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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Ultrathick Boron Carbide Coatings for Nuclear Fusion Targets

Boron carbide is an attractive ablator for next-generation inertial confinement fusion (ICF) targets. Here we describe several aspects of our ongoing systematic studies of the deposition and processing of B 4 C coatings for ICF targets. We show that residual compressive stress in films can be reduced and the deposition rate increased by N-doping. Further, we also demonstrate successful Si substrate etching and surface polishing and discuss remaining challenges and offer potential solutions to the buildup of particulates in the deposition chamber during prolonged coating runs, control of nodular growth defects, and lateral nonuniformity of film properties for deposition conditions with relatively low target-to-substrate distances.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Multiscale Richtmyer-Meshkov instability experiments to isolate the strain rate dependence of strength

Theoretical analysis of Richtmyer-Meshkov instability (RMI) experiments for solid strength shows that the strain rate for a given shock should be inversely proportional to the length scale of the sine wave perturbations when η 0 k , the nondimensional amplitude to wavelength ratio, is held fixed. To isolate the effect of strain rate on strength, free-surface RMI specimens of annealed copper were prepared with three perturbation regions with the same η 0 k but different length scales, characterized by the wavelength λ varying by a factor of 4.9 from 65 to 130 to 320 µ m . Three such targets with different fixed η 0 k ′ s were impacted to a shock pressure of 25 GPa, and the instability evolution was measured with photon Doppler velocimetry. Strengths estimated by comparing hydrocode simulation to the data increased from 700 to 1200 MPa as λ decreased. The different η 0 k targets exercised increasing amounts of plastic strain yet showed no evidence of strain hardening. Physical regime sensitivity analysis determined that for 320 − 65 µ m wavelength perturbations, the effective strain rates increased from 8.7 × 10 6 to 3.3 × 10 7 s − 1 , a factor of 3.8. Thus, the predicted strain rate scaling was mostly achieved but slightly suppressed by increased strength at higher rates. The RMI strength estimates were plotted against constitutive testing data on copper from the literature to show striking evidence of the strength upturn at higher strain rates. Published by the American Physical Society 2024

36 MATERIALS SCIENCE↗
DOE OSTI2022

Verification of a specialized hydrodynamic simulation code for modeling deflagration and detonation of high explosives

A specialized hydrodynamic simulation code has been developed and verified for the simulation of one-dimensional unsteady problems involving the detonation and deflagration of high explosives. To model all the relevant physical processes in these problems, a code is required to simulate compressible hydrodynamics, unsteady thermal conduction, and chemical reactions with complex rate laws. Several verification exercises are presented which test the implementation of these capabilities. The code also requires models for physics processes such as equations of state and conductivity for pure materials and mixtures as well as rate laws for chemical reactions. Additional verification tests are required to ensure that these models are implemented correctly. Though this code is limited in the types of problems it can simulate, its computationally efficient formulation allows it to be used in calibration studies for reactive burn models for high explosives. Furthermore, this study demonstrates how a series of verification tests can be used to ensure that the various physics processes needed to simulate complex phenomenon can be tested to ensure that they are correctly implemented.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1980

Video-compression scheme

Video compression circuit divides picture into elements transmitted at reduced data rate. By sampling elements along diagonals in N-by-N picture blocks, system gives picture quality comparable to that of standard television and superior to most pseudorandom sampling schemes.

Lum, H., Jr.↗
NASA NTRS1981

Aeroacoustics of a porous plug jet noise suppressor

The aeroacoustics of a porous plug jet noise suppressor was investigated. The predicted flow features of isentropic plug nozzles for different pressure ratios or exit flow Mach numbers, throat areas, ratios of the plug to annular nozzle radii, mass flow rates and the available run times possible with the existing compressed air supply system, are compiled. The dimensions and the coordinates of the contour of typical isentropic external expansion plugs with different exit flow Mach numbers are listed. Design details of the experimental facility and the plug nozzle selected for experimental aeroacoustic studies are reported. The analytical flow prediction by method of characteristics of a conical porous plug nozzles is initiated. The role of the shape, size, and porosity of the plug surface in achieving over a perforated conical plug a nearly isentropic shockfree supersonic flow field which is closely similar to the flow field of a contoured isentropic plug nozzle is examined.

Dosanjh, D. S.↗
NASA NTRS1983

Mariner Mark II and the exploration of the solar system

NASA's Solar System Exploration Committee has proposed the Mariner Mark II concept for the next generation of deep-space planetary observation missions, which will yield Voyager- and Galileo-quality focused data sets at a fraction of the costs associated with those spacecraft. Cost-limiting strategies under consideration include the use of reconfigurable designs, a multimission ground support system, and the incorporation of such selected new technologies as an all-X band telemetry system, fiber-optic rate sensors for use as an inertial reference system, image compression, and electronic and optical disk data distribution. It is believed possible to meet cost goals of 150-300 million/mission. The missions under consideration are comet rendezvous and sample return, main belt asteroid flybys, and orbits, flybys and probes of Saturn, Titan, Neptune and Uranus.

Neugebauer, M.↗
NASA NTRS1986

Catching the whispers from Uranus

Sophisticated telecommunications techniques are described that were used to acquire images of Uranus, its 14 moons and ten narrow rings darker than coal. The images, equal in quality to those transmitted from Saturn several years earlier despite the signal being weaker by 6 dB due to the increased distance, were received from Voyager 2 during its January 24, 1986 flyby of Uranus. Solutions to the problem of the weakening signal were found in modifications to Voyager's image processing system and NASA's ground tracking network. In April 1985, Voyager's prime flight data computer was reconfigured to accept only nonimaging science data, and its backup, only imaging data; the latter was reprogrammed to determine only arithmetic differences between adjacent pixel intensities rather than absolute intensities. By image compression, equivalent imaging information could be sent at lower bit rates. Instead of Golay coding, Reed-Solomon onboard encoding was used. These techniques gained the equivalent of 4-dB in imaging yield. Additional improvements were gained by using earth station antennas in pairs (the Parkes radio telescope and the Canberra ground station antenna). Moves under way to prepare for the Voyager encounter with Neptune in 1989 are described (using additional antennas and arrays, scaling up the Deep Space Network antennas from 64 m to 70 m, etc.) to assure almost Saturn-equivalent pictures despite a further 3.5-dB drop in signal strength.

Bartok, C. D.↗
NASA NTRS1989

Image processing using Gallium Arsenide (GaAs) technology

The need to increase the information return from space-borne imaging systems has increased in the past decade. The use of multi-spectral data has resulted in the need for finer spatial resolution and greater spectral coverage. Onboard signal processing will be necessary in order to utilize the available Tracking and Data Relay Satellite System (TDRSS) communication channel at high efficiency. A generally recognized approach to the increased efficiency of channel usage is through data compression techniques. The compression technique implemented is a differential pulse code modulation (DPCM) scheme with a non-uniform quantizer. The need to advance the state-of-the-art of onboard processing was recognized and a GaAs integrated circuit technology was chosen. An Adaptive Programmable Processor (APP) chip set was developed which is based on an 8-bit slice general processor. The reason for choosing the compression technique for the Multi-spectral Linear Array (MLA) instrument is described. Also a description is given of the GaAs integrated circuit chip set which will demonstrate that data compression can be performed onboard in real time at data rate in the order of 500 Mb/s.

Miller, Warner H.↗
NASA NTRS1989

A continuum model of continental deformation above subduction zones - Application to the Andes and the Aegean

A continuum model of continental deformation above subduction zones was developed that combines the viscous sheet and the corner flow models; the continental lithosphere is described by a two-dimensional sheet model that considers basal drag resulting from the viscous asthenosphere flow underneath, and a corner flow model with a deforming overlying plate and a rigid subducting plate is used to calculate the shear traction that acts on the base of the lithosphere above a subduction zone. The continuum model is applied to the Andes and the Aegean deformations, which represent, respectively, compressional and extensional tectonic environments above subduction zones. The models predict that, in a compressional environment, a broad region of uplifted topography will tend to develop above a more steeply dippping slab, rather than above a shallower slab, in agreement with observations in the various segments of the central Andes. For an extensional environment, the model predicts that a zone of compression can develop near the trench, and that extensional strain rate can increase with distance from the trench, as is observed in the Aegean.

Wdowinski, Shimon↗
NASA NTRS1992

Non-LTE radiating acoustic shocks and Ca II K2V bright points

We present, for the first time, a self-consistent solution of the time-dependent 1D equations of non-LTE radiation hydrodynamics in solar chromospheric conditions. The vertical propagation of sinusoidal acoustic waves with periods of 30, 180, and 300 s is calculated. We find that departures from LTE and ionization recombination determine the temperature profiles of the shocks that develop. In LTE almost all the thermal energy goes into ionization, so the temperature rise is very small. In non-LTE, the finite transition rates delay the ionization to behind the shock front. The compression thus goes into thermal energy at the shock front leading to a high temperature amplitude. Further behind the shock front, the delayed ionization removes energy from the thermal pool, which reduces the temperature, producing a temperature spike. The 180 s waves reproduce the observed temporal changes in the calcium K line profiles quite well. The observed wing brightening pattern, the violet/red peak asymmetry and the observed line center behavior are all well reproduced. The short-period waves and the 5 minute period waves fail especially in reproducing the observed behavior of the wings.

Carlsson, Mats↗
NASA NTRS1994

An adaptive technique to maximize lossless image data compression of satellite images

Data compression will pay an increasingly important role in the storage and transmission of image data within NASA science programs as the Earth Observing System comes into operation. It is important that the science data be preserved at the fidelity the instrument and the satellite communication systems were designed to produce. Lossless compression must therefore be applied, at least, to archive the processed instrument data. In this paper, we present an analysis of the performance of lossless compression techniques and develop an adaptive approach which applied image remapping, feature-based image segmentation to determine regions of similar entropy and high-order arithmetic coding to obtain significant improvements over the use of conventional compression techniques alone. Image remapping is used to transform the original image into a lower entropy state. Several techniques were tested on satellite images including differential pulse code modulation, bi-linear interpolation, and block-based linear predictive coding. The results of these experiments are discussed and trade-offs between computation requirements and entropy reductions are used to identify the optimum approach for a variety of satellite images. Further entropy reduction can be achieved by segmenting the image based on local entropy properties then applying a coding technique which maximizes compression for the region. Experimental results are presented showing the effect of different coding techniques for regions of different entropy. A rule-base is developed through which the technique giving the best compression is selected. The paper concludes that maximum compression can be achieved cost effectively and at acceptable performance rates with a combination of techniques which are selected based on image contextual information.

Stewart, Robert J.↗
NASA NTRS2001

Development and Evaluation of Directionally-Solidified NiAl/(CR,MO)-Based Eutectic Alloys for Airfoil Applications

The results of recent efforts to develop directionally-solidified alloys based on the Ni-33Al-31Cr-3Mo eutectic composition are discussed. These developmental efforts included studying the effects of macroalloying and growth rates on microstructure formation as well as the elevated temperature compressive and tensile properties of these alloys. These observations revealed that contrary to conventional opinion, the cellular microstructure was stronger and tougher than the planar eutectic microstructure due to a microstructural refinement of the cell size and interlamellar spacing. The high temperature strengths of these alloys are compared with those of commercial superalloys and advanced NiAl single crystals. The implications of this research on airfoil manufacturing and applications are discussed.

Raj, S. V.↗
NASA NTRS1996

High pressure mechanical seal

A relatively impervious mechanical seal is formed between the outer surface of a tube and the inside surface of a mechanical fitting of a high pressure fluid or hydraulic system by applying a very thin soft metal layer onto the outer surface of the hard metal tube and/or inner surface of the hard metal fitting. The thickness of such thin metal layer is independent of the size of the tube and/or fittings. Many metals and alloys of those metals exhibit the requisite softness, including silver, gold, tin, platinum, indium, rhodium and cadmium. Suitably, the coating is about 0.0025 millimeters (0.10 mils) in thickness. After compression, the tube and fitting combination exhibits very low leak rates on the order or 10.sup.-8 cubic centimeters per second or less as measured using the Helium leak test.

Babel, Henry W.↗
NASA NTRS2011

Novel Materials for Prosthetic Liners

Existing materials for prosthetic liners tend to be thick and airtight, causing perspiration to accumulate inside the liner and potentially causing infection and injury that reduce quality of life. The purpose of this project was to examine the suitability of aerogel for prosthetic liner applications. Three tests were performed on several types of aerogel to assess the properties of each material. Moisture vapor permeability was tested by incubating four aerogel varieties with an artificial sweat solution at 37.0 C and less than 20% relative humidity for 24 hours. Two aerogel varieties were eliminated from the study due to difficulties in handling the material, and further testing proceeded with Pyrogel in 2.0 and 6.0 mm thicknesses. Force distribution was tested by compressing samples under a load of 4448 N at a rate of 2.5 mm/min. Biofilm formation was tested in a high-shear CDC Biofilm Reactor. Results showed that 2.0 mm Pyrogel blanket allowed 55.7 plus or minus 28.7% of an artificial sweat solution to transpire, and 35.5 plus or minus 27.8% transpired through 6.0 mm Pyrogel blanket. Samples also outperformed the load-bearing capabilities of existing liner materials. No statistically significant difference was found between the two Pyrogel thicknesses for either moisture vapor permeability or force distribution. In addition, biofilm formation results showed no change between the two Pyrogel thicknesses. The breathability and load bearing properties of aerogel make it a suitable material for application to prosthetic liners.

Ragolta, Carolina I.↗
NASA NTRS2018

Evaluations of Candidate Materials for Advanced Space-Rated Vacuum Seals to Explore Space Environment Exposure Limits

For many materials used in space hardware, the environment in which they need to operate is harsher than the environment on earth. Exposure to vacuum conditions, atomic oxygen, and ultraviolet radiation can be detrimental, so testing of space hardware in simulated space environments is required. This is especially true for elastomeric components such as seals. NASA is developing advanced space-rated vacuum seals in support of future space exploration missions. These seals must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air during extended-duration missions. In some applications the seals are not mated during portions of the mission and are left uncovered and exposed to the conditions in space for prolonged periods of time prior to mating. Space-rated vacuum seals are often made of silicone because of the material's wide operating temperature range and ability to be molded or extruded into various shapes and cross sections. One approach being considered to achieve improved performance is to add titanium dioxide to the silicone material to make it more resistant to damage from ultraviolet radiation. In this study, seals made of the baseline material with and without 1.5 percent titanium dioxide additive (by weight) were exposed to atomic oxygen and increasing levels of ultraviolet radiation and then leak tested. Test results revealed that seals made of the new material could withstand longer exposures while still satisfying the leak rate requirement even under worst-case conditions of partial compression at the extremes of the anticipated operating temperature range.

Seals↗
NASA NTRS2018

Evaluations of Candidate Materials for Advanced Space-Rated Vacuum Seals to Explore Space Environment Exposure Limits

For many materials used in space hardware, the environment in which they need to operate is harsher than the environment on earth. Exposure to vacuum conditions, atomic oxygen, and ultraviolet radiation can be detrimental, so testing of space hardware in simulated space environments is required. This is especially true for elastomeric components such as seals. NASA is developing advanced space-rated vacuum seals in support of future space exploration missions. These seals must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air during extended-duration missions. In some applications the seals are not mated during portions of the mission and are left uncovered and exposed to the conditions in space for prolonged periods of time prior to mating. Space-rated vacuum seals are often made of silicone because of the material's wide operating temperature range and ability to be molded or extruded into various shapes and cross sections. One approach being considered to achieve improved performance is to add titanium dioxide to the silicone material to make it more resistant to damage from ultraviolet radiation. In this study, seals made of the baseline material with and without 1.5% titanium dioxide additive (by weight) were exposed to atomic oxygen and increasing levels of ultraviolet radiation and then leak tested. Test results revealed that seals made of the new material could withstand longer exposures while still satisfying the leak rate requirement even under worst-case conditions of partial compression at the extremes of the anticipated operating temperature range.

Ultraviolet radiation↗
DOE OSTI2021

Texture and microstructure evolution in thermomechanically processed Mg-Ca and Mg-Zn-Ca alloys

Mg-Zn-Ca alloys have the potential for producing Mg alloy sheets with weaker basal textures and therefore improved formability. Thermomechanical processing (TMP) also plays a substantial role in determining the final sheet texture. The interplay of these variables, TMP and alloying, complicates comparisons of alloys across the literature. This work systematically explores the texture evolution and recrystallization behavior in Mg-Ca and Mg-Zn-Ca alloys during plane strain compression (PSC) using a Gleeble thermomechanical simulator. It is demonstrated that the basal texture intensity and texture characteristics change significantly during post-deformation annealing, particularly in the ternary alloys. It is also shown that careful selection of the TMP processing variables used during PSC is essential to producing weak textures. In particular, it is important to limit the recrystallization that occurs between compressive hits. This is achieved by adjusting solute content, strain rate, and the duration of the soak between passes.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Seismic coupling and uncoupling at subduction zones

Some of the correlations concerning the properties of subduction zones are reviewed. A quantitative global comparison of many subduction zones reveals that the largest earthquakes occur in zones with young lithosphere and fast convergence rates. Maximum earthquake size is directly related to the asperity distribution on the fault plane. This observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. Plate age and rate can control asperity distribution directly through the horizontal compressive stress associated with the vertical and horizontal velocities of subducting slabs. The basalt to eclogite phase change in the down-going oceanic crust may be largely responsible for the uncoupling of subduction zones below a depth of about 40 km.

Ruff, L.↗