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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Self-powered p-NiO/n-ZnO heterojunction ultraviolet photodetectors fabricated on plastic substrates

A self-powered ultraviolet (UV) photodetector (PD) based on p-NiO and n-ZnO was fabricated using low-temperature sputtering technique on indium doped tin oxide (ITO) coated plastic polyethylene terephthalate (PET) substrates. The p-n heterojunction showed very fast temporal photoresponse with excellent quantum efficiency of over 63% under UV illumination at an applied reverse bias of 1.2 V. The engineered ultrathin Ti/Au top metal contacts and UV transparent PET/ITO substrates allowed the PDs to be illuminated through either frontside or backside. Morphology, structural, chemical, and optical properties of sputtered NiO and ZnO films were also investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Features of plastic deformation and fracture of dispersion-strengthened V–Cr–Zr–W alloy depending on temperature of tension

Influence of tension temperature on features of plastic deformation and fracture of V–4.23Cr–1.69Zr–7.56W alloy was investigated by scanning and transmission electron microscopy. It is shown that temperature increase leads to activation of the recovery processes, which manifests in the coarsening of microstructure elements, reducing the dislocation density, relaxation of continuous misorientations.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Quantum effect on the nucleation of plastic deformation carriers and destruction in crystals

New concepts on the irreversible crystal deformation as a structure transformation caused by a change in interatomic interactions at fluctuations of the electron density under loading are described. The change in interatomic interactions lead to the excitation of dynamical displacements of atoms. A model and a theory of a deformable pristine crystal taking into account the excitation of thermally activated and dynamical displacements of atoms are suggested. New mechanisms of the nucleation of plastic deformation carriers and destruction in pristine crystals at the real value of the deforming stress are studied.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Peculiarities of plastic deformation nucleation in copper under nanoindentation

The computer simulation results on the atomic structure of the copper crystallite and its behavior in nanoindentation demonstrate the key role of local structural transformations in nucleation of plasticity. The generation of local structural transformations can be considered as an elementary event during the formation of higher scale defects, including partial dislocations and stacking faults. The cause for local structural transformations, both direct fcc-hcp and reverse hcp-fcc, is an abrupt local increase in atomic volume. A characteristic feature is that the values of local volume jumps in direct and reverse structural transformations are comparable with that in melting and lie in the range 5–7%.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of bursting dynamic features on the generation of multi-clustered structure of neural network with symmetric spike-timing-dependent plasticity learning rule

In this paper, the generation of multi-clustered structure of self-organized neural network with different neuronal firing patterns, i.e., bursting or spiking, has been investigated. The initially all-to-all-connected spiking neural network or bursting neural network can be self-organized into clustered structure through the symmetric spike-timing-dependent plasticity learning for both bursting and spiking neurons. However, the time consumption of this clustering procedure of the burst-based self-organized neural network (BSON) is much shorter than the spike-based self-organized neural network (SSON). Our results show that the BSON network has more obvious small-world properties, i.e., higher clustering coefficient and smaller shortest path length than the SSON network. Also, the results of larger structure entropy and activity entropy of the BSON network demonstrate that this network has higher topological complexity and dynamical diversity, which benefits for enhancing information transmission of neural circuits. Hence, we conclude that the burst firing can significantly enhance the efficiency of clustering procedure and the emergent clustered structure renders the whole network more synchronous and therefore more sensitive to weak input. This result is further confirmed from its improved performance on stochastic resonance. Therefore, we believe that the multi-clustered neural network which self-organized from the bursting dynamics has high efficiency in information processing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Shock compression response of poly(4-methyl-1-pentene) plastic to 985 GPa

Poly(4-methyl-1-pentene) plastic (PMP) is a hydrocarbon polymer with potential applications to inertial confinement fusion experiments and as a Hugoniot impedance matching standard for equation of state experiments. Using Sandia's Z-machine, we performed a series of flyer plate experiments to measure the principal Hugoniot and reshock states of PMP up to 985 GPa. The principal Hugoniot measurements validate density functional theory (DFT) calculations along the Hugoniot. The DFT calculations are further analyzed using a bond tracking method to understand the dissociation pathway under shock compression. Complete dissociation occurs at a compression factor similar to other sp3-hybridized, C-C bonded systems, which suggests a limiting compression for C-C bonds. The combined experimental and DFT results provide a solid basis for constructing an equation of state model for PMP.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

A light-stimulated synaptic transistor with synaptic plasticity and memory functions based on InGaZnO{sub x}–Al{sub 2}O{sub 3} thin film structure

In this work, a synaptic transistor based on the indium gallium zinc oxide (IGZO)–aluminum oxide (Al{sub 2}O{sub 3}) thin film structure, which uses ultraviolet (UV) light pulses as the pre-synaptic stimulus, has been demonstrated. The synaptic transistor exhibits the behavior of synaptic plasticity like the paired-pulse facilitation. In addition, it also shows the brain's memory behaviors including the transition from short-term memory to long-term memory and the Ebbinghaus forgetting curve. The synapse-like behavior and memory behaviors of the transistor are due to the trapping and detrapping processes of the holes, which are generated by the UV pulses, at the IGZO/Al{sub 2}O{sub 3} interface and/or in the Al{sub 2}O{sub 3} layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Crystal Structure of the Nephila clavipes Major Ampullate Spidroin 1A N-terminal Domain Reveals Plasticity at the Dimer Interface

Spider dragline silk is a natural polymer harboring unique physical and biochemical properties that make it an ideal biomaterial. Artificial silk production requires an understanding of the in vivo mechanisms spiders use to convert soluble proteins, called spidroins, into insoluble fibers. Controlled dimerization of the spidroin N-terminal domain (NTD) is crucial to this process. In this paper, we report the crystal structure of the Nephila clavipes major ampullate spidroin NTD dimer. Comparison of our N. clavipes NTD structure with previously determined Euprosthenops australis NTD structures reveals subtle conformational alterations that lead to differences in how the subunits are arranged at the dimer interface. We observe a subset of contacts that are specific to each ortholog, as well as a substantial increase in asymmetry in the interactions observed at the N. clavipes NTD dimer interface. These asymmetric interactions include novel intermolecular salt bridges that provide new insights into the mechanism of NTD dimerization. We also observe a unique intramolecular “handshake” interaction between two conserved acidic residues that our data suggest adds an additional layer of complexity to the pH-sensitive relay mechanism for NTD dimerization. The results of a panel of tryptophan fluorescence dimerization assays probing the importance of these interactions support our structural observations. Based on our findings, we propose that conformational selectivity and plasticity at the NTD dimer interface play a role in the pH-dependent transition of the NTD from monomer to stably associated dimer as the spidroin progresses through the silk extrusion duct.

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

Validation of a crystal plasticity model using high energy diffraction microscopy

High energy diffraction microscopy is used to measure the crystallographic orientation and evolution of lattice strain in an Al-Li alloy. The relative spatial arrangement of the several pancake-shaped grains in a tensile sample is determined through in situ and ex situ techniques. A model for crystal plasticity with continuity of lattice spin is posed, where grains are represented by layers in a finite element mesh following the arrangement indicated by experiment. Comparison is drawn between experiment and simulation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Incorporating physically-based microstructures in materials modeling: Bridging phase field and crystal plasticity frameworks

Here, the mechanical properties of materials systems are highly influenced by various features at the microstructural level. The ability to capture these heterogeneities and incorporate them into continuum-scale frameworks of the deformation behavior is considered a key step in the development of complex non-local models of failure. In this study, we present a modeling framework that incorporates physically-based realizations of polycrystalline aggregates from a phase field (PF) model into a crystal plasticity finite element (CP-FE) framework. Simulated annealing via the PF model yields ensembles of materials microstructures with various grain sizes and shapes. With the aid of a novel FE meshing technique, FE discretizations of these microstructures are generated, where several key features, such as conformity to interfaces, and triple junction angles, are preserved. The discretizations are then used in the CP-FE framework to simulate the mechanical response of polycrystalline α-iron. It is shown that the conformal discretization across interfaces reduces artificial stress localization commonly observed in non-conformal FE discretizations. The work presented herein is a first step towards incorporating physically-based microstructures in lieu of the overly simplified representations that are commonly used. In broader terms, the proposed framework provides future avenues to explore bridging models of materials processes, e.g. additive manufacturing and microstructure evolution of multi-phase multi-component systems, into continuum-scale frameworks of the mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Combined crystal plasticity and grain boundary modeling of creep in ferritic-martensitic steels: I. Theory and implementation

This paper presents a physically-based microstructural model for creep rupture at 600 degrees °C for Grade 91 steel. The model includes constitutive equations that reflect various observed phenomena in Grade 91, and it is incorporated into a mesoscale finite element model with explicit geometry for the prior austenite grains and grain boundaries. Creep within the grains is represented using crystal plasticity for dislocation motion and recovery along with linear viscous diffusional creep for point defect diffusion. The grain boundary models include physics-based models for cavity growth and nucleation that accurately capture tertiary creep and creep rupture. Simulations of creep at 100 MPa are performed, and the contribution of each mechanism is analyzed. The overarching goal is to gain a mechanistic understanding of the material to improve the prediction of creep rupture for long service lives in elevated temperature operating conditions. The creep response of the material at different stress levels, stress states, and temperatures is studied in Part 2 of this paper in order to determine the implications of the simulations on high temperature design practice. Furthermore, the second part explores the effect of triaxial stress states on the creep response and finds a transition from notch-strengthening behavior at high stress to notch-weakening behavior at lower stresses.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Combined crystal plasticity and grain boundary modeling of creep in ferritic-martensitic steels: II. The effect of stress and temperature on engineering and microstructural properties

This paper describes a series of physically-based crystal plasticity finite element method (CPFEM) simulations of long-term creep and creep rupture of Grade 91 steel. It is Part 2 of a two part series of papers. Part 1 describes the simulation framework; this part focuses on specific simulations and on how the predicted long-term creep properties of Grade 91 compare to the assumptions used in current high temperature design practices. This work extends the model developed in Part 1 to look at creep properties at different temperatures, principal stresses, and multiaxial stress states. The simulations show that empirically extrapolating creep rupture stresses from short-term experimental data may substantially over predict the actual long-term creep properties of Grade 91. Additionally, the CPFEM calculations predict a transition from notch strengthening creep behavior for high values of maximum principal stress and moderate notch severity to notch weakening behavior for low principal stresses and more severe notches. The latter regime better categorizes conditions in engineering components designed for long term elevated temperature use, which implies Grade 91 may be a notch weakening material in actual service. This would have a significant impact on high temperature design practices, though confirmatory test data on long-life, low stress notched specimens is difficult to obtain. Finally, one advantage of the physically-based modeling approach adopted here is that the simulation results also elucidate the microstructural mechanisms causing the macroscopic trends in engineering properties predicted by the simulations. This paper shows that the detailed micromechanical mechanisms predicted by the CPFEM simulations can be abstracted with a simple micromechanical model that can be used to both explain the detailed results and make improved predictions of engineering properties from experimental data.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Active learning of a crystal plasticity flow rule from discrete dislocation dynamics simulations

Continuum-scale material deformation models, such as crystal plasticity (CP), can significantly enhance their predictive accuracy by incorporating input from lower-scale (i.e. mesoscale) models. The procedure to generate and extract the relevant information is however typically complex and ad hoc, involving decision and intervention by domain experts, leading to long development times. In this study, we develop a principled approach for calibration of continuum-scale models using lower scale information by representing a CP flow rule as a Gaussian process model. This representation allows for efficient parameter space exploration, guided by the uncertainty embedded in the model through a process known as Bayesian optimization (BO). We demonstrate a semi-autonomous BO loop which instantiates discrete dislocation dynamics simulations whose initial conditions are automatically chosen to optimize the uncertainty of a model CP flow rule. Our self-guided computational pipeline efficiently generated a dataset and corresponding model whose error, uncertainty, and physical feature sensitivities were validated with comparison to an independent dataset four times larger, demonstrating a valuable and efficient active learning implementation readily transferable to similar material systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Active site plasticity and possible modes of chemical inhibition of the human DNA deaminase APOBEC3B

The single-stranded DNA cytosine deaminase APOBEC3B (A3B) functions in innate immunity against viruses, but it is also strongly implicated in eliciting mutations in cancer genomes. Because of the critical role of A3B in promoting virus and tumor evolution, small molecule inhibitors are desirable. However, there is no reported structure for any of the APOBEC3-family enzymes in complex with a small molecule bound in the active site, which hampers the development of small molecules targeting A3B. Here we report high-resolution structures of an active A3B catalytic domain chimera with loop 7 residues exchanged with those from the corresponding region of APOBEC3G (A3G). The structures reveal novel open conformations lacking the catalytically essential zinc ion, with the highly conserved active site residues extensively rearranged. These inactive conformations are stabilized by 2-pyrimidone or an iodide ion bound in the active site. Molecular dynamics simulations corroborate the remarkable plasticity of the engineered active site and identify key interactions that stabilize the native A3B active site. These data provide insights into A3B active site dynamics and suggest possible modes of its inhibition by small molecules, which would aid in rational design of selective A3B inhibitors for constraining virus and tumor evolution.

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

Multiple transient memories in sheared suspensions: Robustness, structure, and routes to plasticity

Multiple transient memories, first discovered in charge-density-wave conductors, are a remarkable and initially counterintuitive example of how a system can store information about its driving. In this class of memories, a system can learn multiple driving inputs, nearly all of which are eventually forgotten despite their continual input. If sufficient noise is present, the system regains plasticity so that it can continue to learn new memories indefinitely. Recently, Keim and Nagel [Phys. Rev. Lett. 107, 010603 (2011)] showed how multiple transient memories could be generalized to a generic driven disordered system with noise, giving as an example simulations of a simple model of a sheared non-Brownian suspension. Here, we further explore simulation models of suspensions under cyclic shear, focusing on three main themes: robustness, structure, and overdriving. We show that multiple transient memories are a robust feature independent of many details of the model. The steady-state spatial distribution of the particles is sensitive to the driving algorithm; nonetheless, the memory formation is independent of such a change in particle correlations. Finally, we demonstrate that overdriving provides another means for controlling memory formation and retention.

42 ENGINEERING↗
DOE OSTI2012

Three-dimensional plastic response in polycrystalline copper via near-field high-energy X-ray diffraction microscopy

The evolution of the crystallographic orientation field in a polycrystalline sample of copper is mapped in three dimensions as tensile strain is applied. Here, using forward-modeling analysis of high-energy X-ray diffraction microscopy data collected at the Advanced Photon Source, the ability to track intragranular orientation variations is demonstrated on an ~2 µm length scale with ~0.1° orientation precision. Lattice rotations within grains are tracked between states with ~1° precision. Detailed analysis is presented for a sample cross section before and after ~6% strain. The voxel-based (0.625 µm triangular mesh) reconstructed structure is used to calculate kernel-averaged misorientation maps, which exhibit complex patterns. Simulated scattering from the reconstructed orientation field is shown to reproduce complex scattering patterns generated by the defected microstructure. Spatial variation of a goodness-of-fit or confidence metric associated with the optimized orientation field indicates regions of relatively high or low orientational disorder. An alignment procedure is used to match sample cross sections in the different strain states. The data and analysis methods point toward the ability to perform detailed comparisons between polycrystal plasticity computational model predictions and experimental observations of macroscopic volumes of material.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Neutron Detection with Large Plastic Scintillators for RPM Applications

Homeland security requests the use Radiation Portal Monitor (RPM). They must be able to detect and differentiate gamma and neutron radiation. Gamma detection is required for illicit transportation of radioactive matter detection. Neutron detection is important to control nonproliferation of enriched material. Manufacturers worldwide propose sensors based on {sup 3}He which give the actual state of art in term of neutron detection. The imminent shortage of {sup 3}He forces manufacturers to find viable alternative. From 10 years sensors providers have the challenge to replace previous {sup 3}He detectors that are known to be the most commonly deployed neutron sensor. As {sup 3}He detectors can only detect neutron, they must be completed with gamma detector. The proposed approach is based on pulse time correlation between adjacent sensors from signal collected by EJ200 plastic scintillators. Results obtained during FP7 Scintilla project test campaigns show the system relevance for replacement of today's {sup 3}He detectors. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Cu/Nb nano-composite wires processed by severe plastic deformation for applications in high pulsed magnets: effects of the multi-scale microstructure on the mechanical properties

Copper-based high strength and high electrical conductivity nano-composite wires reinforced by Nb nano-tubes are prepared by severe plastic deformation, applied with an Accumulative Drawing and Bundling process (ADB), for the windings of high pulsed magnets. The ADB process leads to a multi-scale Cu matrix containing up to N = 85{sub 4} (52.2.10{sup 6}) continuous parallel Nb tubes with diameter down to few tens nano-meters. After heavy strain, the Nb nano-tubes exhibit a homogeneous microstructure with grain size below 100 nm. The Cu matrix presents a multi-scale microstructure with multi-modal grain size distribution from the micrometer to the nano-meter range. The use of complementary characterization techniques at the microscopic and macroscopic level (in-situ tensile tests in the TEM, nano-indentation, in-situ tensile tests under high energy synchrotron beam) shed light on the interest of the multi-scale nature of the microstructure to achieve extreme mechanical properties, therefore allowing for design guidelines to further improve these properties. (authors)

36 MATERIALS SCIENCE↗