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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Initial evaluation of continuous fiber reinforced NiAl composites

NiAl is being evaluated as a potential matrix material as part of an overall program to develop and understand high-temperature structural composites. Currently, continuous fiber composites have been fabricated by the powder cloth technique incorporating either W(218) or single crystal Al2O3 fibers as reinforcements in both binary NiAl and a solute strengthened NiAl(.05 at. pct Zr) matrix. Initial evaluation of these composite systems have included: fiber push-out testing to measure matrix/fiber bond strengths, bend testing to determine strength as a function of temperature and composite structure, and thermal cycling to establish the effect of matrix and fiber properties on composite life. The effect of matrix/fiber bond strength and matrix strength on several composite properties will be discussed.

Noebe, R. D.↗
NASA NTRSDate not supplied

Geopolymer Lunar Concrete under Reduced-Pressure Curing and Vacuum Exposure

Geopolymer concrete has emerged as a promising material for constructing habitats, roads, landing pads, and other necessary infrastructure on the lunar surface. Proper in-situ resource utilization (ISRU) is an important aspect of any candidate lunar construction material. Geopolymer concrete is effective at ISRU, as the lunar regolith can be used in the “as found” condition and mixed with an alkaline solution, such as sodium silicate and sodium hydroxide, which could also be mostly produced in-situ. It is envisioned that any concrete material on the lunar surface would be deposited with additive manufacturing techniques and would require a temporary environmental enclosure to mitigate the harsh lunar environment during construction and curing, such as pressure and temperature. Data are needed to set a benchmark for the conditions to be achieved within the deployable environmental enclosure during printing, as well as the resultant material properties after the enclosure is removed. This novel study investigated the influence of reduced atmospheric pressures during the initial curing period on the compressive strength of geopolymer lunar concrete created with two types of lunar regolith simulant. The simulants used in the study represent the regolith for the lunar mare (OPRL2N) and lunar highlands (OPRH2N) regions. Results show a noticeable decline in strength with a reduction in pressure and visible degradation. After the deployable environmental enclosure is removed from the printed segment of infrastructure on the lunar surface, it would then be exposed to the harsh vacuum environment. To understand the importance of curing time required within the deployable enclosure before it is removed, samples were cast and cured for different lengths of time and then exposed to a vacuum chamber capable of achieving 100 mTorr. Control samples were also cast at the same time but left in a standard laboratory environment after curing. The weight change and compressive strength as a function of time in the vacuum chamber were monitored for up to 56 days. The results showed that exposure to the vacuum limits further reaction and strength gain in comparison to control samples left in the laboratory environment. This research is in strong alignment with the 2020 NASA Technology Taxonomy materials area (12.1) and the in-situ resource utilization area (7.1), as it provides necessary data on the geopolymer lunar concrete material to support safe and sustainable options for maintaining a human presence on the Moon.

Moon to Mars Planetary Autonomous Construction Tec↗
DOE OSTI2017

Effects of interaction strength, doping, and frustration on the antiferromagnetic phase of the two-dimensional Hubbard model

Recent quantum-gas microscopy of ultracold atoms and scanning tunneling microscopy of the cuprates reveal new detailed information about doped Mott antiferromagnets, which can be compared with calculations. Using cellular dynamical mean-field theory, we map out the antiferromagnetic (AF) phase of the two-dimensional Hubbard model as a function of interaction strength U, hole doping δ, and temperature T . The Néel phase boundary is nonmonotonic as a function of U and δ. Frustration induced by second-neighbor hopping reduces Néel order more effectively at small U. The doped AF is stabilized at large U by kinetic energy and at small U by potential energy. The transition between the AF insulator and the doped metallic AF is continuous. At large U, we find in-gap states similar to those observed in scanning tunneling microscopy. Finally, we predict that, contrary to the Hubbard bands, these states are only slightly spin polarized.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Stability of new exact solutions of the nonlinear Schrödinger equation in a Pöschl–Teller external potential

Here, we discuss the stability properties of the solutions of the general nonlinear Schrödinger equation in 1 + 1 dimensions in an external potential derivable from a parity-time ($ \newcommand{\PT}{\mathcal{PT}} \PT$ ) symmetric superpotential $W(x)$ that we considered earlier in Kevrekidis et al (2015 Phys. Rev. E 92 042901). In particular we consider the nonlinear partial differential equation $ \{i \, \partial_t + \partial_x^2 - V(x) + g \vert \psi(x, t) \vert ^{2\kappa} \} \, \psi(x, t) = 0 \>, $ for arbitrary nonlinearity parameter κ, where $g= \pm1$ and V is the well known Pöschl–Teller potential which we allow to be repulsive as well as attractive. Using energy landscape methods, linear stability analysis as well as a time dependent variational approximation, we derive consistent analytic results for the domains of instability of these new exact solutions as a function of the strength of the external potential and κ. For the repulsive potential we show that there is a translational instability which can be understood in terms of the energy landscape as a function of a stretching parameter and a translation parameter being a saddle near the exact solution. In this case, numerical simulations show that if we start with the exact solution, the initial wave function breaks into two pieces traveling in opposite directions. If we explore the slightly perturbed solution situations, a 1% change in initial conditions can change significantly the details of how the wave function breaks into two separate pieces. For the attractive potential, changing the initial conditions by 1% modifies the domain of stability only slightly. For the case of the attractive potential and negative g perturbed solutions merely oscillate with the oscillation frequencies predicted by the variational approximation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Mesoscale Phase Field Modeling of Glass Strengthening Under Triaxial Compression

Recent hydraulic bomb and confined sleeve tests on transparent armor glass materials such as borosilicate glass and soda-lime glass showed that the glass strength was a function of confinement pressure. The measured stress-strain relation is not a straight line as most brittle materials behave under little or no confinement. Moreover, borosilicate glass exhibited a stronger compressive strength when compared to soda-lime glass, even though soda-lime has higher bulk and shear moduli as well as apparent yield strength. To better understand these experimental findings, a mesoscale phase field model is developed to simulate the nonlinear stress versus strain behaviors under confinement by considering heterogeneity formation under triaxial compression and the energy barrier of a micro shear banding event (referred to as pseudo-slip hereafter) in the amorphous glass. With calibrated modeling parameters, the simulation results demonstrate that the developed phase field model can quantitatively predict the pressure-dependent strength, and it can also explain the difference between the two types of glasses from the perspective of energy barrier associated with a pseudo-slip event.

Confined Borosilicate↗
NASA NTRS2024

Residual Strength of Hypervelocity Impacted Silica

Windows in the International Space Station (ISS) are subject to ongoing micrometeoroid and orbital debris (MMOD) damage. The reliability of the windows is ensured by monitoring of damage, life prediction, and measurement of the residual strength of man-made and natural hypervelocity impacted window materials. Information on the residual strength of man-made craters and MMOD craters harvested from space shuttle windows was used to estimate strength as a function of damage dimensions and thereby derive design allowables for U.S. and Russian fused silicas used in the ISS. An effect of impact angle is apparent, with 0° impacts exhibiting the lowest strength for Russian quartz-derived silica. The crater morphology for fused silica consists of a central pit, crush zone, shallow rings, and radial cracks dividing shallow, petal-like lateral cracks (petaloids). The morphology of alkaline glass differs from that of fused silica, with a more distinct pit and pulverized region, and bell-shaped and tail-like features below the pit.

International space station,↗
DOE OSTI2017

Experimental determination of solubilities of di-calcium ethylenediaminetetraacetic acid hydrate [Ca2C10H12N2O8·7H2O(s)] in NaCl and MgCl2 solutions to high ionic strengths and its Pitzer model: Applications to geological disposal of nuclear waste and other low temperature environments

In this study, solubility measurements on di-calcium ethylenediaminetetraacetic acid [Ca 2 C 10 H 12 N 2 O 8 (s), abbreviated as Ca 2 EDTA(s)] as a function of ionic strength are conducted in NaCl solutions up to I = 5.0 mol•kg –1 and in MgCl 2 solutions up to I = 7.5 mol•kg –1 , at room temperature (22.5 ± 0.5oC).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Exploring the limit of accuracy for density functionals based on the generalized gradient approximation: Local, global hybrid, and range-separated hybrid functionals with and without dispersion corrections

The limit of accuracy for semi-empirical generalized gradient approximation (GGA) density functionals is explored by parameterizing a variety of local, global hybrid, and range-separated hybrid functionals. The training methodology employed differs from conventional approaches in 2 main ways: (1) Instead of uniformly truncating the exchange, same-spin correlation, and opposite-spin correlation functional inhomogeneity correction factors, all possible fits up to fourth order are considered, and (2) Instead of selecting the optimal functionals based solely on their training set performance, the fits are validated on an independent test set and ranked based on their overall performance on the training and test sets. The 3 different methods of accounting for exchange are trained both with and without dispersion corrections (DFT-D2 and VV10), resulting in a total of 491 508 candidate functionals. For each of the 9 functional classes considered, the results illustrate the trade-off between improved training set performance and diminished transferability. Since all 491 508 functionals are uniformly trained and tested, this methodology allows the relative strengths of each type of functional to be consistently compared and contrasted. The range-separated hybrid GGA functional paired with the VV10 nonlocal correlation functional emerges as the most accurate form for the present training and test sets, which span thermochemical energy differences, reaction barriers, and intermolecular interactions involving lighter main group elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2000

How Molecular Structure Affects Mechanical Properties of an Advanced Polymer

density was performed over a range of temperatures below the glass transition temperature. The physical characterization, elastic properties and notched tensile strength all as a function of molecular weight and test temperature were determined. For the uncrosslinked SI material, it was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature. For the crosslinked PETI-SI material, it was shown that the effect of crosslinking significantly enhances the mechanical performance of the low molecular weight material; comparable to that exhibited by the high molecular weight material.

Nicholson, Lee M.↗
DOE OSTI2015

Non-Gaussian wave packet dynamics in anharmonic potential: Cumulant expansion treatment

This manuscript utilizes cumulant expansion as an alternative algebraic approach to evaluating integrals and solving a system of nonlinear differential equations for probing anharmonic dynamics in condensed phase systems using Morse oscillator. These integrals and differential equations become harder to solve as the anharmonicity of the system goes beyond that of Morse oscillator description. This algebraic approach becomes critically important in case of Morse oscillator as it tends to exhibit divergent dynamics and numerical uncertainties at low temperatures. The autocorrelation function is calculated algebraically and compared to the exact one for they match perfectly. It is also compared to the approximate autocorrelation function using the differential equations technique reported in Toutounji (2014) for weak and strong electron–phonon coupling cases. It is found that the present cumulant method is more efficient, and easier to use, than the exact expression. Deviation between the approximate autocorrelation function and the exact autocorrelation function starts to arise as the electron–phonon coupling strength increases. The autocorrelation function obtained using cumulants identically matches the exact autocorrelation function, thereby surpassing the approach presented in Toutounji (2014). The advantage of the present methodology is its applicability to various types of electron–phonon coupling cases. Additionally, the herein approach only uses algebraic techniques, thereby avoiding both the divergence integral and solving a set of linear first- and second-order partial differential equations as was done in previous work. Model calculations are presented to demonstrate the accuracy of the herein work.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1983

Oscillator strengths and collision strengths for S II

Calculations are presented of the collision strengths for electron impact excitation of S II from the ground 3s(2)3p(3)(4)S0 state to excited states 3s3p(4)(4)p, 3s(2(3p(2)4s(4)P, and 3s(2)3p(2)3d(4)P. The collision strengths are calculated in a close-coupling approximate ion for the energy range up to 10 to the 6th K. In addition, oscillator strengths are given for these transitions, as well as for some UV lines which have lower states 3s(2)3p(3)(2)D(O) and 3s(2)3p(3)(2)P(0). The calculation of the collision strengths involves the use of configuration interaction target wave functions which give oscillator strengths accurate to 30 percent in most cases.

Ho, Y. K.↗
DOE OSTI2017

Experimental Determination of Solubilities of Tri-calcium Di-Citrate Tetrahydrate [Ca 3 [C 3 H 5 O(COO) 3 ] 2 •4H 2 O] Earlandite in NaCl and MgCl 2 Solutions to High Ionic Strengths and Its Pitzer Model: Applications to Nuclear Waste Isolation and Other Low Temperature Environments

In this study, solubility measurements on tri-calcium di-citrate tetrahydrate [Ca 3 [C 3 H 5 O(COO) 3 ]2•4H 2 O, abbreviated as Ca 3 [Citrate] 2 •4H 2 O] as a function of ionic strength are conducted in NaCl solutions up to I = 5.0 mol•kg –1 and in MgCl 2 solutions up to I = 7.5 mol•kg –1 , at room temperature (22.5 ± 0.5°C). The solubility constant (log K$0\atop{sp}$) for Ca 3 [Citrate] 2 •4H 2 O and formation constant (logβ$0\atop{1}$) for Ca[C 3 H 5 O(COO) 3 ] – Ca 3 [C 3 H 5 O(COO) 3 ] 2 •4H 2 O (earlandite) = 3Ca 2+ + 2[C 3 H 5 O(COO) 3 ] 3– + 4H 2 O (1) Ca 2+ + [C 3 H 5 O(COO) 3 ] 3– = Ca[C 3 H 5 O(COO) 3 ] – (2) are determined as –18.11 ± 0.05 and 4.97 ± 0.05, respectively, based on the Pitzer model with a set of Pitzer parameters describing the specific interactions in NaCl and M g Cl 2 media.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1986

The behavior of fuel-lean premixed flames in a standard flammability limit tube under controlled gravity conditions

Fuel-lean flames in methane-air mixtures from 4.90 to 6.20 volume percent fuel and propane-air mixtures from 1.90 to 3.00 volume percent fuel were studied in the vicinity of the limit for a variety of gravity conditions. The limits were determined and the behavior of the flames studied for one g upward, one g downward, and zero g propagation. Photographic records of all flammability tube firings were obtained. The structure and behavior of these flames were detailed including the variations of the curvature of the flame front, the skirt length, and the occurrence of cellular instabilities with varying gravity conditions. The effect of ignition was also discussed. A survey of flame speeds as a function of mixture strength was made over a range of lean mixture compositions for each of the fuels studied. The results were presented graphically with those obtained by other researchers. The flame speed for constant fractional gravity loadings were plotted as a function of gravity loadings from 0.0 up to 2.0 g's against flame speeds extracted from the transient gravity flame histories for corresponding gravity loadings. The effects of varying gravity conditions on the extinguishment process for upward and downward propagating flames were investigated.

Wherley, B. L.↗
NASA NTRSDate not supplied

Residual Strength of Hypervelocity Impacted Silica

Windows in the International Space Station are subjected to on-going micrometeoroid and orbital debris damage (MMOD). The reliability of the windows is being ensured by monitoring of damage, life prediction, and measurement of the residual strength of man-made and natural hypervelocity impact damage. The residual strength of man-made craters and MMOD craters harvested from space shuttle windows were used to estimate strength as a function of damage dimensions and thereby derive design allowables for U.S. and Russian fused silicas used in the ISS. US and Russian silica exhibit similar mechanical properties. An effect of impact angle is apparent, with 0o impacts exhibiting the lowest strength for Russian quartz-derived silica. The crater morphology for fused silica consists of a central pit, crush zone, shallow rings and radial cracks dividing petaloids. Morphology of alkaline glass is different from than that of fused silica, with a more distinct pit and pulverized region, and bell and tail-like features below the pit.

Silicia↗
NASA NTRS1999

Effect of Interface Shape and Magnetic Field on the Microstructure of Bulk Ge:Ga

Thermal and compositional gradients induced during the growth process contribute significantly to the development of defects in the solidified boule. Thermal gradients and the solid-liquid interface shape can be greatly effected by ampoule material. Compositional gradients are strongly influenced by interface curvature and convective flow in the liquid. Results of this investigation illustrate the combined influences of interface shape and convective fluid flow. An applied magnetic field was used to reduce the effects of convective fluid flow in the electrically conductive melt during directional solidification. Several 8 mm diameter boules of Ga-doped Ge were grown at different field strengths, up to 5 Tesla, in four different ampoule materials. Compositional profiles indicate mass transfer conditions ranged from completely mixed to diffusion controlled. The influence of convection in the melt on the developing crystal microstructure and defect density was investigated as a function of field strength and ampoule material. Chemical etching and electron backscattered electron diffraction were used to map the crystal structure of each boule along the center plane. Dislocation etch pit densities were measured for each boule. Results show the influence of magnetic field strength and ampoule material on overall crystal quality.

Cobb, S. D.↗
NASA NTRS1983

Plasma polymerized high energy density dielectric films for capacitors

High energy density polymeric dielectric films were prepared by plasma polymerization of a variety of gaseous monomers. This technique gives thin, reproducible, pinhole free, conformable, adherent, and insoluble coatings and overcomes the processing problems found in the preparation of thin films with bulk polymers. Thus, devices are prepared completely in a vacuum environment. The plasma polymerized films prepared all showed dielectric strengths of greater than 1000 kV/cm and in some cases values of greater than 4000 kV/cm were observed. The dielectric loss of all films was generally less than 1% at frequencies below 10 kHz, but this value increased at higher frequencies. All films were self healing. The dielectric strength was a function of the polymerization technique, whereas the dielectric constant varied with the structure of the starting material. Because of the thin films used (thickness in the submicron range) surface smoothness of the metal electrodes was found to be critical in obtaining high dielectric strengths. High dielectric strength graft copolymers were also prepared. Plasma polymerized ethane was found to be thermally stable up to 150 C in the presence of air and 250 C in the absence of air. No glass transitions were observed for this material.

Yamagishi, F. G.↗
DOE OSTI2024

Intern Poster

Digital Image Correlation (DIC) is an optical technique that combines image registration and tracking methods for accurate two-dimensional and three-dimensional changes in images. DIC software can be used to track the contour, deformation, and strain of a sample. In the Advanced Test Reactor (ATR) at INL (Idaho National Laboratory) there exists a small working window of samples that can become irradiated. Hundreds of graphite disks called piggybacks have undergone this irradiation as part of the Advanced Reactor Technologies (ART) program. After irradiation, it is desirable to understand the change in tensile strength as a function of dose. Due to the limited space in the ATR, typical dog bone tensile tests reduce the number of graphite samples from hundreds to tens. However, there does exist an ASTM standard, D8289, which uses disc compression of graphite to estimate the tensile strength of the specimen with the Brazilian Disk test fixture. While only used as an estimate, which is typically off by a third, it is the purpose of this study to identify how to amend D8289 to remove the word "estimate" with the help of DIC.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Intersublattice magnetocrystalline anisotropy using a realistic tight-binding method based on maximally localized Wannier functions

Using a realistic tight-binding Hamiltonian based on maximally localized Wannier functions, we investigate the two-ion magnetocrystalline anisotropy energy (MAE) in L 1 0 transition metal compounds. MAE contributions from throughout the Brillouin zone are obtained using magnetic force theorem calculations with and without perturbation theory. The results from both methods agree with each other, and both reflect features of the Fermi surface. The intrasublattice and intersublattice contributions to MAE are evaluated using a Green's function method. We find that the sign of the intersublattice contribution varies among compounds, and that its amplitude may be significant, suggesting MAE can not be resolved accurately in a single-ion manner. The results are further validated by scaling spin-orbit-coupling strength in density functional theory. Altogether, this realistic tight-binding method provides an effective approach to evaluate and analyze MAE while retaining the accuracy of corresponding first-principles methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗