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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

HOTCFGM-2D: A Coupled Higher-Order Theory for Cylindrical Structural Components with Bi-Directionally Components with Bi-Directionally Graded Microstructures

The objective of this two-year project was to develop and deliver to the NASA-Glenn Research Center a two-dimensional higher-order theory, and related computer codes, for the analysis and design of cylindrical functionally graded materials/structural components for use in advanced aircraft engines (e.g., combustor linings, rotor disks, heat shields, brisk blades). To satisfy this objective, two-dimensional version of the higher-order theory, HOTCFGM-2D, and four computer codes based on this theory, for the analysis and design of structural components functionally graded in the radial and circumferential directions were developed in the cylindrical coordinate system r-Theta-z. This version of the higher-order theory is a significant generalization of the one-dimensional theory, HOTCFGM-1D, developed during the FY97 for the analysis and design of cylindrical structural components with radially graded microstructures. The generalized theory is applicable to thin multi-phased composite shells/cylinders subjected to steady-state thermomechanical, transient thermal and inertial loading applied uniformly along the axial direction such that the overall deformation is characterized by a constant average axial strain. The reinforcement phases are uniformly distributed in the axial direction, and arbitrarily distributed in the radial and circumferential direction, thereby allowing functional grading of the internal reinforcement in the r-Theta plane. The four computer codes fgmc3dq.cylindrical.f, fgmp3dq.cylindrical.f, fgmgvips3dq.cylindrical.f, and fgmc3dq.cylindrical.transient.f are research-oriented codes for investigating the effect of functionally graded architectures, as well as the properties of the multi-phase reinforcement, in thin shells subjected to thermomechanical and inertial loading, on the internal temperature, stress and (inelastic) strain fields. The reinforcement distribution in the radial and circumferential directions is specified by the user. The thermal and inelastic properties of the individual phases can vary with temperature. The inelastic phases are presently modeled by the power-law creep model generalized to multi-directional loading (within fgmc3dq.cylindrical.f and fgmc3dq.cylindrical.transient.f for steady-state and transient thermal loading, respectively), and incremental plasticity and GVIPS unified viscoplasticity theories (within the steady-state loading versions fgmp3dq.cylindrical.f and fgmgvips3dq.cylindrical.f).

Pindera, Marek-Jerzy↗
NASA NTRS2001

Viscoplastic Model Development to Account for Strength Differential: Application to Aged Inconel 718 at Elevated Temperature

The magnitude of yield and flow stresses in aged Inconel 718 are observed to be different in tension and compression. This phenomenon, called the Strength differential (SD), contradicts the metal plasticity axiom that the second deviatoric stress invariant alone is sufficient for representing yield and flow. Apparently, at least one of the other two stress invariants is also significant. A unified viscoplastic model was developed that is able to account for the SD effect in aged Inconel 718. Building this model involved both theory and experiments. First, a general threshold function was proposed that depends on all three stress invariants and then the flow and evolution laws were developed using a potential-based thermodynamic framework. Judiciously chosen shear and axial tests were conducted to characterize the material. Shear tests involved monotonic loading, relaxation, and creep tests with different loading rates and load levels. The axial tests were tension and compression tests that resulted in sufficiently large inelastic strains. All tests were performed at 650 C. The viscoplastic material parameters were determined by optimizing the fit to the shear tests, during which the first and the third stress invariants remained zero. The threshold surface parameters were then fit to the tension and compression test data. An experimental procedure was established to quantify the effect of each stress invariant on inelastic deformation. This requires conducting tests with nonproportional three-dimensional load paths. Validation of the model was done using biaxial tests on tubular specimens of aged Inconel 718 using proportional and nonproportional axial-torsion loading. These biaxial tests also helped to determine the most appropriate form of the threshold function; that is, how to combine the stress invariants. Of the set of trial threshold functions, the ones that incorporated the third stress invariant give the best predictions. However, inclusion of the first stress invariant does not significantly improve the model predictions. The model shows excellent predictive capability for nonproportional load paths. Additionally, it reduces to the well-known models of Mises Drucker and Drucker-Prager. The requisite experiments involve reasonably simple load paths in the axial-shear stress plane and hence can be performed on a variety of different materials: be they metallic, geological. polymeric, ceramic or granular. The general form of the threshold function allows representation of inelastic deformation in a range of materials.

Iyer, Saiganesh↗
NASA NTRS1998

Constitutive Theory Developed for Monolithic Ceramic Materials

With the increasing use of advanced ceramic materials in high-temperature structural applications such as advanced heat engine components, the need arises to accurately predict thermomechanical behavior that is inherently time-dependent and that is hereditary in the sense that the current behavior depends not only on current conditions but also on the material's thermomechanical history. Most current analytical life prediction methods for both subcritical crack growth and creep models use elastic stress fields to predict the time-dependent reliability response of components subjected to elevated service temperatures. Inelastic response at high temperatures has been well documented in the materials science literature for these material systems, but this issue has been ignored by the engineering design community. From a design engineer's perspective, it is imperative to emphasize that accurate predictions of time-dependent reliability demand accurate stress field information. Ceramic materials exhibit different time-dependent behavior in tension and compression. Thus, inelastic deformation models for ceramics must be constructed in a fashion that admits both sensitivity to hydrostatic stress and differing behavior in tension and compression. A number of constitutive theories for materials that exhibit sensitivity to the hydrostatic component of stress have been proposed that characterize deformation using time-independent classical plasticity as a foundation. However, none of these theories allow different behavior in tension and compression. In addition, these theories are somewhat lacking in that they are unable to capture the creep, relaxation, and rate-sensitive phenomena exhibited by ceramic materials at high temperatures. The objective of this effort at the NASA Lewis Research Center has been to formulate a macroscopic continuum theory that captures these time-dependent phenomena. Specifically, the effort has focused on inelastic deformation behavior associated with these service conditions by developing a multiaxial viscoplastic constitutive model that accounts for time-dependent hereditary material deformation (such as creep and stress relaxation) in monolithic structural ceramics. Using continuum principles of engineering mechanics, we derived the complete viscoplastic theory from a scalar dissipative potential function.

Janosik, Lesley A.↗
NASA NTRS1999

Viscoplastic Constitutive Theory Demonstrated for Monolithic Ceramic Materials

Development of accurate three-dimensional (multiaxial) inelastic stress-strain models is critical in utilizing advanced ceramics for challenging 21st century high-temperature structural applications. The current state of the art uses elastic stress fields as a basis for both subcritical crack growth and creep life prediction efforts aimed at predicting the time dependent reliability response of ceramic components subjected to elevated service temperatures. However, to successfully design components that will meet tomorrow's challenging requirements, design engineers must recognize that elastic predictions are inaccurate for these materials when subjected to high-temperature service conditions such as those encountered in advanced heat engine components. Analytical life prediction methodologies developed for advanced ceramics and other brittle materials must employ accurate constitutive models that capture the inelastic response exhibited by these materials at elevated service temperatures. A constitutive model recently developed at the NASA Lewis Research Center helps address this issue by accounting for the time-dependent (inelastic) material deformation phenomena (e.g., creep, rate sensitivity, and stress relaxation) exhibited by monolithic ceramics exposed to high-temperature service conditions. In addition, the proposed formulation is based on a threshold function that is sensitive to hydrostatic stress and allows different behavior in tension and compression, reflecting experimental observations obtained for these material systems.

Janosik, Lesley A.↗
NASA NTRS2003

High-Fidelity Micromechanics Model Enhanced for Multiphase Particulate Materials

This 3-year effort involves the development of a comprehensive micromechanics model and a related computer code, capable of accurately estimating both the average response and the local stress and strain fields in the individual phases, assuming both elastic and inelastic behavior. During the first year (fiscal year 2001) of the investigation, a version of the model called the High-Fidelity Generalized Method of Cells (HFGMC) was successfully completed for the thermo-inelastic response of continuously reinforced multiphased materials with arbitrary periodic microstructures (refs. 1 and 2). The model s excellent predictive capability for both the macroscopic response and the microlevel stress and strain fields was demonstrated through comparison with exact analytical and finite element solutions. This year, HFGMC was further extended in two technologically significant ways. The first enhancement entailed the incorporation of fiber/matrix debonding capability into the two-dimensional version of HFGMC for modeling the response of unidirectionally reinforced composites such as titanium matrix composites, which exhibit poor fiber/matrix bond. Comparison with experimental data validated the model s predictive capability. The second enhancement entailed further generalization of HFGMC to three dimensions to enable modeling the response of particulate-reinforced (discontinuous) composites in the elastic material behavior domain. Next year, the three-dimensional version will be generalized to encompass inelastic effects due to plasticity, viscoplasticity, and damage, as well as coupled electromagnetothermomechanical (including piezoelectric) effects.

Pindera, Marek-Jerzy↗
DOE OSTI2021

Neutral Pion Electroproduction Cross sections from 12 GeV Jefferson Lab for x B > 0 . 3

Nuclear physics aims at understanding structure of the building blocks of the atom, the protons and neutrons in terms of their constituents, the quarks and gluons. Traditionally, this was accomplished through studies of their static properties and the underlying one-dimensional quark and gluon momentum distributions. Over the last few decades, realization has grown that the true study of the proton dynamical structure has to come from more exclusive reactions. These deep exclusive processes describe a subset of unique inelastic processes in which all particles in their final state are detected. Such processes can allow access to Generalized Parton Distributions, or GPDs, a conceptual mechanism that lies at the root of three-dimensional spatial imaging of the proton?s quark-gluon substructure. In particular, photon electroproduction as well as meson electroproduction are two kinds of deep inelastic processes that can allow access to GPDs. Deeply Virtual Compton Scattering (DVCS) is a type of deep inelastic process, and is known as one of the cleanest ways to access GPDs.

Ali, Salina↗
DOE OSTI2022

Proton Scattering in NOvA Test Beam

The NuMI Off-axis $\nu_e$ Appearance (NOvA) experiment is a two-detector, long baseline, neutrino oscillation experiment, which aims to make a determination of the neutrino mass ordering, the octant of $\theta_{23}$, and measure possible charge-parity (CP) violation. Determining these parameters is a step towards answering some of the fundamental questions about neutrinos. Are neutrinos their own antiparticle? Could neutrinos be responsible for the matter-antimatter asymmetry of the universe? How do neutrinos get their mass? Answering these questions requires precise measurements of the parameters that govern how neutrinos behave, namely the mass squared splittings, mixing angles, and possible CP-violating phase factor in the PNMS matrix. Reaching high precision requires minimizing both statistical and systematic errors. As NOvA continues to accumulate data, the sizes of our statistical errors continue to shrink such that in a couple of years they will be comparable to our systematic errors. NOvA's current systematic errors are dominated by energy and calibration uncertainties. The Test Beam program was initiated to address these uncertainties by assessing the detector response in an environment where more parameters of the incoming particles are known. One of the main goals of the Test Beam program is to garner a better understanding of our systematic errors, particularly in energy measurement and detector response, so that the modeling of these parameters can be improved. I studied protons in the Test Beam Detector with momenta around \unit[1]{GeV/c}, the high end of the momentum range relevant to quasielastic neutrino interactions in NOvA. One question this sample can help to answer is if we correctly simulate the fraction of protons that have an inelastic scattering interaction versus ranging out. If protons inelastically scatter at different rates in our simulation and data, the correction applied to the hadronic system when reconstructing neutrino energy could be inaccurate, since events with inelastic scattering will have less visible energy in the detector. This is particularly important for quasielastic $\nu_\mu$ events, which have the lowest hadronic energy resolution, and therefore give us our best measurements of $\Delta m_{32}^2$ and $\theta_{23}$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Disentangling the EMC effect: from free to bound nucleon structure

Deep inelastic scattering experiments using electron beams on fixed targets allow for the study of the structure of nucleons. While the structure of the free proton has been well measured, the free neutron structure and the modification of nucleon structure in the nuclear environment, the EMC effect, remain open questions. Studies suggest that the EMC effect may arise due to strongly-interacting nucleon-nucleon systems, referred to as short-range correlations. The BAND experiment at the Thomas Jefferson National Accelerator Facility seeks to probe the bound proton structure when in a strongly-interacting state, using spectator-tagged deep inelastic scattering. This thesis presents the results of the BAND experiment, demonstrating the proton is modified when strongly-interacting with the spectator neutron in deuterium. This thesis also explores efforts to describe inclusive and tagged deep inelastic scattering data within a uniform theoretical framework to explore nucleon structure modification effects and extract the free neutron structure.

Segarra, Efrain↗
DOE OSTI2025

Constraints on magnetism and correlations in RuO 2 from lattice dynamics and Mössbauer spectroscopy

We provide experimental evidence for the absence of a magnetic moment in bulk RuO 2 , a candidate altermagnetic material, by using a combination of Mössbauer spectroscopy, nuclear forward scattering, inelastic X-ray and neutron scattering, and density functional theory calculations. Using complementary Mössbauer and nuclear forward scattering, we determine the Ru magnetic hyperfine splitting to be negligible. Inelastic X-ray and neutron scattering-derived lattice dynamics of RuO 2 are compared to density functional theory calculations of varying flavors. Comparisons among theory with experiments indicate that electronic correlations, rather than magnetic order, are key in describing the lattice dynamics.

Mössbauer spectroscopy↗
DOE OSTI2025

Imaging the photochemistry of cyclobutanone using ultrafast electron diffraction: Experimental results

We investigated the ultrafast structural dynamics of cyclobutanone following photoexcitation at λ = 200 nm using gas-phase megaelectronvolt ultrafast electron diffraction. Our investigation complements the simulation studies of the same process within this special issue. It provides information about both electronic state population and structural dynamics through well-separable inelastic and elastic electron scattering signatures. We observe the depopulation of the photoexcited S 2 state of cyclobutanone with n3s Rydberg character through its inelastic electron scattering signature with a time constant of (0.29 ± 0.2) ps toward the S 1 state. The S 1 state population undergoes ring-opening via a Norrish Type-I reaction, likely while passing through a conical intersection with S 0 . The corresponding structural changes can be tracked by elastic electron scattering signatures. These changes appear with a delay of (0.14 ± 0.05) ps with respect to the initial photoexcitation, which is less than the S 2 depopulation time constant. This behavior provides evidence for the ballistic nature of the ring-opening once the S 1 state is reached. The resulting biradical species react further within (1.2 ± 0.2) ps via two rival fragmentation channels yielding ketene and ethylene, or propene and carbon monoxide. Furthermore, our study showcases the value of both gas-phase ultrafast diffraction studies as an experimental benchmark for nonadiabatic dynamics simulation methods and the limits in the interpretation of such experimental data without comparison with such simulations.

Carbon monoxide↗
DOE OSTI2022

Electronic structure of the frustrated diamond lattice magnet NiRh 2 O 4

We report the A -site spinel NiRh 2 O 4 is the only known realization of a spin-1 diamond lattice magnet and is predicted to host unconventional magnetic phenomena driven by frustrated nearest and next-nearest neighbor exchange as well as orbital degeneracy. Previous works found no sign of magnetic order but found a gapped dispersive magnetic excitation indicating a possible valence bond magnetic ground state. However, the presence of many competing low energy degrees of freedom and limited empirical microscopic constraints complicates further analysis. Here we carry out resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy (XAS), and inelastic neutron scattering (INS) to characterize the local electronic structure and lattice dynamics of NiRh 2 O 4 . The RIXS data can be partly described by a single-ion model for tetrahedrally coordinated Ni 2+ and indicates a tetragonal distortion Δt 2 = 70 meV that splits the t 2 orbitals into a high energy orbital singlet and lower energy orbital doublet. We identify features of the RIXS spectra that are consistent with a Rh-Ni two-site excitation indicating strong metal-metal hybridization mediated by oxygen in NiRh 2 O 4 . We also identify signatures of electron-phonon coupling through the appearance of phonon sidebands that dress crystal field excitations. These results establish the key energy scales relevant to the magnetism in NiRh 2 O 4 and further demonstrate that covalency and lattice dynamics play essential roles in controlling the magnetic ground states of A -site spinels.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Supporting Data for "Constraints on magnetism and correlations in RuO2 from lattice dynamics and Mössbauer spectroscopy"

Contents of this DOI are data for the research paper "Constraints on magnetism and correlations in RuO2 from lattice dynamics and Mossbauer spectroscopy" by the authors: George Yumnam, et. al. The dataset contains data from inelastic x-ray scattering measurements of RuO2 single crystals performed at the Advanced Photon Source in Argonne National Lab. This dataset also contains data from inelastic neutron scattering experiments of RuO2 powder performed at the ARCS spectrometer at Spallation Neutron Source at ORNL. Supporting theoretical calculations based on density functional theory with r2SCAN and DFT+U methods is also included in this dataset. Please see the README.txt files for more information of the dataset and file contents. For comments and questions, please contact: George Yumnam (yumnamg@ornl.gov) and/or Raphael P Hermann (hermannrp@ornl.gov)

density functional theory↗
DOE OSTI2025

Porosity in nuclear graphite and its impact on nuclear reactor science and criticality safety applications

Porosity in nuclear-grade graphite significantly influences its low-energy neutron scattering, yet its effect on underlying phonon properties remains debated. Here, this work integrates inelastic and small-angle neutron scattering (INS/SANS) experiments, advanced atomistic simulations with a novel machine-learned potential (DeepMD), total cross-section measurements, and neutronics calculations (SCALE, MCNP, OpenMC) to investigate porosity’s impact on neutron thermalization. INS measurements on diverse graphite grades reveal no discernible porosity effect on phonon spectra, which align with crystalline graphite. Conversely, total cross-section data below ≈10 meV show increased scattering attributable to SANS. Our DeepMD simulations demonstrate that realistic micropores do not distort phonon spectra, challenging the assumptions in current ENDF/B-VIII.1 porosity thermal scattering laws (TSLs). These TSLs, based on random atom removal, produce unphysical phonon spectra and inflate inelastic cross-sections. Augmenting a crystalline TSL with an SANS component accurately captures experimental total cross-sections. Neutronics benchmarks (ICSBEP/IRPhE) show ENDF porosity TSLs unphysically increase neutron multiplication factor, keff. Crucially, incorporating SANS physics (NCrystal/OpenMC) indicates accurately modeled porosity negligibly affects keff, reactor physics, or criticality safety.

Critical benchmarks↗
DOE OSTI2023

Hexadecapole strength in the rare isotopes 74,76 Kr

In the Ge-Sr mass region, isotopes with neutron number N ≤ 40 are known to feature rapid shape changes with both nucleon number and angular momentum. To gain new insights into their structure, inelastic proton scattering experiments in inverse kinematics were performed on the rare isotopes 74,76 Kr. This work focuses on observables related to the J π = $4$$^{+}_{1}$ states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters β 4 were determined for the J π = $4$$^{+}_{1}$ states of 74,76 Kr from inelastic proton scattering cross sections. Two possible coupled-channels solutions were found. A comparison to predictions from nuclear energy density functional theory, employing both non-relativistic and relativistic functionals, clearly favors the large, positive β 4 solutions. These β 4 values are unambiguously linked to the well deformed prolate configuration. Given the β 2 - β 4 trend, established in this work, it appears that β 4 values could provide a sensitive measure of the nuclear shell structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Demonstration of a laser-driven, narrow spectral bandwidth x-ray source for collective x-ray scattering experiments

X-ray Thomson scattering (XRTS) is a powerful diagnostic technique that involves an x-ray source interacting with a dense plasma sample, resulting in a spectrum of elastically and inelastically scattered x-rays. Depending on the plasma conditions, one can measure a range of parameters from the resulting spectrum, including plasma temperature, electron density, and ionization state. To achieve sensitivity to collective electron oscillations, XRTS measurements require limited momentum transfer where the spectral separation of elastic and inelastic scattering is small. Such measurements require an x-ray probe source with a narrow bandwidth in order to reduce the spectral overlap between scattering contributions, allowing for the different features to be more precisely deconvolved. In this investigation, we discuss the theory behind how the bandwidth for a common XRTS probe, Zn He-α emission at 9 keV, can be reduced using a Cu K-edge filter.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Geometrical frustration versus Kitaev interactions in BaCo 2 (AsO 4 ) 2

Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid (KSL) state. One of the front-runners is BaCo 2 (AsO 4 ) 2 (BCAO), where it was suggested that the exchange processes between Co 2+ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze a comprehensive inelastic neutron scattering (INS) study of BCAO with fields in the honeycomb plane. Combining the constraints from the magnon excitations in the high-field polarized state and the inelastic spin structure factor measured in zero magnetic field, we examine two leading theoretical models: the Kitaev-type JK Γ Γ ′ model and the XXZ - J 1 - J 3 model. We show that the existing experimental data can be consistently accounted for by the XXZ - J 1 - J 3 model but not by the JK Γ Γ ′ model, and we discuss the implications of these results for the realization of a spin liquid phase in BCAO and more generally for the realization of the Kitaev model in cobaltates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Magnetic exchange interactions in the van der Waals layered antiferromagnet MnPSe 3

Two-dimensional van der Waals compounds with magnetic ions on a honeycomb lattice are hosts to a variety of exotic behavior. The magnetic interactions in one such compound, MnPSe 3 , are investigated with elastic and inelastic neutron scattering. Magnetic excitations are observed in the magnetically ordered regime and persist to temperatures well above the ordering temperature, T N =74K, consistent with low dimensional magnetic interactions. The inelastic neutron scattering results allow a model spin Hamiltonian to be presented that includes dominant intralayer interactions of J 1ab =0.45 meV, J 2ab =0.03 meV, J 3ab =0.19 meV, consistent with theoretical predictions. Furthermore, despite the quasi-2D behavior, appreciable interlayer interactions of J c =0.031(5) meV are required to model the data. No evidence for anisotropy in the form of a spin gap is observed in the data collected. The measurements on MnPSe 3 are contrasted with those on MnPS 3 and reveal a large increase in the interlayer exchange interaction in MnPSe 3 that may stabilize the similar ordering temperatures in the bulk compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Magnetoelastic coupling, negative thermal expansion, and two-dimensional magnetic excitations in FeAs

We present a temperature-dependent investigation of the local structure and magnetic dynamics of the FeAs binary. The magnetic susceptibility χ (T) result shows an anomalous broad feature up to 550 K, with χ continuing to increase above the Néel antiferromagnetic ordering temperature (T N =70K), peaking at ~250 K, then decreasing gently above. It is remarkable that this peak susceptibility temperature corresponds to the onset of anisotropic negative thermal expansion in both the a and c axes, suggesting that magnetic interactions are affecting the structure even well above the Néel point. A systematic investigation into local bonding correlations, from time-of-flight neutron pair distribution function analyses, shows the octahedral volume around each Fe site growing monotonically while adjacent octahedra tilt toward one another before relaxing away past this peak in the anomalous magnetic susceptibility. We use inelastic-neutron scattering to map spin-wave excitations in FeAs at temperatures above and below the T N . We find magnetic excitations near T N to be very different from the excitations in the ground state at 1.5 K. Spin waves measured at 1.5 K are three dimensional (3D), however, in the vicinity of the magnetic transition, the magnetic fluctuations clearly indicate two-dimensional (2D) character in this intrinsically 3D crystal structure. Unlike the undoped 2D parents of iron-arsenide superconductors, where the magnetic correlations are considerably weaker along the c axis than in the ab plane, inelastic neutron scattering here shows that the spin fluctuations in the 3D FeAs binary are nearly 2D in the bc plane at 90 K. These results demonstrate the importance of short-range correlations in understanding the magnetic properties of transition-metal binaries, and suggest how 2D excitations, even in a 3D structure, can potentially become a breeding ground for unconventional superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗