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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Analytic analysis of load alignment for coning extreme‐scale rotors

Abstract Extreme‐scale wind turbines (rated powers greater than 10 MW) with large rotor diameters and conventional upwind designs must resist extreme downwind and gravity loads. This can lead to significant structural design challenges and high blade masses that can impede the reduction of levelized cost of wind energy. Herein, the theoretical basis for downwind load alignment is developed. This alignment can be addressed with active downwind coning to reduce/eliminate flapwise bending loads by balancing the transverse components of thrust, centrifugal, and gravitational force. Equations are developed herein that estimates the optimal coning angle that reduces flapwise loads by a specified amount. This analysis is then applied to a 13.2‐MW scale with 100‐m‐level wind turbine blades, where it is found that a load alignment coning schedule can substantially reduce the root flapwise bending moments. This moment reduction in this example can allow the rotor mass to be decreased significantly when compared with a conventional upwind three‐bladed rotor while maintaining structural performance and annual energy output.

Noyes, Carlos↗
DOE OSTI2019

An infrared and Raman spectroscopic study of PbSO4-anglesite at high pressures

Infrared and Raman spectra of the ABX 4 compound anglesite (PbSO 4 ) were collected to 43 GPa at 300 K in three separate pressure media. A major transition in the spectra initiates at 23 GPa that is characterized by shifting and/or splitting of most of the fundamental vibrations of the sulfate group. On decompression, PbSO 4 reverts to the ambient anglesite (barite) structure. This transition is kinetically impeded within more hydrostatic pressure media and does not proceed to completion within a neon medium even at pressures as high as 43 GPa. The previously observed spectral shift at 13 GPa occurs in less hydrostatic media (such as 4:1 methanol:ethanol), and involves subtle splitting of a few modes, particularly the (SO 4 ) 2- tetrahedral stretching and bending-derived Raman and infrared modes. Another possible shift occurs near 33 GPa, and primarily involves the appearance of new sulfate antisymmetric bending modes in the infrared spectrum and the onset of new sulfate antisymmetric stretching modes in the Raman spectrum. It is likely that PbSO 4 begins to convert sluggishly to the $P2_12_12_1$ ABX4 structure starting at 23 GPa, with a possible additional crystallographic distortion or shift in compression mechanism occurring near 33 GPa. The spectral shift at 13 GPa in non-hydrostatic media may be a differential stress-induced structural distortion, or a subtle transition that is not accessible within more hydrostatic media. Our results emphasize that apparently equilibrium transitions such as that at 23 GPa may be notably suppressed within more hydrostatic media.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Properties of Veneered Flat Pressed Wood Plastic Composites by One-Step Process Pressing

The aim of this study was to develop, manufacture and determine properties of veneer overlaid flat pressed wood plastic composite (WPC) panels from recycled low density polyethylene (rLDPE), wood particles and different kinds of veneer (rotary-cut birch veneer and sliced oak veneer) using various adhesives by one-step hot pressing. Food packaging polyethylene film (PE film) as recycled stretch wraps, recycled low density polyethylene (rLDPE) particles and phenol formaldehyde (PF) resin were applied as adhesive for the bonding of veneer to the surface of WPC. No modification additives were used for the manufacture of WPC. It was found that compared with non-veneered WPC, the panels sandwiched with natural veneers greatly improved their properties. The bending strength was improved in 1.9–2.6 and 7.9–10 times across and along veneer fibers respectively for both types of investigated veneer. The highest values of bending strength were observed in WPC panels veneered with rotary-cut birch veneer. However, the water resistance of veneered WPC panels was reduced in comparison with non-veneered. The WPC specimens veneered with both types of veneer using PE film had better mechanical properties and water resistance than those of the specimens made with other two types of adhesives. The veneering of WPC panels enables to significantly improve adhesion properties of these veneered surfaces for their further finishing. In addition, the veneering of WPC panels hides the surface defects and provides a uniform application of different paints, varnishes and films to the surface of such materials. Overlaying WPC panels with wood veneers improves their appearance and properties resulting in eco-friendly value-added products.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Properties of Resistive Hydrogen Sensors as a Function of Additives of 3D-Metals Introduced in the Volume of Thin Nanocrystalline SnO{sub 2} Films

Analysis of the results of studying electrical and gas sensitive characteristics of the molecular hydrogen sensors based on thin nanocrystalline SnO{sub 2} films coated with dispersed Au layers and containing Au+Ni and Au+Co impurities in the bulk showed that the characteristics of these sensors are more stable under the prolonged exposure to hydrogen in comparison with Au/SnO{sub 2}:Sb, Au films modified only with gold. It has been found that introduction of the nickel and cobalt additives increases the band bending at the grain boundaries of tin dioxide already in freshly prepared samples, which indicates an increase in the density N{sub i} of the chemisorbed oxygen. It is important that during testing, the band bending eφ{sub s} at the grain boundaries of tin dioxide additionally slightly increases. It can be assumed that during crystallization of films under thermal annealing, the 3d-metal atoms in the SnO{sub 2} volume partially segregate on the surface of microcrystals and form bonds with lattice oxygen, the superstoichiometric tin atoms are formed, and the density N{sub i} increases. If the bonds of oxygen with nickel and cobalt are stronger than those with tin, then, under the prolonged tests, atomic hydrogen will be oxidized not by lattice oxygen, but mainly by the chemisorbed one. In this case, stability of the sensors’ characteristics increases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis and Comparison of Two cBN Composites with Starting Ternary Carbide Binders

Ti{sub 3}SiC{sub 2} and Ti{sub 3}AlC{sub 2} are two promising binders for the ultrahard composite polycrystalline cubic boron nitride (PcBN). In this study, the cBN composites with Ti{sub 3}SiC{sub 2} and Ti{sub 3}AlC{sub 2} binders with different binder contents were synthesized under the same high pressure (~5.5 GPa) and high temperature (1350 °C) conditions. Their mechanical properties were measured separately, including Vickers hardness, bending hardening, and compression hardening. Together with XRD results, the phase compounds were also investigated. The decomposition and reaction processes were affected by binder content. Some new compounds formed during sintering, these compounds were TiC, TiSi{sub 2,} SiC, TiB{sub 2}, SiB{sub 4}, TiB{sub 2}, and TiC{sub 0.7}N{sub 0.3} in Ti{sub 3}SiC{sub 2}-cBN composites, as well as TiC{sub 0.7}N{sub 0.3}, TiB{sub 2}, and AlN in Ti{sub 3}AlC{sub 2}-cBN composites. The microstructure of the cracks surface was obtained after the bending tests, and was used to further investigate and compare their crack mode by SEM. The crack surface profile and elementary analysis on the oxidative surface were also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Zr Content on Mechanical Properties of Diamond/Cu-Zr Composites Produced by Gas Pressure Infiltration

Diamond particle-reinforced Zr-alloyed Cu matrix (diamond/Cu-xZr) composites were produced by a gas pressure infiltration route, with x = 0.0, 0.3, 0.5, 0.75, and 1.0 wt.%. The x-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterization confirms the formation of ZrC at the diamond/Cu interface. With increasing Zr content, the tensile, bending, and compressive strengths of the diamond/Cu-Zr composites are found to firstly increase and then decrease. The maximum tensile, bending, and compressive strengths at 0.75 wt.% Zr are 108, 360, and 441 MPa, respectively. The variation of the mechanical properties is attributed to the formation of interfacial ZrC. The increase in amount of ZrC strengthens the interface, but large ZrC particles formed at high Zr content are harmful to the interfacial bonding. The result suggests that the mechanical properties of diamond/Cu composites can be enhanced by Cu matrix alloying with Zr.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanical Properties and Microstructure of High-Strength Steel Controlled by Hot Stamping Process

A novel design and manufacturing method, dubbed “precast,” of the cooling system and tools for a hot forming process was proposed in this paper. The integrated structures of the punch and blank holder were determined by analyzing the bending and reverse-bending deformation of the forming parts. The desired crashworthiness performance of an automotive front bumper constructed with this process was obtained by a tailored phase transformation, which generated martensite-bainite in the middle and full martensite transformation in the corner areas. Varying cooling effects in the formed parts caused the highest temperature to be located in the bottom and the lowest on the end of the formed parts. Moreover, the microstructural distributions demonstrated that the bottom possessed a relatively lower content of martensite, while, conversely, the end possessed a higher content. This was precisely the most desired phase distributions for the hot formed parts. For the six-process cycle stamping, the temperatures reached a stable status after an initial rapid increase in the first three process cycles. The microstructural results verified the feasibility of the hot forming tools under multiprocess cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental and Modeling Studies on the Microstructures and Properties of Oxidized Aluminum Nitride Ceramic Substrates

Oxidation of aluminum nitride (AlN) ceramic substrates doped with 2 wt.% Y{sub 2}O{sub 3} was performed in air at temperatures ranging from 1000 to 1300 °C for various lengths of time. Microstructure, bending strength, and thermal conductivity of the oxidized AlN substrates were studied experimentally and also via mathematical models. The results show that the oxide layer formed on the AlN substrates is composed of α-Al{sub 2}O{sub 3} nanocrystallines and interconnected micropores. Longitudinal and transverse cracks are induced in the oxide layer under tensile and shear stresses, respectively. Intergranular oxidation of the AlN grains close to the oxide layer/AlN interface also occurs, leading to widening and cracking of the AlN grain boundaries. These processes result in the monotonous degradation of bending strength and thermal conductivity of the oxidized AlN substrates. Two mathematic models concerning these properties of the oxidized AlN substrates versus the oxide layer thickness were put forward. They fit well with the experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Fabrication, Microstructures, and Properties of 50 vol.% SiCp/6061Al Composites via Hot Pressing

Nearly fully dense 50 vol.% SiCp/6061Al composites were fabricated via hot pressing (HPing) at temperatures ranging from 610 to 650 °C, with the axial load and holding time fixed as 25 MPa and 120 min, respectively. The interfacial reactions, microstructures, and properties of the SiCp/Al alloy were studied. The interface reaction between SiCp and the Al alloy was suppressed at annealing temperatures of 620 °C and below; however, the reaction intensified as the annealing temperature increased, producing Al{sub 4}C{sub 3}, Si, and Mg{sub 2}Si. With an increase in HPing temperature from 610 to 630 °C, the 6061Al alloy melted and gradually filled the pores in the SiC particles under the applied load. The density, bending strength, and thermal conductivity (TC) of the composites increased, whereas the coefficient of thermal expansion (CTE) of the composites decreased. With an increase in HPing temperature increased from 630 to 650 °C, the 6061Al alloy melt leaked through the sintered bodies, resulting in the microstructural degradation and property reduction of the composites. The 50 vol.% SiCp/6061Al composites fabricated by HPing at 630 °C exhibited optimal comprehensive properties [bending strength, 332.4 MPa; TC, 186.3 W(m K){sup −1}; and CTE, 7.9 × 10{sup −6}/°C (20-100 °C)], which were attributed to the highest relative density and the best SiCp/Al interfacial structure of the composites.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Mechanical Properties of B{sub 4}C-Blended M3:2 High-Speed Steel Powders Consolidated by Sintering and Heat Treatment

Water-atomized powders of M3:2 high-speed steel (HSS) were blended with B{sub 4}C and consolidated by cold press sintering. With the addition of B{sub 4}C (~ 0.2 vol.%), satisfactory mechanical properties were achieved for HSS by sintering at a temperature as low as 1190 °C [e.g., 53.2 ± 0.2 in the Rockwell hardness (HRC) and 3074 ± 56 MPa in bending strength]. High relative density (98.5%) and good strength were attributed to the mechanism described as follows: First, the atoms of boron and carbon escaped after the reaction between B{sub 4}C and iron matrix. Then, the sintered HSS was strengthened by boron atoms while they were distributed in M{sub 6}C or MC carbides and iron matrix. Second, a plenty of M{sub 6}C carbides were formed due to the release of carbon atoms. As a result, the value of solidus temperature was reduced. In addition, mechanical properties were greatly improved by heat treatment (quenching and tempering) (e.g., 61.2 ± 0.3 in HRC, 4356 ± 64 MPa in bending strength, and 42.3 ± 0.5 MPa m{sup 1/2} in fracture toughness, respectively).

36 MATERIALS SCIENCE↗
DOE OSTI2023

Room Temperature Stamping of High-Strength Aluminum for Lightweight Structural Automotive Components

The use of aluminum (Al) 7xxx series in automobile structural applications is limited by factors such as its low room-temperature formability in T6 temper and the need for off-line artificial aging to regain high strength if it is formed in soft temper. In this study, two tempers were established that enable Al 7075 blanks to be room temperature stamped to create side impact beams that achieve near-T6 strength without post-forming artificial aging. It is shown that natural aging at room temperature, after solution treatment and before stamping, provides an alternative to high temperature pre-aging and hot stamping techniques in 7xxx alloys. Both tempers enabled room temperature stamping of the beams without cracking, indicating good formability. The Al beams were ~38% lighter than the benchmark boron steel beam. Further, the hardness in the low-deformation regions of the stamped Al beams were within 88% of a conventional 7075-T6 sheet. Paint-bake treatment of the beams appeared to cause over aging, lowering the ultimate tensile strength and ductility. Finite element three point bending simulations of the beams showed higher bending force and energy absorption before failure for the Al 7075 showing good promise for 7xxx series Al as a light-weight alternative to steel beams.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Mapping local deformation behavior in single cell metal lattice structures

The deformation behavior of metal lattice structures is extremely complex and challenging to predict, especially since strain is not uniformly distributed throughout the structure. Understanding and predicting the failure behavior for these types of light-weighting structures is of great interest due to the excellent scaling of stiffness- and strength-to weight ratios they display. Therefore, there is a need to perform simplified experiments that probe unit cell mechanisms. This study reports on high resolution mapping of the heterogeneous structural response of single unit cells to the macro-scale loading condition. Two types of structures, known to show different stress-strain responses, were evaluated using synchrotron radiation micro-tomography while performing in-situ uniaxial compression tests to capture the local micro-strain deformation. These structures included the octet-truss, a stretch-dominated lattice, and the rhombic-dodecahedron, a bend-dominated lattice. The tomographic analysis showed that the stretch- and bend-dominated lattices exhibit different failure mechanisms and that the defects built into the structure cause a heterogeneous localized deformation response. Also shown here is a change in failure mode for stretch-dominated lattices, where there appears to be a transition from buckling to plastic yielding for samples with a relative density between 10 and 20%. In conclusion, the experimental results were also used to inform computational studies designed to predict the mesoscale deformation behavior of lattice structures. Here an equivalent continuum model and a finite element model were used to predict both local strain fields and mechanical behavior of lattices with different topologies.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Facile healing of cracks in organic–inorganic halide perovskite thin films

Organic-inorganic halide perovskite (OIHP) thin films at the heart of the burgeoning thin-film perovskite solar cells (PSCs) technology possess poor mechanical properties, which is likely to limit the long-term reliability of PSCs as they are poised for commercialization. In an effort to address this issue, in this work we demonstrate that through-thickness cracks induced by bending-tension in thin films of the two prototypical OlHPs, methylammonium lead triiodide (MAPbl(3)) and formamidinium lead triiodide (FAPbl(3)), can be healed easily. This is through the application of either a moderate compressive stress (bending-compression) at room temperature or a simple heat-treatment at modest temperatures. The crack-healing process is found to be time-dependent, which indicates that facile mass-transport in OlHPs plays a key role in this phenomenon. An explanation for this phenomenon is provided, one based on the fundamentals of brittle fracture. This discovery has broad implications for the prevention and/or restoration of the overall performance, environmental stability, and mechanical reliability of PSCs, and other devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Domain patterns and super-elasticity of freestanding BiFeO 3 membranes via phase-field simulations

Super-elasticity of functional ferroelectric oxides offers promises for integrating ferroelectric films into flexible electronics. However, super-elastic deformation is a complex phenomenon related to possibly multiple concurrent mechanisms. Fundamentally understanding how multiple mechanisms contribute to the super-elasticity of ferroelectric oxides is crucial to realizing their potential flexible electronic applications. In this study, we employ phase-field simulations to model the dynamics of ferroelectric domain patterns of freestanding BiFeO 3 membranes to understand the origin of their super-elasticity under substantial bending deformation (5% strain). It is demonstrated that both a reversible Rhombohedral-Tetragonal (R-T) phase transition and a nearly reversible domain evolution of BiFeO 3 membranes contribute to accommodating the large deformation and thus their super-elasticity. The dynamics of domain evolution also reveal the formation of an exotic ferroelectric vortex and polarization rotation before the phase transition. We constructed a diagram of phases and domain patterns as a function of the membrane thickness and bending angle, which allows one to readily predict the emergence of T phase and ferroelectric vortex in bent BFO membranes. These results not only provide fundamental understanding of mesoscale super-elastic mechanisms but also reveal exotic domain states of ferroelectric membranes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Epitaxial Growth and Band Alignment of p-NiO/n-Fe2O3 Heterojunction on Al2O3(0001)

Fe2O3 is one of the promising oxide semiconductors as photoanodes for photoelectrochemical water splitting, but its efficiency is still limited by the short diffusion length of photo-excited carriers. Using the internal electric field formed at a p-n heterojunction (HJ) is an efficient strategy to mitigate such limitation. Accordingly, the interfacial atomic structure and band alignment are the most crucial parameters for efficiency optimization. In this work, we report on the epitaxial growth and determination of the band energy alignment of NiO/Fe2O3 p-n heterojunction grown on Al2O3(0001) substrate by pulsed laser deposition. We show that high crystalline quality NiO(111) thin films can be grown on Fe2O3(0001) with epitaxial relationships of [1 ¯11]NiO||[0001 ¯ ]Fe2O3(out-of-plane), [1 ¯1 ¯0]NiO||[011 ¯0]Fe2O3 and [1 ¯12 ¯ ]NiO||[21 ¯1 ¯0]Fe2O3(in-plane). The rotation of NiO hexagons by 30° can effectively reduce the lattice mismatch from ~17.4% to ~1.58%. High resolution X-ray photoelectron spectroscopy reveals that valence and conduction band offset of NiO/Fe2O3 heterojunction are 0.7 eV and 2.3 eV with an upward band bending potential of 0.23 eV for Fe2O3 and a downward band bending potential of 0.32 eV for NiO, respectively. This kind of interfacial band alignment not only facilitates the charge separation, but lowers the overpotentials for oxygen evolution reaction.

Photoelectrochemical Water Splitting, Oxide Semico↗
DOE OSTI2020

Atomistic modeling of energy band alignment in CdTe(1 0 0) and CdTe(1 1 1) surfaces

An atomic-scale perspective of energy band alignment in CdTe surfaces has not been spatially studied despite the major role surfaces play in forming interfaces within CdTe-based thin film photovoltaic devices. Atomistic modeling based on density functional theory coupled with surface Green’s function is used for calculating energy band alignment of CdTe surfaces. The CdTe(1 0 0) ((1×1) and c(2×2) reconstruction) and CdTe(1 1 1) ((1×1) and (2×2) reconstruction) facets without and with surface relaxation provide insightful band bending characteristics that influence charge carrier transport. Results show that unrelaxed (1×1) CdTe(1 0 0) and CdTe(1 1 1) surfaces bend the valence band downward with surface polarity dictating the surface potential magnitude. The reconstructed CdTe(1 0 0) c(2×2) and CdTe(1 1 1) (2×2) surfaces result in favorable surface electronic features in relation to their unreconstructed variants. In addition, the structurally relaxed CdTe(1 1 1) surfaces develop an internal energy cusp potential that may enhance hole charge transport toward the back of CdTe solar cell devices. In conclusion, energy band alignments calculated within the study lead to a detailed understanding of how CdTe surfaces may affect CdTe-based thin film photovoltaic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A New Computational Method for Membrane Compressibility: Bilayer Mechanical Thickness Revisited

Because lipid bilayers can bend and stretch in ways similar to thin elastic sheets, physical models of bilayer deformation have utilized mechanical constants such as the moduli for bending rigidity (κ C ) and area compressibility (K A ). However, the use of these models to quantify the energetics of membrane deformation associated with protein-membrane interactions, and the membrane response to stress is often hampered by the shortage of experimental data suitable for the estimation of the mechanical constants of various lipid mixtures. Although computational tools such as molecular dynamics simulations can provide alternative means to estimate K A values, current approaches suffer significant technical limitations. Here, in this study, we present a novel, to our knowledge, computational framework that allows for a direct estimation of K A values for individual bilayer leaflets. The theory is based on the concept of elasticity and derives K A from real-space analysis of local thickness fluctuations sampled in molecular dynamics simulations. We explore and validate the model on a large set of single and multicomponent bilayers of different lipid compositions and sizes, simulated at different temperatures. The calculated bilayer compressibility moduli agree with values estimated previously from experiments and those obtained from a standard computational method based on a series of constrained tension simulations. We further validate our framework in a comparison with an existing polymer brush model and confirm the polymer brush model’s predicted linear relationship with proportionality coefficient of 24, using elastic parameters calculated from the simulation trajectories. The robustness of the results that emerge from the method allows us to revisit the origins of the bilayer mechanical (compressible) thickness and in particular its dependence on acyl-chain unsaturation and the presence of cholesterol.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

On the Mechanism of Bilayer Separation by Extrusion, or Why Your LUVs Are Not Really Unilamellar

Extrusion through porous filters is a widely used method for preparing biomimetic model membranes. Of primary importance in this approach is the efficient production of single bilayer (unilamellar) vesicles that eliminate the influence of interlamellar interactions and strictly define the bilayer surface area available to external reagents such as proteins. Sub-microscopic vesicles produced using extrusion are widely assumed to be unilamellar, and large deviations from this assumption would dramatically impact interpretations from many model membrane experiments. In this work, using three probe-free methods—small-angle X-ray and neutron scattering (SAXS and SANS) and cryogenic electron microscopy (cryoEM)—we report unambiguous evidence of extensive multilamellarity in extruded vesicles composed of neutral phosphatidylcholine lipids, including for the common case of neutral lipids dispersed in physiological buffer and extruded through 100 nm diameter pores. In such preparations, only ~35% of lipids are externally accessible, and this fraction is highly dependent on preparation conditions. Charged lipids promote unilamellarity, as does decreasing solvent ionic strength, indicating the importance of electrostatic interactions in determining the lamellarity of extruded vesicles. Smaller extrusion pore sizes also robustly increase the fraction of unilamellar vesicles, suggesting a role for membrane bending. Taken together, these observations suggest a mechanistic model for extrusion, wherein formation of unilamellar vesicles involves competition between bilayer bending and adhesion energies. The findings presented here have wide-ranging implications for the design and interpretation of model membrane studies, especially ensemble-averaged observations relying on the assumption of unilamellarity.

59 BASIC BIOLOGICAL SCIENCES↗