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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Porosity and Permeability of Chondritic Materials

We have investigated the porosity of a large number of chondritic interplanetary dust particles and meteorites by three techniques: standard liquid/gas flow techniques, a new, non-invasive ultrasonic technique, and image processing of backscattered images . The latter technique is obviously best suited to sub-kg sized samples. We have also measured the gas and liquid permeabilities of some chondrites by two techniques: standard liquid/gas flow techniques, and a new, non-destructive pressure release technique. We find that chondritic IDP's have a somewhat bimodal porosity distribution. Peaks are present at 0 and 4% porosity; a tail then extends to 53%. These values suggest IDP bulk densities of 1.1 to 3.3 g/cc. Type 1-3 chondrite matrix porosities range up to 30%, with a peak at 2%. The bulk porosities for type 1-3 chondrites have the same approximate range as exhibited by matrix, indicating that other components of the bulk meteorites (including chondrules and aggregates) have the same average porosity as matrix. These results reveal that the porosity of primitive materials at scales ranging from nanogram to kilogram are similar, implying similar accretion dynamics operated through 12 orders of size magnitude. Permeabilities of the investigated chondrites vary by several orders of magnitude, and there appears to be no simple dependence of permeability with degree of aqueous alteration, or chondrite type.

Zolensky, Michael E.↗
NASA NTRSDate not supplied

Thermochemical Instabilities at High Temperature Ceramic Surfaces

The surface of silicon-based high temperature ceramics exhibits thermochemical instabilities when exposed to oxygen-rich high enthalpy flows. These instabilities manifest as sudden temperature jumps of several hundred degrees and rapid material failure, when temperatures exceed 2000 K. Understanding and predicting these phenomena is critical to the design of thermal protection systems for sustained high speed flight vehicles. In this talk we review a series of test cases where surface temperature jumps were observed during plasmatron wind tunnel testing of ceramic materials, including ZrB2-SiC ultra-high temperature ceramics, C/SiC ceramic matrix composites, and silicone-based coatings for low-density carbon phenolic ablators. The underlying physical processes occurring when Si-containing ceramics are exposed to high enthalpy air flow include formation of passivating scales at low temperatures, passive to active oxidation transition, melting of oxide scales, changes in surface radiative properties, formation of porosity and changes in effective conductivity, surface catalytic recombination and transitions in catalytic properties, as well as high-temperature phase changes. The role of these processes in promoting thermochemical instabilities for the different material systems is discussed.

Ultra High Temperature Ceramics, UHTC↗
DOE OSTI2022

Slides for MS&T2022: Carbon-Carbon Composites from 3D Printed Preforms Graphitized by Electric Field Assisted Sintering

Formation of Carbon-Carbon (C-C) composite materials requires putting a carbon fiber preform through a cycle of densification, carbonization, and graphitization. This cycle is then repeated until the desired properties are achieved. The graphitization phase is particularly energy demanding as it involves heating the components to in excess of 2000°C. In traditional furnaces this is also quite time consuming as typical heating rates are low, and the actual heat treatment may be limited by component dimensions, as heat is conducted throughout the part primarily by thermal diffusion. Joule heating by means of Electric Field Assisted Sintering (EFAS) systems enables high heating rates and causes the part to be heated from the inside, which eliminates the thermal diffusion time constraint. In our process, C-C composites are formed by pyrolyzation of 3D-printed carbon fiber preforms, vacuum infiltration of naphthalene based mesophase pitch, and carbonization. The part is then graphitized in the EFAS system. By this method graphitization of the composite matrix was achieved in less than an hour. A part density of greater than 1.6g/cc (up to 1.9g/cc demonstrated) was achieved after only two rounds of infiltration and a single graphitization. Overall the process took less than a week which is significantly faster than traditional methods. Optical microscopy and XRD results are discussed to elucidate the internal porosity and characterize the degree of graphitization. Testing was performed showing the impact on fiber direction to electrical and thermal properties of the final part.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Estimation of the Kelvin–Helmholtz Unstable Boundary

The Kelvin–Helmholtz (KH) instability is one of the most important mechanisms of the viscous-like interaction between the solar wind and the magnetosphere (MSP), which transport the mass, energy, momentum, and magnetic flux. Thus, it is important to examine whether the magnetopause boundary is KH unstable or not. Based on the KH onset conditions, this report proposes to use a matrix to identify the most KH unstable direction based on the in situ measurements of the density, velocity, and magnetic field in the MSP and magnetosheath. The range of the KH unstable direction can be easily estimated based on the eigenvalues of the matrix. The eigenvectors of the matrix provide a new boundary normal coordinate system, which could be useful for 2-D KH instability simulation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Rarefied solids

One important limit to creating low density materials is the objects' own weight. As a solid or colloidal matrix becomes more rarefied, gravity acts destructively to compress its suporting skeleton. We describe experimental results and propose a model which matches the low gravity behavior of rarefied or fractal solids. On parabolic airplane flights, we sought to demonstrate a key component of producing higher surface area fractals. Flight paths were selected to give a range of gravity levels: 0.01 g/g(sub 0) (low), 0.16 g(sub 0) (Lunar), 0.33 g/g(sub 0) (Martian), 1 g/g(sub 0) (Earth) and 1.8 g/g(sub 0) (high) (where g(sub 0) = 980 cm/sq s). Results using the model material of hydrophobic silica indicated that stable agglomeration of such tenuous objects can increase markedly in reduced gravity. Optical characterization revealed that fractal dimension changed directly with varying gravity. As measured by fractal dimension, effective surface area and roughness increased by 40% in low gravity. This finding supports the conclusion that relieving internal weight stresses on delicate aggregates can enhance their overall size (by two orders of magnitude) and internal surface area. We conclude that gravitational restructuring limits the overall size and void content of low-density solids. These sparse colloidal regimes may present new and technologically attractive physics, ranging from improved insulators, liquid-like tension in a 'solid' matrix, and characteristically low conductivities for sound and (8 to 14 micrometers wavelength) infrared radiation.

Noever, D. A.↗
DOE OSTI2020

Long-range quadrupole electron-phonon interaction from first principles

Lattice vibrations in materials induce perturbations on the electron dynamics in the form of long-range (dipole and quadrupole) and short-range (octopole and higher) potentials. The dipole Fröhlich term can be included in current first-principles electron-phonon (e-ph) calculations and is present only in polar materials. The quadrupole e-ph interaction is present in both polar and nonpolar materials, but currently it cannot be computed from first principles. In this work, we show an approach to compute the quadrupole e-ph interaction and include it in ab initio calculations of e-ph matrix elements. The accuracy of the approach is demonstrated by comparing with direct density functional perturbation theory calculations. We apply our method to silicon as a case of a nonpolar semiconductor and tetragonal PbTiO 3 as a case of a polar piezoelectric material. In both materials we find that the quadrupole term strongly impacts the e-ph matrix elements. Analysis of e-ph interactions for different phonon modes reveals that the quadrupole term mainly affects optical modes in silicon and acoustic modes in PbTiO 3 , although the quadrupole term is needed for all modes to achieve quantitative accuracy. The effect of the quadrupole e-ph interaction on electron scattering processes and transport is shown to be important. Our approach enables accurate studies of e-ph interactions in broad classes of nonpolar, polar, and piezoelectric materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1981

Effects of multiple scattering and surface albedo on the photochemistry of the troposphere

The effect of treatment of incoming solar radiation on the photochemistry of the troposphere is discussed. A one dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families was developed. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. The photochemical model is coupled to a radiative transfer model that calculates the radiation field due to the incoming solar radiation which initiates much of the photochemistry of the troposphere. Vertical profiles of tropospheric species were compared with the Leighton approximation, radiative transfer, matrix inversion model. The radiative transfer code includes the effects of multiple scattering due to molecules and aerosols, pure absorption, and surface albedo on the transfer of incoming solar radiation. It is indicated that significant differences exist for several key photolysis frequencies and species number density profiles between the Leighton approximation and the profiles generated with, radiative transfer, matrix inversion technique. Most species show enhanced vertical profiles when the more realistic treatment of the incoming solar radiation field is included

Augustsson, T. R.↗
NASA NTRS1985

Superconducting magnet

Extensive computer based engineering design effort resulted in optimization of a superconducting magnet design with an average bulk current density of approximately 12KA/cm(2). Twisted, stranded 0.0045 inch diameter NbTi superconductor in a copper matrix was selected. Winding the coil from this bundle facilitated uniform winding of the small diameter wire. Test coils were wound using a first lot of the wire. The actual packing density was measured from these. Interwinding voltage break down tests on the test coils indicated the need for adjustment of the wire insulation on the lot of wire subsequently ordered for construction of the delivered superconducting magnet. Using the actual packing densities from the test coils, a final magnet design, with the required enhancement and field profile, was generated. All mechanical and thermal design parameters were then also fixed. The superconducting magnet was then fabricated and tested. The first test was made with the magnet immersed in liquid helium at 4.2K. The second test was conducted at 2K in vacuum. In the latter test, the magnet was conduction cooled from the mounting flange end.

Source record↗
DOE OSTI2021

Mechanisms of Ti 3 Al precipitation in hcp α -Ti

Here, nucleation and growth of Ti3Al α( 2 ) ordered domains in alpha-Ti-Al-X alloys were characterised using a combination of transmission electron microscopy, atom probe tomography and small angle X-ray scattering. Model alloys based on Ti-7Al (wt.%) and containing O, V and Mo were aged at 550 °C for times up to 120d and the resulting precipitate dispersions were observed at intermediate points. Precipitates grew to around 30nm in size, with a volume fraction of 6-10% depending on tertiary solutes. Interstitial O was found to increase the equilibrium volume fraction of α 2 , while V and Mo showed relatively little influence. Addition of any of the solutes in this study, but most prominently Mo, was found to increase nucleation density and decrease precipitate size and possibly coarsening rate. Coarsening can be described by the Lifshitz-Slyozov-Wagner model, suggesting a matrix diffusion-controlled coarsening mechanism (rather than control by interfacial coherency). Solutionising temperature was found to affect nucleation number density with an activation energy of E f = 1.5 +/- 0.4 eV, supporting the hypothesis that vacancy concentration affects α 2 nucleation. The observation that all solutes increase nucleation number density is also consistent with a vacancy-controlled nucleation mechanism.

36 MATERIALS SCIENCE↗
NASA NTRS2013

Radiative Transfer Theory Verified by Controlled Laboratory Experiments

We report the results of high-accuracy controlled laboratory measurements of the Stokes reflection matrix for suspensions of submicrometer-sized latex particles in water and compare them with the results of a numerically exact computer solution of the vector radiative transfer equation (VRTE). The quantitative performance of the VRTE is monitored by increasing the volume packing density of the latex particles from 2 to 10. Our results indicate that the VRTE can be applied safely to random particulate media with packing densities up to 2. VRTE results for packing densities of the order of 5 should be taken with caution, whereas the polarized bidirectional reflectivity of suspensions with larger packing densities cannot be accurately predicted. We demonstrate that a simple modification of the phase matrix entering the VRTE based on the so-called static structure factor can be a promising remedy that deserves further examination.

Radiative transfer↗
DOE OSTI2024

Correlations of conserved quantities at finite baryon density

Correlations involving the seven conserved quantities, namely energy, baryon number, electric charge, strangeness, and the three components of momentum, give rise to correlations in heavy-ion collisions. Through the utilization of a simple one-dimensional hydrodynamic model, we calculate the evolution of the entire 7×7 matrix of correlations as a function of relative spatial rapidity. This comprehensive analysis accounts for finite baryon density, which results in off-diagonal correlations between the charge-related quantities and the energy-momentum quantities. These correlations in coordinate space are subsequently transformed into correlations in momentum space using statistical weighting. As a result, the entire matrix of correlations is revealed to be highly sensitive to the equation of state, viscosity, and diffusivity.

Equations of state of nuclear matter↗
DOE OSTI2021

Microstructural and micromechanical characteristics of ultra-high performance concrete with superabsorbent polymer (SAP)

In this study, the hydration product, C-S-H density, and pore structure at different layers from the drying surface were measured. Besides, the zone affected by the released internal curing water from SAP was identified by assessing the nanoindentation modulus. The results found that the SAP affected the moisture distribution and changed the evaporation and self-desiccation rates in the inner and outer layers. Such imposed moisture gradients affected the micromechanical properties of UHPC at different layers due to the change in the hydration degree of the binder, the density of C-S-H, and the pore structure of the matrix. The addition of SAP improved the hydration dynamics and transferred the LD C-S-H into HD or UHD C-S-H. As the distance from the drying surface increased, the affected zone of SAP increased from 60 to 120 μm, showing the more effectiveness of SAP at inner layers.

36 MATERIALS SCIENCE↗
NASA NTRS1997

A novel culture morphology resulting from applied mechanical strain

To demonstrate that cells both perceive and respond to external force, a strain/relaxation regimen was applied to normal human fetal and aged dermal fibroblasts cultured as monolayers on flexible membranes. The precisely controlled protocol of stretch (20% elongation of the culture membrane) at 6.67 cycles/min caused a progressive change in the monolayers, such that the original randomly distributed pattern of cells became a symmetric, radial distribution as the cell bodies aligned parallel to the applied force. High cell density interfered with the success of re-alignment in the fetal cell cultures observed, which may reflect a preference in this cell strain for cell-cell over cell-matrix contacts. The chronologically aged cells observed did not demonstrate this feature, aligning efficiently at all seeding densities examined. The role of microfilaments in force perception and transmission was investigated through the addition of cytochalasin D in graded doses. Both intercellular interactions and cytoskeletal integrity mediate the morphological response to mechanical strain.

NASA Discipline Cell Biology↗
DOE OSTI2023

Development and characterization of a low-density TiNbZrAlTa refractory high entropy alloy with enhanced compressive strength and plasticity

A new refractory high entropy alloy (RHEA) is designed by combining refractory elements Nb and Ta with Ti, Zr, and Al, resulting in a (TiNbZr) 89 (AlTa) 11 alloy composition with a low-density of 6.0 g/cm 3 . The novel RHEA features a BCC matrix with B2 and Zr 5 Al 3 nano precipitates, exhibiting a compressive yield strength of ~890 MPa and specific yield strength of ~148.3 MPa g -1 cm 3 . Remarkably, the alloy demonstrates excellent compressive plasticity of ~70% at 298 K. As the temperature increases to 873 K, 1073 K, and 1273 K, the yield strength of the RHEA gradually decreases to ~610 MPa, ~ 210 MPa, and ~ 60 MPa, respectively. These results indicate that this novel RHEA showcases a combination of good specific strength and plasticity. Post-compression, B2, and Zr 5 Al 3 phases are observed. In conclusion, the second-phase particles dispersed throughout the grains hinder dislocation motion and contribute to the formation of sub-grain boundaries during hot compression.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Influence of defect characteristics on tensile deformation of an additively manufactured stainless steel: Evolutions of texture and intergranular strain

The micromechanics of plastic deformation behavior of a selective laser melt processed austenitic stainless steel were studied by investigating the evolutions of texture and intergranular strain using in situ high-energy synchrotron x-ray diffraction (sXRD). The effects of defect characteristics on tensile behavior were studied using three different samples: a near full-density sample with elliptical closed voids and two samples with lack-of-fusion (LOF) defects tensile loaded either perpendicular or parallel to their major axes. The evolutions of pole figures and inverse pole figures show that the full-density specimen develops a strong (111)/(200) fiber texture along the loading direction. For both LOF specimens, the evolution of texture is qualitatively similar to the full-density counterpart, but the development of the fiber texture was much slower, indicating a limited plasticity at a given macroscopic strain. The intergranular strain evolution in the full-density specimen is similar to that of a wrought 316L stainless steel. Conversely, a significantly different intergranular strain development was observed in a LOF specimen, where tensile strain development was observed in both the axial and transverse directions. Finally, the influence of defect type, density, and orientation on the local stress states in the steel matrix and the evolutions of intergranular strains is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effect of fiber sizing and glass fiber laminate hybridization on vibration damping and mechanical properties of banana fiber reinforced polypropylene composites

Modern automotive applications demand lightweight, multifunctional materials to reach mileage goals and natural fiber reinforced composites (NFRCs) are one of the classes of materials proposed as a solution. NFRCs exhibit good vibration damping properties and have low density, but are often limited by processing challenges, poor-fiber matrix compatibility and variable performance. Herein, we investigate non-woven wet-lay of comingled banana fiber (BF), recycled glass fiber (rGF), and polypropylene (PP) fibers to in situ sizing and preparation of composite feedstocks for compression molding. BF and rGF hybrids were prepared by stacking rGF layers during compression molding to produce composites with various fiber ratios. The effect of fiber content, in-situ sizing and ratio of BF to rGF on tensile, flexural and vibration damping performance are investigated. Key results are the significant increase in tensile strength by in situ sizing (40 % sized at 60 wt% BF) and in flexural modulus (+58 % sized at 60 wt% BF) and flexural strength (+41 % sized 60 wt% BF) compared to the unsized equivalent. For BF-rGF hybrid composites with40 wt% total fiber content, flexural strength and modulus were improved by 51 % and 231 % respectively for a 1:1 ratio BF:rGF compared to BF reinforced system. Lastly, identifying the cross-over point where damping and stiffness are optimized for a hybrid composite. These findings demonstrate that these composites can be used as alternative to synthetic fiber or mineral filled composites in automotive applications, particularly where weight reduction, vibration damping and stiffness are desired.

Banana fiber↗
DOE OSTI2020

Basis light-front quantization for a chiral nucleon-pion Lagrangian

We present the first application of the basis light-front quantization method to a simple chiral model of the nucleon-pion system as a relativistic bound state for the physical proton. In this work, the light-front mass-squared matrix of the nucleon-pion system is obtained within a truncated basis. The mass and the corresponding light-front wave function (LFWF) of the proton are computed by numerical diagonalization of the resulting mass-squared matrix. With the boost-invariant LFWF, we calculate the probability density distribution of the pion's longitudinal momentum fraction and the Dirac form factor of the proton.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1993

Plastic Foam Withstands Greater Temperatures And Pressures

Improved plastic foam suitable for use in foam-core laminated composite parts and in tooling for making fiber/matrix-composite parts. Stronger at high temperatures, more thermally and dimensionally stable, machinable, resistant to chemical degradation, and less expensive. Compatible with variety of matrix resins. Made of polyisocyanurate blown with carbon dioxide and has density of 12 to 15 pounds per cubic feet. Does not contibute to depletion of ozone from atmosphere. Improved foam used in cores of composite panels in such diverse products as aircraft, automobiles, railroad cars, boats, and sporting equipment like surfboards, skis, and skateboards. Also used in thermally stable flotation devices in submersible vehicles. Machined into mandrels upon which filaments wound to make shells.

Cranston, John A.↗