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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

A Novel Ultrasonic Method for Characterizing Microstructural Gradients in Tubular Structures

Ultrasonic velocity and time-of-flight (TOF) imaging that uses back surface reflections to gage volumetric material quality is highly suited for quantitative characterization of microstructural gradients including those due to pore fraction, density, fiber fraction, and chemical composition variations. However, a weakness of conventional pulse echo ultrasonic velocity and TOF imaging is that the image shows the effects of thickness as well as microstructural variations, unless the part is uniformly thick. This limits this imaging method's usefulness in practical applications. Prior studies have described a pulse echo TOF based ultrasonic imaging method that requires using a single transducer in combination with a reflector plate placed behind samples which, eliminates the effect of thickness variation in the image. In those studies, this method was successful at isolating ultrasonic variations due to material in plate like samples of silicon nitride, metal matrix composite, and polymer matrix composite. In this study, the method is engineered for inspection of more complex shaped structures- those having (hollow) tubular or curved geometry. The experimental inspection technique and results are described as applied to a polymer matrix composite "proof of concept" tube that contains machined patches of various depths and an as manufactured monolithic silicon nitride ceramic tube that might be used in "real world" applications.

Roth, Don J.↗
NASA NTRS2000

Gamma-Ray Pulsars: Observations

High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The six or more pulsars seen by CGRO/EGRET show that the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. Unless a new pulsed component appears at higher energies, progress in gamma-ray pulsar studies will be greatest in the 1-10 GeV range . Ground-based telescopes whose energy ranges extend downward toward 10 GeV should make important measurements of the spectral cutoffs. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a possible launch in 2005, will provide a major advance in sensitivity, energy range, and sky coverage.

Thompson, David J.↗
NASA NTRS2000

Gamma Ray Pulsars: Observations

High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The six or more pulsars seen by CGRO/EGRET show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. Unless a new pulsed component appears at higher energies, progress in gamma-ray pulsar studies will be greatest in the 1-20 GeV range. Ground-based telescopes whose energy ranges extend downward toward 10 GeV should make important measurements of the spectral cutoffs. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2005, will provide a major advance in sensitivity, energy range, and sky coverage.

Thompson, David J.↗
NASA NTRS2004

Gamma Ray Pulsars: Multiwavelength Observations

High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The seven or more pulsars seen by instruments on the Compton Gamma Ray Observatory (CGRO) show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. For all the known gamma-ray pulsars, multiwavelength observations and theoretical models based on such observations offer the prospect of gaining a broad understanding of these rotating neutron stars. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2006, will provide a major advance in sensitivity, energy range, and sky coverage.

Thompson, David J.↗
NASA NTRS2006

Maximum von Mises Stress in the Loading Environment of Mass Acceleration Curve

Method for calculating stress due to acceleration loading: 1) Part has been designed by FEA and hand calculation in one critical loading direction judged by the analyst; 2) Maximum stress can be due to loading in another direction; 3) Analysis procedure to be presented determines: a) The maximum Mises stress at any point; and b) The direction of maximum loading associated with the "stress". Concept of Mass Acceleration Curves (MAC): 1) Developed by JPL to perform preliminary structural sizing (i.e. Mariners, Voyager, Galileo, Pathfinder, MER,...MSL); 2) Acceleration of physical masses are bounded by a curve; 3) G-levels of vibro-acoustic and transient environments; 4) Convergent process before the couple loads cycle; and 5) Semi-empirical method to effectively bound the loads, not a simulation of the actual response.

von Mises stress↗
NASA NTRS2000

Application of the Spectral Element Method to Acoustic Radiation

This report summarizes research to develop a capability for analysis of interior noise in enclosed structures when acoustically excited by an external random source. Of particular interest was the application to the study of noise and vibration transmission in thin-walled structures as typified by aircraft fuselages. Three related topics are focused upon. The first concerns the development of a curved frame spectral element, the second shows how the spectral element method for wave propagation in folded plate structures is extended to problems involving curved segmented plates. These are of significance because by combining these curved spectral elements with previously presented flat spectral elements, the dynamic response of geometrically complex structures can be determined. The third topic shows how spectral elements, which incorporate the effect of fluid loading on the structure, are developed for analyzing acoustic radiation from dynamically loaded extended plates.

Doyle, James F.↗
NASA NTRS1992

Surface generation and editing operations applied to structural support of aerospace vehicle fuselages

The Solid Modeling Aerospace Research Tool (SMART) is a computer aided design tool used in aerospace vehicle design. Modeling of structural components using SMART includes the representation of the transverse or cross-wise elements of a vehicle's fuselage, ringframes, and bulkheads. Ringframes are placed along a vehicle's fuselage to provide structural support and maintain the shape of the fuselage. Bulkheads are also used to maintain shape, but are placed at locations where substantial structural support is required. Given a Bezier curve representation of a cross sectional cut through a vehicle's fuselage and/or an internal tank, this project produces a first-guess Bezier patch representation of a ringframe or bulkhead at the cross-sectional position. The grid produced is later used in the structural analysis of the vehicle. The graphical display of the generated patches allows the user to edit patch control points in real time. Constraints considered in the patch generation include maintaining 'square-like' patches and placement of longitudinal, or lengthwise along the fuselage, structural elements called longerons.

Schwartz, Susan K.↗
DOE OSTI2019

Viscosities and working region predictions for bismuth aluminoborosilicate glasses

Bismuth aluminoborosilicate glasses were prepared using a standard melt-quench technique, and the viscosity and thermal properties were measured and analyzed. Electron microprobe analysis was used to examine glass homogeneity. Fragility was calculated based on Mauro–Yue–Ellison–Gupta–Allan model fits to the viscosity curves. The system is characterized by an open structure with high fragility (44-59). Based on microanalysis and differential scanning calorimetry results, the addition of network intermediate Al2O3 appears to mitigate both phase separation and crystallization. From thermal property data, mixture models were created to predict the glass transition temperatures and softening temperatures as functions of composition. Based on K-fold validation findings, the first-order mixture model predictions of glass transition and softening appear to approximate actual values better than models with any additional second-order terms.

Gardner, Levi↗
NASA NTRS2005

Surface structure of an invariant manifold of a Halo Orbit (extended abstract)

We extract the surface structure of the unstable invariant manifold tube projected into position space, of a halo orbit near L2. We do this by using transversal planes to intersect trajectories that approximate the tube. From these intersection points we construct spline-interpolated cross section curves which give a good idea of the structure of the tube. For example, we show that, for the value of (mu) we use, the tube pinches, develops a self-intersection, develops loop-inside-tube structure, pinches some more, and so on. We also construct surfaces made of quadrilaterals and triangles from these cross-sections. The transversal planes are obtained by taking planes orthogonal to a curve that follows the general shape of the tube. One such curve we use, is the unstable invariant manifold of the equilibrium point L2 itself. In another example, we take a circle that follows the tube, as the curve for finding planes transversal to the tube. Our method is complementary to the method of taking cross-sections of constant time (the isochronous method), as used by some other researchers. The isochronous method is good at revealing the temporal structure of trajectories on a tube. However, due to the unequal speeds of different trajectories, it is harder to use for long length surface extraction. In contrast, using our method, we show cross-sections of the tube through an angular extent of nearly (pi) during which the tube becomes extremely convoluted. We also show that tubes of different energies, that start out in certain ordering, do not obey the ordering after a while. Our work is motivated by applications to space mission design.

invariant manifold↗
NASA NTRS1994

Strain gage selection in loads equations using a genetic algorithm

Traditionally, structural loads are measured using strain gages. A loads calibration test must be done before loads can be accurately measured. In one measurement method, a series of point loads is applied to the structure, and loads equations are derived via the least squares curve fitting algorithm using the strain gage responses to the applied point loads. However, many research structures are highly instrumented with strain gages, and the number and selection of gages used in a loads equation can be problematic. This paper presents an improved technique using a genetic algorithm to choose the strain gages used in the loads equations. Also presented are a comparison of the genetic algorithm performance with the current T-value technique and a variant known as the Best Step-down technique. Examples are shown using aerospace vehicle wings of high and low aspect ratio. In addition, a significant limitation in the current methods is revealed. The genetic algorithm arrived at a comparable or superior set of gages with significantly less human effort, and could be applied in instances when the current methods could not.

Source record↗
DOE OSTI2020

Effect of 60 Co γ-radiation on the tetrafluoroethylene/perfluoro(methyl vinyl ether) copolymer

The chemical and paramagnetic composition of the surface of the tetrafluoroethylene / perfluoro(methyl vinyl ether) copolymer (MFA) was investigated before and after γ-irradiation. The content of fluorine and carbon decreases at radiolysis of MFA, as well as the proportion of oxygen increases as a result of the oxidation reaction of radicals formed during γ-irradiation. The electron paramagnetic resonance (EPR) spectrum of the copolymer irradiated at 77 K contains the radicals ~CF 2 C∙FCF 2 ~ (1) and >CFOC∙F 2 (2). The absence of ~CF 2 C∙F 2 radicals, which can be formed at radiolytic rupture of the C—C bond of the copolymer main chain is associated with the effect of recombination of the resulting radical pair. The EPR spectrum of irradiated MFA at 300 K only recorded radical (1), which transform into peroxide radicals when air oxygen is introduced into the irradiated sample. Thermomechanical curves of native and radiolyzed MFA show three structural states of the amorphous block (glass, transition region, plateau of highly elastic deformation), as well as melting and molecular flow of the copolymer. The radio thermoluminescence curve shows five maxima associated with the emission of light during the recombination of stabilized ions and radicals during heating of the pre-irradiated MFA at 77 K. The temperature of the luminescence peak maximum at 336 K is close to the temperature of the onset of the devitrification of the chains of the amorphous block of MFA on the thermomechanical curve at 341 K. Irradiation leads to an increase in crystallinity of MFA. The heat of fusion of irradiated MFA on the Differential Scanning Calorimeter (DSC) curve is 50 % higher than the fusion heat of native copolymer. During the heating of γ-irradiated MFA, the relative content of COF molecules in the thermal decomposition products increases by an order of magnitude.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Structure and density of silicon carbide to 1.5 TPa and implications for extrasolar planets

There has been considerable recent interest in the high-pressure behavior of silicon carbide, a potential major constituent of carbon-rich exoplanets. In this work, the atomic-level structure of SiC was determined through in situ X-ray diffraction under laser-driven ramp compression up to 1.5 TPa; stresses more than seven times greater than previous static and shock data. Here we show that the B1-type structure persists over this stress range and we have constrained its equation of state (EOS). Using this data we have determined the first experimentally based mass-radius curves for a hypothetical pure SiC planet. Interior structure models are constructed for planets consisting of a SiC-rich mantle and iron-rich core. Carbide planets are found to be ~10% less dense than corresponding terrestrial planets.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2006

Measuring the Thermophysical and Structural Properties of Glass-Forming and Quasicrystal-Forming Liquids

The thermophysical properties of glass-forming and quasicrystal-forming alloys show many interesting features in the undercooled liquid range. Some of the features in the thermophysical property curves are expected to reflect changes in the structure and coordination of the liquid. These measurements require containerless processing such as electrostatic levitation to access the undercooled liquid regime. An overview of the state of the art in measuring the thermophysical properties and structure of undercooled liquid glass-forming and quasicrystal-forming alloys will be presented, along with the status of current measurements.

Hyers, Robert W.↗
DOE OSTI2021

Dispersion curve regression – assisted wideband local wavenumber analysis for characterizing three-dimensional (3D) profile of hidden corrosion damage

Corrosion as common damage in civil, petrochemical, nuclear, and aerospace structures affects the integrity and safety of the structures and may lead to catastrophic failures. This paper presents dispersion curve regression-assisted local wavenumber analysis method, which can analyze the time–space wavefield containing wideband information of wave-damage interaction and further extract the structural information carried by such wavefield for characterizing hidden corrosion damage in an isotropic plate. To acquire the time–space wavefield, a noncontact scanning laser Doppler vibrometer is used. In our analysis method, the acquired time–space wavefield is firstly processed to generate a local wavenumber function. The derived wavenumber function is further analyzed with a dispersion curve regression step, which searches in a set of theoretical frequency-wavenumber dispersion curves for different plate thicknesses and identifies the optimal plate thickness whose theoretical curve best matches the frequency-wavenumber relation contained in the local wavenumber function. By this means, a 3D profile including both in plane and thickness dimensions of the structure can be constructed for corrosion visualization and quantification. The experimental study demonstrates that our method can quantify the profile of hidden uniform corrosion in metal plates in terms of its in-plane shape and size as well as its out-of-plane depth in the subwavelength scale. Moreover, compared to previous Lamb wave-based corrosion inspection methods, our technique allows for noncontact 3D characterization of hidden corrosion from a far distance to the structure. Finally, we believe this work will inspire new 3D damage quantification methods that are based on wavefield analysis as well as enable potential applications for the quantification of hidden corrosion in civil, petrochemical, nuclear, and aerospace structures.

42 ENGINEERING↗
DOE OSTI2022

A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1929

Curves showing column strength of steel and duralumin tubing

Given here are a set of column strength curves that are intended to simplify the method of determining the size of struts in an airplane structure when the load in the member is known. The curves will also simplify the checking of the strength of a strut if the size and length are known. With these curves, no computations are necessary, as in the case of the old-fashioned method of strut design. The process is so simple that draftsmen or others who are not entirely familiar with mechanics can check the strength of a strut without much danger of error.

Ross, Orrin E↗
NASA NTRS1995

Net-Shape Tailored Fabrics For Complex Composite Structures

Proposed novel looms used to make fabric preforms for complex structural elements, both stiffening elements and skin, from continuous fiber-reinforced composite material. Components of looms include custom reed and differential fabric takeup system. Structural parts made best explained by reference to curved "I" cross-section frame. Technology not limited to these fiber orientations or geometry; fiber angles, frame radius of curvature, frame height, and flange width changed along length of structure. Weaving technology equally applicable to structural skins, such as wing of fuselage skins.

Farley, Gary L.↗
DOE OSTI2019

Probing Reactivity of Gold Atoms with Acetylene and Ethylene with VUV Photoionization Mass Spectrometry and Ab Initio Studies

Reaction of gold atoms with acetylene and ethylene in a laser ablation source produces a number of gold-containing species. Their photoionization efficiency (PIE) curves are measured using tunable vacuum ultraviolet (VUV) radiation at the Advanced Light Source. Their structures are assigned by comparing the experimental ionization energies and PIE curves to those of potential isomers calculated at the CAM-B3LYP/aug-cc-pVTZ level. For smaller molecules, the contribution of ionization to excited electronic states of the cation is also included using photoionization cross sections calculated using ePolyScat . Reaction with acetylene produces adducts Au(C 2 H 2 ) and Au(C 2 H 2 ) 2 , as well as HAu(C 4 H 2 ). Reaction with ethylene leads to adducts Au(C 2 H 4 ), Au(C 2 H 4 ) 2 , an adduct with a gold dimer, Au 2 (C 2 H 4 ), as well as the gold hydrides AuH, HAu(C 2 H 4 ), and HAu(C 4 H 4 ). [Au,C4,H7] is also observed, and it likely corresponds to a gold alkyl, H 2 C$=$C(H)-Au(C 2 H 4 ). Reactions leading to production of odd-hydrogen species are endothermic and are likely due to translationally or electronically excited gold atoms. These measurements provide the first directly measured ionization energy for gold hydride, IE(AuH) = 10.25 ± 0.05 eV. Combining this value with the dissociation energy of AuH + gives a dissociation energy D 0 (AuH) = 3.15 ± 0.12 eV. Several other ionization energies are measured: IE(Au 2 (C 2 H 4 )) = 8.42 ± 0.05 eV, IE(HAu(C 2 H 4 )) = 9.35 ± 0.05 eV, IE(HAu(C 4 H 2 )) = 8.8 ± 0.1 eV, and IE(HAu(C 4 H 4 )) = 8.8 ± 0.1 eV.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗