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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

At Extreme Strain Rates, Pure Metals Thermally Harden while Alloys Thermally Soften

When materials are deformed at extreme strain rates, >10 6 s -1 , a counterintuitive mechanical response is seen where the strength and hardness of pure metals increases with increasing temperature. This anti-thermal hardening is due to dislocations meeting resistance to their motion from phonons in the crystal lattice. However, here, using optically-driven microballistic impact testing to measure dynamic strength and hardness, we show that when the composition is systematically varied away from high purity, the mechanical response of metals transitions from phonon drag of dislocations back to thermally activated pinning of dislocations, even at the highest strain rates. This boundary from “hotter-is-stronger” to “hotter-is-softer” is observed and mapped for nickel, titanium and gold. Furthermore, the ability to tune between deformation mechanisms with very different temperature dependencies speaks to new directions for alloy design in extreme conditions.

Ballistic transport↗
NASA NTRS1956

A Study of the Efficiency of High-strength, Steel, Cellular-core Sandwich Plates in Compression

Structural efficiency curves are presented for high-strength, stainless-steel, cellular-core sandwich plates of various proportions subjected to compressive end loads for temperatures of 80 F and 600 F. Optimum proportions of sandwich plates for any value of the compressive loading intensity can be determined from the curves. The efficiency of steel sandwich plates of optimum proportions is compared with the efficiency of solid plates of high-strength steel and aluminum and titanium alloys at the two temperatures.

SANDWICH AND LAMINATES↗
DOE OSTI2015

Boron nitride nanotubes and nanoplatelets as reinforcing agents of polymeric matrices for bone tissue engineering

Abstract This study investigates the mechanical properties and in vitro cytotoxicity of one‐ and two‐dimensional boron nitride nanomaterials‐reinforced biodegradable polymeric nanocomposites. Poly(propylene fumarate) (PPF) nanocomposites were fabricated using crosslinking agent N ‐vinyl pyrrolidone and inorganic nanomaterials: boron nitride nanotubes (BNNTs) and boron nitride nanoplatelets (BNNPs) dispersed at 0.2 wt % in the polymeric matrix. The incorporation of BNNPs and BNNTs resulted in a ∼38 and ∼15% increase in compressive (Young's) modulus, and ∼31 and ∼6% increase in compressive yield strength compared to PPF control, respectively. The nanocomposites showed a time‐dependent increased protein adsorption for collagen I protein. The cytotoxicity evaluation of aqueous BNNT and BNNP dispersions (at 1–100 μg/mL concentrations) using murine MC3T3 preosteoblast cells showed ∼73–99% viability. The cytotoxicity evaluation of media extracts of nanocomposites before crosslinking, after crosslinking, and upon degradation (using 1×–100× dilutions) showed dose‐dependent cytotoxicity responses. Crosslinked nanocomposites showed excellent (∼79–100%) cell viability, cellular attachment (∼57–67%), and spreading similar to cells grown on the surface of tissue culture polystyrene control. The media extracts of degradation products showed a dose‐dependent cytotoxicity. The favorable cytocompatibility results in combination with improved mechanical properties of BNNT and BNNP nanocomposites opens new avenues for further in vitro and in vivo safety and efficacy studies towards bone tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 406–419, 2017.

Farshid, Behzad↗
DOE OSTI2015

On the pore-scale mechanisms leading to brittle and ductile deformation behavior of crystalline rocks

Deformation mechanisms found at the pore scale are responsible for producing large strains in porous rocks. Furthermore, they include cataclastic flow, dislocation creep, dynamic recrystallization, diffusive mass transfer, and grain boundary sliding, among others. Here, we focus on two dominant pore-scale mechanisms resulting from purely mechanical, isothermal loading: crystal plasticity and micro-fracturing. We examine the contributions of each mechanism to the overall behavior at a scale larger than the grains but smaller than the specimen, which is commonly referred to as the mesoscale. Crystal plasticity is assumed to occur as dislocations along the many crystallographic slip planes, whereas micro-fracturing entails slip and frictional sliding on microcracks. It is observed that under combined shear and tensile loading, micro-fracturing generates a softer response compared to crystal plasticity alone, which is attributed to slip weakening where the shear stress drops to a residual level determined by the frictional strength. For compressive loading, however, micro-fracturing produces a stiffer response than crystal plasticity due to the presence of frictional resistance on the slip surface. Behaviors under tensile, compressive, and shear loading invariably show that porosity plays a critical role in the initiation of the deformation mechanisms. Both crystal plasticity and micro-fracturing are observed to initiate at the peripheries of the pores, consistent with results of experimental studies.

58 GEOSCIENCES↗
DOE OSTI2019

Enhanced Mechanical, Tribological, and Thermal Properties of Fe{sub 3}Al Composites with Carbon Nanotubes

In this work, Fe{sub 3}Al-based composites reinforced with carbon nanotubes were fabricated by a hot-press sintering process under various sintering pressures. The effects of sintering pressure and additives (alumina and lanthanum) on both the physical and the mechanical properties were systematically investigated. Results showed that with the sintering pressure of 15 MPa and incorporation of carbon nanotubes (CNTs), the microhardness of Fe{sub 3}Al composite exhibited a peak value at 1038.1 HV, which was ~ 60% higher than those without the addition of carbon nanotubes (644.9 HV). Also, both the compressive yield strength and the thermal conductivity of Fe{sub 3}Al composite were also significantly improved. Results of wear test showed the Fe{sub 3}Al composite exhibited a low wearing rate (10{sup −6}-10{sup −5} order of magnitude) and a friction coefficient (0.53-0.67).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation on Equal-Channel Angular Pressing-Induced Grain Refinement in an Aluminum Matrix Composite Reinforced with Al-Cu-Ti Metallic Glass Particles

In the present study, a homogeneous ultrafine grain structure composite consisting of metallic glass particles reinforcements was developed by equal-channel angular pressing (ECAP) process. The microstructure of composite was characterized using x-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. The uniaxial compression test was used to determine the mechanical properties. The mechanisms of grain refinement during ECAP process were discussed based on the microstructural evolutions. A composite was successfully produced after four passes of ECAP, having an average grain size of 610 nm and compressive yield strength of 242 MPa. Also, the yield strength of composite after each pass was quantitatively estimated by considering all the effective strengthening mechanism. The findings showed that the dislocations strengthening mechanism with contribution of more than 50% plays a major role in strengthening the composite. There was a negligible gap between the experimental and theoretical values of yield strength for all ECAP pass numbers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Cobalt Content on Thermal, Mechanical, and Microstructural Properties of Al{sub 0.4}FeCrNiCo{sub x} (x = 0, 0.25, 0.5, 1.0 mol) High-Entropy Alloys

Al{sub 0.4}FeCrNiCo{sub x} (x = 0, 0.25, 0.5, 1.0 mol) high-entropy alloys are developed by arc melting route to investigate the effect of cobalt content on thermal, mechanical, and microstructural properties. The phase, microstructure, and chemical composition are analyzed using x-ray diffraction, transmission electron microscope, and scanning electron microscope with attached energy-dispersive x-ray spectrometer. The obtained results have shown that the Al{sub 0.4}FeCrNiCo{sub x} (x = 0-0.5 mol) high-entropy alloys form a simple FCC + BCC-type solid solution and Al{sub 0.4}FeCrNiCo{sub x=1} HEA forms a single-phase FCC structure. The compressive yield strength, microhardness, and thermal conductivity are observed to decrease from 965.22 to 233.37 MPa, 253.6 to 155.6 HV, and from 4.87 to 2.674 W/mK, respectively, whereas the electrical resistivity is observed to increase from 150.30 to 273.74 µΩ-cm with the addition of cobalt from x = 0-1 mol. Differential scanning calorimetry analysis has indicated that the Al{sub 0.4}FeCrNiCo{sub x} (x = 0, 0.25, 0.5, 1.0 mol) high-entropy alloys are thermally stable up to 1000 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Y{sub 2}O{sub 3} Addition on the Microstructure, Wear Resistance, and Corrosion Behavior of W-4.9Ni-2.1Fe Heavy Alloy

Binding and particle phases are the two important parameters influencing materials properties. In this study, a series of novel W-4.9Ni-2.1Fe-xY{sub 2}O{sub 3} (in weight%) alloys with different Y{sub 2}O{sub 3} contents are prepared by secondary ball milling and spark plasma sintering (SPS) techniques to obtain uniformly distributed γ-(Ni, Fe) binding phases and finer grains. The microstructure, mechanical, wear resistance, and corrosion behavior of the sintered bodies with different Y{sub 2}O{sub 3} were obtained by x-ray diffraction, scanning electron microscopy, Rockwell hardness tester, friction wear tester, and three-dimensional profile instruments. The results showed that a certain addition of Y{sub 2}O{sub 3} led to refined grains and uniformed microstructures; but, if excessive, a weak grain refinement would be appeared. Moreover, the grain size tends to be stable with enhancing of the Y{sub 2}O{sub 3} content. Considering properties such as density, hardness, compression yield strength, grain size, and uniform distribution of tungsten hard phase and γ-(Ni, Fe) binding phase, the comprehensive optimal amount of 0.7 wt.% of Y{sub 2}O{sub 3} was attained for the alloy. Meanwhile, the SPS sintered body also exhibited the best friction, wear behavior, and corrosion resistance in 3.5% of NaCl solution.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Strengthening Mechanisms and Deformation Behavior of Industrially-Cast and Lab-Cast Dual-Phase High Entropy Alloy

An iron-rich high entropy alloy Al 0.65 CoCrFe 2 Ni comprising of both FCC and BCC phases was designed and fabricated using induction melting at a large industrial scale and suction casting at a small lab scale. Spinodally decomposed interdendritic regions were uniformly distributed in the industrially melted alloy, and a finer dendritic structure with smaller sized spinodal structures was observed in the alloy suction cast at lab scale. The suction cast alloy fabricated at the lab scale exhibited significantly higher compressive yield strength compared to the industrially cast alloy. The relative strengthening contributions in the alloys due to solid solution, grain boundary, dislocation interactions and interphase boundary were analyzed. Dislocation hardening was the major contributor responsible for the higher strength of the SC alloy. The deformation behavior in the alloys was examined with the help of orientation image mapping. Finally, intense slip band formation at large strains in the industrially melted alloy indicates that cold working can be an effective technique to enhance the strength of the dual-phase high entropy alloy processed at a large scale.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Photocatalytic NO{sub x} abatement by calcium aluminate cements modified with TiO{sub 2}: Improved NO{sub 2} conversion

Photocatalytic activity of TiO{sub 2} was studied in two types of calcium aluminate cement (CAC) under two different curing regimes. The effect of the TiO{sub 2} addition on the setting time, consistency and mechanical properties of the CACs was evaluated. The abatement of gaseous pollutants (NO{sub x}) under UV irradiation was also assessed. These cementitious matrices were found to successfully retain NO{sub 2}: more abundant presence of aluminates in white cement (w-CAC, iron-lean) helped to better adsorb NO{sub 2}, thus improving the conversion performance of the catalyst resulting in a larger NO{sub x} removal under UV irradiation. As evidenced by XRD, SEM, EDAX and zeta potential analyses, the presence of ferrite in dark cement (d-CAC, iron-reach) induced a certain chemical interaction with TiO{sub 2}. The experimental findings suggest the formation of new iron titanate phases, namely pseudobrookite. The reduced band-gap energy of these compounds compared with that of TiO{sub 2} accounts for the photocatalytic activity of these samples.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural packing- and rheology-based binder selection and characterization for Ultra-high Performance Concrete (UHPC)

This paper reports strategies to design the binder phase of ultra-high performance concretes (UHPC) from commonly available cement replacement (fly ash, slag, microsilica, metakaolin) and fine filler (limestone) materials. A packing algorithm is used to extract the number density, mean centroidal distance, and coordination number of the microstructure. Similarly, rheological studies on the pastes provide yield stress, plastic viscosity, and min-slump spread. The selection criteria involves using the three microstructural and three rheological parameters individually or in combination to define packing and flow coefficients. The selection criteria is flexible enough to allow users modify the constraints depending on the application. In this study, only ternary and quaternary blends, with a total cement replacement of 30% by mass are selected for further characterization. The highly efficient microstructural packing in these mixtures and better workability that facilitated dispersion of particles to enhance the reactivity results in beneficial pore structure and mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Comparison of three state-of-the-art crystal plasticity based deformation twinning models for magnesium alloys

In magnesium alloys, deformation twinning and its interactions with dislocation slip are responsible for a sigmoidal shape stress–strain behavior and an asymmetrical tension–compression yield strength in magnesium alloys. The sensitivity of twinning to the underlying microstructure renders the crystal plasticity method the most commonly adopted modeling approach for magnesium-twinning. This paper compares three state-of-the-art crystal plasticity-based twinning models from the literature, namely the elastic-viscoplastic self-consistent twinning-detwinning (EVPSC-TDT) model, crystal plasticity finite element model based on enhanced predominate twin reorientation approach (CPFE-ePTR), and the crystal plasticity finite element model based on “discrete twinning” approach (CPFE-DT). A polycrystalline microstructure is simulated with all three methods to compare the resulting stress–strain curves and lattice strains to those from the experimentally measured data. All three methods showed the capability of capturing the experimental results with different levels of accuracy. Additionally, the EVPSC-TDT method avoids solving the finite element matrices and showed the highest computational efficiency. The CPFE-ePTR model shows a higher accuracy in capturing the lattice strain. The CPFE-DT relies on high-resolution finite element mesh and is much slower than the other two methods, but it captured the local deformation concentration and stress reversal phenomena near the twin band, which was not possible with the other two methods. Based on the comparison, guidance for the selection of the appropriate model based on the specific modeling target is provided in this paper.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Development of high-early-strength fiber-reinforced self-compacting concrete

High-early-strength fiber-reinforced self-compacting concrete (FRSCC) is a practical material for the precast concrete industry to double its production capacity. In this study, we developed high-early-strength FRSCC mixtures that achieved a compressive and flexural strength of at least 24 MPa and 3.5 MPa, respectively, at 6 h, using commercially available components, typical mixing procedures, and air curing. A mix design process was developed based on the literature and experimental results. The effect of six different fiber reinforcements on the fresh and mechanical properties of concrete was analyzed. The cost limit was set at 523 USD/m 3 to make the concrete mix cost-effective.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Short-range correlations control the G/K and Poisson ratios of amorphous solids and metallic glasses

The bulk modulus of many amorphous materials, such as metallic glasses, behaves nearly in agreement with the assumption of affine deformation, namely that the atoms are displaced just by the amount prescribed by the applied strain. In contrast, the shear modulus behaves as for nonaffine deformations, with additional displacements due to the structural disorder which induce a marked material softening to shear. The consequence is an anomalously large ratio of the bulk modulus to the shear modulus for disordered materials characterized by dense atomic packing, but not for random networks with point atoms. We explain this phenomenon with a microscopic derivation of the elastic moduli of amorphous solids accounting for the interplay of nonaffinity and short-range particle correlations due to excluded volume. Short-range order is responsible for a reduction of the nonaffinity which is much stronger under compression, where the geometric coupling between nonaffinity and the deformation field is strong, whilst under shear this coupling is weak. Predictions of the Poisson ratio based on this model allow us to rationalize the trends as a function of coordination and atomic packing observed with many amorphous materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Equation of state of rhenium and application for ultra high pressure calibration

The isothermal equation of state of rhenium has been measured by powder X-ray diffraction experiments up to 144 GPa at room temperature in a diamond anvil cell. A helium pressure transmitting medium was used to minimize the non-hydrostatic stress on the sample. The fit of pressure-volume data yields a bulk modulus K{sub 0} = 352.6 GPa and a pressure derivative of the bulk modulus K′{sub 0}=4.56. This equation of state differs significantly from a recent determination [Dubrovinsky et al., Nat. Commun. 3, 1163 (2012)], giving here a lower pressure at a given volume. The possibility of using rhenium gasket X-ray diffraction signal, with the present equation of state, to evaluate multi-Mbar pressures in the chamber of diamond anvil cells is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Deformation and fracture behavior of composite structured Ti-Nb-Al-Co(-Ni) alloys

Tensile ductility of the Ti-based composites, which consist of a β-Ti phase surrounded by ultrafine structured intermetallics, is tunable through the control of intermetallics. The two Ti-based alloys studied exhibit similar compressive yield strength (about 1000 MPa) and strain (about 35%–40%) but show a distinct difference in their tensile plasticity. The alloy Ti{sub 71.8}Nb{sub 14.1}Ni{sub 7.4}Al{sub 6.7} fractures at the yield stress while the alloy Ti{sub 71.8}Nb{sub 14.1}Co{sub 7.4}Al{sub 6.7} exhibits about 4.5% of tensile plastic deformation. To clarify the effect of microstructure on the deformation behavior of these alloys, tensile tests were carried out in the scanning electron microscope. It is shown that the distribution as well as the type of intermetallics affects the tensile ductility of the alloys.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗