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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Optical Quantum Receiver For Binary Signals

In quantum optical receiver, both amplitude and phase of received optical signal measured to extract as much information as possible, thereby reducing error probability. Phase-modulated received signal mixed with equal amplitude replica of optical carrier generated in phase locked loop. Two signals interfere with each other at photomultiplier cathode. Probability of error with this scheme close to theoretical minimum and implemented with current technology.

Vilnrotter, V. A.↗
NASA NTRS1984

Nature of gamma-prime precipitates in rheocast IN-100 alloy

The microstructures of commercial VIM-cast and rheocast (Apelian and Cheng, 1983) IN-100 superalloy are investigated optically and by two-stage replica TEM, with an emphasis on the nature of the gamma-prime (GP) precipitates. Photomicrographs at magnifications of 39, 390, 2145, and 6630 are presented and discussed. VIM-cast IN-100 has dendritic structure, 10-20-micron primary GP particles, and uniformly distributed cuboid GP precipitates of a uniform size (about 0.5 micron). Rheocast IN-100 (stirred 20 min at 350 rpm, 1291 C, and 0.0006 torr) has a nondendritic structure, 20-100-micron primary GP particles, and a smaller volume fraction of cuboid GP precipitates with a bimodal (either 1-1.5 microns or less than 0.5 micron) size distribution. Such distribution should increase fatigue-crack-nucleation resistance.

Surappa, M. K.↗
NASA NTRS1985

Shuttle structural dynamics characteristics: The analysis and verification

The space shuttle introduced a new dimension in the complexity of the structural dynamics of a space vehicle. The four-body configuration exhibited structural frequencies as low as 2 hertz with a model density on the order of 10 modes per hertz. In the verification process, certain mode shapes and frequencies were identified by the users as more important than others and, as such, the test objectives were oriented toward experimentally extracting those modes and frequencies for analysis and test correlation purposes. To provide the necessary experimental data, a series of ground vibration tests (GVT's) was conducted using test articles ranging from the 1/4-scale structural replica of the space shuttle to the full-scale vehicle. The vibration test and analysis program revealed that the mode shapes and frequency correlations below 10 hertz were good. The quality of correlation of modes between 10 and 20 hertz ranged from good to fair and that of modes above 20 hertz ranged from poor to good. Since the most important modes, based on user preference, were below 10 hertz, it was judged that the shuttle structural dynamic models were adequate for flight certifications.

Modlin, C. T., Jr.↗
NASA NTRS1985

On-orbit Systems Identification of Flexible Spacecraft Technol., 1984, Pt. 2 p 465-481

Future spacecraft include configurations which are too flexible to be adequately tested prior to flight and which will require on-orbit systems identification to ensure safe operation of the flight control system. The structural dynamics model will evolve and its accuracy will improve in stages as ground tests of full-scale components and replica-scale models are performed. State Space Modeling and Conditional Maximum Likelihood Parameter Estimation methodology can provide the formal probability-based framework for the process of upgrading a model as additional test results are obtained. Although the number of unknown parameters can be reduced by the use of canonical forms for the stability matrix, the number of unknown model parameters quickly becomes unmanageable unless advantage is taken of the relationship of a much fewer number of global model parameters. Distributed parameter systems or partial differential equation models are one way to take advantage of such global parameters to reduce the number of unknown model parameters.

Taylor, L.↗
NASA NTRS1985

The coorbital hypothesis

Voyager I and II have revealed the existence of 1980S1 and 1980S3 in the same orbit that add to the discovery of the Lagrange satellite 1980S6 for Dione and 1980S13 - 1980S25 for Thetys as a replica to the Trojan planets in the Jupiter orbit. These bodies may issue from the rupture of a primitive gaseous ring through a disturbance. The Lagrange figures keep stable while the rest of the objects drift in near paths and interact at each transit so as to form a gradual binary. The Moon - Earth system may have a such origin.

Andlauer, G.↗
NASA NTRS1984

Electroform replication used for multiple X-ray mirror production

The electroforming technique for producing X-ray mirrors is described, and results of X-ray tests performed on copies made from a simple conical mandrel are reported. The design of the mandrel is depicted and the total reflectivity as well as the full-wave half modulation resolution are shown as a function of energy. The reported work has improved on previous studies by providing smaller grazing angles, making measurements at higher energies, producing about four times as many replicas from one mandrel, and obtaining better angular resolution.

Kowalski, M. P.↗
NASA NTRS1985

Strength and microstructure of sintered Si3N4 with rare-earth-oxide additions

Room temperature, 700-, 1000-, 1200-, and 1370-C examinations of the effect of 1.7-2.6 mol pct rare earth oxide additions to sintered Si3N4 are conducted. While the room temperature-1000 C bend strengths were higher for this material with Y2O3 additions than with CeO2, La2O3, or Sm2O3, the reverse was true at 1200-1370 C. This phenomenon is explained on the basis of microstructural differences, since quantitative microscopy of SEM replicas showed the Si3N4-Y2O3 composition to contain both a higher percentage of elongated grains and a coarser microstructure than the other three alternatives. The elongated grains appear to increase this composition's low temperature strength irrespective of microstructural coarseness; this coarseness, however, decreases strength relative to the other compositions at higher temperatures.

Sanders, W. A.↗
NASA NTRS1987

Electron-Focus Adjustment for Photo-Optical Imagers

Internal electron focus made independent of optical focus. Procedure enables fine tuning of internal electron-focusing system of photo-optical imager, without complication by imperfections of associated external optics. Applicable to imager in which electrons emitted from photocathode in optical focal plane, then electrostatically and/or magnetically focused to replica of image in second focal plane containing photodiodes, phototransistorss, charge-coupled devices, multiple-anode outputs, or other detectors.

Fowler, Walter B.↗
NASA NTRS1985

Closure measurements on short fatigue cracks

Single-edged notched specimens, 2.3 mm thick, of 2024-T3 aluminum were cyclicly loaded at R-ratios of 0.5, 0.0, -1.0 and -2.0. The notch roots were periodically inspected with an optical microscope to locate the initiation of very short cracks. Acetate replicas were also taken. The loads were selected to produce fatigue lives of 500,000 cycles or less. Crack opening displacements were measured at single positions across cracks as short as 0.035 mm and as long as the full thickness of the specimen. The opening load ratios for the short cracks are somewhat smaller than for long cracks at positive R-ratios, but are considerably smaller for negative R-ratios.

Lee, J. J.↗
NASA NTRS1986

Short fatigue cracks in notched aluminum specimens

The short-crack fatigue behavior in notched specimens of Al 2024-T3 was studied at values of the stress ratio, R, equal to 0.5, 0.0, -1.0, and -2.0. Crack growth was monitored using a replica technique for cracks ranging in length from a few tens of a micron to the specimen's thickness (2.3 mm). Crack opening displacement was measured for surface cracks as short as 0.035 mm using the interferometric strain/displacement gage, a laser-based optical technique described by Sharpe (1982). It was found that the growth rates of short cracks were faster than the rates of long cracks for R values of -1.0 and -2.0. No significant difference was observed for R = 0.0, and at R = 0.5, the short cracks actually grew more slowly that the long ones. At all R values, the closure stresses measured for short cracks were smaller than those predicted for large cracks.

Lee, J. J.↗
NASA NTRS1987

Analysis of lateral stability of X-29 drop model using system identification methodology

A 22-percent dynamically scaled replica of the X-29 forward-swept-wing aircraft is currently being flown in radio-controlled drop tests at NASA Langley's Plumtree Test Site. Flight data were recorded from early flights in the test program, which consisted mainly of large amplitude maneuvers over wide angle-of-attack ranges with several uncontrolled wing rock episodes. A system identification study of the recorded data was undertaken to examine the stability and control derivatives which influence the lateral behavior of this vehicle with particular emphasis on the wing rock phenomenon. All major lateral stability derivatives and the damping-in-roll derivative were identified for 5-80 deg angle-of-attack by using a data partitioning methodology and a modified stepwise regression algorithm. No control effectiveness derivatives could be identified from the flights conducted so far.

Raney, David L.↗
NASA NTRS1988

Mold For Casting Radius-Inspection Specimens

Thin replicas viewed on comparator without sectioning. New mold machined from piece of transparent poly(methyl methacrylate). Fits around base of post. Two slots machined into inner surface form channels for casting inspection sections. Bottom of mold fits flush against surface around bottom of post. When surface slanted, mold automatically aligns in proper orientation. Time required to inspect elliptical radii located at bottoms of series of small posts reduced from 18 hours to 3 hours.

Ball, Robert N.↗
NASA NTRS1987

Hard- and software problems of spaced meteor observations by optical electronics

An optical electronic facility is being used for meteor observations along with meteor radars and astronomical TV. The main parts of the facility are cameras using UM-92 optical electronic image tubes. The three cascade optical electronic image tube with magnetic focusing has a 40 mm cathode and resolution in the center of up to 30 pairs of lines/mm. The photocathode is of a multislit S-20 type. For meteor spectra observations, replica gratings of 200 and 300 lines/mm are used as the dispersive element.

Shafiev, R. I.↗
NASA NTRS1988

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Johnson, W. S.↗
NASA NTRS1988

Closure measurements of naturally initiating small cracks

The initiation and growth of cracks in smooth 2024-T3 aluminum specimens have been investigated using acetate replicas. Crack opening displacements were measured as a function of load at several positions along the crack as it grew across the thickness of the specimen and became a through-the-thickness crack of a few millimeters in length. Tests run for R-ratios of 0.5, 0.0 and -1.0 showed that closure loads were well predicted by Newman's (1984) model. It is noted that small cracks grow slightly faster than would be predicted by long-crack data, and it is suggested that effects other than plasticity-induced closure must be taken into account.

Sharpe, W. N., Jr.↗
NASA NTRS1988

Short-crack growth behaviour in an aluminum alloy: An AGARD cooperative test program

An AGARD Cooperative Test Program on the growth of short fatigue cracks was conducted to define the significance of the short-crack effect, to compare test results from various laboratories, and to evaluate an existing analytical crack-growth prediction model. The initiation and growth of short fatigue cracks (5 micrometer to 2 mm) from the surface of a semi-circular notch in 2024-T3 aluminum alloy sheet material were monitored under various load histories. The cracks initiated from inclusion particle clusters or voids on the notch surface and generally grew as surface cracks. Tests were conducted under several constant-amplitude (stress ratios of -2, -1, 0, and 0.5) and spectrum (FALSTAFF and Gaussian) loading conditions at 3 stress levels each. Short crack growth was recorded using a plastic-replica technique. Over 250 edge-notched specimens were fatigue tested and nearly 950 cracks monitored by 12 participants from 9 countries. Long crack-growth rate data for cracks greater than 2 mm in length were obtained over a wide range in rates (10 to the -8 to 10 to the -1 mm/cycle) for all constant-amplitude loading conditions. Long crack-growth rate data for the FALSTAFF and Gaussian load sequences were also obtained.

Newman, J. C., Jr.↗
NASA NTRS1989

Lateral stability analysis for X-29A drop model using system identification methodology

A 22-percent dynamically scaled replica of the X-29A forward-swept-wing airplane has been flown in radio-controlled drop tests at the NASA Langley Research Center. A system identification study of the recorded data was undertaken to examine the stability and control derivatives that influence the lateral behavior of this vehicle with particular emphasis on an observed wing rock phenomenon. All major lateral stability derivatives and the damping-in-roll derivative were identified for angles of attack from 5 to 80 degrees by using a data-partitioning methodology and a modified stepwise regression algorithm.

Raney, David L.↗
NASA NTRS1988

Closure measurements on short fatigue cracks

Single-edged notched specimens, 2.3 mm thick, of 2024-T3 aluminum were cyclically loaded at R-ratios of 0.5, 0.0, -1.0, and -2.0. The notch roots were periodically inspected with an optical microscope to locate the initiation of very short cracks. Acetate replicas were also taken. The loads were selected to produce fatigue lives of 500,000 cycles or less. Crack opening displacements were measured at single positions across cracks as short as 0.035 mm and as long as the full thickness of the specimen. The opening load ratios for the short cracks are somewhat smaller than for long cracks at positive R-ratios, but are considerably smaller for negative R-ratios.

Lee, Joo-Jin↗