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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The 371 deg C(700 deg F) properties of celion 6000/n-phenylnadimide modified PMR polyimide composites

The 371 C (700 F) properties of Celion 6000/N-phenylnadimide modified PMR-15 polyimide composites were investigated to determine the feasibility of using these materials at a 371 C (700 F) service temperature. The processing characteristics and physical and mechanical properties of the composite systems are presented. The results of the 371 C (700 F) thermo-oxidation stability study suggest that the composite materials can be considered for short term (at least 100 hours) application at 371 C (700 F).

Pater, R. H.↗
NASA NTRS2008

Lunar Dust 101

Largely due to rock and soil samples returned during the Apollo program, much has been learned about the composition and properties of lunar regolith. Although, for the most part, the mineral composition resembles terrestrial minerals, the characteristics of the lunar environment have led to very different weathering processes. These result in substantial differences in the particle shapes, particle size distributions, and surface chemistry. These differences lead to non-intuitive adhesion, abrasion, and possible health properties that will pose challenges to future lunar missions. An overview of lunar dust composition and properties will be given with a particular emphasis on possible health effects.

Gaier, James R.↗
DOE OSTI2020

Combinatorial Exploration and Mapping of Phase Transformation in a Ni–Ti–Co Thin Film Library

Combinatorial synthesis and high-throughput characterization of a Ni–Ti–Co thin film materials library are reported for exploration of reversible martensitic transformation. The library was prepared by magnetron co-sputtering, annealed in vacuum at 500 °C without atmospheric exposure, and evaluated for shape memory behavior as an indicator of transformation. Composition, structure, and transformation behavior of the 177 pads in the library were characterized using high-throughput wavelength dispersive spectroscopy (WDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and four-point probe temperature-dependent resistance (R(T)) measurements. A new, expanded composition space having phase transformation with low thermal hysteresis and Co > 10 at. % is found. Unsupervised machine learning methods of hierarchical clustering were employed to streamline data processing of the large XRD and XPS data sets. Through cluster analysis of XRD data, we identified and mapped the constituent structural phases. Finally, composition–structure–property maps for the ternary system are made to correlate the functional properties to the local microstructure and composition of the Ni–Ti–Co thin film library.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Effective medium approximation for the refractive index of stratified metal oxide composites synthesized by atomic layer deposition

Atomic layer deposition (ALD) is a unique method for synthesizing conformal layers with precise composition. It is especially useful for the synthesis of mixed metal oxides for functional materials. One application of interest is the use of ALD for tailoring the refractive index of coatings. In homogeneously distributed composites of metal oxides, the refractive properties can be approximated as the average of the indices of the components. This is known as an effective medium approximation (EMA) and can be used to design the macroscopic properties of composites. ALD produces layered, anisotropic films, so the validity of an EMA in describing these films is not clear. Here, we use optical simulations and experimental characterization of stratified composites of TiO 2 and Al 2 O 3 to study the application of an EMA to the transmission and reflection behavior of ALD-prepared mixed metal oxide thin films. We found that when the characteristic layer thickness is smaller than roughly 10 nm, the optical spectra of theoretical and experimental ALD films match the equivalent theoretical spectra for a material with a refractive index calculated from a simple, compositionally weighted EMA. Hence, this EMA could describe the transmission and reflectance spectra in ALD-derived TiO2–Al 2 O 3 nanolaminates when the films were sufficiently stratified even without thorough characterization of the real layers in the films. As a result, we demonstrated that ALD can be used to prepare effectively homogenous mixed metal oxide films with a predictable, tailorable refractive index of any value between those of the TiO 2 and Al 2 O 3 component materials.

42 ENGINEERING↗
NASA NTRS1995

The effect of interface properties on nickel base alloy composites

This program was performed to assess the extent to which mechanical behavior models can predict the properties of sapphire fiber/nickel aluminide matrix composites and help guide their development by defining improved combinations of matrix and interface coating. The program consisted of four tasks: 1) selection of the matrices and interface coating constituents using a modeling-based approach; 2) fabrication of the selected materials; 3) testing and evaluation of the materials; and 4) evaluation of the behavior models to develop recommendations. Ni-50Al and Ni-20AI-30Fe (a/o) matrices were selected which gave brittle and ductile behavior, respectively, and an interface coating of PVD YSZ was selected which provided strong bonding to the sapphire fiber. Significant fiber damage and strength loss was observed in the composites which made straightforward comparison of properties with models difficult. Nevertheless, the models selected generally provided property predictions which agreed well with results when fiber degradation was incorporated. The presence of a strong interface bond was felt to be detrimental in the NiAI MMC system where low toughness and low strength were observed.

Groves, M.↗
DOE OSTI2020

Tuning the mechanical properties of nanoglass-metallic glass composites with brick and mortar designs

We use molecular dynamics simulations to characterize the tensile deformation and failure of metallic glass (MG)-nanoglass (NG) composites designed with a brick and mortar architecture consisting of a 3 nm-grain-size NG matrix and a MG second phase. Results show that the overall strength of the matrix is significantly improved by the second phase without sacrificing the large NG matrix ductility. The mechanical synergy of the two phases is optimized by arranging the MG bricks in a staggered way, which effectively delocalizes the plastic deformation, hindering the buildup of local stress hot spots and the generation of critical shear bands.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Environmental and high strain rate effects on composites for engine applications

The complex environmental and loading conditions experienced by many turbine engine components impose severe durability and damage tolerance requirements for component materials. Programs are being conducted to establish the structural performance of composite materials under anticipated engine operating environments. A description is presented of the results obtained in connection with several of these programs. A comparison of predicted and measured hygrothermal effects is considered along with hygrothermal effects on defect growth, high strain rate effects on composite mechanical properties, dynamic stress intensity factors for composites, and the indentation laws for composite impact analysis.

Chamis, C. C.↗
DOE OSTI2023

An ab initio molecular dynamics study of varied compositions of the $\text{LiF-NaF-KF}$ molten salt

With increasing interest in molten salt reactors, there becomes a demand for investigations into thermophysical properties of salt systems. The LiF-NaF-KF (FLiNaK) salt system is a primary candidate for use in these reactors. However, the thermophysical properties of compositions outside the eutectic composition are still largely unknown. In this article, properties of ten unique compositions, including four ternary compositions, are investigated using ab initio molecular dynamics simulations across five temperatures between 900 K and 1300 K. The properties of interest are the density, thermal expansion, bulk modulus, compressibility, heat capacity, and enthalpy of mixing. In general, the results were found to be in good agreement with other literature and experimental results. The density and heat capacity had a tendency to be slightly underpredicted. No conclusions could be drawn about the bulk modulus and compressibility in terms of compositional dependence. The thermal expansion had a negative trend with respect to the LiF concentration and no trends were observed for the NaF or KF concentration. The enthalpy of mixing shows minima for the ternary compositions, with the near-equiatomic composition exhibiting the lowest values. Here this work shows the potential for compositional tailoring in the FLiNaK system to optimize thermophysical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of Al:Si and (Al+Na):Si Ratios on the Properties of the International Simple Glass, Part II: Structure

High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al+Na):Si substitutions in a simplified nuclear waste model glass (ISG, International Simple Glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and 27Al, 23Na, 29Si, and 11B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD simulations were used to generate atomistic structural models of the borosilicate glasses and simulation results were validated by the experimental structural data. Short-range (e.g., bond distance, coordination number, etc.) and medium-range (e.g., oxygen speciation, network connectivity, polyhedral linkages) structural features of the borosilicate glasses were systematically investigated as a function of the degree of substitution. The results show that bond distance and coordination number of the cation-oxygen pairs are relatively insensitive to Al:Si and (Al+Na):Si substitutions with the exception of the B-O pair. Additionally, the Al:Si substitution results in an increase of tri-bridging oxygen species, while (Al+Na):Si substitution creates non-bridging oxygen species. Charge compensator preferences were found for Si-[NBO] (Na+), [3]B-[NBO] (Na+), [4]B (mostly Ca2+), [4]Al (nearly equally split Na+ and Ca2+), and [6]Zr (mostly Ca2+). The network former-BO-network former linkages preferences were also tabulated; Si-O-Al and Al-O-Al were preferred at the expense of lower Si-O-[3]B and [3]B-O-[3]B linkages. These results provide insights on the structural origins of property changes such as glass transition temperature caused by the substitutions, providing a basis for future improvements of theoretical and computer simulation models.

Lu, Xiaonan↗
NASA NTRS2000

Accelerated Testing of Polymeric Composites Using the Dynamic Mechanical Analyzer

Creep properties of IM7/K3B composite material were obtained using three accelerated test methods at elevated temperatures. Results of flexural creep tests using the dynamic mechanical analyzer (DMA) were compared with results of conventional tensile and compression creep tests. The procedures of the three test methods are described and the results are presented. Despite minor differences in the time shift factor of the creep compliance curves, the DMA results compared favorably with the results from the tensile and compressive creep tests. Some insight is given into establishing correlations between creep compliance in flexure and creep compliance in tension and compression. It is shown that with careful consideration of the limitations of flexure creep, a viable and reliable accelerated test procedure can be developed using the DMA to obtain the viscoelastic properties of composites in extreme environments.

Abdel-Magid, Becky M.↗
NASA NTRS1989

Structural tailoring of laminate properties

In this study, structural synthesis techniques have been applied to tailor the composite laminate properties from the micromechanics to the laminate level for a desirable structural response. It is also demonstrated how to establish upper and lower bounds on design variables based on reliability considerations. The question of reliability arises in fiber composite analysis and design because of the inherent scatter that is observed in the constituent material properties in the experimental data. The symmetric composite laminates subject to mechanical loading are considered and no hygrothermal effects are taken into account in the present research. Application examples illustrate the effects of various ply and laminate parameters on the overall properties and structural response of composite laminates.

Thanedar, P. B.↗
NASA NTRS2023

Satellite characterization of global stratospheric sulfate aerosols released by Tonga volcano

Large volcanic eruptions create an enhanced layer of sulfate aerosols in the stratosphere. These sulfuric acid droplets persist for many months, altering the climate and stratospheric chemistry. Sulfate aerosols scatter sunlight back to space, cooling the surface of the Earth and absorb outgoing thermal radiation, heating the stratosphere. The calculation of the climate impact of sulfate aerosols depends on their physical properties such as droplet size and chemical composition. These properties are not well known, and this uncertainty contributes to the errors in climate model predictions. Here we derive the first empirical formula that predicts the composition of stratospheric sulfate aerosols from volcanic eruptions from the air temperature and water vapor pressure. Measurements of atmospheric infrared transmittance of the Hunga Tonga-Hunga Ha'apai sulfate aerosol plume by the Atmospheric Chemistry Experiment (ACE) satellite were analyzed to determine composition (weight percent of sulfuric acid) and median particle radius. These data are supplemented by measurements of the Raikoke and Nabro eruptions. Our analysis allows the properties of volcanic aerosols in the stratosphere to be predicted reliably in atmospheric models.

P Bernath↗
NASA NTRSDate not supplied

Using PACE Aerosol Optical and Microphysical Properties to Capture Aerosol Composition

Improvements in air quality and Earth’s climate predictions can only be achieved through improvements of the aerosol speciation in chemical transport models, using observational constraints. Aerosol speciation (e.g., organic aerosols, black carbon, sulfate, nitrate, ammonium, dust or sea salt) is typically determined using in situ instrumentation. Continuous, routine surface network aerosol composition measurements are not uniformly widespread over the globe. Satellites, on the other hand, can provide a maximum coverage of the horizontal and vertical atmosphere but observe aerosol optical properties (and not aerosol speciation) based on remote sensing instrumentation. Combinations of satellite-derived aerosol optical properties can inform on air mass aerosol types (e.g., clean marine, dust, polluted continental). We investigate the relative skill of various combinations of aerosol optical properties used as tools to define air mass aerosol types and how much these optical properties can capture dominant aerosol speciation.

Meloe Shenandoah Kacenelenbogen↗
NASA NTRS2006

Simulated Data for High Temperature Composite Design

The paper describes an effective formal method that can be used to simulate design properties for composites that is inclusive of all the effects that influence those properties. This effective simulation method is integrated computer codes that include composite micromechanics, composite macromechanics, laminate theory, structural analysis, and multi-factor interaction model. Demonstration of the method includes sample examples for static, thermal, and fracture reliability for a unidirectional metal matrix composite as well as rupture strength and fatigue strength for a high temperature super alloy. Typical results obtained for a unidirectional composite show that the thermal properties are more sensitive to internal local damage, the longitudinal properties degrade slowly with temperature, the transverse and shear properties degrade rapidly with temperature as do rupture strength and fatigue strength for super alloys.

Chamis, Christos C.↗
NASA NTRS2006

Processing and Properties of a Phenolic Composite System

Phenolic resin systems generate water as a reaction by-product via condensation reactions during curing at elevated temperatures. In the fabrication of fiber reinforced phenolic resin matrix composites, volatile management is crucial in producing void-free quality laminates. A commercial vacuum-bag moldable phenolic prepreg system was selected for this study. The traditional single-vacuum-bag (SVB) process was unable to manage the volatiles effectively, resulting in inferior voidy laminates. However, a double vacuum bag (DVB) process was shown to afford superior volatile management and consistently yielded void-free quality parts. The DVB process cure cycle (temperature /pressure profiles) for the selected composite system was designed, with the vacuum pressure application point carefully selected, to avoid excessive resin squeeze-outs and achieve the net shape and target resin content in the final consolidated laminate parts. Laminate consolidation quality was characterized by optical photomicrography for the cross sections and measurements of mechanical properties. A 40% increase in short beam shear strength, 30% greater flexural strength, 10% higher tensile and 18% higher compression strengths were obtained in composite laminates fabricated by the DVB process.

Hou, Tan-Hung↗
NASA NTRS1992

The structure of horizontal-branch models. I - The zero-age horizontal branch

A detailed study of the structure of zero-age horizontal-branch (ZAHB) models is studied in order to show how the hydrostatic structure of these models changes with the input parameters and determines the H-R diagram location of a given model. The properties of composite polytropes on the homology-invariant (U,V)-plane are demonstrated. A variety of test models and sequences were constructed to elucidate the underlying factors that give rise to the wide variation in HB model properties with composition. The roles of the CNO elements as nuclear catalysts and of the envelope sources, as well as the envelope helium abundance are reexamined. It is found that, for stars of a fixed range of mass arriving on the HB, the stellar distribution is determined mainly by CNO for low metallicities (Fe/H of less than about -1), but mainly by opacity sources for high metallicities. The value of Fe/H where CNO ceases to dominate depends significantly on the adopted opacity and will decrease if and when opacity estimates are revised upward.

Dorman, Ben↗