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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 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Efficient 2-μm laser oscillation of 5% Tm{sup 3+} : KLu(WO{sub 4}){sub 2} disks and 5% Tm{sup 3+} : KLu(WO{sub 4}){sub 2}/KLu(WO{sub 4}){sub 2} composite structures

The spectral and lasing characteristics of active disk elements made of double potassium – lutetium tungstates 5% Tm : KLuW and 5% Tm : KLuW/KLuW composite structures are comparatively studied. Laser power of about 5 W in the cw regime at a wavelength of 1.85 μm was achieved in a composite sample with the active layer thickness of 250 μm. Under quasi-cw pumping, the slope efficiency of all the studied samples exceeded 50%. It is experimentally shown that the internal stresses in the composite structures strongly affect the spectral characteristics of the laser radiation. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Radial Transport and Meridional Circulation in Accretion Disks

Radial transport of particles, elements and fluid driven by internal stresses in three-dimensional (3D) astrophysical accretion disks is an important phenomenon, potentially relevant for the outward dust transport in protoplanetary disks, origin of the refractory particles in comets, isotopic equilibration in the Earth–Moon system, etc. To gain better insight into these processes, we explore the dependence of meridional circulation in 3D disks with shear viscosity on their thermal stratification, and demonstrate a strong effect of the latter on the radial flow. Previous locally isothermal studies have normally found a pattern of the radial outflow near the midplane, switching to inflow higher up. Here we show, both analytically and numerically, that a flow that is inward at all altitudes is possible in disks with entropy and temperature steeply increasing with height. Such thermodynamic conditions may be typical in the optically thin, viscously heated accretion disks. Disks in which these conditions do not hold should feature radial outflow near the midplane, as long as their internal stress is provided by the shear viscosity. Our results can also be used for designing hydrodynamical disk simulations with a prescribed pattern of the meridional circulation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Exploiting ultra-large linear elasticity over a wide temperature range in nanocrystalline NiTi alloy

Many shape memory alloys can support large recoverable strains of a few percent by reversible stress-induced martensite transformation, yet they behave non-linear within a narrow operating temperature range. Developing the bulk metallic materials with ultra-large linear elasticity over a wide temperature range has proven to be difficult. In this work, a material design concept was proposed, that is true elastic deformation and reversible twinning-detwinning deformation run in parallel to overcome this challenge. By engineering the residual internal stress to realize the concurrency of true elastic deformation and twinning-detwinning deformation, a bulk nanocrystalline NiTi that possesses an ultra-large linear elastic strain up to 5.1 % and a high yield stress of 2.16 GPa over a wide temperature range of 270 °C was developed. This study offers a new avenue for developing the metallic materials with ultra-large linear elasticity over a wide temperature range of 270 °C (from 70 °C to -197 °C).

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nanostructural states in Nb-Al mechanocomposite after combined deformation treatment

Nanostructural states were investigated, that were formed in Nb-Al system-based mechanocomposite after combined deformation treatment that includes mechanical activation in a planetary ball mill and subsequent consolidation by torsion under pressure on Bridgman anvils. The formation of the layered structure, consisting of Nb and Al nanobands with width from several to several tens of nanometers was revealed. The structural states with high elastic curvature of crystal lattice and high level of local internal stresses found in Nb and Al subgrains were investigated by transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2016

CrAlN coating to enhance the power loss and magnetostriction in grain oriented electrical steel

Grain oriented electrical steels (GOES) are coated with aluminium orthophosphate on top of a forsterite (Mg{sub 2}SiO{sub 4}) layer to provide stress and insulation resistance to reduce the power loss and magnetostriction. In this work Chromium Aluminium Nitride (CrAlN) was coated on GOES samples with electron beam physical vapour deposition and was tested in the single strip and magnetostriction tester to measure the power loss and magnetostriction before and after coating. Power loss was reduced by 2% after coating and 6 % post annealing at 800 °C. For applied compressive stress of 6 MPa, the magnetostrictive strain was zero with the CrAlN coating as compared to 22 and 24 μϵ for fully finished GOES and GOES without phosphate coating. The thickness of the coating was found to be 1.9 ± 0.2 μm estimated with Glow Discharge Optical Emission Spectroscopy (GDOES). The magnetic domain imaging showed domain narrowing after coating. The reduction in power loss and magnetostriction was due to the large residual compressive stress and Young’s modulus (270 GPa) of the coating.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Shape effect on drying behavior of cement-based materials: Mechanisms and numerical analysis

The shape of the specimen or structure has a direct impact on the behavior of drying concrete. This effect is not taken into account in most of shrinkage models and codes. Only the current B4 model and its previous version B3 model incorporate a shape factor. The determination of this coefficient is based on the nonlinear moisture diffusion analysis, which can explain the shape effect on the shrinkage rate. However, the model integrates this coefficient in the ultimate shrinkage values as well. An experimental study has been performed to confirm and understand this behavior. The mass loss and drying shrinkage of cylinders showed higher rate and ultimate values than the prisms, for the same effective cross section thickness. To explain this result, the drying, the differential shrinkage, the internal stress and the damaged depth were determined for both shapes through numerical modeling. The main input data of the model were the measured mass loss and shrinkage. The calculated desorption isotherm curve of the cylinder was below that of the prism, which is consistent with its higher ultimate mass-loss. The determination of stress profiles indicates slower stress mitigation for the cylinder. The cylinder develops a larger relative damaged area, defined as the part of the specimen where cracking is likely to occur due to tensile stresses. The results actually show that differential shrinkage between the edge and the core is more pronounced for the cylinder and decreases with time.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Influence of deformation on structural-phase state of weld material in St3 steel

The structural-phase condition of the weld material subjected to the plastic deformation was investigated using the translucent diffraction electron microscopy method. The investigations were carried out near the joint of the weld and the base metal. The seam was done by the method of manual arc welding without artificial defects. The St3 steel was taken as the welded material. Influence of the plastic deformation on morphology, phase composition, defect structure and its parameters of weld metal was revealed. All investigations were done at the distance of 0.5 mm from the joint of the weld and the base metal at the deformation degrees from 0 to 5% and after destruction of a sample. It was established that deformation of the sample did not lead to qualitative changes in the structure (the structure is still presented by ferrite-pearlite mixture) but changed the quantitative parameters of the structure, namely, with the increase of plastic deformation a part of the pearlite component becomes more and more imperfect. In the beginning it turns into the destroyed pearlite then into ferrite, the volume fraction of pearlite is decreased. The polarization of dislocation structure takes place but it doesn’t lead to the internal stresses that can destroy the sample.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Interdiffusion and stress development in single-crystalline Pd/Ag bilayers

Interdiffusion and stress evolution in single-crystalline Pd/single-crystalline Ag thin films were investigated by Auger electron spectroscopy sputter-depth profiling and in-situ X-ray diffraction, respectively. The concentration-dependent chemical diffusion coefficient, as well as the impurity diffusion coefficient of Ag in Pd could be determined in the low temperature range of 356 °C–455 °C. As a consequence of the similarity of the strong concentration-dependences of the intrinsic diffusion coefficients, the chemical diffusion coefficient varies only over three orders of magnitude over the whole composition range, despite the large difference of six orders of magnitude of the self-diffusion coefficients of Ag in Ag and Pd in Pd. It is shown that the Darken-Manning treatment should be adopted for interpretation of the experimental data; the Nernst-Planck treatment yielded physically unreasonable results. Apart from the development of compressive thermal stress, the development of stress in both sublayers separately could be ascribed to compositional stress (tensile in the Ag sublayer and compressive in the Pd sublayer) and dominant relaxation processes, especially in the Ag sublayer. The effect of these internal stresses on the values determined for the diffusion coefficients is shown to be negligible.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Influence of crystallographic orientation on the response of copper crystallites to nanoindentation

Molecular dynamics simulation was performed to study the features of nucleation and development of plastic deformation in copper crystallites in nanoindentation with different crystallographic orientations of their loaded surface: (011), (001), and (111). Atomic interaction was described by a potential constructed in terms of the embedded atom method. It is shown that behavior of the crystallite reaction force correlates well with a change in the fraction of atoms involved in local structural rearrangements. The generation of local structural changes decreases the slope of the crystallite reaction force curve or results in an extremum due to internal stress relaxation. Analysis of structural changes in the material being indented demonstrates that the orientation of its loaded surface greatly affects the features of nucleation and development of plastic deformation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1971

Relative susceptibility of titanium alloys to hot-salt stress-corrosion

Susceptibility of titanium alloys to hot-salt stress-corrosion cracking increased as follows: Ti-2Al-11Sn-5Zr-0.2Si(679), Ti-6Al-2Sn-4Zr-2Mo(6242), Ti-6Al-4V(64), Ti-6Al-4V-3Co(643), Ti-8Al-1Mo-1V(811), and Ti-13V-11Cr-3A1(13-11-3). The Ti-5Al-6Sn-2Zr-1Mo-0.25Si(5621S) alloy was both the least and most susceptible depending on heat treatment. Such rankings can be drastically altered by heat-to-heat and processing variations. Residual compressive stresses and cyclic exposures also reduce susceptibility to stress-corrosion. Simulated turbine-engine compressor environmental variables such as air velocity, pressure, dewpoint, salt concentration, and salt deposition temperature have only minor effects. Detection of substantial concentrations of hydrogen in all corroded alloys confirmed the existence of a hydrogen embrittlement mechanism.

Gray, H. R.↗
DOE OSTI2019

Influence of Detwinning on the Shape Memory Effect in Ni{sub 55}Fe{sub 18}Ga{sub 27} Single Crystals

Deformation mechanisms, one-way and two-way shape memory effects were studied in the mode of compression in the [011] single crystal of the Ni{sub 55}Fe{sub 18}Ga{sub 27} alloy where the detwinning occurred during deformation and in the [001] single crystal where the detwinning was forbidden. It was found that the [001] and [011] crystals deformed by different mechanisms during compression to 5% (reorientation was in [001] crystal, and the reorientation and detwinning were in [011] crystal) and from 15 to 20% (the 14 M → L1{sub 0} transition was in [001] crystal and plastic deformation of 14 M phase was in [011]). The compression of both single crystals from 5 to 15% occurred due to the same mechanisms: the 10 M ↔ 14 M transformation and the plastic deformation of the 14 M martensite. The 14 M and L1{sub 0} phases were stable under load, and they transformed to the 10 M martensite on unloading. It was shown that the crystal orientation and detwinning hardly affected the value of the one-way shape memory effect since both crystals were in the 10 M martensite after preliminary deformation. In this case, the transformation of 10 M martensite to the austenite on heating was accompanied by a strain of about 5% and this was the maximum value of the shape memory effect. It was found that the detwinning significantly affected the temperature ranges of strain recovery. In the [011] crystal, the strain recovered in a very narrow interval on heating (1-2°C), whereas in the [001] crystal the shape memory effect was observed in “normal” temperature range (~ 10°C). The detwinning resulted in the formation of a large oriented internal stress during the preliminary deformation that increased the value of the two-way shape memory effect that was observed in [011] crystals in comparison with the [001] crystals.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Effects of hot-salt stress corrosion on titanium alloys.

Susceptibility of titanium alloys to hot-salt stress-corrosion cracking increased as follows: Ti-2Al-11Sn-5Zr-1Mo-0.2Si (679), Ti-6Al-2Sn-4Zr-2Mo (6242), Ti-6Al-4V (64), Ti-6Al-4V-3Co (643), Ti-8Al-1Mo-1V (811), and Ti-13V-11Cr-3Al (13-11-3). The Ti-5Al-6Sn-2Zr-1Mo-0.25Si (5621S) alloy was both the least and most susceptible, depending on heat treatment. Such rankings can be drastically altered by heat-to-heat variations and processing conditions. Residual compressive stresses reduce susceptibility to stress-corrosion. Detection of substantial concentrations of hydrogen in all corroded alloys confirmed the generality of a previously proposed hydrogen embrittlement mechanism.

Gray, H. R.↗
DOE OSTI2018

Spark Plasma Sintering of high-density fine-grained Y2.5Nd0.5Al5O12+SiC composite ceramics

Highlights: • YAG + (10, 20) wt.% α-SiC high-density ceramics obtained by SPS. • YAG + α-SiC ceramics have a more fine-grained structure than pure garnet. • The optimal sintering temperature of YAG + SiC ceramics is lower than that of garnet. • Introduction of α-SiC particles creates internal stress fields in garnet. • Introduction of α-SiC particles results in lower sintering activation energy of garnet. - Abstract: Spark Plasma Sintering (SPS) has been used to produce samples of fine-grained composites Y{sub 2.5}Nd{sub 0.5}Al{sub 5}O{sub 12} + x wt.% α-SiC (x = 1020) with ∼98–99% density. The microstructure of the composites has been studied, as well as the impact of α-SiC particles on the mechanical properties and kinetics of composite sintering. The introduction of the α-SiC part has been demonstrated to form a more fine-grained structure and under the given SPS conditions change the sintering mechanism in ceramics. The study has also demonstrated that introduction of α-SiC particles into garnet results in formation of internal stress fields, which, in turn, leads to a decrease in the activation energy of sintering of fine-grained composites at high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Laser-excited optical emission response of CdTe quantum dot/polymer nanocomposite under shock compression

Laser-driven shock compression experiments and corresponding finite element method simulations are carried out to investigate the blueshift in the optical emission spectra under continuous laser excitation of a dilute composite consisting of 0.15% CdTe quantum dots by weight embedded in polyvinyl alcohol polymer. This material is a potential candidate for use as internal stress sensors. The analyses focus on the time histories of the wavelength blue-shift for shock loading with pressures up to 7.3 GPa. The combined measurements and calculations allow a relation between the wavelength blueshift and pressure for the loading conditions to be extracted. It is found that the blueshift first increases with pressure to a maximum and subsequently decreases with pressure. This trend is different from the monotonic increase of blueshift with pressure observed under conditions of quasistatic hydrostatic compression. Additionally, the blueshift in the shock experiments is much smaller than that in hydrostatic experiments at the same pressure levels. The differences in responses are attributed to the different stress states achieved in the shock and hydrostatic experiments and the time dependence of the mechanical response of the polymer in the composite. The findings offer a potential guide for the design and development of materials for internal stress sensors for shock conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Optically switchable natural silk

An optically active bio-material is created by blending natural silk fibers with photoisomerizable chromophore molecules—azobenzenebromide (AzBr). The material converts the energy of unpolarized light directly into mechanical work with a well-defined direction of action. The feasibility of the idea to produce optically driven microsized actuators on the basis of bio-material (silk) is proven. The switching behavior of the embedded AzBr molecules was studied in terms of UV/Vis spectroscopy. To test the opto-mechanical properties of the modified fibers and the structural changes they undergo upon optically induced switching, single fiber X-ray diffraction with a micron-sized synchrotron radiation beam was combined in situ with optical switching as well as with mechanical testing and monitoring. The crystalline regions of silk are not modified by the presence of the guest molecules, hence occupy only the amorphous part of the fibers. It is shown that chromophore molecules embedded into fibers can be reversibly switched between the trans and cis conformation by illumination with light of defined wavelengths. The host fibers respond to this switching with a variation of the internal stress. The amplitude of the mechanical response is independent of the applied external stress and its characteristic time is shorter than the relaxation time of the usual mechanical response of silk.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Enhanced lithium ion storage in nanoimprinted carbon

Disordered carbons processed from polymers have much higher theoretical capacity as lithium ion battery anode than graphite, but they suffer from large irreversible capacity loss and have poor cyclic performance. Here, a simple process to obtain patterned carbon structure from polyvinylpyrrolidone was demonstrated, combining nanoimprint lithography for patterning and three-step heat treatment process for carbonization. The patterned carbon, without any additional binders or conductive fillers, shows remarkably improved cycling performance as Li-ion battery anode, twice as high as the theoretical value of graphite at 98 cycles. Localized electrochemical strain microscopy reveals the enhanced lithium ion activity at the nanoscale, and the control experiments suggest that the enhancement largely originates from the patterned structure, which improves surface reaction while it helps relieving the internal stress during lithium insertion and extraction. This study provides insight on fabricating patterned carbon architecture by rational design for enhanced electrochemical performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Contributions of Stress And Oxidation on the Formation of Whiskers in Pb-Free Solders

This report summarizes the research activities of WP-1754. The study focusses on the environmental factors influencing formation of lead free whiskers on electrodeposited tin coatings over copper (or copper containing) substrates. Much of the initial results are summarized in an interim report. From the initial results, two main areas were chosen to be the focus of additional research: the demonstration of effects of elastic stress state in the nucleation of whiskers and the confirmation of the effect of oxygen/nitrogen ratio in the formation of whiskers. Different levels of elastic stress were induced with the incorporation of a custom designed fixture that loaded the substrates in a four-point bending configuration and were maintained in an environmental chamber under conditions deemed favorable for whisker growth. The results show that induced elastic stress slightly increased the concentration of nucleation sites of whiskers. The effects of oxygen content were studied by aging substrates in gas vials of varying absolute pressure and different oxygen/nitrogen ratios. The concentration of whiskers were measured and appear to be sensitive to absolute pressure but are not sensitive to oxygen content (as previously observed).

36 MATERIALS SCIENCE↗
NASA NTRS1997

Damage Initiation and Ultimate Tensile Strength of Scaled [0 deg n/90 deg n/0 deg n]sub T Graphite-Epoxy Coupons

Previous research on scaling effects in composite materials has demonstrated that the stress levels at first ply failure and ultimate failure of composite laminates are dependent on the size of the laminate. In particular, the thickness dimension has been shown to be the most influential parameter in strength scaling of composite coupons loaded in tension. Geometrically and constitutively scaled laminates exhibit decreasing strength with increasing specimen size, and the magnitude of the strength-size effect is a function of both material properties and laminate stacking sequence. Some of the commonly used failure criteria for composite materials such as maximum stress, maximum strain, and tensor polynomial (e.g., Tsai-Wu) cannot account for the strength-size effect. In this paper, three concepts are developed and evaluated for incorporating size dependency into failure criteria for composite materials. An experimental program of limited scope was performed to determine the first ply failure stress in scaled cross-ply laminates loaded in tension. Test specimens were fabricated of AS-4/3502 graphite-epoxy composite material with laminate stacking sequences of [0 deg n/90 deg n/o deg n]subT where n=1-6. Two experimental techniques were used to determine first ply failure, defined as a transverse matrix crack in the 90 deg ply: (1) step loading with dye penetrant x-ray of the specimen at each load interval, and (2) acoustic emission. The best correlation between first ply failure analysis and experimental data was obtained using a modified Weibull approach which incorporated the residual thermal stress and the outer ply constraint, as well as the ply thickness effect. Finally, a second set of experiments was performed to determine the tensile response and ultimate failure of the scaled cross-ply laminates. The results of these experiments indicated no influence of specimen size on tensile response or ultimate strength.

Jackson, Karen E.↗