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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

NDE of advanced ceramics

Radiographic, ultrasonic, and scanning laser acoustic microscopy (SLAM) techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus X-ray techniques were found capable of detecting minute high-density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was capable also of detecting voids, inclusions, and cracks in finished test bars. Consideration is given to the potential for applying thermoacoustic microscopy techniques to green and densified ceramics. Some limitations and the detection probability statistics of the aforementioned nondestructive evaluation (NDE) processes are also discussed.

Klima, S. J.↗
NASA NTRS1986

Nondestructive characterization of structural ceramics

Ultrasonic velocity and attenuation measurements were used to characterize density and microstructure in monolithic silicon nitride and silicon carbide. Research samples of these structural ceramics exhibited a wide range of density and microstructural variations. It was shown that bulk density variations correlate with and can be estimated by velocity measurements. Variations in microstructural features such as grain size or shape and pore morphology had a minor effect on velocity. However, these features had a pronounced effect on ultrasonic attenuation. The ultrasonic results are supplemented by low-energy radiography and scanning laser acoustic microscopy.

Klima, S. J.↗
NASA NTRS1986

NDE of structural ceramics

Radiographic, ultrasonic, scanning laser acoustic microscopy (SLAM), and thermo-acoustic microscopy techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus X-ray techniques were found capable of detecting minute high density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was also capable of detecting voids, inclusions and cracks in finished test bars. Consideration is given to the potential for applying thermo-acoustic microscopy techniques to green and densified ceramics. The detection probability statistics and some limitations of radiography and SLAM also are discussed.

Klima, S. J.↗
NASA NTRS1987

Laser Scanner for Tile-Cavity Measurement

Irregular surfaces mapped and digitized for numerical-control machinery. Fast, accurate laser scanning system measures size and shape of cavity without making any physical contact with cavity and walls. Measurements processed into control signals for numerically controlled machining of tile or block to fit cavity. System generates map of grid points representing cavity and portion of outer surface surrounding cavity. Map data used to control milling machine, which cuts tile or block to fit in cavity.

Yoshino, Stanley Y.↗
NASA NTRS1987

Determining Directions of Ultrasound in Solids

Ultrasound shadows cast by grooves. Improved method for determining direction of ultrasound in materials is shadow method using Scanning laser acoustic microscopy (SLAM). Direction of ultrasound calculated from dimensions of groove and portion of surface groove shields from ultrasound. Method has variety of applications in nontraditional quality-control applications.

Generazio, Edward R.↗
NASA NTRS1986

NDE reliability and process control for structural ceramics

The reliability of microfocus x-radiography and scanning laser acoustic microscopy for detecting microvoids in silicon nitride and silicon carbide was statistically evaluated. Materials- and process-related parameters that influenced the statistical findings in research samples are discussed. The use of conventional x-radiography in controlling and optimizing the processing and sintering of an Si3N4-Si02-Y203 composition designated NASA 6Y is described. Radiographic evaluation and guidance helped develop uniform high-density Si3N4 modulus-of-rupture bars with improved four-point flexural strength (857, 544, and 462 MPa at room temperature, 1200 C, and 1370 C, respectively) and reduced strength scatter.

Baaklini, G. Y.↗
NASA NTRS1986

Quantitative thermal characterization of thin plates

The principles of quantitative thermal testing of the mechanical integrity of platelike structures are discussed. In this technique, a scanned laser pulse is used to inject a thermal pattern in a sample, and a thermal IR imager is used to document the evolution of the pattern subsequent to injection. The measurements are remote, noncontacting, and one-sided, and the algorithms used to obtain diffusivity are all emissivity-independent. The results yielded by application of the three analytical techniques, used to obtain diffusivity values from the image data on stainless steel, a graphite-epoxy composite, brass, and aluminum 2024 samples, are presented.

Welch, C. S.↗
NASA NTRS1986

Construction of a 2- by 2-foot transonic adaptive-wall test section at the NASA Ames Research Center

The development of a new production-size, two-dimensional, adaptive-wall test section with ventilated walls at the NASA Ames Research Center is described. The new facility incorporates rapid closed-loop operation, computer/sensor integration, and on-line interference assessment and wall corrections. Air flow through the test section is controlled by a series of plenum compartments and three-way slide vales. A fast-scan laser velocimeter was built to measure velocity boundary conditions for the interference assessment scheme. A 15.2-cm- (6.0-in.-) chord NACA 0012 airfoil model will be used in the first experiments during calibration of the facility.

Morgan, Daniel G.↗
NASA NTRS1987

Temperature measurement in a compressible flow field using laser-induced iodine fluorescence

The thermometric capability of a two-line fluorescence technique using iodine seed molecules in air is investigated analytically and verified experimentally in a known steady compressible flow field. Temperatures ranging from 165 to 295 K were measured in the flowfield using two iodine transitions accessed with a 30-GHz dye-laser scan near 543 nm. The effect of pressure broadening on temperature measurement is evaluated.

Fletcher, D. G.↗
NASA NTRS1987

NDE reliability and process control for structural ceramics

The reliability of microfocus X-radiography and scanning laser acoustic microscopy for detecting microvoids in silicon nitride and silicon carbide was statistically evaluated. Materials- and process-related parameters that influenced the statistical findings in research samples are discussed. The use of conventional X-radiography in controlling and optimizing the processing and sintering of an Si3N4-SiO2-Y2O3 composition designated NASA 6Y is described. Radiographic evaluation and guidance helped develop uniform high-density Si3N4 modulus-of-rupture bars with improved four-point flexural strength (857, 544, and 462 MPa at room temperature, 1200 C, and 1370 C, respectively) and reduced strength scatter.

Baaklini, G. Y.↗
NASA NTRS1988

Reliability Of Inspection By SLAM

Scanning laser acoustic microscopy finds flaws in ceramic specimens. Laser light used to detect distortions, on angstrom scale, produced on surface of specimen by ultrasonic waves transmitted through specimen. From distortion, SLAM creates picture on video monitor of such defects as voids, inclusions, and cracks.

Roth, Don J.↗
NASA NTRS1988

Thermal Remote Anemometer Device

Thermal Remote Anemometer Device developed for remote, noncontacting, passive measurement of thermal properties of sample. Model heated locally by scanning laser beam and cooled by wind in tunnel. Thermal image of model analyzed to deduce pattern of airflow around model. For materials applications, system used for evaluation of thin films and determination of thermal diffusivity and adhesive-layer contact. For medical applications, measures perfusion through skin to characterize blood flow and used to determine viabilities of grafts and to characterize tissues.

Heyman, Joseph S.↗
NASA NTRS1987

Intelligent robotic tracker

An intelligent tracker capable of robotic applications requiring guidance and control of platforms, robotic arms, and end effectors has been developed. This packaged system capable of supervised autonomous robotic functions is partitioned into a multiple processor/parallel processing configuration. The system currently interfaces to cameras but has the capability to also use three-dimensional inputs from scanning laser rangers. The inputs are fed into an image processing and tracking section where the camera inputs are conditioned for the multiple tracker algorithms. An executive section monitors the image processing and tracker outputs and performs all the control and decision processes. The present architecture of the system is presented with discussion of its evolutionary growth for space applications. An autonomous rendezvous demonstration of this system was performed last year. More realistic demonstrations in planning are discussed.

Otaguro, W. S.↗
NASA NTRS1988

Nondestructive evaluation of sintered ceramics

Radiography and several acoustic and thermoacoustic microscopy techniques are investigated for application to structural ceramics for advanced heat engines. A comparison is made of the results obtained from the use of scanning acoustic microscopy (SAM), scanning laser acoustic microscopy (SLAM), and thermoacoustic microscopy (TAM). These techniques are evaluated on research samples of green and sintered monolithic silicon nitrides and silicon carbides in the form of modulus-of-rupture (MOR) bars containing deliberately introduced flaws. Strengths and limitations of the techniques are described, with the emphasis being on statistics of detectability of flaws that constitute potential fracture origins. Further, it is shown that radiographic evaluation and guidance helped develop uniform high-density Si3N4 MOR bars with improved four-point flexural strength (875, 544, and 462 MPa at room temperature, 1200 C, 1370 C, respectively) and reduced scatter in bend strength.

Baaklini, George Y.↗
NASA NTRS1986

Nondestructive evaluation of structural ceramics

Research on nondestructive evaluation (NDE) of structural ceramics for heat engine applications is reviewed. Microfocus radiography and scanning laser acoustic microscopy are the NDE techniques highlighted. The techniques were applied to research samples of sintered silicon nitride and silicon carbide in the form of modulus-of-rupture (MOR) bars. The strength and limitations of the aforementioned techniques are given in terms of probablility of detection for voids in green and sintered MOR bars. Voids for this purpose were introduced by seeding green ceramic bars and characterizing each void in terms of its size, shape, location, and nature before and after sintering. The effects of material density, microstructure, surface finish, thickness, void depth, and size characteristics on detectability are summarized.

Vary, Alex↗
NASA NTRS1987

Excimer laser annealing: A gold process for CZ silicon junction formation

A cold process using an excimer laser for junction formation in silicon has been evaluated as a way to avoid problems associated with thermal diffusion. Conventional thermal diffusion can cause bulk precipitation of SiOx and SiC or fail to completely activate the dopant, leaving a degenerate layer at the surface. Experiments were conducted to determine the feasibility of fabricating high quality p-n junctions using a pulsed excimer laser for junction formation at remelt temperature with ion-implanted surfaces. Solar-cell efficiency exceeding 16 percent was obtained using Czochralski single-crystal silicon without benefit of back surface field or surface passivation. Characterization shows that the formation of uniform, shallow junctions (approximately 0.25 micron) by excimer laser scanning preserves the minority carrier lifetime that leads to high current collection. However, the process is sensitive to initial surface conditions and handling parameters that drive the cost up.

Wong, David C.↗
NASA NTRS1987

Time- and position-varying infrared scene simulation

Rapidly changing infrared scenes can be generated as a function of position using thermally produced irradiance. This can be done most conveniently by using a variable dwell-time, variable diameter, and scanning laser beam to deposit a predetermined amount of laser energy, as a function of position, on the target surface. An infrared target simulator has been designed and tested to perform within stringent temperature simulation requirements: heating rate of over 100 K/sec is achieved, and temperature gradients of 200 K/mm can be maintained. Problems with heat transfer between adjacent elements at different temperatures are solved by modeling the thermal layer on the target surface as a low-pass filter, which cuts off all the frequencies above the thermal cutoff frequency. When the system approach is taken to the infrared simulation design, the optical system limited performance results in the best realizable performance. In this case, the thermal layer on the target surface is designed so that the thermal cutoff frequency is above the optical cutoff frequency.

Scholl, Marija S.↗
NASA NTRS1988

Sensor fusion of range and reflectance data for outdoor scene analysis

In recognizing objects in an outdoor scene, range and reflectance (or color) data provide complementary information. Results of experiments in recognizing outdoor scenes containing roads, trees, and cars are presented. The recognition program uses range and reflectance data obtained by a scanning laser range finder, as well as color data from a color TV camera. After segmentation of each image into primitive regions, models of objects are matched using various properties.

Kweon, In SO↗