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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Conservative solute transport processes and associated transient storage mechanisms: Comparing streams with contrasting channel morphologies, land use and land cover

Abstract Land use within a watershed impacts stream channel morphology and hydrology and, therefore, in‐stream solute transport processes and associated transient storage mechanisms. This study evaluated transport processes in two contrasting stream sites where channel morphology was influenced by the surrounding land use, land cover, climate and geologic controls: Como Creek, CO, a relatively undisturbed, high gradient, forested stream with a gravel bed and complex channel morphology, and Clear Creek, IA, an incised, low‐gradient stream with low‐permeability substrate draining an agricultural landscape. We performed conservative stream tracer injections at these sites to address the following questions: (1) How does solute transport vary between streams with differing morphologies? and (2) How does solute transport at each stream site change as a function of discharge? We analysed in‐stream tracer time series data and compared results quantifying solute attenuation in surface and subsurface transient storage zones. Significant trends were observed in these metrics with varying discharge conditions at the forested site but not at the agricultural site. There was a broad range of transport mechanisms and evidence of substantial exchange with both surface and hyporheic transient storage in the relatively undisturbed, forested stream. Changing discharge conditions activated or deactivated different solute transport mechanisms in the forested site and greatly impacted advective travel time. Conversely in the simplified agricultural stream, there was a narrow range of solute transport behaviour across flows and predominantly surface transient storage at all measured discharge conditions. These results demonstrate how channel simplification inhibits available solute transport mechanisms across varying discharge conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Modifications to Nano- and Microstructural Quality and the Effects on Mechanical Integrity in Paget's Disease of Bone

ABSTRACT Paget's disease of bone (PDB) is the second most common bone disease mostly developing after 50 years of age at one or more localized skeletal sites; it is associated with severely high bone turnover, bone enlargement, bowing/deformity, cracking, and pain. Here, to specifically address the origins of the deteriorated mechanical integrity, we use a cohort of control and PDB human biopsies to investigate multiscale architectural and compositional modifications to the bone structure (ie, bone quality) and relate these changes to mechanical property measurements to provide further insight into the clinical manifestations (ie, deformities and bowing) and fracture risk caused by PDB. Here, at the level of the collagen and mineral (ie, nanometer-length scale), we find a 19% lower mineral content and lower carbonate-to-phosphate ratio in PDB, which accounts for the 14% lower stiffness and 19% lower hardness promoting plastic deformation in pathological bone. At the microstructural scale, trabecular regions are known to become densified, whereas cortical bone loses its characteristic parallel-aligned osteonal pattern, which is replaced with a mosaic of lamellar and woven bone. Although we find this loss of anisotropic alignment produces a straighter crack path in mechanically-loaded PDB cases, cortical fracture toughness appears to be maintained due to increased plastic deformation. Clearly, the altered quality of the bone structure in PDB affects the mechanical integrity leading to complications such as bowing, deformities, and stable cracks called fissure fractures associated with this disease. Although the lower mineralization and loss of aligned Haversian structures do produce a lower modulus tissue, which is susceptible to deformities, our results indicate that the higher levels of plasticity may compensate for the lost microstructural features and maintain the resistance to crack growth. © 2014 American Society for Bone and Mineral Research

Zimmermann, Elizabeth A.↗
DOE OSTI2016

Microscale modeling of effective mechanical and electrical properties of textiles

Here, a computational framework for assisting in the development of novel textiles is presented. Electronic textiles are key in the rapidly growing field of wearable electronics for both consumer and military uses. There are two main challenges to the modeling of electronic textiles: the discretization of the textile microstructure and the interaction between electromagnetic and mechanical fields. A director-based beam formulation with an assumed electrical current is used to discretize the fabric at the level of individual fibrils. The open-source package FEniCS was used to implement the finite element model. Contact integrals were added into the FEniCS framework so that multiphysics contact laws can be incorporated in the same framework, leveraging the code generation and automated differentiation capabilities of FEniCS to produce the tangents needed by the implicit solution method. The computational model is used to construct and determine the mechanical, thermal, and electrical properties of a representative volume elements of a plain woven textile. Dynamic relaxation to solve the mechanical fields and the electrical and thermal fields is solved statically for a given mechanical state. The simulated electrical responses are fit to a simplified Kirchhoff network model to determine effective resistances of the textile.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Mechanism of N[superscript 10]-formyltetrahydrofolate synthetase derived from complexes with intermediates and inhibitors

N{sup 10}-formyltetrahydrofolate synthetase (FTHFS) is a folate enzyme that catalyzes the formylation of tetrahydrofolate (THF) in an ATP dependent manner. Structures of FTHFS from the thermophilic homoacetogen, Moorella thermoacetica, complexed with (1) a catalytic intermediate-formylphosphate (XPO) and product-ADP; (2) with an inhibitory substrate analog-folate; (3) with XPO and an inhibitory THF analog, ZD9331, were used to analyze the enzyme mechanism. Nucleophilic attack of the formate ion on the gamma phosphate of ATP leads to the formation of XPO and the first product ADP. A channel that leads to the putative formate binding pocket allows for the binding of ATP and formate in random order. Formate binding is due to interactions with the gamma-phosphate moiety of ATP and additionally to two hydrogen bonds from the backbone nitrogen of Ala276 and the side chain of Arg97. Upon ADP dissociation, XPO reorients and moves to the position previously occupied by the beta-phosphate of ATP. Conformational changes that occur due to the XPO presence apparently allow for the recruitment of the third substrate, THF, with its pterin moiety positioned between Phe384 and Trp412. This position overlaps with that of the bound nucleoside, which is consistent with a catalytic mechanism hypothesis that FTHFS works via a sequential ping-pong mechanism. More specifically, a random bi uni uni bi ping-pong ter ter mechanism is proposed. Additionally, the native structure originally reported at a 2.5 {angstrom} resolution was redetermined at a 2.2 {angstrom} resolution.

08 HYDROGEN↗
DOE OSTI2024

Constraints on a generalization of geometric quantum mechanics from neutrino and B0-$$ \overline{B^0} $$ oscillations

Abstract Nambu Quantum Mechanics, proposed in Phys. Lett. B536, 305 (2002), is a deformation of canonical Quantum Mechanics in which the manifold over which the “phase” of an energy eigenstate time evolves is modified. This generalization affects oscillation and interference phenomena through the introduction of two deformation parameters that quantify the extent of deviation from canonical Quantum Mechanics. In this paper, we constrain these parameters utilizing atmospheric neutrino oscillation data, andB 0 -$$ \overline{B^0} $$ B 0 ¯ oscillation data from Belle. Surprisingly, the bound from atmospheric neutrinos is stronger than the bound from Belle. Various features of Nambu Quantum Mechanics are also discussed.

Physics↗
DOE OSTI2011

Chemical and Mechanical Degradation of Sulfonated Poly(sulfone) Membranes in Vanadium Redox Flow Batteries

A sulfonated poly(sulfone) (S-Radel{reg_sign}) membrane with high proton conductivity and low vanadium ion diffusion showed high initial performance in a vanadium redox flow battery (VRFB) but suffered damage during charge/discharge cycling. The S-Radel membrane had different degradation behaviors in flow cell cycling and ex-situ vanadium ion immersion tests. The S-Radel membrane immersed in V5+ solution cracked into small pieces, but in the VRFB cell, the membrane underwent internal delamination preferentially on the side of the membrane that faced the positive electrode. A vanadium-rich interface was observed near the membrane surface that experienced delamination and Raman spectroscopic analysis of the surfaces of the membrane indicated a slightly depressed 1026 cm-1 band corresponding to the sulfonate SO2 stretch for the degraded surface. Even though the S-Radel membrane underwent severe mechanical damage during the flow cell cycling, significant chemical degradation was not obvious from the spectroscopic analyses. For the VRFB containing an S-Radel membrane, an increase in membrane resistance caused an abnormal voltage depression during the discharge cycle. The reversible increase in membrane resistance and severe mechanical degradation of the membrane during cycling may be attributed repeated formation and dissolution of particles inside the membrane. The mechanical stresses imposed by the particles coupled with a small amount of chemical degradation of the polymer by V5+, are likely degradation mechanisms of the S-Radel membrane in VRFBs under high state-of-charge conditions.

25 ENERGY STORAGE↗
DOE OSTI2018

Understanding the influence of carbon addition on the corrosion behavior and mechanical properties of Al alloy “covetics”

The recent invention of a new processing method for metals and alloys involving the addition of carbon has led to several reports demonstrating an enhancement in the mechanical properties of the materials known as covetics. In this work the corrosion behavior and mechanical properties of a 6061 aluminum-carbon covetic are investigated and explained. Covetic samples with carbon added were found to exhibit a corrosion potential 40-70mV higher than samples processed without the addition of carbon. However, the corrosion current density of the covetic with carbon added relative to samples without carbon added was also increased. Surface characterization following the corrosion testing using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction revealed significant differences between the covetic with carbon added and the covetic parent material processed without carbon addition. After corrosion, the surface of the covetic with carbon added showed a alloying element rich surface morphology from the parent alloy and exhibited a smaller grain size than the material processed without carbon. Additionally, changes in the mechanical properties of the covetic were observed with both the hardness and the compressive strength of the covetic increasing as a result of carbon addition. Finally, the observed change in corrosion behavior and mechanical properties of the covetic with carbon added, along with the physical characterization, are consistent with the formation of a secondary phase in the alloy induced by carbon addition during the process used to make the covetic.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Investigation of the Mechanical Properties of GdBa{sub 2}Cu{sub 3}O{sub 7−δ} Added with Nanosized Ferrites ZnFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} Using Ultrasonic Measurement

Recently, there is much interest in studying the effect of nanosized ferrites addition on high- T{sub c} superconductors. However, little information is available on the mechanical properties. We have investigated the effect of (CoFe{sub 2}O{sub 4}){sub x} and (ZnFe{sub 2}O{sub 4}){sub x} nanosized ferrites with 0.01 ≤ x ≤ 0.40 on the mechanical properties of the high- T{sub c} superconducting compound GdBa{sub 2}Cu{sub 3}O{sub 7−δ} (Gd-123) prepared by the conventional solid-state reaction technique. Elastic parameters including shear modulus (G), bulk modulus (B), and Young’s modulus (E) of all samples were inspected using ultrasonic measurements and compared with Vickers microhardness results. Furthermore, the porosity of the samples was investigated and correlated to Young’s modulus, which was corrected to zero porosity using different models. The corrected values were correlated with Vickers microhardness. Moreover, the Debye temperature (θ{sub D}) and the electron-phonon coupling factor (λ) were also determined as a function of x. We observed that the different nanoparticles addition has influenced the Gd-123 compound differently. For (ZnFe{sub 2}O{sub 4}){sub x} added samples, the mechanical properties and Debye temperature improved up to x = 0.06, then deteriorated with further addition. However, (CoFe{sub 2}O{sub 4}){sub x} addition improved the mechanical properties for all samples with x up to 0.40. We found that the proportionality constant between the corrected values of E and H{sub v} and G and H{sub v} are strongly dependent on the porosity corrections and the kind of superconducting material. This indicates that the widely used formula E = 81.96 H{sub v} may not be valid for all types of superconducting materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Flux Pinning Mechanism in BaSnO{sub 3}-Added GdBa{sub 2}Cu{sub 3}O{sub 7-x} Films with Different Thickness

Types of flux pinning mechanism in pure and BaSnO{sub 3} (BSO)-added GdBa{sub 2}Cu{sub 3}O{sub 7-x} (GdBCO) superconducting films have been determined by using the Dew-Hughes model. We have found that as the BSO content increases up to 4 wt%, dominant pinning mechanism of GdBCO films has changed from normal surface pinning due to intrinsic linear defects to normal point pinning by BSO addition. Careful analysis on the scaling of the flux pinning for the 4 wt% BSO-doped GdBCO films with various film thicknesses revealed that the pinning mechanism came from the hybrid pinning of two kinds of pinning types. In addition to the normal point pinning by BSO addition, another type of Δκ-pinning was observed to be prominent in the thinner films in low magnetic field region as normal point pinning was deteriorated. Through the EXAFS analysis, it was found that the Δκ-pinning is possibly originated from the oxygen deficiency in localized position. These results suggested that film thickness directly affects the flux pinning mechanism of the BSO-doped GdBCO films, and in the application point of view, an optimization of the film thickness may be crucial to operate normal point pinning induced by BSO addition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Small Fatigue Crack Growth Mechanisms and Interfacial Stability in Cold-Spray 6061 Aluminum Alloys and Coatings

Cold-spray-processed aluminum alloys have static mechanical properties superior to those of aerospace cast alloys, and similar to those of their wrought counterparts, making them good candidates for structural applications. However, their broad and confident use relies upon systematic fatigue crack growth studies to investigate and demonstrate the materials' performance in critical high-integrity components. In this work, the fatigue crack growth behavior in early stages (small crack growth regime) was investigated for cold-spray processed 6061 aluminum alloys and coatings, at stress ratio R = 0.1, in room temperature laboratory air. The effects of the characteristic microstructure and initial flaw size on the fatigue crack growth response were systematically examined, and the crack growth mechanisms at the microstructural scale were established and compared to those of long cracks. The mechanical interfacial stability of coatings was examined in cold-spray 6061-rolled 6061-T6 couples. An original method of quantifying the deposition-substrate interfacial strength, and correlating it to the response under cyclic loading via crack-interface stability maps, was developed. The proposed methodology is based on combined scratch testing and fracture mechanics formulations, and failure at the coating-substrate interface can be predicted for any crack growth scenario under cyclic loading. The method can be broadly used for the design and optimization of cold-spray and other coatings, as well as in structural repair.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A Coupled Small and Wide-Angle X-Ray Scattering Study of Phase Transformation Mechanisms in U-6Wt Pct Nb

The elevated temperature phase transformation kinetics of U-6wt%Nb in both wrought and cast conditions were investigated using in-situ high energy synchrotron X-ray scattering. The evolution of the phase content, γ-phase composition, and microstructure morphology was determined through the analysis of simultaneously collected wide-angle diffraction and small-angle scattering (SAXS) data. The results of the wide-angle scattering analysis, especially the phase fractions and average composition of the γ-phase, provide model parameters to enable a quantitative analysis using the SAXS data. Greater clarity regarding the kinetics of different precipitation mechanisms, namely the continuous precipitation (CP) of α-U within the γ-phase matrix and the discontinuous (DP) grain boundary precipitation of a lamellar microstructure, consisting of α-U and Nb-rich γ-phase are obtained from the coupled measurement modes. These results indicate that the CP mechanism is responsible for the initial precipitation of α-U at all temperatures considered. Near the nose in the time-temperature-transformation (TTT) diagram at ~798 K, both mechanisms are active during the early stages of phase transformation. However, the DP mechanism has an increasingly long incubation period with decreasing temperature below the TTT nose. In conclusion, the average interlamellar spacing obtained from the SAXS analysis increases with time, providing further evidence of the so-called divergent DP behavior previously observed in U-6wt%Nb alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Processing Parameter Control of Lifetime-Limiting Failure Mechanisms in Al-Si Cast Alloys at Room and Elevated Temperatures

Aluminum-silicon cast alloys widely used throughout the transportation sector, A356, 319, and A390, have been studied with respect to chemical compositions and processing parameters that control the resultant mechanical behavior. First, the development of strengthening mechanisms is discussed in terms of the role that alloying elements, solidification behavior, and thermal treatments play. Based on this understanding, an extensive matrix of material conditions was developed and characterized in order to provide practical guidelines for alloy development. In order to provide an understanding of lifetime-limiting failure mechanisms, fatigue crack growth and hot compressive dwell behaviors were further investigated. Fatigue crack growth tests were conducted for all alloys at R = 0.1 and room temperature, and creep–fatigue of 319 was studied at R = − 1.5 and 250 °C. The role of processing parameters in controlling the mechanical properties is identified and discussed, and recommendations for optimized design are made.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Heat Treatment on Microstructure and Mechanical Properties of Laser Additively Manufactured AISI H13 Tool Steel

The effect of heat treatment on microstructure and mechanical properties (microhardness, wear resistance and impact toughness) of laser additively manufactured AISI H13 tool steel was systemically investigated. To understand the variation of microstructure and mechanical properties under different heat treatments, the as-deposited samples were treated at 350, 450, 550, 600 and 650 °C/2 h, respectively. Microstructure and phase transformation were investigated through optical microscopy, scanning electron microscope and transmission electron microscope. The mechanical properties were characterized by nanoindentation tests, Charpy tests and high-temperature wear tests. The microstructure of as-deposited samples consisted of martensite, ultrafine carbides and retained austenite. After the tempering treatment, the martensite was converted into tempered martensite and some fine alloy carbides which precipitated in the matrix. When treated at 550 °C, the greatest hardness and nanohardness were 600 HV{sub 0.3} and 6119.4 MPa due to many needle-like carbides precipitation. The value of hardness increased firstly and then decreased when increasing the temperature. When tempered temperatures exceeded 550 °C, the carbides became coarse, and martensitic matrix recrystallized at the temperature of 650 °C. The least impact energy was 6.0 J at a temperature of 550 °C. Samples tempered at 550 °C had larger wear volume loss than that of others. Wear resistances of all samples under atmospheric condition at 400 °C showed an oxidation mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High-Temperature Mechanical Properties of the P/M Extruded Mg-SiC{sub p} Composites

In the present study, pure magnesium reinforced with 0, 5, 10 and 15 vol.% SiC particulates was successfully prepared by powder metallurgy technique before being hot extruded. The average 14 μm grain size of the composite specimens remained almost unchanged after addition of SiC particles, while their dimensional stability was improved because of the reduction in the coefficient of thermal expansion (CTE) from 28.6 × 10{sup −6} K{sup −1} in pure Mg to 27.3, 25.3 and 23.4 × 10{sup −6} K{sup −1} in the Mg-5% SiC, Mg-10% SiC and Mg-15% SiC composites, respectively. Mechanical properties of the specimens were investigated in the temperature range of 298-498 K, implementing shear punch testing and hot hardness techniques. Depending on the test temperature, addition of SiC particles to the pure Mg matrix increased shear yield stress and ultimate shear strength of the materials by 5-25 and 6-23 MPa, respectively. The shear strength improvement was mainly attributed to the CTE mismatch strengthening mechanism (9.5-25.5 MPa), and to a lesser extent (1-4.5 MPa), to the load transfer mechanism. Finally, using the modified Clyne model, the contribution of different strengthening mechanisms to the total shear strength improvement in the composites was evaluated.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Pouring Temperature and Electromagnetic Stirring on Porosity and Mechanical Properties of A357 Aluminum Alloy Rheo-Diecasting

Semisolid slurry of A357 aluminum alloy was prepared using a temperature-controllable electromagnetic stirrer and rheo-diecast at different temperatures. The effects of pouring temperature and electromagnetic stirring (EMS) on the porosity in rheo-diecast samples, as well as the relation between porosity and mechanical properties, were investigated. The results show that pouring temperature and EMS had minor influences on rheo-diecast microstructure but marked influence on the porosity. With decreasing slurry pouring temperature, the porosity decreased first and then increased, whereas the maximum pore ratio (ratio of shape factor to diameter of the largest pore) increased first and then decreased. The maximum pore ratio determines the level of tensile strength and elongation, and higher mechanical properties can be obtained with smaller and rounder pores in samples. The mechanical properties of the rheo-diecast samples increased linearly with increasing maximum pore ratio. The maximum pore ratio was 1.43 µm{sup −1}, and the minimum porosity level was 0.37% under EMS condition for the rheo-diecast samples obtained at a pouring temperature of 608 °C. With this porosity condition, the maximum tensile strength and elongation were achieved at 274 MPa and 4.9%, respectively. It was also revealed that EMS improves mechanical properties by reduction in porosity and an increase in maximum pore ratio.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Processing Parameter Effects on Residual Stress and Mechanical Properties of Selective Laser Melted Ti6Al4V

Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. Post-process heat treatments can be applied to SLM components to remove in-built residual stress and improve ductility. Residual stress buildup and the mechanical properties of SLM parts can be controlled by varying the SLM process parameters. This investigation studies the effect of layer thickness on residual stress and mechanical properties of SLM Ti6Al4V parts. This is the first-of-its kind study on the effect of varying power and exposure in conjunction with keeping the energy density constant on residual stress and mechanical properties of SLM Ti6Al4V components. It was found that decreasing power and increasing exposure for the same energy density lowered the residual stress and improved the % elongation of SLM Ti6Al4V parts. Increasing layer thickness resulted in lowering the residual stress at the detriment of mechanical properties. The study is based on detailed experimental analysis along with finite element simulation of the process using ABAQUS to understand the underlying physics of the process.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Deformation Mechanism of AZ31 Magnesium Alloy Under Dynamic Strain Rate

A hot-rolled AZ31Mg alloy sheet was subjected to dynamic plastic deformation parallel to the rolling direction, and microstructural evolutions and mechanical properties of the deformed samples were examined. It has been found that dynamic strain rate could facilitate {10-12} twin nucleation and growth and leads to a lower yield stress of about 20 MPa and an early end to twinning characteristic (happening at a strain point of about 6%) shown in the stress–strain curve. {10-12} twinning mechanism dominates the early plastic deformation; but when plastic strain exceeds ~ 9%, dislocation–slip mechanism instead of {10-12} twinning dominates the later plastic deformation. And this premature transformation of the dominant deformation mechanisms from {10-12} twinning to dislocation slip is caused by dynamic strain rate. The effect of dynamic strain rate on the number of twin nucleations remains unclear, and the more systematic researches are needed in the future.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Drawing Direction Effect on Microstructure and Mechanical Properties of Twinning-Induced Plasticity Steel During Wire Drawing

The effect of drawing direction on microstructure and mechanical properties in twinning-induced plasticity (TWIP) steel during wire drawing has been investigated to improve drawability for wire rod applications. The steel wires subjected to unidirectional (UD) and reverse-directional (RD) wire drawing were analyzed. The yield and tensile strength processed by the RD were slightly higher than those by the UD, whereas the ductility and drawability have inverse features, which is totally different from the results of plain carbon steel and Al wire. Although final shear strain of wires deformed by the RD is lower than that by the UD, the RD wires had a more complex stress history and a higher <111> texture component at the surface area, which encouraged twinning rate, resulting in fast exhaustion of ductility, finally earlier fracture of wires. In contrast to the materials deformed by mainly slip mechanism, the RD process cannot improve the ductility and drawability in TWIP steel due to the stress state dependency of twinning mechanism. Also, based on the different strengthening behaviors between pearlitic and TWIP steels during UD and RD, it is induced that microstructure and applied stress state simultaneously control the mechanical properties.

36 MATERIALS SCIENCE↗