Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Behavior”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Interface microstructure effects on dynamic failure behavior of layered Cu/Ta microstructures

Abstract Structural metallic materials with interfaces of immiscible materials provide opportunities to design and tailor the microstructures for desired mechanical behavior. Metallic microstructures with plasticity contributors of the FCC and BCC phases show significant promise for damage-tolerant applications due to their enhanced strengths and thermal stability. A fundamental understanding of the dynamic failure behavior is needed to design and tailor these microstructures with desired mechanical responses under extreme environments. This study uses molecular dynamics (MD) simulations to characterize plasticity contributors for various interface microstructures and the damage evolution behavior of FCC/BCC laminate microstructures. This study uses six model Cu/Ta interface systems with different orientation relationships that are as- created, and pre-deformed to understand the modifications in the plasticity contributions and the void nucleation/evolution behavior. The results suggest that pre-existing misfit dislocations and loading orientations (perpendicular to and parallel to the interface) affect the activation of primary and secondary slip systems. The dynamic strengths are observed to correlate with the energy of the interfaces, with the strengths being highest for low-energy interfaces and lowest for high-energy interfaces. However, the presence of pre-deformation of these interface microstructures affects not only the dynamic strength of the microstructures but also the correlation with interface energy.

42 ENGINEERING↗
DOE OSTI2015

On the correlation between microscopic structural heterogeneity and embrittlement behavior in metallic glasses

To establish a relationship between microstructure and mechanical properties, we systematically annealed a Zr-based bulk metallic glass (BMG) at 100 ~ 300°C and measured their mechanical and thermal properties. The as-cast BMG exhibits some ductility, while the increase of annealing temperature and time leads to the transition to a brittle behavior that can reach nearly-zero fracture energy. The differential scanning calorimetry did not find any significant changes in crystallization temperature and enthalpy, indicating that the materials still remained fully amorphous. Elastic constants measured by ultrasonic technique vary only slightly with respect to annealing temperature and time, which does obey the empirical relationship between Poisson’s ratio and fracture behavior. Nanoindentation pop-in tests were conducted, from which the pop-in strength mapping provides a “mechanical probe” of the microscopic structural heterogeneities in these metallic glasses. Based on stochastically statistic defect model, we found that the defect density decreases with increasing annealing temperature and annealing time and is exponentially related to the fracture energy. A ductile-versus-brittle behavior (DBB) model based on the structural heterogeneity is developed to identify the physical origins of the embrittlement behavior through the interactions between these defects and crack tip.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Particle anisotropy tunes emergent behavior in active colloidal systems

Studies of active particle systems have demonstrated that particle anisotropy can impact the collective behavior of a system, motivating a systematic study. Here, we report a systematic computational investigation of the role of anisotropy in shape and active force director on the collective behavior of a two-dimensional active colloidal system. We find that shape and force anisotropy can combine to produce critical densities both lower and higher than those of disks. Furthermore, we demonstrate that changing particle anisotropy tunes what we define as a “collision efficiency” of inter-particle collisions in leading to motility-induced phase separation (MIPS) of the system. We use this efficiency to determine the relative critical density across systems. Additionally, we observe that local structure in phase-separated clusters is the same as the particle's equilibrium densest packing, suggesting a general connection between equilibrium behavior and non-equilibrium cluster structure of self-propelled anisotropic particles. In engineering applications for active colloidal systems, shape-controlled steric interactions such as those described here may offer a simple route for tailoring emergent behaviors.

42 ENGINEERING↗
DOE OSTI2023

Anti-Arrhenius behavior of electron transfer reactions in molecular dimers

Rates of chemical reactions typically accelerate as the temperature rises, following the Arrhenius law. However, electron transfer reactions may exhibit weak temperature dependence or counterintuitive behavior, known as anti-Arrhenius behavior, wherein reaction rates decrease as temperature increases. Solvent reorganization energy and torsion-induced changes in electronic couplings could contribute to this unusual behavior, but how each contributes to the overall temperature dependence is unclear. One can decelerate the charge recombination process in photogenerated radical pairs or charge-separated states by harnessing this often-overlooked phenomenon. This means that we could achieve long-lived radical pairs without relying on conventional cooling. Using a series of homo molecular dimers, we showed that the degree of torsional hindrance dictates temperature-dependent torsion-induced changes in electronic coupling and, therefore, charge recombination rates. The overall temperature dependence is controlled by how changes in electronic coupling and the temperature-dependent solvent reorganization energy contribute to the rates of charge recombination. Our findings pave the way for rationally designing molecules that exhibit anti-Arrhenius behavior to slow down charge recombination, opening possibilities for applications in energy-related and quantum information technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Effect of poly[oligo(ethylene glycol) methyl ether methacrylate] side chain length on the brush swelling behavior in A/B/A–B ternary blends with polystyrene

The phase behavior of ternary blends composed of two homopolymers (A, B) and their corresponding diblock copolymer (A–B) has been widely studied, with emphasis on the volumetrically symmetric isopleth and the formation of bicontinuous microemulsions. However, almost all the previous studies employed linear polymers, and little is known about the impact of polymer architecture on the phase behavior of such ternary blends. Here, in this work, we report the self-assembly of three sets of ternary blends of polystyrene (PS) and poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA n ), with different lengths of oligo(ethylene glycol) side chains n. Small-angle X-ray scattering was used to probe the phase behavior at different compositions and temperatures. The order-to-disorder transition temperature was found to be impacted by the side chain length. It was also observed that longer side chains lead to poorer miscibility of homopolymers in the corresponding block, resulting in a more “dry-brush” like swelling behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Radial behavior of the pulsed dielectric-barrier discharge in atmospheric helium

The radial behavior of the pulsed dielectric-barrier discharge in atmospheric helium is studied by a two-dimensional, self-consistent fluid model. It is found that the two discharges ignited during one voltage pulse can possess different radial behaviors, and the discharge behavior is determined by the electron density distribution right before this discharge is ignited. The electron density distributions before the two discharges start depend on the time intervals between two discharges and their previous discharge processes. If the electron density distribution is radially uniform at the end of the previous discharge, the shorter the time interval between two discharges is, the more uniform the electron density distribution before the next discharge is, and thus the more homogenous the subsequent discharge becomes. In pulsed discharge, the time intervals between two discharges are mainly determined by the duration and repetition frequency of applied voltage pulse. These results are further supported by the investigation of the discharge behaviors under different pulse durations and repetition frequencies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Effect of stoichiometry on the dielectric properties and soft mode behavior of strained epitaxial SrTiO3 thin films on DyScO3 substrates

The effect of stoichiometry on the dielectric properties and soft mode behavior of strained epitaxial Sr1-xTiO3 films grown on DyScO3 substrates is reported. Direct comparisons between nominally stoichiometric and non-stoichiometric films have been performed through measurements of lattice parameters, temperature-dependent permittivities, second harmonic generation, and terahertz dielectric spectra. The nominally stoichiometric film shows dispersion-free low-frequency permittivity with a 23 sharp maximum and pronounced soft mode behavior. Our results suggest that strained perfectlystoichiometric SrTiO3 films should not show relaxor behavior and that relaxor behavior emergesfrom defect dipoles that arise from non-stoichiometry in the highly polarizable strained SrTiO3 matrix

ferroelectric↗
DOE OSTI2013

Weak ferromagnetic behavior of BiFeO{sub 3} at low temperature

Polycrystalline BiFeO{sub 3}, having a spherical shape with a diameter of about 78 {mu}m, has been synthesized by low-temperature hydrothermal method. The observed Raman and x-ray photo electron spectroscopy (XPS) spectra of the sample show the spectra of typical single-phased BiFeO{sub 3}, and the x-ray diffractometry (XRD) measurement further confirmed that the synthesized sample is single phase. The value of isomer shift from Moessbauer analysis indicates the Fe{sup 3+} ionic state without Fe{sup 2+} ionic state as observed from XPS measurement. The experimentally measured M-H curves show antiferromagnetic behavior at 295 K and weak ferromagnetic behavior at 4.2 K. The appearance of two different magnetic behaviors is due to the fact that the antiferromagnetic coupling becomes weak because of the presence of two distorted octahedral sites. Since the effect of the lattice distortion strongly depends on the thermal agitation effect, the weak ferromagnetic behavior can be observed only at 4.2 K. The detailed Moessbauer spectra analysis result confirms the existence of two distortion octahedral sites, which is in an agreement with XRD results.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Phase behaviors of supramolecular graft copolymers with reversible bonding

Phase behaviors of supramolecular graft copolymers with reversible bonding interactions were examined by the random-phase approximation and real-space implemented self-consistent field theory. The studied supramolecular graft copolymers consist of two different types of mutually incompatible yet reactive homopolymers, where one homopolymer (backbone) possesses multifunctional groups that allow second homopolymers (grafts) to be placed on. The calculations carried out show that the bonding strength exerts a pronounced effect on the phase behaviors of supramolecular graft copolymers. The length ratio of backbone to graft and the positions of functional groups along the backbone are also of importance to determine the phase behaviors. Phase diagrams were constructed at high bonding strength to illustrate this architectural dependence. It was found that the excess unbounded homopolymers swell the phase domains and shift the phase boundaries. The results were finally compared with the available experimental observations, and a well agreement is shown. The present work could, in principle, provide a general understanding of the phase behaviors of supramolecular graft copolymers with reversible bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Atom probe tomography evaporation behavior of C-axis GaN nanowires: Crystallographic, stoichiometric, and detection efficiency aspects

The field evaporation behavior of c-axis GaN nanowires was explored in two different laser-pulsed atom probe tomography (APT) instruments. Transmission electron microscopy imaging before and after atom probe tomography analysis was used to assist in reconstructing the data and assess the observed evaporation behavior. It was found that the ionic species exhibited preferential locations for evaporation related to the underlying crystal structure of the GaN and that the species which evaporated from these locations was dependent on the pulsed laser energy. Additionally, the overall stoichiometry measured by APT was significantly correlated with the energy of the laser pulses. At the lowest laser energies, the apparent composition was nitrogen-rich, while higher laser energies resulted in measurements of predominantly gallium compositions. The percent of ions detected (detection efficiency) for these specimens was found to be considerably below that shown for other materials, even for laser energies which produced the expected Ga:N ratio. The apparent stoichiometry variation and low detection efficiency appear to be a result of evaporation of Ga ions between laser pulses at the lowest laser energies and evaporation of neutral N{sub 2} species at higher laser energies. All of these behaviors are tied to the formation of nitrogen-nitrogen bonds on the tip surface, which occurred under all analysis conditions. Similar field evaporation behaviors are therefore expected for other materials where the anionic species readily form a strong diatomic bond.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Influence of carbon content on the copper-telluride phase formation and on the resistive switching behavior of carbon alloyed Cu-Te conductive bridge random access memory cells

In this paper, we investigate the influence of the carbon content on the Cu-Te phase formation and on the resistive switching behavior in carbon alloyed Cu{sub 0.6}Te{sub 0.4} based conductive bridge random access memory (CBRAM) cells. Carbon alloying of copper-tellurium inhibits the crystallization, while attractive switching behavior is preserved when using the material as Cu-supply layer in CBRAM cells. The phase formation is first investigated in a combinatorial way. With increasing carbon content, an enlargement of the temperature window in which the material stays amorphous was observed. Moreover, if crystalline phases are formed, subsequent phase transformations are inhibited. The electrical switching behavior of memory cells with different carbon contents is then investigated by implementing them in 580 μm diameter dot TiN/Cu{sub 0.6}Te{sub 0.4}-C/Al{sub 2}O{sub 3}/Si memory cells. Reliable switching behavior is observed for carbon contents up to 40 at. %, with a resistive window of more than 2 orders of magnitude, whereas for 50 at. % carbon, a higher current in the off state and only a small resistive window are present after repeated cycling. This degradation can be ascribed to the higher thermal and lower drift contribution to the reset operation due to a lower Cu affinity towards the supply layer, leading cycle-after-cycle to an increasing amount of Cu in the switching layer, which contributes to the current. The thermal diffusion of Cu into Al{sub 2}O{sub 3} under annealing also gives an indication of the Cu affinity of the source layer. Time of flight secondary ion mass spectroscopy was used to investigate this migration depth in Al{sub 2}O{sub 3} before and after annealing, showing a higher Cu, Te, and C migration for high carbon contents.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Behavior of microwave-heated silicon carbide particles at frequencies of 2.0–13.5 GHz

Silicon carbide is a key material in microwave (MW) processing and is used widely as a thermal insulator and catalytic agent. In this study, we experimentally investigated the temperature dependence of the MW-absorption properties of SiC particles at frequencies of 2.0–13.5 GHz. We heated SiC particles of different sizes using MW radiation. The heating behaviors of the particles were then compared with their MW-absorption properties. The heating behavior of the particles was dependent on their radii; this result was in keeping with theoretical predictions. Furthermore, the β-SiC particles exhibited anomalous behaviors when subjected to microwave heating at temperatures of 1100 °C and higher. These behaviors were attributable to the transformation of β-SiC into the α-phase. The underlying mechanism for this transformation is discussed on the basis of the results of X-ray diffraction analysis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Hysteresis and compensation behaviors of spin-3/2 cylindrical Ising nanotube system

The hysteresis and compensation behaviors of the spin-3/2 cylindrical Ising nanotube system are studied within the framework of the effective-field theory with correlations. The effects of the Hamiltonian parameters are investigated on the magnetic and thermodynamic quantities, such as the total magnetization, hysteresis curves, and compensation behaviors of the system. Depending on the Hamiltonian parameters, some characteristic hysteresis behaviors are found, such as the existence of double and triple hysteresis loops. According to Néel classification nomenclature, the system displays Q-, R-, P-, N-, M-, and S- types of compensation behaviors for the appropriate values of the system parameters. We also compare our results with some recently published theoretical and experimental works and find a qualitatively good agreement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Anisotropic magnetodielectric coupling behavior of Ca{sub 3}Co{sub 1.4}Rh{sub 0.6}O{sub 6} due to geometrically frustrated magnetism

We have investigated the magnetic, dielectric, and magnetodielectric (MDE) behavior of a geometrically frustrated spin-chain system, Ca{sub 3}Co{sub 1.4}Rh{sub 0.6}O{sub 6} (related to Ca{sub 3}CoRhO{sub 6}), in the single crystalline form for different orientations. The results bring out that the magnetic behavior of this compound is by itself interesting in the sense that this compound exhibits an anisotropic glassy-like magnetic behavior with a huge frequency (ν) dependence of ac susceptibility (χ) peak for an orientation along the spin-chain in the range of 30–60 K; this behavior is robust to applications of large external magnetic fields (H) unlike in canonical spin-glasses. The temperature dependence of dielectric constant also shows strong ν-dependence with similar robustness to H. The isothermal H-dependent dielectric results at low temperatures establish anisotropic MDE coupling. It is intriguing to note that there is a “step” roughly at one-third of saturation values as in the case of isothermal magnetization curves for same temperatures (for orientation along spin-chain), a correlation hitherto unrealized for geometrically frustrated systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Surface plasmon resonances behavior in visible light of non-metal perovskite oxides AgNbO{sub 3}

We investigate the surface plasmon resonances (SPRs) behavior of silver niobate (AgNbO{sub 3}) experimentally and theoretically. Result shows that the localized SPRs (LSPRs) of AgNbO{sub 3} combining with its interband transitions enlarge the absorption band across the whole ultraviolet-visible range. The LSPRs behavior in visible-light is mainly ascribed to the metal-like state of silver ion and self-assembled microstructures of AgNbO{sub 3} microcrystal. The ab initio density functional theory calculations are carried out to obtain the further insight of the SPRs behaviors. Theoretical study indicates that the Ag atoms are weakly bound in the perovskite structure, leading to a metal-like state, which was the key factor to SPRs behavior of AgNbO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effect of moisture on the traction-separation behavior of cellulose nanocrystal interfaces

Interfaces and stress transfer between cellulose nanocrystals (CNCs) dictate the mechanical properties of hierarchical cellulose materials such as neat films and nanocomposites. An interesting question that remains is how the behavior of these interfaces changes due to environmental stimuli, most notably moisture. We present analyses on the traction-separation behavior between Iβ CNC elementary fibrils, providing insight into how the presence of a single atomic layer of water at these interfaces can drastically change the mechanical behavior. We find that molecular water at the interface between hydrophilic CNC surfaces has a negligible effect on the tensile separation adhesion energy. However, when water cannot hydrogen bond easily to the surface (i.e., hydrophobic surface), it tends to maintain hydrogen bonds with other water molecules across the interface and form a capillary bridge that serves to increase the energy required to separate the crystals. Under shear loading, water lowers the energy barriers to sliding by reducing the atomic friction and consequently the interlayer shear modulus between crystals. Our simulations indicate that these nanoscale interfaces and physical phenomena such as interfacial adhesion, interlayer shear properties, and stick-slip friction behavior can be drastically altered by the presence of water.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Impact of implementing the Meyer-Neldel behavior of carrier emission pre-factors in solar cell and optical detector modeling

The Meyer-Neldel behavior reported for the emission probabilities of electrons and holes was included in our code, replacing the gap state capture cross sections of the Shockley-Read-Hall formalisms with capture cross sections containing an exponential function of the trap energy depth. The Meyer-Neldel energies for electrons and holes are the slopes of these exponentials. Our results indicate that emission probabilities of neutral states no deeper than approximately 0.45 eV and 0.37 eV from the conduction and valence band edges, respectively, can show a Meyer-Neldel behavior only, while on the other hand, its implementation in deeper gap states makes the replication of experimental J-V curves of p-i-n solar cells and detectors impossible. The Meyer-Neldel behavior can be included in all neutral capture cross sections of acceptor-like tail states without affecting the J-V characteristics, while it cannot be included in all capture cross sections of neutral donor-like tail states and/or defect states without predicting device performances below the experimental figures, that become even lower when it is also included in charged capture cross sections. The implementation of the anti Meyer-Neldel behavior at tail states gives rise to slightly better and reasonable device performances.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2015

Tuning of electrostatic vs. depletion interaction in deciding the phase behavior of nanoparticle-polymer system

Nanoparticle-polymer system interestingly show a re-entrant phase behavior where charge stabilized silica nanoparticles (phase I) undergo particle clustering (phase II) and then back to individual particles (phase I) as a function of polymer concentration. Such phase behavior arises as a result of dominance of various interactions (i) nanoparticle-nanoparticle electrostatic repulsion (ii) polymer induced attractive depletion between nanoparticles and (iii) polymer-polymer repulsion, at different concentration regimes. Small-angle neutron scattering (SANS) has been used to study the evolution of interaction during this re-entrant phase behavior of nanoparticles by contrast-marching the polymer. The SANS data have been modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The degree of both of these parts has been separately tuned by varying the polymer concentration and ionic strength of the solution. Both of these parts are found to have long-range nature. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the strength of depletion leading to re-entrant phase behavior. The clusters formed under depletion attraction are found to have surface fractal morphology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗