, Steve L.↗

NASA NTRS1990

Shape optimization and CAD

Structural optimization has attracted the attention since the days of Galileo. Olhoff and Taylor have produced an excellent overview of the classical research within this field. However, the interest in structural optimization has increased greatly during the last decade due to the advent of reliable general numerical analysis methods and the computer power necessary to use them efficiently. This has created the possibility of developing general numerical systems for shape optimization. Several authors, eg., Esping; Braibant & Fleury; Bennet & Botkin; Botkin, Yang, and Bennet; and Stanton have published practical and successful applications of general optimization systems. Ding and Homlein have produced extensive overviews of available systems. Furthermore, a number of commercial optimization systems based on well-established finite element codes have been introduced. Systems like ANSYS, IDEAS, OASIS, and NISAOPT are widely known examples. In parallel to this development, the technology of computer aided design (CAD) has gained a large influence on the design process of mechanical engineering. The CAD technology has already lived through a rapid development driven by the drastically growing capabilities of digital computers. However, the systems of today are still considered as being only the first generation of a long row of computer integrated manufacturing (CIM) systems. These systems to come will offer an integrated environment for design, analysis, and fabrication of products of almost any character. Thus, the CAD system could be regarded as simply a database for geometrical information equipped with a number of tools with the purpose of helping the user in the design process. Among these tools are facilities for structural analysis and optimization as well as present standard CAD features like drawing, modeling, and visualization tools. The state of the art of structural optimization is that a large amount of mathematical and mechanical techniques are available for the solution of single problems. By implementing collections of the available techniques into general software systems, operational environments for structural optimization have been created. The forthcoming years must bring solutions to the problem of integrating such systems into more general design environments. The result of this work should be CAD systems for rational design in which structural optimization is one important design tool among many others.

Rasmussen, John↗

NASA NTRS1992

Kennedy Space Center's NASA/Contractor Team-Centered Total Quality Management Seminar: Results, methods, and lessons learned

It is apparent to everyone associated with the Nation's aeronautics and space programs that the challenge of continuous improvement can be reasonably addressed only if NASA and its contractors act together in a fully integrated and cooperative manner that transcends the traditional boundaries of proprietary interest. It is, however, one thing to assent to the need for such integration and cooperation; it is quite another thing to undertake the hard tasks of turning such a need into action. Whatever else total quality management is, it is fundamentally a team-centered and team-driven process of continuous improvement. The introduction of total quality management at KSC, therefore, has given the Center a special opportunity to translate the need for closer integration and cooperation among all its organizations into specific initiatives. One such initiative that NASA and its contractors have undertaken at KSC is a NASA/Contractor team-centered Total Quality Management Seminar. It is this seminar which is the subject of this paper. The specific purposes of this paper are to describe the following: Background, development, and evolution of Kennedy Space Center's Total Quality Management Seminar; Special characteristics of the seminar; Content of the seminar; Meaning and utility of a team-centered design for TQM training; Results of the seminar; Use that one KSC contractor, EG&G Florida, Inc. has made of the seminar in its Total Quality Management initiative; and Lessons learned.

Kinlaw, Dennis C.↗

NASA NTRS1993

Illness/injury pattern complex 40 (Titan)

On July 31, 1991, EG&G Medical began providing medical support at the Titan Area Clinic (TAC). The hours of operation are 0700-2300, Monday through Friday, with Emergency Medical Services (EMS) provided 24-hours a day, seven days a week. The TAC consists of a 10 x 10 ft section of a trailer that also houses Bechtel Safety. Supplies consisted of an examining table, an eye wash chair, first aid equipment, over-the-counter medications, spine boards, a portable rescuscitator, etc. All of the nurses are Advanced Cardiac Life Support (ACLS) certified. Although the Titan Area Clinic is strictly a first-aid station with no ACLS facilities on-site, it is staffed with an Occupational Health Nurse with ACLS certification. If ACLS or additional help is needed, the nurse activates EMS by dialing 911. The nurse responds to any medical problems or emergencies on the complex, but activates EMS prior to leaving the TAC. A Bechtel Safety Representative accompanies the nurse to the site and assists as needed. Other aspects of the complex and its functions are presented.

Blasdell, Sharon↗

NASA NTRS1992

SAR backscatter from coniferous forest gaps

A study is in progress comparing Airborne Synthetic Aperture Radar (AIRSAR) backscatter from coniferous forest plots containing gaps to backscatter from adjacent gap-free plots. Issues discussed are how do gaps in the range of 400 to 1600 sq m (approximately 4-14 pixels at intermediate incidence angles) affect forest backscatter statistics and what incidence angles, wavelengths, and polarizations are most sensitive to forest gaps. In order to visualize the slant-range imaging of forest and gaps, a simple conceptual model is used. This strictly qualitative model has led us to hypothesize that forest radar returns at short wavelengths (eg., C-band) and large incidence angles (e.g., 50 deg) should be most affected by the presence of gaps, whereas returns at long wavelengths and small angles should be least affected. Preliminary analysis of 1989 AIRSAR data from forest near Mt. Shasta supports the hypothesis. Current forest backscatter models such as MIMICS and Santa Barbara Discontinuous Canopy Backscatter Model have in several cases correctly predicted backscatter from forest stands based on inputs of measured or estimated forest parameters. These models do not, however, predict within-stand SAR scene texture, or 'intrinsic scene variability' as Ulaby et al. has referred to it. For instance, the Santa Barbara model, which may be the most spatially coupled of the existing models, is not truly spatial. Tree locations within a simulated pixel are distributed according to a Poisson process, as they are in many natural forests, but tree size is unrelated to location, which is not the case in nature. Furthermore, since pixels of a simulated stand are generated independently in the Santa Barbara model, spatial processes larger than one pixel are not modeled. Using a different approach, Oliver modeled scene texture based on an hypothetical forest geometry. His simulated scenes do not agree well with SAR data, perhaps due to the simple geometric model used. Insofar as texture is the expression of biological forest processes, such as succession and disease, and physical ones, such as fire and wind-throw, it contains useful information about the forest, and has value in image interpretation and classification. Forest gaps are undoubtedly important contributors to scene variance. By studying the localized effects of gaps on forest backscatter, guided by our qualitative model, we hope to understand more clearly the manner in which spatial heterogeneities in forests produce variations in backscatter, which collectively give rise to scene texture.

Day, John L.↗

NASA NTRS1993

Characteristics of products generated by selective sintering and stereolithography rapid prototyping processes

The trend in the modern global economy towards free market policies has motivated companies to use rapid prototyping technologies to not only reduce product development cycle time but also to maintain their competitive edge. A rapid prototyping technology is one which combines computer aided design with computer controlled tracking of focussed high energy source (eg. lasers, heat) on modern ceramic powders, metallic powders, plastics or photosensitive liquid resins in order to produce prototypes or models. At present, except for the process of shape melting, most rapid prototyping processes generate products that are only dimensionally similar to those of the desired end product. There is an urgent need, therefore, to enhance the understanding of the characteristics of these processes in order to realize their potential for production. Currently, the commercial market is dominated by four rapid prototyping processes, namely selective laser sintering, stereolithography, fused deposition modelling and laminated object manufacturing. This phase of the research has focussed on the selective laser sintering and stereolithography rapid prototyping processes. A theoretical model for these processes is under development. Different rapid prototyping sites supplied test specimens (based on ASTM 638-84, Type I) that have been measured and tested to provide a data base on surface finish, dimensional variation and ultimate tensile strength. Further plans call for developing and verifying the theoretical models by carefully designed experiments. This will be a joint effort between NASA and other prototyping centers to generate a larger database, thus encouraging more widespread usage by product designers.

Cariapa, Vikram↗