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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Three dimensions, two microscopes, one code: Automatic differentiation for x-ray nanotomography beyond the depth of focus limit

Conventional tomographic reconstruction algorithms assume that one has obtained pure projection images, involving no within-specimen diffraction effects nor multiple scattering. Advances in x-ray nanotomography are leading toward the violation of these assumptions, by combining the high penetration power of x-rays, which enables thick specimens to be imaged, with improved spatial resolution that decreases the depth of focus of the imaging system. We describe a reconstruction method where multiple scattering and diffraction effects in thick samples are modeled by multislice propagation and the 3D object function is retrieved through iterative optimization. We show that the same proposed method works for both full-field microscopy and for coherent scanning techniques like ptychography. Our implementation uses the optimization toolbox and the automatic differentiation capability of the open-source deep learning package TensorFlow, demonstrating a straightforward way to solve optimization problems in computational imaging with flexibility and portability.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Computational and Experimental Investigations of the Molecular Scale Structure and Dynamics of Gologically Important Fluids and Mineral-Fluid Interfaces

United States Department of Energy grant DE-FG02-10ER16128, “Computational and Spectroscopic Investigations of the Molecular Scale Structure and Dynamics of Geologically Important Fluids and Mineral-Fluid Interfaces” (Geoffrey M. Bowers, P.I.) focused on developing a molecular-scale understanding of processes that occur in fluids and at solid-fluid interfaces using the combination of spectroscopic, microscopic, and diffraction studies with molecular dynamics computer modeling. The work is intimately tied to the twin proposal at Michigan State University (DOE DE-FG02-08ER15929; same title: R. James Kirkpatrick, P.I. and A. Ozgur Yazaydin, co-P.I.).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

A submillimeter tripler using a quasi-waveguide structure

A new type of frequency multiplier structure is being developed which is suitable for application at frequencies above 1 THz. This structure preserves some of the properties of waveguide for mode control, yet is not truly single mode. The device resembles a sectoral horn, with a varactor diode mounted near the throat. Input and output coupling are through the same aperture, requiring a quasi-optical diplexer. Initial tests are directed at building a tripler at 500 GHz, for comparison with waveguide structures. The diplexer is a blazed diffraction grating with appropriate focusing optics. Model studies show that the impedance match to a varactor should be good, and initial tests of the beam patterns of the prototype indicate that optical coupling efficiency should be very high. The structure also has the potential for use as a fundamental mixer, or as a third harmonic mixer.

Erickson, Neal R.↗
DOE OSTI2014

Understanding Irreversible Degradation of Nb3Sn Wires with Fundamental Fracture Mechanics

Irreversible performance degradation of advanced Nb3Sn superconducting wires subjected to transverse or axial mechanical loading is a critical issue for the design of large-scale fusion and accelerator magnets such as ITER and LHC. Recent SULTAN tests indicate that most cable-in-conduit conductors for ITER coils made of Nb3Sn wires processed by various fabrication techniques show similar performance degradation under cyclic loading. The irreversible degradation due to filament fracture and local strain accumulation in Nb3Sn wires cannot be described by the existing strand scaling law. Fracture mechanic modeling combined with X-ray diffraction imaging of filament micro-crack formation inside the wires under mechanical loading may reveal exciting insights to the wire degradation mechanisms. We apply fundamental fracture mechanics with a singularity approach to study influence of wire filament microstructure of initial void size and distribution to local stress concentration and potential crack propagation. We report impact of the scale and density of the void structure on stress concentration in the composite wire materials for crack initiation. These initial defects result in an irreversible degradation of the critical current beyond certain applied stress. We also discuss options to minimize stress concentration in the design of the material microstructure for enhanced wire performance for future applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Understanding the limitations and potential of micro tensile testing of tungsten and needs for crystal plasticity modelling

Tungsten is the leading plasma facing material candidate due to its exceptional properties. Understanding the response to neutron irradiation is crucial for the lifetime evaluation of tungsten. The limited space in nuclear reactors and the high levels of radioactivity of the specimens after irradiation are significant barriers to accurately measuring the mechanical properties after neutron irradiation. Testing of micro tensile specimens is one approach to reduce the total amount of irradiated material needed for a set of mechanical testing experiments. However, micro samples are not necessarily measuring the bulk material properties, as size effects produce higher measured mechanical properties than is observed in engineering size counterparts. Determining the minimal sample size for reliable bulk property measurement, combined with modeling efforts, is essential. We conducted room temperature tensile tests on tungsten micro tensile specimens fabricated with focused ion beam, plasma focused ion beam and femto-second laser ablation system to dimension of 2×2×7?µm³, 7×7×18?µm³, and 80×100×233?µm³ (width×thickness×gauge-length), respectively. Elevated tensile testing was performed up to 475°C on 5×5×18?µm³ specimens fabricated with focused ion beam. The smallest specimens exhibited a high degree of ductility and strength, whereas the largest specimens demonstrated behavior akin to bulk tungsten. To investigate the effects introduced by the micro specimen fabrication processes and to obtain the necessary bulk dislocation density for the crystal plasticity model, we employed X-ray diffraction depth profiling. This measurement was performed using different X-ray sources with varying penetration depths. Finally, the potential and limitations of micro mechanical tests for tungsten will be discussed.

36 - MATERIALS SCIENCE↗
DOE OSTI2018

Mechanism-based constitutive modeling of ZEK100 magnesium alloy with crystal plasticity and in-situ HEXRD experiment

The constitutive behavior of a hexagonal close-packed (HCP) polycrystalline ZEK100 magnesium alloy was investigated here using combined high energy X-ray diffraction (HEXRD) from a synchrotron source and crystal plasticity modeling approach. The in-situ tensile test data coupled with the HEXRD enabled the tracking of the lattice strain evolution during deformation. The microscopic behavior represented by lattice strain and the macroscopic behavior represented by stress-strain curves were then used together as objective function to estimate the critical resolved shear stress (CRSS) and hardening parameters of available slip and deformation twin systems in the ZEK100 alloy. An enhanced predominant twinning reorientation (ePTR) scheme was proposed in the current work, and the ePTR parameters were determined for the first time by the use of basal plane peak intensity along loading direction measured from HEXRD. Two crystal plasticity models, the computationally efficient elastic-plastic self-consistent (EPSC) and crystal plasticity finite element (CPFE) models, were developed incorporating the deformation twinning for the HCP-structured metals. The determined constitutive parameters were further validated by comparing the predicted deformation texture with the measured one. The work provides a useful and computationally-efficient modeling scheme to understand the slip/twin induced deformation behaviors of the ZEK100 alloy in micro- and macro-scales.

36 MATERIALS SCIENCE↗
DOE OSTI2024

3D Nanocrystallography and the Imperfect Molecular Lattice

Crystallographic analysis relies on the scattering of quanta from arrays of atoms that populate a repeating lattice. While large crystals built of lattices that appear ideal are sought after by crystallographers, imperfections are the norm for molecular crystals. Additionally, advanced X-ray and electron diffraction techniques, used for crystallography, have opened the possibility of interrogating micro- and nanoscale crystals, with edges only millions or even thousands of molecules long. These crystals exist in a size regime that approximates the lower bounds for traditional models of crystal nonuniformity and imperfection. Accordingly, data generated by diffraction from both X-rays and electrons show increased complexity and are more challenging to conventionally model. New approaches in serial crystallography and spatially resolved electron diffraction mapping are changing this paradigm by better accounting for variability within and between crystals. The intersection of these methods presents an opportunity for a more comprehensive understanding of the structure and properties of nanocrystalline materials.

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

IR Heat Treatment of Hybrid Steel-Al Joints

The technical objective of this CRADA is to develop and model a heat treatment process based on Infra- Red (IR) heating of a overcast Al/steel bimetallic joint to produce a T5 temper in a shorter period of time than is currently achievable and, separately, to produce a modified T6 temper for improved mechanical properties without the loss of joint integrity. IR heat treatments have been demonstrated to provide reduced processing time, reduced energy requirements, and improved material properties of Al components, including strength and elongation, relative to convective thermal heat treatment methods. A prototype IR furnace was assembled to heat treat these joints. The residual stress state of the joints were modeled in the as-cast condition, as well as the T5 and T6 condition. Neutrons were used to measure the residual stresses in the joints for various heat treatments. ORNL is uniquely equipped to partner with Vehma in the experimental evaluation and modeling of Al/steel bi-metallic joints. ORNL possesses a long history of microstructural, crystallographic and mechanical characterization of structural materials. Unique facilities at ORNL for this work include the NRSF2/HB-2B beamline at the High Flux Isotope Reactor (HFIR) for residual stress measurements with neutron diffraction, metallurgical expertise for heat treating and modeling capability of the manufacturing of these joints for residual stress prediction. All of these capabilities were utilized in this CRADA. The CRADA began in April 2011 and ended in September 2014 (41 months).

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2016

Sagdeev potential approach for quantum ion-acoustic solitary waves in an electron-positron-ion plasma

Sagdeev pseudopotential method is employed to study the arbitrary amplitude quantum ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma by using one dimensional quantum hydrodynamic model together with the Poisson equation. Sagdeev potential function is obtained in terms of electrostatic potential and analyzed with and without the effect of quantum diffraction parameter H. Effects of the parameter H on both the amplitude and width of the solitary waves have been observed. It is also observed that the positron density can affect the wave propagation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Accounting for partiality in serial crystallography using ray-tracing principles

Serial crystallography generates partial reflections from still diffraction images. Partialities are estimated with EVAL ray-tracing simulations, thereby improving merged reflection data to a similar quality as conventional rotation data. Serial crystallography generates ‘still’ diffraction data sets that are composed of single diffraction images obtained from a large number of crystals arbitrarily oriented in the X-ray beam. Estimation of the reflection partialities, which accounts for the expected observed fractions of diffraction intensities, has so far been problematic. In this paper, a method is derived for modelling the partialities by making use of the ray-tracing diffraction-integration method EVAL. The method estimates partialities based on crystal mosaicity, beam divergence, wavelength dispersion, crystal size and the interference function, accounting for crystallite size. It is shown that modelling of each reflection by a distribution of interference-function weighted rays yields a ‘still’ Lorentz factor. Still data are compared with a conventional rotation data set collected from a single lysozyme crystal. Overall, the presented still integration method improves the data quality markedly. The R factor of the still data compared with the rotation data decreases from 26% using a Monte Carlo approach to 12% after applying the Lorentz correction, to 5.3% when estimating partialities by EVAL and finally to 4.7% after post-refinement. The merging R{sub int} factor of the still data improves from 105 to 56% but remains high. This suggests that the accuracy of the model parameters could be further improved. However, with a multiplicity of around 40 and an R{sub int} of ∼50% the merged still data approximate the quality of the rotation data. The presented integration method suitably accounts for the partiality of the observed intensities in still diffraction data, which is a critical step to improve data quality in serial crystallography.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Deformation of binary and boron-doped Ni 3 Al alloys at high pressures studied with synchrotron x-ray diffraction

In situ x-ray synchrotron diffraction experiments were carried out on nickel-based high-strength superalloys under pressure to understand their deformation mechanism using a diamond anvil cell (DAC). Radial x-ray diffraction determines the room-temperature equations of state and yield strengths of binary Ni 3 Al alloy and 500 ppm boron-doped Ni 3 Al to pressures of 20 and 46 GPa, respectively. Crystallographic preferred orientations observed in these superalloys due to anisotropic stress field in DAC indicate the onset of plastic deformation. Inverse pole figure analysis reveals that the underlying deformation mechanisms change from an octahedral slip to a simultaneous activation of octahedral and cube slips upon doping with boron. The yield-strength values were found to increase with pressure and are comparable to those determined from axial diffraction experiments. The results indicate that the yield strength of Ni 3 Al:B is about 0.5 GPa higher (at pressures below 20 GPa) due to grain boundary strengthening by boron. It is shown that due to high elastic anisotropy of Ni 3 Al alloy, the yield-strength estimations from diffraction experiments strongly depend on the micromechanical model used to convert the measured elastic strains into stresses.

42 ENGINEERING↗
DOE OSTI2018

Simulation of kinematic Kikuchi diffraction patterns from atomistic structures

One of the limitations of atomistic simulations is that many of the computational tools used to extract structural information from atomic trajectories provide metrics that are not directly compatible with experiments for validation. In this work, to bridge between simulation and experiment, a method is presented to produce simulated Kikuchi diffraction patterns using data from atomistic simulations, without requiring a priori specification of the crystal structure or defect periodicity. The Kikuchi pattern simulation is based on the kinematic theory of diffraction, with Kikuchi line intensities computed via a discrete structure factor calculation. Reciprocal lattice points are mapped to Kikuchi lines using a geometric projection of the reciprocal space data. This method is validated using single crystal atomistic models, and the novelty of this approach is emphasized by simulating kinematic Kikuchi diffraction patterns from an atomistic model containing a nanoscale dislocation loop. Deviations in kinematic Kikuchi line intensities are explained considering the displacement field of the dislocation loop, as is done in diffraction contrast theory.

42 ENGINEERING↗
NASA NTRS1986

Multistep modeling of protein structure: application to bungarotoxin

Modelling of bungarotoxin in atomic details is presented in this article. The model-building procedure utilizes the low-resolution crystal coordinates of the c-alpha atoms of bungarotoxin, sequence homology within the neurotoxin family, as well as high-resolution x-ray diffraction data of cobratoxin and erabutoxin. Our model-building procedure involves: (a) principles of comparative modelling, (b) embedding procedures of distance geometry, and (c) use of molecular mechanics for optimizing packing. The model is not only consistent with the c-alpha coordinates of crystal structure, but also agrees with solution conformational features of the triple-stranded beta sheet as observed by NOE measurements.

NASA Discipline Exobiology↗
DOE OSTI2018

Texture simulation of a severely cold rolled low carbon steel using polycrystal modeling

Characteristic textures of cold-rolled low carbon steel consist of the RD//$\langle$110$\rangle$ fiber (α fiber) and ND//$\langle$111$\rangle$ fiber (γ fiber). Although the development of the γ fiber has been successfully modeled by the relaxed constraints polycrystal plasticity model, modeling of the α fiber has been less successful. Here, we investigate mechanisms underlying the development of a strong α fiber in a low carbon steel during cold rolling to large thickness reductions of 90%, 98%, and 99.8%. We compare the deformation textures measured using X-ray and electron backscatter diffraction methods with those simulated using polycrystal models, employing one of four homogenization schemes: the Taylor model, Secant model, Tangent model and an intermediate stiffness model between the Secant and Tangent models. The measured textures consist of an extremely strong α fiber and unusually weak γ fiber. The calculated textures achieve the best agreement with the measured ones when (1) the intermediate stiffness model is used to account for grain shape effects, (2) the flow rule exponent (n) is chosen to allow for multiple slip in grains, (3) latent hardening effects are suppressed, (4) $\langle$111$\rangle$ slip on {110}, {112} and {123} planes is made available for deformation, and (5) the grains shape is permitted to evolve individually. Taken together, these aspects represent indirectly the effects of cross slip on slip activity, suggesting that the strong α fiber in severely cold rolled steel results from cross slip. Although the cross slip is a well accepted mechanism in b.c.c. crystals, its connection to α fiber dominance in texture development during severe rolling deformation has not been established before.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Data publication with the structural biology data grid supports live analysis

Access to experimental X-ray diffraction image data is fundamental for validation and reproduction of macromolecular models and indispensable for development of structural biology processing methods. Here, we established a diffraction data publication and dissemination system, Structural Biology Data Grid (SBDG; data.sbgrid.org), to preserve primary experimental data sets that support scientific publications. Data sets are accessible to researchers through a community driven data grid, which facilitates global data access. Our analysis of a pilot collection of crystallographic data sets demonstrates that the information archived by SBDG is sufficient to reprocess data to statistics that meet or exceed the quality of the original published structures. SBDG has extended its services to the entire community and is used to develop support for other types of biomedical data sets. In conclusion, it is anticipated that access to the experimental data sets will enhance the paradigm shift in the community towards a much more dynamic body of continuously improving data analysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Characterizing dislocation configurations and their evolution during creep of a new 12% Cr steel

Highlights: • Applicability of different techniques to characterize particular dislocation configuration. • XRD models in combination with TEM and EBSD to measure the dislocation density. • Substructure evolution during creep of a new 12% Cr steel is discussed. - Abstract: In this research, different types of dislocations are characterized and quantified in a newly developed 12% Cr steel in as-received as well as in crept conditions. X-ray diffraction (XRD) patterns are analyzed using three different models. The dislocation densities are determined employing the Convolution Multiple Whole Profile (CMWP) fitting, the analysis of the asymptotic part of the X-ray line profile (Groma's method), and the Rietveld refinement coupling Popa's and Williamson-Smallman approaches. CMWP method is used to measure the internal dislocation density inside the subgrains consisting of mobile and dipole dislocations, and the results show good agreement with Transmission Electron Microscopy (TEM) measurements. Groma's method is used to evaluate the total dislocation density, with results comparable to those obtained from the combination of Electron Backscatter Diffraction (EBSD) and TEM. Rietveld method gives the internal dislocation density or mobile dislocation density depending on the model chosen. The experimentally determined results such as creep strain, dislocation densities and subgrain size are compared with theoretical predictions and they are found in good agreement.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Algorithms in Diffraction Profile Analysis

This chapter introduces several approaches to crystallographic structure refinement from diffraction profile data including the Rietveld method, global optimization methods, and Bayesian modeling. First, the Rietveld method and related nonlinear least squares approaches to analyzing diffraction profiles are briefly discussed. We then review the most common algorithms within global optimization as alternative methods of structure solution: grid search, simulated annealing, and genetic algorithms. As the Rietveld method is the standard tool for analyzing diffraction profile data, we catalogue its challenges and limitations. A Bayesian approach to diffraction profile analysis is presented as an alternative, along with several sampling algorithms including Gibbs sampling, variants of Metropolis sampling, Hamiltonian Monte Carlo, and approximate Bayesian computing. These sampling algorithms are applied to the fitting of a neutron diffraction profile from a National Institute of Standards and Technology silicon standard reference material, and their results are compared.

Singh, Susheela↗