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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

A theoretical study of solid solution strengthening in the refractory medium entropy alloy Nb 45 Ta 25 Ti 15 Hf 15

The refractory medium-entropy alloy (RMEA) Nb 45 Ta 25 Ti 15 Hf 15 exhibits exceptional tensile ductility and fracture toughness at ambient temperature, but its engineering applications are limited by a lack of high temperature strength. Using a machine-learning interatomic potential (MLIP) with near-density functional theory (DFT) accuracy, we conducted molecular dynamics (MD) and statics simulations of the behavior of dislocations with both screw and edge characters. We also analyze experimentally measured yield strengths using the Rao-Suzuki model and the Maresca-Curtin model modified to include a temperature-dependent shear modulus and a bulk modulus-dependent misfit volume, thereby uncovering the mechanisms underlying the yielding of this RMEA. Compared with the published experimental yield strength, the models parameterized by the MLIP effectively reproduce the experimental results over a wide temperature range. The models and MD simulations indicate that yielding is governed by screw dislocations, with dipole dragging as the dominant mechanism. In MD simulations, we observed a potential softening mechanism not considered by the Rao-Suzuki screw model: slow migration of interstitial jogs along the dislocation core, which could lead to the annihilation of vacancy and interstitial jog pairs by their combination.

BCC complex concentrated alloys↗
DOE OSTI2021

Facilitating Large‐Scale Snow Shedding from In‐Field Solar Arrays using Icephobic Surfaces with Low‐Interfacial Toughness

Abstract Large‐scale accrual of snow and ice on solar arrays in northern latitudes can cause significant power generation losses during winter. Depending on environmental conditions, snow can encompass a wide range in physical characteristics from dry snow (modulus ≈100 kPa and density ≈0.1 g cm −3 ) to bulk ice (modulus ≈8 GPa and density ≈0.9 g cm −3 ). This variation in snow morphology has made the development of a passive, broad‐spectrum, snow and ice‐shedding surface challenging. Here, the authors develop one of the first surfaces that simultaneously possesses both low‐interfacial strength ( τ˄ ice < 50 kPa) and toughness (Γ ice < 0.5 J m −2 ) with ice. These surfaces, fabricated via the addition of mobile polymer chains/oils to a thin polymeric coating, require extremely low detachment forces for ice, enabling its passive shedding at virtually any accretion length scale. Preliminary evidence that the new surfaces can shed different forms of snow and ice from field‐deployed solar arrays, over a range of subzero temperatures for several weeks, leading to significant increases in power generation is provided. The optically transparent surfaces are easily scalable and can be widely deployed by the solar industry in areas that see persistent snow. Other applications include automotive windshields, LIDAR covers for autonomous vehicles, and cold climate optical sensors.

Dhyani, Abhishek↗
DOE OSTI2021

High Pressure Brillouin Spectroscopy and X-ray Diffraction of Cerium Dioxide

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports of anomalous compressibility and strength in nanocrystalline cerium dioxide, the acoustic velocities are found to be insensitive to grain size and enhanced strength is not observed in nanocrystalline CeO 2 . Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO 2 are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus, G 0 = 63 (3) GPa, and adiabatic bulk modulus, K S0 = 142 (9) GPa, which is considerably lower than the isothermal bulk modulus, K T0 ~ 230 GPa, determined by high-pressure X-ray diffraction experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Hydrogen Bonding Stiffens Peptide Amphiphile Supramolecular Filaments by Aza-Glycine Residues

Peptide amphiphiles (PAs) are a class of molecules comprised of short amino acid sequences conjugated to hydrophobic moieties that may exhibit self-assembly in water into supramolecular structures. Here, we investigate here how mechanical properties of hydrogels formed by PA supramolecular nanofibers are affected by hydrogen bond densities within their internal structure by substituting glycine for aza-glycine (azaG) residues. We found that increasing the number of PA molecules that contain azaG up to 5 mol% in PA supramolecular nanofibers increases their persistence length fivefold and decreases their diffusion coefficients as measured by fluorescence recovery after photobleaching. When these PAs are used to create hydrogels, their bulk storage modulus (G') was found to increase as azaG PA content in the supramolecular assemblies increases up to a value of 10 mol% and beyond this value a decrease was observed, likely due to diminished levels of nanofiber entanglement in the hydrogels as a direct result of increased supramolecular rigidity. Interestingly, we found that the bioactivity of the scaffolds toward dopaminergic neurons derived from induced pluripotent stem cells can be enhanced directly by persistence length independently of storage modulus. We hypothesize that this is due to interactions between the cells and the extracellular environment across different size scales: from filopodia adhering to individual nanofiber bundles to cell adhesion sites that interact with the hydrogel as a bulk substrate. Fine tuning of hydrogen bond density in self-assembling peptide biomaterials such as PAs provides an approach to control nanoscale stiffness as part of an overall strategy to optimize bioactivity in these supramolecular systems. supramolecular biomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mechanical Characterization of Loblolly Pine

Biorefineries are faced with various material flow challenges during feeding and handling, due to inherent variability and inhomogeneity of biomass feedstocks. This impacts the efficiency of refinery processes and unit operations. Proper characterization of bulk properties allows for optimal process design and reduction of overall costs. This work is aimed at evaluating the physical and mechanical properties that impact bulk flow of loblolly pine. Cyclic axial compression tests are performed to elucidate consolidation behavior under different stress conditions. The results are then used to develop correlations between material parameters (particle size, tissue type, moisture content) and Elastic Modulus of bulk samples.

09 BIOMASS FUELS↗
DOE OSTI2021

Direct Observation of Interfacial Mechanical Failure in Thiophosphate Solid Electrolytes with Operando X-Ray Tomography

Herein, the mechanical behaviors of Li 10 GeP 2 S 12 (LGPS) solid electrolytes during electrochemical cycling using operando X-ray tomography are investigated. It is demonstrated that the bulk mechanical decomposition of LGPS when cycled against lithium is a direct result of electrochemical reduction of the solid electrolyte at the LGPS/Li 0 interface. The reductive decomposition of LGPS during lithium plating results in the formation of low-density domains at the electrode/electrolyte interface, which impose sufficient mechanical stress on the underlying LGPS to crack the SE pellet. The critical stress developed prior to pellet fracture is significantly lower than the bulk shear modulus of LGPS, suggesting that the electrochemical instability of LGPS dramatically worsens the mechanical stability of the material near the LGPS/Li 0 interface. It is also shown that the application of a highly concentrated liquid electrolyte to the LGPS surface suppresses the reductive decomposition of LGPS, improving both the electrochemical performance and mechanical stability of the bulk LGPS solid electrolyte.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Molecular dynamics simulation of the effect of cooling rate on the structure and properties of lithium disilicate glass

The effects of cooling rate on the structure and properties of lithium disilicate (LS2) glass are investigated using molecular dynamics (MD) computer simulations. The evolution of structural features such as pair distribution function, bond angle distribution, and Li coordination distribution are determined, and correlated with dynamic and static properties to elucidate the effects of cooling rate. The density, elastic moduli, and diffusion coefficient are found to be highly sensitive to cooling rate, whereas the Si pair distribution function and bond angle distribution are weakly affected by the cooling rate. Additionally, the changes of Si-O-Si bond angle and Li coordination number suggest the formation of Li cluster at lower cooling rates. Furthermore, by comparing results from other simulations and reported experiments, we confirm that the increase of cooling rate leads to an increase of conductivity and a decrease of density. Finally, at very high cooling rates, we find that all the atoms in LS2-glass do not relax simultaneously, but do so in two distinct configurations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Determination of single-crystal elastic moduli of Li RE F 4 ( RE =Y, Gd, and Tb) by resonant ultrasound spectroscopy

The tetragonal fluoro-scheelite Li RE F 4 compounds (RE = rare earth) have been shown to exhibit a variety of useful optical and magnetic properties. While LiYF 4 has been widely studied, many of the fundamental thermodynamic properties of other members of this family remain unknown. Here, we report the complete elastic tensors (C ij ) of single-crystalline LiYF 4 , LiTbF 4 , and LiGdF 4 using resonant ultrasound spectroscopy and density functional theory (DFT). Here we compare the results for LiYF 4 with prior experimental results using time-of-flight ultrasound methods. This is the first report, however, of the experimental elastic tensors of LiTbF 4 and LiGdF 4 . The present results point to a softening of the elastic moduli of the Li RE F 4 system when Y is replaced by the larger ionic radius of Tb or Gd. Furthermore, we find that just 0.3% doping with Nd on the Y site also leads to a slight softening of the moduli. The variation of the elastic moduli as a function of temperature up to 216°C was also measured. A nearly linear softening of all seven independent elastic moduli was observed with increasing temperature. Phonon dispersions and phonon density of states obtained by DFT support the experimental finding of a significantly higher sound velocity due to lighter Y atoms in LiYF 4 , as compared to heavier LiTbF 4 and LiGdF 4 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Exploring the hardness and high-pressure behavior of osmium and ruthenium-doped rhenium diboride solid solutions

Rhenium diboride (ReB 2 ) exhibits high differential strain due to its puckered boron sheets that impede shear deformation. Here, we demonstrate the use of solid solution formation to enhance the Vickers hardness and differential strain of ReB 2 . ReB 2 -structured solid solutions (Re 0.98 Os 0.02 B 2 and Re 0.98 Ru 0.02 B 2 , noted as “ReOsB 2 ” and “ReRuB 2 ”) were synthesized via arc-melting from the pure elements. In-situ high-pressure radial x-ray diffraction was performed in the diamond anvil cell to study the incompressibility and lattice strain of ReOsB 2 and ReRuB 2 up to ~56 GPa. Both solid solutions exhibit higher incompressibility and differential strain than pure ReB 2 . However, while all lattice planes are strengthened by doping osmium (Os) into the ReB 2 structure, only the weakest ReB 2 lattice plane is enhanced with ruthenium (Ru). These results are in agreement with the Vickers hardness measurements of the two systems, where higher hardness was observed in ReOsB 2 . The combination of high-pressure studies with experimentally observed hardness data provides lattice specific information about the strengthening mechanisms behind the intrinsic hardness enhancement of the ReB 2 system.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Nanolamellar phase transition in an additively manufactured eutectic high-entropy alloy under high pressures

Much is unknown about how phase transitions link to micro-/nano-structures in high-entropy systems, especially under extreme pressure and temperature conditions. This work studies the evolution of dual-phase nanolamellar eutectic high-entropy alloy phases of AlCoCrFeNi 2.1 generated by laser powder-bed fusion (L-PBF) for pressures up to 42 GPa. We compare quasi-hydrostatic high pressure synchrotron x-ray diffraction studies on L-PBF printed cylindrical samples up to 5.5 GPa (large-volume Paris–Edinburgh cell) to those carried out on an L-PBF printed foil in a diamond anvil cell where the pressure reached 42 GPa. Our results show that the initially alternating face-centered cubic (FCC) and body-centered cubic (BCC) nanolamellar structure of AlCoCrFeNi 2.1 transformed into single-phase FCC nanolamellae under high pressure with BCC–FCC phase transformation completion at 21 ± 3 GPa. Our results indicate a diffusionless BCC–FCC transformation in this additively manufactured far-from-equilibrium microstructure and demonstrate that the FCC phase is stable up to very high pressures. The measured equation of state for the FCC phase of AlCoCrFeNi 2.1 is presented up to 42 GPa and shows excellent agreement between the data obtained in large-volume press and diamond anvil cell experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

ET-AL: Entropy-targeted active learning for bias mitigation in materials data

Growing materials data and data-driven informatics drastically promote the discovery and design of materials. While there are significant advancements in data-driven models, the quality of data resources is less studied despite its huge impact on model performance. In this work, we focus on data bias arising from uneven coverage of materials families in existing knowledge. Observing different diversities among crystal systems in common materials databases, we propose an information entropy-based metric for measuring this bias. To mitigate the bias, we develop an entropy-targeted active learning (ET-AL) framework, which guides the acquisition of new data to improve the diversity of underrepresented crystal systems. We demonstrate the capability of ET-AL for bias mitigation and the resulting improvement in downstream machine learning models. This approach is broadly applicable to data-driven materials discovery, including autonomous data acquisition and dataset trimming to reduce bias, as well as data-driven informatics in other scientific domains.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Using deep machine learning to interpret proton radiography data from a pulsed power experiment

Deep machine learning is used to analyze a proton radiograph from a tin pulsed power experiment and determine density values for each pixel in the image. Two promising convolutional neural network architectures that have proven to be effective for image analysis in other applications are applied to analyze a proton radiograph and find density values. The process of creating a suitable training dataset is described, involving the Lagrangian hydrodynamic model used for simulations of the experiment, the proton radiography forward model to make synthetic images for training, and the manner in which data augmentation is used to expand the resulting image dataset. It is shown that machine learning not only produces a reasonable density field but is also able to predict features in the density field that are suggested by the proton radiograph but not captured by simulations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Symmetry and scaling in one-dimensional compressible two-phase flow

Investigations of shock compression of heterogeneous materials often focus on the shock front width and overall profile. The number of experiments required to fully characterize the dynamic response of a material often belie the structure–property relationships governing these aspects of a shock wave. Recent observations measured a pronounced shock-front width on the order of 10 s of ns in particulate composites. We focus on particulate composites with disparate densities and investigate whether the mechanical interactions between the phases are adequate to describe this emergent behavior. The analysis proceeds with a general Mie–Grüneisen equation of state for the matrix material, a general drag force law with general power-law scaling for the particle-matrix coupling of the phases, and a volume fraction-dependent viscosity. Lie group analysis is applied to one-dimensional hydrodynamic flow equations for the self-consistent interaction of particles embedded in a matrix material. The particle phase is characterized by a particle size and volume fraction. The Lie group analysis results in self-similar solutions reflecting the symmetries of the flow. The symmetries lead to well-defined scaling laws, which may be used to characterize the propagation of shock waves in particle composites. An example of the derived scaling laws for shock attenuation and rise time is shown for experimental data on shock-driven tungsten-loaded polymers. A key result of the Lie analysis is that there is a relationship between the exponents characterizing the form of the drag force and the exponent characterizing the shock velocity and its attenuation in a particulate composite. Comparison to recent experiments results in a single exponent that corresponds to a conventional drag force.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Thermally frustrated phase transition at high pressure in B 2-ordered FeV

X-ray diffraction measurements of equiatomic B2-ordered FeV were performed in a diamond-anvil cell at room temperature at several pressure points up to 80 GPa that showed the cubic phase to be stable with no indication of structural phase transitions. Density functional theory at 0 K predicts Fermi surface nesting, an electronic topological transition, and a phonon dynamical instability within the experimentally investigated pressure range. Nevertheless, the instability is absent in phonon dispersion curves extracted from ab initio molecular dynamics simulations below the critical volume at temperatures as low as 10 K, indicating that thermal atomic displacements can frustrate the phase transition by renormalizing the phonon dispersion curves. Ferrimagnetism is critical for the stability of the cubic phase at low temperature, but thermal atomic displacements are enough to support the structure at and above the Néel temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ab initio prediction of rapid kinetics of Fe impurities in δ -Pu

Here, we study the formation energies of iron impurities in δ-Pu within spin–orbital-polarized density functional theory (SOP-DFT). The thermodynamic solubility limit of iron in δ-Pu is calculated, indicating low miscibility. We show that surprisingly, Fe impurities at equilibrium are almost equally likely to occupy octahedral interstitial sites or substitutional sites, with slight preference for the former. In contrast, we find the energy of the tetrahedral interstitial Fe to be nearly 1 eV higher than the octahedral one. We explore the energy landscape for Fe impurity hopping diffusion and conclude that Fe impurities in δ-Pu are divided into two populations: (i) Immobile substitutional Fe impurities and (ii) highly mobile interstitial Fe impurities. The latter, (ii), migrate between octahedral interstitial sites with an energy barrier of around 0.2 eV. The energy barrier for exchange between the two populations is calculated to exceed 0.7 eV. Finally, we discuss the role of magnetic order on the impurity energetics.

Atomic structure↗
DOE OSTI2021

Pantropical Tree Sapwood Hydraulic Properties, 1991 - 2014

This data package contains sapwood pressure-volume parameters including osmotic potential at full turgot, turgor loss point, bulk elastic modulus, and others, determined by curve fitting to raw isotherm data (paired measurements of water content and water potential). Raw data were digitized from published figures. Data are from natural tropical and subtropical forests or savannas and span rainfall gradients from deciduous dry tropical forests to everwet tropical forests, and come from the following countries: Argentina, Panama, Brazil, Costa Rica, and Madagascar. Included in the attached zip file are four CSV files. sapwood_PV_recal_headers.csv: description of variables in the two files below sapwood_PV_recal_corrected.csv: bias-corrected sapwood PV data (see Methods in the associated reference) sapwood_PV_recal_uncorrected.csv: uncorrected sapwood PV data (see Methods in the associated reference) sapwood_PV_references.csv: citation, bibliographic reference, and DOI for the published references from which data were extracted.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Pantropical Tree Leaf Hydraulic Properties, 1986 - 2015

This data package contains leaf pressure-volume parameters (osmotic potential at full turgor, turgor loss point, bulk elastic modulus, and others). Data was obtained by combining new data I gleaned from original publications not already in the following compilations (after removing the extratropical data): Bartlett, M. K., Zhang, Y., Kreidler, N., Sun, S., Ardy, R., Cao, K., and Sack, L.: Global analysis of plasticity in turgor loss point, a key drought tolerance trait, Ecol Lett, 17, 1580-1590, 2014. Bartlett, M. K., Scoffoni, C., and Sack, L.: The determinants of leaf turgor loss point and prediction of drought tolerance of species and biomes: a global meta-analysis, Ecology Letters, 15, 393-405, 2012. Maréchaux, I., Bartlett, M. K., Sack, L., Baraloto, C., Engel, J., Joetzjer, E., Chave, J., and Kitajima, K.: Drought tolerance as predicted by leaf water potential at turgor loss point varies strongly across species within an Amazonian forest, Functional Ecology, 29, 1268-1277, 2015. Data are from natural tropical and subtropical forests or savannas and span rainfall gradients from deciduous dry tropical forests to everwet tropical forests, and come from countries all throughout the pantropics. The attached zip file contains data organized into three CSV files.

54 ENVIRONMENTAL SCIENCES↗