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At least 217 records · Page 12

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NASA NTRS2024

Short-Term Elevated Temperature Mechanical Performance and Microstructure of A Niobium-Zirconium Alloy Produced via Laser Powder Bed Fusion In-Situ Alloying

Nb-1Zr is a readily fabricable, dispersion-strengthened niobium alloy with improved elevated temperature properties compared to commercially pure niobium. This low to moderate strength niobium alloy is desirable in thermal management systems for fission power and propulsion applications; however, pre-alloyed spherical feedstock for powder-based additive manufacturing processes is generally unavailable. Laser powder bed fusion (L-PBF) in-situ alloying of a Nb-1Zr chemistry was performed using a high-purity niobium feedstock coated with 1 wt% of zirconium-based ceramic compound nano-powders: ZrO 2 , ZrC, and ZrH 2 . The additively manufactured material was mechanically tested at elevated temperatures within a controlled environment in the as-built condition. For comparison, traditionally manufactured wrought feedstock was also tested within an identical environment. Examination of the materials’ microstructure and short-term elevated temperature mechanical response determined: in-situ alloying of spherical Nb powder feedstock with Zr-based ceramic nanoparticles can be successfully implemented; the ZrO 2 addition offered the greatest elevated temperature stability and strength but exhibited brittle behavior; the ZrC addition achieved a balance of room temperature ductility and elevated temperature strength; and the ZrH 2 -modified material had the lowest as-built interstitial content and showed high ductility with mechanical performance most similar to wrought Nb-1Zr.

Niobium Alloy↗

NASA NTRSDate not supplied

Atmospheric Variability and Measurement Uncertainty: Pitfalls in Averaging in situ Data

Satellite measurements and atmospheric models, two essential components of the integrated global observing system, provide crucial tools for monitoring and predicting regional and global foci, spanning numerous Earth Science fields. Unfortunately, models can lack the spatial and temporal resolution needed to resolve finer scale structure. Satellite measurements also have similar tempo-spatial restriction issues, but additionally can only measure certain species and can have biases that must be evaluated. Ground measurement networks are critical components of this system, by providing both independent inputs of species needed by models (including those that satellites do not provide) and assisting with investigation of biases in satellite products. Similarly, aircraft measurements play a vital role in closing the gaps between satellite measurements, model products, and ground monitoring networks by providing high accuracy, high-resolution data on local to regional spatial scales. Therefore, both ground-based and airborne observations are widely used to assess model predictions and satellite observations. One of the great challenges in using both ground and aircraft data in this fashion is matching the data temporally and spatially to the model/satellite data. A meaningful comparison with model or satellite requires a solid assessment of the variability of the in-situ measurements, which include both the instrument uncertainty and the statistical uncertainty due to atmospheric variability. While instrument uncertainty is generally more straightforwardly characterized, it can be challenging to accurately capture this variability uncertainty as it often presents in a non-Gaussian manner (e.g. emission plumes, frontal passages). We will present results examining spatial and temporal variability over a selection of scales relevant to satellite measurements and models of several in situ measurement species spanning both airborne and ground measurements. The extent of non-Gaussian variability will be quantified, and we will discuss additional statistical parameters that help assess the fitness of gaussian variability assumption when temporally or spatially averaging.

satellite validation↗

NASA NTRS1972

Detection of soil microorganism in situ by combined gas chromatography mass spectrometry

Experimental tests were made to determine whether analysis of volatile metabolic products, formed in situ, is a viable procedure for an extraterrestrial life detection system. Laboratory experiments, carried out under anaerobic conditions with addition of carbon source, extended to include a variety of soils and additional substrates. In situ experiments were conducted without amendment using a vacuum sampling system.

Alexander, M.↗

NASA NTRS1973

In situ spectroradiometric quantification of ERTS data

The task of correlating in situ spectral reflectance measurements with ERTS imagery has commenced. A method of additive color analysis of a single multispectral band taken on different dates indicates that ERTS-1 bulk images have sufficient spatial and spectral fidelity to show indications of the presence of soil moisture in desert playas and changes in soil moisture with time. The chain of causality between soil moisture, in situ spectral reflectance, and ERTS multispectral scanner image density remains to be established during the subsequent phases of this study.

Yost, E.↗

NASA NTRS1973

In situ polymerization of monomers for polyphenylquinoxaline/graphite

Methods currently used to prepare fiber reinforced, high temperature resistant polyphenylquinoxaline (PPQ) composites employ extremely viscous, low solids content solutions of high molecular weight PPQ polymers. An improved approach, described in this report, consists of impregnating the fiber with a solution of the appropriate monomers instead of a solution of previously synthesized high molecular weight polymer. Polymerization of the monomers occurs in situ on the fiber during the solvent removal and curing stages. The in situ polymerization approach greatly simplifies the fabrication of PPQ graphite fiber composites. The use of low viscosity monomeric type solutions facilitates fiber wetting, permits a high solids content, and eliminates the need for prior polymer synthesis.

Serafini, T. T.↗

NASA NTRS1974

In situ polymerization of monomers for polyphenylquinoxaline/graphite fiber composites

Serafini, T. T.↗

NASA NTRS1974

In-situ measurements of lunar heat flow

During the Apollo program two successful heat flow measurements were made in situ on the lunar surface. At the Apollo 15 site a value of 0.0000031 watts/sqcm was measured and at the Apollo 17 site a value of 0.0000022 watts/sqcm was determined. Both measurements have uncertainty limits of + or - 20% and have been corrected for perturbing topographic effects. The apparent difference between the observations may correlate with observed variations in the surface abundance of thorium. Comparison with earlier determinations of heat flow, using the microwave emission spectrum from the moon, gives support to the high gradients and heat flows observed in situ.

Langseth, M. G.↗

NASA NTRS1976

A means of in-situ measurements of neutral H and He on an out-of-the-ecliptic mission

On an out-of-the-ecliptic mission, in situ measurements of densities and temperature of interstellar neutral H and He in the heliosphere should complement observations based on backscattered Lyman-alpha intensities. A means of performing the in situ measurements is briefly described.

Hsieh, K. C.↗

NASA NTRS1976

Oxidation of metals and alloys in controlled atmospheres using in situ transmission electron microscopy and Auger spectrography

Single-crystalline thin films of copper were oxidized at an isothermal temperature of 425 C and at an oxygen partial pressure of .005 Torr in situ in a high-resolution electron microscope. The specimens were prepared by epitaxial vapor deposition onto polished 100 and 110 faces of rocksalt and mounted in a hot stage inside an ultra-high-vacuum specimen chamber of the microscope. Large amounts of sulfur, carbon, and oxygen were detected by Auger electron spectroscopy on the surface of the as-received films and were removed in situ by ion-sputter etching immediately prior to the oxidation. The nucleation and growth characteristics of Cu2O on Cu were studied. Results show that neither stacking faults nor dislocations are associated with the Cu2O nucleation sites. The growth of Cu2O nuclei is linear with time. The experimental findings, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving (a) the formation of a surface-charge layer, (b) oxygen saturation in the metal and (c) nucleation, followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

Rao, D. B.↗

NASA NTRS1976

Conference on In Situ Composites, 2nd, Bolton Landing, N.Y., September 2-5, 1975, Proceedings

The present collection of papers deals with advances in several areas of interest in in-situ composites. Major areas discussed include solidification and structural control, physical properties, mechanical behavior, stability, environmental response, and development of new metallic and ceramic systems. New evidence about directional solidification in terms of temperature gradients is presented along with solidification rates for successful formation of in-situ composite structures. Much is learned about the factors that control structure in directionally solidified eutectic alloys and the relationship of properties to structure, especially the change in properties as a function of operating environment. Less progress is achieved in the area of physical properties than in the area of mechanical properties. Individual items are announced in this issue.

Jackson, M. R.↗

NASA NTRS1977

In-situ measurements of lunar heat flow

During the Apollo program two successful heat flow measurements were made in situ on the lunar surface. At the Apollo 15 site a value of .0000031 W/sq cm was measured, and at the Apollo 17 site a value of .0000022 W/sq cm was determined. Both measurements have uncertainty limits of + or - 20 percent and have been corrected for perturbing topographic effects. The apparent difference between the observations may correlate with observed variations in the surface abundance of thorium. Comparison with earlier determinations of heat flow, using the microwave emission spectrum from the moon, gives support to the high gradients and heat flows observed in situ.

Langseth, M. B.↗

NASA NTRS1978

In situ ply strength: An initial assessment

The in situ ply strengths in several composites were calculated using laminate fracture data for appropriate low modulus, and high modulus fiber composites were used in conjunction with the least squares method. The laminate fracture data were obtained from tests on Modmor-I graphite/epoxy, AS-graphite/epoxy, boron/epoxy and E-glass/epoxy. The results show that the calculated in situ ply strengths can be considerably different from those measured in unidirectional composites, especially the transverse strengths and those in angleplied laminates with transply cracks.

Chamis, C. C.↗

NASA NTRS1977

A miniature 48-channel pressure sensor module capable of in situ calibration

A new high data rate pressure sensor module with in situ calibration capability has been developed by the Langley Research Center to help reduce energy consumption in wind-tunnel facilities without loss of measurement accuracy. The sensor module allows for nearly a two order of magnitude increase in data rates over conventional electromechanically scanned pressure sampling techniques. This module consists of 16 solid state pressure sensor chips and signal multiplexing electronics integrally mounted to a four position pressure selector switch. One of the four positions of the pressure selector switch allows the in situ calibration of the 16 pressure sensors; the three other positions allow 48 channels (three sets of 16) pressure inputs to be measured by sensors. The small size of the sensor module will allow mounting within many wind-tunnel models, thus eliminating long tube lengths and their corresponding slow pressure response.

Gross, C.↗

NASA NTRS1978

In situ ply strengths - An initial assessment

The in situ ply strengths in several composites were calculated using a computational procedure developed for this purpose. Laminate fracture data for appropriate low modulus and high modulus fiber composites were used in the laminate analysis in conjunction with the method of least squares. The laminate fracture data were obtained from tests on Modmor-I graphite/epoxy, AS-graphite/epoxy, boron/epoxy and E-glass/epoxy. The results obtained show that the calculated in situ ply strengths can be considerably different from those measured in unidirectional composites, especially the transverse strengths and those in angleplied laminates with transply cracks.

Chamis, C. C.↗

NASA NTRS1978

Comparison of in situ and remotely sensed ocean waves off Marineland, Florida

Comparison between X-band and L-band radar imagery of sea waves is made. Sea truth was obtained by in situ pitch-and-roll buoy measurements. Under the low wind and wave conditions of the tests, superior wave imagery and more useful Fourier transforms were obtained with X-band SAR as compared to L-band with equivalent signal-to-noise ratio and synthetic aperture resolution. A comparison between X-band wave images and the in situ measurements shows agreement in the dominant wave direction to within a few degrees. The normalized spectra show a striking resemblance in spectral shape.

Shemdin, O. H.↗

NASA NTRS1979

Three methods for in situ cross-linking of polyvinyl alcohol films for application as ion-conducting membranes in potassium hydroxide electrolyte

Three methods of in situ cross-linking polyvinyl alcohol films are presented. They are: (1) acetalization with a dialdehyde such as glutaraldehyde, (2) acetalization with aldehyde groups formed by selective oxidative cleaving of the few percent of 1,2 diol units present in polyvinyl alcohol, and (3) cross-linking by hydrogen abstraction by reaction with hydrogen atoms and hydroxyl radicals from irradiated water. For the third method, improvement in film conductivity in KOH solution at the expense of mechanical strength is obtained by the presence of polyacrylic acid in the polyvinyl alcohol films. Resistivities in 45 percent KOH are given for in situ cross-linked films prepared by each of the three methods.

Philipp, W. H.↗

NASA NTRS1980

In situ ozone data for evaluation of the laser absorption spectrometer ozone remote sensor: 1979 southeastern Virginia urban plume study summer field program

Ozone data from the 1979 Southeastern Virginia Urban Study (SEV-UPS) field program are presented. The SEV-UPS was conducted for evaluation of an ozone remote sensor, the Laser Absorption Spectrometer. During the measurement program, remote-sensor evaluation was in two areas; (1) determination of the remote sensor's accuracy, repeatability, and operational characteristics, and (2) demonstration of the application of remotely sensed ozone data in air-quality studies. Data from six experiments designed to provide in situ ozone data for evaluation of the sensor in area 1, above, are presented. Experiments consisted of overflights of a test area with the remote sensor aircraft while in situ measurements with a second aircraft and selected surface stations provided correlative ozone data within the viewing area of the remote sensor.

Gregory, G. L.↗

NASA NTRS1980

Stratospheric free chlorine measured by balloon-borne in situ resonance fluorescence

Eight balloon-borne in situ measurements of ClO in the stratosphere are analyzed and are compared with recent model calculations. While the use of in situ stratospheric studies of free radicals to test models by comparing observed and predicted concentration profiles is essential for a prognosis of changes in stratospheric ozone, resulting from future changes in stratospheric ozone, such studies provide only limited insight into the nature of stratospheric photochemistry, because natural variability and the large number of fast reactions which compete in the coupling among the key radicals frustrate a detailed comparison between a mean distribution provided by the models and an instantaneous distribution provided by a single observation.

Anderson, J. G.↗