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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

A Report on the Activities, Publications, and Pending Research of DHS/DOD Sponsored Post-doctoral Research Associate at Los Alamos National Laboratory

Since beginning at Los Alamos National Laboratory in February of 2012, I have been working as a DHS./DNDO Postdoctoral Research Associate under the mentorship of Lav Tandon and Khalil Spencer (NA-22 and mass spectrometry). The focus of my efforts, in addition to pursuing needed training and qualifications, has been the application of various instrumental approaches (e.g. Thermal Ionization Mass Spectrometry; TIMS) to a range of systems of interest in materials characterization and nuclear forensics. Research to be pursued in the coming months shall include the continued use of such approaches to advance current methods for: modified total evaporation, monitoring critical minor isotope systems, and chronometry. Each of the above points will be discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1988

Kinetic isolation tether experiment

Progress was made on the analysis of tether damping and on experimentation of the control system on the laboratory simulator. The damping analysis considers the dynamics of a long tether connecting two spacecraft in Earth orbit, one of the spacecraft having dominant mass. In particular, it considers the material damping of the tether. The results show that, with properly chosen tether material and braiding structure, longitudinal vibration of the tethered system is well damped. A particularly effective method of implementing attitude control for tethered satellites is to use the tether tension force to generate control torques by moving the tether attach point relative to the satellite center of mass. A scaled, one dimensional laboratory simulation of the KITE mission was built and preliminary experiments of the proposed attitude control system were performed. The simulator was built to verify theoretical predictions of attitude controllability, and to investigate the technological requirements in order to implement this concept. A detailed description of the laboratory apparatus is provided, and in addition, the results of the preliminary experiments are presented and discussed.

Powell, J. David↗
NASA NTRS1989

Measuring Thermal Conductivities Of Rough Specimens

Thermal conductivity of irregularly surfaced specimen measured more accurately and reliably by use of heat-transfer adhesive establishing contact between specimen and reference standards. Method useful when specimen made up of fragments of material. Adhesive ensures good thermal contact to pieces not matching others in height. In rough-surfaced or unequally sized specimens, heat-flow pattern becomes distorted, and temperatures at measurement points do not accurately represent those throughout reference standards and specimen. Filling voids with conductive adhesive restores nearly uniform distribution heat flow.

Striepens, Aloys H.↗
NASA NTRS2016

Experimental Investigation of the Distribution of Shock Effects in Regolith Impact Ejecta Using an Ejecta Recovery Chamber

Because the mass-flux of solar system meteoroids is concentrated in the approx. 200 microns size range, small-scale impacts play a key role in driving the space weathering of regoliths on airless bodies. Quantifying this role requires improved data linking the mass, density and velocity of the incoming impactors to the nature of the shock effects produced, with particular emphasis on effects, such as production of impact melt and vapor, that drive the optical changes seen in space weathered regoliths. Of particular importance with regard to space weathering is understanding not only the composition of the shock melt created in small-scale impacts, but also how it is partitioned volumetrically between the local impact site and more widely distributed ejecta. To improve the ability of hypervelocity impact experiments to obtain this type of information, we have developed an enclosed sample target chamber with multiple-geometry interior capture cells for in-situ retention of ejecta from granular targets. A key design objective was to select and test capture cell materials that could meet three requirements: 1) Capture ejecta fragments traveling at various trajectories and velocities away from the impact point, while inducing minimal additional damage relative to the primary shock effects; 2) facilitate follow-up characterization of the ejecta either on or in the cell material by analytical SEM, or ex-situ by microprobe, TEM and other methods; and 3) enable the trajectories of the captured and characterized ejecta to be reconstructed relative to the target.

Christoffersen, R.↗
NASA NTRS2019

Integration of MAC/GMC into CalculiX, an Open Source Finite Element Code

An analysis framework is presented that makes available multiscale analysis of composite structures using the open-source FEA solver package CalculiX CrunchiX (CCX). At the center of this framework is the coupling of the Finite Element Analysis - Micromechanics Analysis Code (FEAMAC) library from NASA's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) to allow micromechanics analysis. The results show that the proposed coupling can be used with appropriate care for multiscale FEA simulations of composite materials. The largest error reported in this validation was in a four-point bend test specimen with an error of less than 1% difference in the maximum deflection of the beam.

Yapor Genao, Francisco A.↗
NASA NTRS2019

Validation of Floating Node Method Using Three-Point Bend Doubler Under Quasi-Static Loading

The NASA Advanced Composite Project (ACP), an industry/government/university partnership, has embarked upon the task of developing technology that can aid in reducing the time line for structural certification of aircraft composite parts using a combination of technologies, one of which is high fidelity damage progression computational methods. Phase II of this project included a task for validating an approach based on the Floating Node Method combined with Directional Cohesive Elements (FNM-DCZE). This paper discusses predicted damage onset and growth in a three-point bend doubler specimen compared to experimental results. Sensitivity of the simulations to mesh refinement as well as key material properties and thermal effects are studied and reported. Overall, qualitative results suggest the main aspects of the damage progression have been captured, with the simulated damage morphology and sequence of events resembling closely what was observed experimentally. Quantitatively, the first load-peak is predicted. However, the re-loading observed in the experiments, after the first load peak, is not captured numerically, suggesting further investigation may be worth pursuing.

Selvarathinam, Alex S.↗
DOE OSTI2021

Optoelectronic property comparison for isostructural Cu 2 BaGeSe 4 and Cu 2 BaSnS 4 solar absorbers

To target mitigation of anti-site defect formation in Cu 2 ZnSnS 4–x Se x , a new class of chalcogenides, for which Ba or Sr (group 2) replace Zn (group 12), has recently been introduced for prospective solar absorber application. Cu 2 BaGeSe 4 (CBGSe) and Cu 2 BaSnS 4 (CBTS) are two such compounds, which share a common trigonal crystal structure (P3 1 space group) and similar quasi-direct band gap (~2 eV). While CBTS-based films have already been studied, there are no reports yet on films and solar cells based on related CBGSe. To identify key differences and similarities in the electronic properties between these two materials, electronic characteristics (e.g., carrier concentration, mobility, electron affinity, defect levels, recombination, and charge carrier kinetics) of vacuum-deposited CBGSe and CBTS films are compared using a variety of characterization methods. Hall effect measurements reveal that CBGSe films have relatively higher hole carrier concentration and lower mobility (3 × 10 15 cm –3 , 0.6 cm 2 V –1 s –1 ) compared to CBTS (5 × 10 12 cm –3 , 3.5 cm 2 V –1 s –1 ). Photoelectron spectroscopy yields low electron affinity values for both CBGSe (3.7 eV) and CBTS (3.3 eV), pointing to the necessity of pursuing low electron affinity buffer materials for both types of absorbers. At low temperatures, CBGSe films show free-exciton photoluminescence, as well as pronounced deep-level emission at ~1.4 eV, while CBTS films exhibit a strong bound-exciton signal with noticeably less intense deep-level emission than for CBGSe. Charge carrier kinetics, transport, and recombination properties of both types of films are also analyzed using optical-pump terahertz-probe spectroscopy and time-resolved microwave conductivity. The first CBGSe prototype solar cells (using chemical bath deposited CdS as a buffer layer) show a maximum of 1.5% efficiency with ~0.62 V open-circuit voltage. Furthermore, the measured properties point to possible limiting factors for CBGSe and related films for PV and optoelectronics and provide insights on possible approaches for improvement within this multinary chalcogenide family.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Electronic structure of LaBr 3 from quasiparticle self-consistent G W calculations

Rare-earth-based scintillators in general and lanthanum bromide (LaBr3) in particular represent a challenging class of materials due to pronounced spin-orbit coupling and subtle interactions between d and f states that cannot be reproduced by standard density functional theory (DFT). Here a detailed investigation of the electronic band structure of LaBr3 using the quasiparticle self-consistent GW (QPscGW) method is presented. This parameter-free approach is shown to yield an excellent description of the electronic structure of LaBr 3 . Specifically, it is able to reproduce the band gap, the correct level ordering and spacing of the 4f and 5d states, as well as the spin-orbit splitting of La-derived states. The QPscGW results are subsequently used to benchmark several computationally less demanding techniques including DFT+U, hybrid exchange-correlation functionals, and the G 0 W 0 method. Spin-orbit coupling is included self-consistently at each QPscGW iteration and maximally localized Wannier functions are used to interpolate quasiparticle energies. The QPscGW results provide an excellent starting point for investigating the electronic structure of excited states, charge self-trapping, and activator ions in LaBr 3 and related materials.

36 MATERIALS SCIENCE↗
NASA NTRS1991

The effects of space radiation on thin films of YBa2Cu3O(7-x)

This investigation had two objectives: (1) to determine the effects of space radiation on superconductor parameters that are most important in space applications; and (2) to determine whether this effect can be simulated with Co-60 gamma rays, the standard test method for space materials. Thin films of yttrium barium copper oxide (YBCO) were formed by coevaporation of Y, BaF2, and Cu and post-annealing in wet oxygen at 850 C for 3.5 h. The substrate used was (100) silicon with an evaporated zirconia buffer layer. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were the zero resistance transition temperature T(sub c) and the room temperature resistance. The samples were then exposed to Co-60 gamma-rays in air and in pure nitrogen, and to 780 keV electrons, in air. The parameters were then remeasured. The results are summarized. The results indicate little or no degradation in the parameters measured for samples exposed up to 10 Mrads of gamma-rays in nitrogen. However, complete degradation is preliminarily attributed to the high level of ozone generated in the chamber by the gamma-ray interaction with air. It can be concluded that: (1) the electron component of space radiation does not degrade the critical temperature of the YBCO films described, at least for energies around 800 keV and doses similar to those received by surface materials on spacecraft in typical remote sensing missions; and (2) for qualifying this and other superconducting materials against the space-radiation threat the standard test method used in the aerospace industry, namely, exposure to Co-60 gamma-rays in air, may require some further investigation. As a minimum, the sample must be either in vacuum or in positive nitrogen pressure.

Herschitz, R.↗
DOE OSTI2021

Atomistic modeling of meso -timescale processes with $\mathrm{SEAKMC}$: A perspective and recent developments

On-the-fly kinetic Monte Carlo (kMC) methods have recently garnered significant attentions after successful applications to various atomic-scale problems using a timescale outside the reach of classical molecular dynamics. These methods play a critical role in modeling atomistic meso-timescale processes, and it is therefore essential to further improve their capabilities. In this report we review one of the on-the-fly kMC methods, Self-Evolving Atomistic kinetic Monte Carlo (SEAKMC) and propose two schemes that considerably enhance the efficiency of saddle point searches (SPSs) during the simulations. The performance of these schemes is tested using the diffusion of point defects in bcc Fe. In addition, we discuss approaches to significantly mitigate limitations of these schemes, which further improves their efficiencies. Importantly, these schemes improve the SPS efficiency not only for SEAKMC but also for other on-the-fly kMC methods, broadening the applications of on-the-fly kMC simulations to complex meso-timescale problems.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Evolution of microstructures in radiation fields using a coupled binary-collision Monte Carlo phase field approach

The simulation of radiation effects in materials broadly falls into two categories. At short time and length scales lies the modeling of primary radiation damage, such as point defect creation, energy deposition, and ballistic mixing. This is followed by the modeling at longer time scales of thermally activated microstructure evolution and defect reactions, such as recombination, clustering, and coarsening. The binary collision Monte Carlo method is an established, numerically efficient method for the computation of primary radiation damage. Conversely, the phase field method is a state of the art method for microstructure evolution on longer time and length scales. Here we present a concurrent coupling of these two methods, overcoming the difference between the discrete object Monte Carlo paradigm for primary radiation damage and the continuum field variable approach for microstructure evolution. The coupling is bidirectional, in which the microstructure evolution in the MOOSE finite element frame- work provides the spatial scattering data set for the charged particle trans- port and receives point defect, mass transport, and heat source terms from the simulated collision cascades that contribute to the field variable evolution. The concurrent coupling scheme is implemented in the code Magpie and demonstrated by investigating patterning for a model irradiated immiscible binary alloy. The results from the coupled binary collision Monte Carlo/phase field simulations reproduce the results of analytical models for phase separation, phase mixing, and patterning, supporting the approach and indicating its utility for modeling real materials systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

Significance Producing strong and defect-free materials is an important objective in developing many new materials. Thermal treatments aimed at defect elimination often lead to undesirable levels of strength and other properties. Although monotonic loading can reduce or even eliminate dislocations in submicroscale single crystals, such “mechanical healing” causes severe plastic deformation and significant shape changes. Inspired by observing an easier pullout of a partly buried object after shaking it first, we demonstrate that “cyclic healing” of the small-volume single crystals can indeed be achieved through repeated low-amplitude straining. The cyclic healing method points to versatile avenues for tailoring the defect structure and strengthening of nanoscale metal crystals without the need for thermal annealing or severe plastic deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Barkhausen noise as an intrinsic fingerprint for ferromagnetic components

Here in this work, the suitability of magnetic Barkhausen noise as an intrinsic fingerprint of ferromagnetic components is determined. This technique has potential for this application because it is based inherently on the near surface microstructural features of ferromagnetic materials. All materials typically display some variation in their microstructure simply as a result of the manufacturing process (rolling, heat treating, welding, grinding), thus providing the potential that Barkhausen noise measurements between nominally similar components will be unique. In this work, we demonstrate that Barkhausen noise measurements are both repeatable in time for a single sample made from a ferromagnetic material, and unique across a number of instances of nominally similar samples. The results of this work have profound implications in a variety of applications in forensics and physical security. For example, consider the fabrication of the next generation of tamper-evident containers and devices using conventional processes for steel. In addition, since Barkhausen noise is sensitive to changes in microstructures due to grinding and welding, these measurements can be used to detect clandestine repairs and tampering. Finally, because the method inherently results in a time series measurement at each point on a sample, it is expected to have far higher dimensionality than physically similar eddy current measurement. However, the higher dimensionality of Barkhausen measurements suggest that they should be harder to counterfeit than eddy current measurements.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Geometrically Nonlinear Static Analysis of 3D Trusses Using the Arc-Length Method

Rigorous analysis of geometrically nonlinear structures demands creating mathematical models that accurately include loading and support conditions and, more importantly, model the stiffness and response of the structure. Nonlinear geometric structures often contain critical points with snap-through behavior during the response to large loads. Studying the post buckling behavior during a portion of a structure's unstable load history may be necessary. Primary structures made from ductile materials will stretch enough prior to failure for loads to redistribute producing sudden and often catastrophic collapses that are difficult to predict. The responses and redistribution of the internal loads during collapses and possible sharp snap-back of structures have frequently caused numerical difficulties in analysis procedures. The presence of critical stability points and unstable equilibrium paths are major difficulties that numerical solutions must pass to fully capture the nonlinear response. Some hurdles still exist in finding nonlinear responses of structures under large geometric changes. Predicting snap-through and snap-back of certain structures has been difficult and time consuming. Also difficult is finding how much load a structure may still carry safely. Highly geometrically nonlinear responses of structures exhibiting complex snap-back behavior are presented and analyzed with a finite element approach. The arc-length method will be reviewed and shown to predict the proper response and follow the nonlinear equilibrium path through limit points.

Hrinda, Glenn A.↗
DOE OSTI2013

Carbon nanosheet-titania nanocrystal composites from reassembling of exfoliated graphene oxide layers with colloidal titania nanoparticles

Nanoporous composites of carbon nanosheets (CNS) and titania nanoparticles (NPs) were synthesized by reassembling of delaminated graphite oxide (GO) layers with titania clear sol (TCS), and their structural and porous properties were examined by various physico-chemical methods such as XRD, TG/DTA, FT-IR, Raman, FE-SEM/TEM, and low temperature N{sub 2} adsorption. It was found that the facile approach, which utilizes the electrostatic attraction between the negatively charged GO layers and the positively charged TCS particles, leads to a well composed CNS and ultrafine TiO{sub 2} NPs material whose titania amount reaches up to 71 wt%. The titania phase in these composite materials is mainly anatase, which is resistible against high temperature calcination, but also contains a little amount of rutile and brookite depending on synthesis condition. The porosity of the composite is improved and partially affected by the size distributions of TiO{sub 2} NPs. The unique structure, better porosity, and compatible surface affinity of these composites bring about an adsorption concentration-promoted photocatalytic effects toward organic dyes by successfully combining both properties of CNS and titania NPs. - Graphical Abstract: Carbon nanosheet-titania nanocrystal composites can be synthesized by a facile delamination-reassembling method from graphene oxide and colloidal titania. Highlights: Black-Right-Pointing-Pointer A facile delamination-reassembling method for graphene oxide-titania nanocomposite. Black-Right-Pointing-Pointer A nanoporous composite containing mixed phase titania nanocrystals. Black-Right-Pointing-Pointer Partition effect of carbon nanosheets preventing TiO{sub 2} nanoparticles from aggregating. Black-Right-Pointing-Pointer Adsorption concentration-promoted photocatalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Synthesis and thermoelectric properties of RuO{sub 2} nanorods

We have explored the effect of the O/Ru ratio on the morphology and the Seebeck coefficient of RuO{sub 2} nanorods (space group P4{sub 2}/mnm) synthesized by reactive sputtering. At an O/Ru ratio of 1.69, a faceted surface is observed, while nanorod formation occurs at O/Ru ratios of 2.03 and 2.24. Using classical molecular dynamics with the potential parameters derived in this work, we show that volatile species enable nanorod formation. Based on ab initio calculations, two effects of the nanorod formation on the Seebeck coefficient are observed: (i) increase due to additional states in the vicinity of the Fermi level and (ii) decrease due to oxygen point defects (volatile species). These two competing effects give rise to a moderate increase in the Seebeck coefficient upon nanorod formation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Controlled synthesis of MnSn(OH){sub 6}/graphene nanocomposites and their electrochemical properties as capacitive materials

We report the synthesis of novel MnSn(OH){sub 6}/graphene nanocomposites produced by a co-precipitation method and their potential application for electrochemical energy storage. The hydroxide decorated graphene nanocomposites display better performance over pure MnSn(OH){sub 6} nanoparticles because the graphene sheets act as conductive bridges improving the ionic and electronic transport. The crystallinity of MnSn(OH){sub 6} nanoparticles deposited on the surface of graphene sheets also impacts the capacitive properties as electrodes. The maximum capacitance of 31.2 F/g (59.4 F/g based on the mass of MnSn(OH){sub 6} nanoparticles) was achieved for the sample with a low degree of crystallinity. No significant degradation of capacitance occurred after 500 cycles at a current density of 1.5 A/g in 1 M Na{sub 2}SO{sub 4} aqueous solution, indicating an excellent electrochemical stability. The results serve as an example demonstrating the potential of integrating highly conductive graphene networks into binary metal hydroxide in improving the performance of active electrode materials for electrochemical energy storage applications. - Graphical abstract: Graphite oxide (GO) can be synthesized by oxidizing graphite using Hummers method. Graphene was reduced from GO by thermal exfoliation. In this work, MnSn(OH){sub 6}/graphene nano-composites were synthesized by a simple co-precipitation method and their electrochemical performances have been explored. Highlights: Black-Right-Pointing-Pointer Noval MnSn(OH){sub 6}/graphene nano-composites were synthesized. Black-Right-Pointing-Pointer Microstructure can be tailored by changing the reaction temperature and time. Black-Right-Pointing-Pointer Crystallinity of MnSn(OH){sub 6} nanoparticles impacts capacitive properties as electrode. Black-Right-Pointing-Pointer Nano-composites display improved electrochemical performance over MnSn(OH){sub 6} alone. Black-Right-Pointing-Pointer Results serve as an example demonstrating the potential for energy storage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗