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At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Nambu and Compositeness

The Nambu--Jona-Lasinio model is the simplest field theory of a composite scalar boson, consisting of a pair of chiral fermions. A bound state emerges from an assumed point-like 4-fermion interaction and is described by local effective field, $\Phi(x)$. We review this in the context of the renormalization group and show some its phenomenological successes, such as the QCD chiral dynamics and the prediction of stable heavy-light resonances that reveal the single light quark chiral dynamics. We also review some NJL--inspired composite Higgs models. We then describe a novel UV completion of the NJL model, to an extended interaction, where the solution is described by a bilocal effective, Yukawa field, $\Phi(x,y)$. I conclude with a personal recollection of Yoichiro Nambu.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

IONIC COMPOSITION STRUCTURE OF CORONAL MASS EJECTIONS IN AXISYMMETRIC MAGNETOHYDRODYNAMIC MODELS

We present the ionic charge state composition structure derived from axisymmetric MHD simulations of coronal mass ejections (CMEs), initiated via the flux-cancellation and magnetic breakout mechanisms. The flux-cancellation CME simulation is run on the Magnetohydrodynamics-on-A-Sphere code developed at Predictive Sciences, Inc., and the magnetic breakout CME simulation is run on ARC7 developed at NASA GSFC. Both MHD codes include field-aligned thermal conduction, radiative losses, and coronal heating terms which make the energy equations sufficient to calculate reasonable temperatures associated with the steady-state solar wind and model the eruptive flare heating during CME formation and eruption. We systematically track a grid of Lagrangian plasma parcels through the simulation data and calculate the coronal density and temperature history of the plasma in and around the CME magnetic flux ropes. The simulation data are then used to integrate the continuity equations for the ionic charge states of several heavy ion species under the assumption that they act as passive tracers in the MHD flow. We construct two-dimensional spatial distributions of commonly measured ionic charge state ratios in carbon, oxygen, silicon, and iron that are typically elevated in interplanetary coronal mass ejection (ICME) plasma. We find that the slower CME eruption has relatively enhanced ionic charge states and the faster CME eruption shows basically no enhancement in charge states-which is the opposite trend to what is seen in the in situ ICME observations. The primary cause of the difference in the ionic charge states in the two simulations is not due to the different CME initiation mechanisms per se. Rather, the difference lies in their respective implementation of the coronal heating which governs the steady-state solar wind, density and temperature profiles, the duration of the connectivity of the CME to the eruptive flare current sheet, and the contribution of the flare-heated plasma associated with the reconnection jet outflow into the ejecta. Despite the limitations inherent in the first attempt at this novel procedure, the simulation results provide strong evidence in support of the conclusion that enhanced heavy ion charge states within CMEs are a direct consequence of flare heating in the low corona. We also discuss future improvements through combining numerical CME modeling with quantitative ionic charge state calculations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

A predictive modeling tool for damage analysis and design of hydrogen storage composite pressure vessels

In this study, a predictive modeling tool is developed for damage analysis and design of hydrogen (H 2 ) storage composite pressure vessels. It integrates micromechanics of matrix cracking into a continuum damage mechanics (CDM) description for damage evolution, and three-dimensional (3D) finite element (FE) modeling of the vessel structural response. At the scale of the composite layer (mesoscale), the temperature-dependent stiffness reduction law in terms of the damage variable for transverse matrix cracking is computed using an Eshelby-Mori-Tanaka approach for the initial composite thermoelastic properties and a self-consistent model for the stiffness reduction as a function of the damage variable. While transverse matrix cracking obeying a damage evolution relation can progressively evolve from an initiation to a saturation state, fiber failure is predicted by a micromechanical fiber rupture criterion that accounts for the fiber strength and matrix stress. The implementation of this integrated multiscale modeling model into a 3D FE formulation enables damage analysis and design of H 2 storage composite pressure vessels. The developed tool is illustrated through 3D damage analyses of a cryogenically compressed H 2 storage vessel model subjected to thermomechanical loadings to investigate effects of the helical layer fiber orientation and loading scenario on damage development, vessel integrity and burst pressure.

08 HYDROGEN↗
DOE OSTI2022

Hanford Site Composite Analysis: LLBG-200-W B Vadose Zone Model

The objectives of the vadose modeling for the updated Hanford Site Composite Analysis (CA) are to simulate the flow and transport of water and radionuclide releases from the surface to the water table and to provide radionuclide transfer rates to the CA saturated zone model (CP-57037, Model Package Report: Plateau to River Groundwater Model, Version 8.3). Water additions include natural recharge and water discharged to the ground as a result of industrial processes associated with Hanford Site operations. Contaminant sources include radionuclides in water discharged to the ground during operations and radionuclides disposed “dry” in solid waste burial grounds or other means. The following 16 radionuclides were selected for this modeling effort: carbon-14 (C-14), chlorine-36 (Cl-36), tritium (H-3), iodine-129 (I-129), neptunium-237 (Np-237), rhenium-187 (Re-187), strontium-90 (Sr-90), technetium-99 (Tc-99), uranium-232 (U-232), uranium-233 (U-233), uranium-234 (U-234), uranium-235 (U-235), uranium-236 (U-236), uranium-238 (U-238), radium-226 (Ra-226), and thorium-230 (Th-230). The simulation time starts in 1943 and ends at 12070, which is 10,000 years after assumed Hanford Site closure in 2070. The parallel version of the Subsurface Transport Over Multiple Phases (STOMP 1 ) simulator, officially named the exascale Subsurface Transport Over Multiple Phases (eSTOMP), is used to simulate flow and transport for the vadose models. The documentation for the STOMP code is comprehensive. The theoretical and numerical approaches applied in the STOMP code are documented in a published theory guide (PNNL-12030, STOMP Subsurface Transport Over Multiple Phases Version 2.0 Theory Guide). The code has undergone a rigorous verification procedure against analytical solutions, laboratory-scale experiments, and field-scale demonstrations. The application guide (PNNL-11216, STOMP Subsurface Transport Over Multiple Phases Application Guide) provides instructive examples in the application of the code to classical groundwater problems. The user’s guide (PNNL-15782, STOMP: Subsurface Transport Over Multiple Phases Version 4.0: User’s Guide) describes the general use, input file formatting, compilation, and execution of the code. The primary output of the vadose zone modeling is radionuclide transfer rates to the groundwater for input into the saturated zone model. The rates will be summed over the 100 by 100 m saturated zone model grid cells that fall within the vadose zone model source domain.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

COSMOGENIC NEUTRINOS CHALLENGE THE COSMIC-RAY PROTON DIP MODEL

The origin and composition of ultra-high-energy cosmic rays (UHECRs) remain a mystery. The proton dip model describes their spectral shape in the energy range above 10{sup 9} GeV by pair production and photohadronic interactions with the cosmic microwave background. The photohadronic interactions also produce cosmogenic neutrinos peaking around 10{sup 9} GeV. We test whether this model is still viable in light of recent UHECR spectrum measurements from the Telescope Array experiment and upper limits on the cosmogenic neutrino flux from IceCube. While two-parameter fits have been already presented, we perform a full scan of the three main physical model parameters: source redshift evolution, injected proton maximal energy, and spectral index. We find qualitatively different conclusions compared to earlier two-parameter fits in the literature: a mild preference for a maximal energy cutoff at the sources instead of the Greisen–Zatsepin–Kuzmin cutoff, hard injection spectra, and strong source evolution. The predicted cosmogenic neutrino flux exceeds the IceCube limit for any parameter combination. As a result, the proton dip model is challenged at more than 95% C.L. This is strong evidence against this model independent of mass composition measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

THE SOLAR ABUNDANCE PROBLEM: THE EFFECT OF THE TURBULENT KINETIC FLUX ON THE SOLAR ENVELOPE MODEL

Recent three-dimensional (3D) simulations have shown that the turbulent kinetic flux (TKF) is significant. We discuss the effects of TKF on the size of the convection zone and find that the TKF may help solve the solar abundance problem. The solar abundance problem is that, with new abundances, the solar convection zone depth, the sound speed in the radiative interior, the helium abundance, and the density in the convective envelope are not in agreement with helioseismic inversions. We have performed Monte Carlo simulations on solar convective envelope models with different profiles of TKF to test its effects. The solar abundance problem is revealed in the standard solar convective envelope model with AGSS09 composition, which shows significant differences (∼10)) in density from the helioseismic inversions, but the differences in the model with the old composition GN93 is small (∼0.5)). In the testing models with a different TKF imposed, it is found that the density profile is sensitive to the value of TKF at the base of the convective envelope and insensitive to the structure of TKF in the convection zone. The required value of turbulent kinetic luminosity at the base is about –13% to – 19% L {sub ☉}. Comparing with the 3D simulations, this value is plausible. This study is for the solar convective envelope only. Evolutionary solar models with TKF are required to investigat the effects of TKF on the solar interior structure below the convection zone and the whole solar abundance problem, but the profile of the TKF in the overshoot region is necessary.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

Finite element models for predicting crack growth characteristics in composite materials

Two dimensional and quasi-three dimensional, linear elastic finite element models for the prediction of crack growth characteristics, including crack growth direction, in laminated composite materials are presented. Mixed mode crack growth in isotropic materials, unidirectional and laminated composites is considered. The modified crack closure method is used to predict the applied load level for crack extension and two failure theories, modifications of the point stress and the Hashin failure criteria, are proposed to predict the direction of crack extension in composites. Comparisons are made with the Tsai-Wu failure criterion and the Sih strain energy density criterion as well as with experimental results. It is shown that the modified versions of point stress and Hashin criteria compare well with experiment.

Buczek, M. B.↗
NASA NTRS1995

Modeling the Properties of 3D Woven Composites

An extensive study has been completed of the internal geometry, the mechanisms of failure, and the micromechanics of local failure events in graphite/epoxy composites with three dimensional (3D) woven reinforcement. This work has led to the development of models for predicting elastic constants, strength, notch sensitivity, and fatigue life. A summary is presented here.

Cox, Brian N.↗
NASA NTRS2012

Understanding Differences in the Response to Composition Change as Simulated by CCMVal Models

Chemistry climate models (CCMs) have a common conceptual basis. Differences in implementation lead to differences in the stratospheric ozone response to changes in composition and climate. Although evaluation by CCMVal-2 identified strengths and weaknesses of participant models, the evaluation results were not used to discriminate among projections for future ozone evolution, at least in part because the overall diagnostic evaluation did not cleanly relate to the differences in CCM response. Here we use a subset of CCMVal diagnostics and additional analysis to understand the differences in response. In the upper stratosphere, differences in simulated temperature and total odd nitrogen prior to increases in chlorine loading explain the large differences in CCM sensitivity. In the lower atmosphere, there are two principle contributions to differences in CCM sensitivity to chlorine and climate change. First, differences in the lower stratospheric ClO affect simulated sensitivity to chlorine. CCMs with best transport performance match NDACC column HCl measurements at a broad range of latitudes. Other CCMs disagree with observations due to differences in total inorganic chlorine, partitioning between HCl and ClONO2, or both. Differences in ClONO2 are directly related to differences in simulated ClO. Second, although all CCMs predict increased tropical upwelling, the rate of increase varies and contributes to differences in tropical ozone and the 60N-60S column average.

Douglass, Anne R.↗
NASA NTRS2018

A Dual Spring Modeling Approach for Static and Fatigue Failure Assessments of Carbon/Epoxy Composite Sub-Elements

A dual spring model is developed for the static and fatigue damage predictions of laminates interface in composite structures. Stress concentrations can be induced by the defects formed in the fabrication or service process. A conventional S-N based fatigue damage model may not be accurate to predict the fatigue life of a structure with high stress concentration. With the dual spring model, static delamination failure can be simulated using springs of cohesive type material model while fatigue delamination development can be predicted using linear springs, where the crack driving force is computed based on virtual crack closure technique (VCCT). A Paris law type fatigue growth law with its mode mixity is applied for fatigue crack growth prediction. After verified using benchmark examples, including Double Cantilever Beam (DCB), End-Notched Flexure (ENF) and Mix-Mode Bending (MMB), the proposed dual spring model is applied in the static and fatigue damage prediction of NASA/Boeing sub-elements and UTC sub-elements.

Cui, Xiaodong↗
NASA NTRS1981

Determination of load sequence effects on the degradation and failure of composite materials

A theoretical model was established to predict the fatigue behavior of composite materials, with emphasis placed on predictions of the degradation of residual strength and residual stiffness during fatigue cycling. The model parameters were evaluated from three test series including static strength fatigue life and residual strength tests. The tests were applied to two graphite/epoxy laminates. Load sequence effects were emphasized for both laminates and the predicted results agreed quite well with subsequent verification tests. Dynamic as well as static stiffness reduction data were collected by use of a PDP11-03 computer, which performed quite satisfactorily and permitted the recording of a substantial amount of dynamic stiffness reduction data.

Yang, J. N.↗
DOE OSTI2011

Chemical structures of low-pressure premixed methylcyclohexane flames as benchmarks for the development of a predictive combustion chemistry model

The chemical compositions of three low-pressure premixed flames of methylcyclohexane (MCH) are investigated with the emphasis on the chemistry of MCH decomposition and the formation of aromatic species, including benzene and toluene. The flames are stabilized on a flat-flame (McKenna type) burner at equivalence ratios of φ = 1.0, 1.75, and 1.9 and at low pressures between 15 Torr (= 20 mbar) and 30 Torr (= 40 mbar). The complex chemistry of MCH consumption is illustrated in the experimental identification of several C 7 H 12 , C 7 H 10 , C 6 H 12 , and C 6 H 10 isomers sampled from the flames as a function of distance from the burner. Three initiation steps for MCH consumption are discussed: ring-opening to heptenes and methyl-hexenes (isomerization), methyl radical loss yielding the cyclohexyl radical (dissociation), and H abstraction from MCH. Mole fraction profiles as a function of distance from the burner for the C 7 species supplemented by theoretical calculations are presented, indicating that flame structures resulting in steeper temperature gradients and/or greater peak temperatures can lead to a relative increase in MCH consumption through the dissociation and isomerization channels. Trends observed among the stable C 6 species as well as 1,3-pentadiene and isoprene also support this conclusion. Relatively large amounts of toluene and benzene are observed in the experiments, illustrating the importance of sequential H-abstraction steps from MCH to toluene and from cyclohexyl to benzene. Furthermore, modeled results using the detailed chemical model of Pitz et al. (Proc. Combust. Inst.2007, 31, 267–275) are also provided to illustrate the use of these data as a benchmark for the improvement or future development of a MCH mechanism.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS1978

Causes of compositional variations within mare basalt suites

The short-range unmixing model, which explains compositional variations produced during crystallization of a single undifferentiated basalt flow, has been applied to the variations found within each of the suites of mare basalts. Based on this modelling, the following suites of mare basalts could represent random samples from single, undifferentiated lava flows: Apollo 11 A (high K), Apollo 15 olivine, Apollo 17 A-U, Apollo 17 B, Apollo 17 C. The short range unmixing model fails to account for variations within the Apollo 12 olivine-pigeonite group and Apollo 12 ilmenite group, which are well explained by fractional crystallization. The fact that the compositional variations within a suite of samples of unknown affinity can be explained in terms of short-range unmixing of a single lava does not mean that they are necessarily related in that way. It does, however, mean that independent evidence (stratigraphic, petrographic, isotropic, or age) is required to support arguments for the variations being caused by fraction crystallization or different magma batches.

Lindstrom, M. M.↗
NASA NTRS2015

Empirical Model Development for Predicting Shock Response on Composite Materials Subjected to Pyroshock Loading

The NASA Engineering and Safety Center (NESC) received a request to develop an analysis model based on both frequency response and wave propagation analyses for predicting shock response spectrum (SRS) on composite materials subjected to pyroshock loading. The model would account for near-field environment (approx. 9 inches from the source) dominated by direct wave propagation, mid-field environment (approx. 2 feet from the source) characterized by wave propagation and structural resonances, and far-field environment dominated by lower frequency bending waves in the structure. This report documents the outcome of the assessment.

Gentz, Steven J.↗
NASA NTRS2015

Empirical Model Development for Predicting Shock Response on Composite Materials Subjected to Pyroshock Loading

The NASA Engineering and Safety Center (NESC) received a request to develop an analysis model based on both frequency response and wave propagation analyses for predicting shock response spectrum (SRS) on composite materials subjected to pyroshock loading. The model would account for near-field environment (~9 inches from the source) dominated by direct wave propagation, mid-field environment (approximately 2 feet from the source) characterized by wave propagation and structural resonances, and far-field environment dominated by lower frequency bending waves in the structure. This document contains appendices to the Volume I report.

Gentz, Steven J.↗
DOE OSTI2018

Nozzle clogging factors during fused filament fabrication of spherical particle filled polymers

Fused filament fabrication with reinforced or filled polymers provides improved material properties compared to ordinary feedstock. A current limitation of these materials is the occurrence of nozzle clogging at higher filler contents. In this paper, an experiment is designed to identify the factors causing nozzle clogging. Glass sphere-filled polycarbonate is investigated by varying nozzle and filler diameters, the resin viscosity, the filler content, and the extrusion pressure. Equations identifying nozzle clogging and intermittent clogging conditions are provided. Based on these results, a model for the clogging of sphere-filled polymers is proposed. Last, a mathematical model is derived, which approximates the printability of filled polymers without the preparation of composites. Finally, this model is based on the nozzle geometry, the filler type and content, the resin viscosity, and the printer’s maximum extrusion force.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Selective growth of Ni4Ti3 precipitate variants induced by complicated cyclic stress during laser additive manufacturing of NiTi-based composites

Highlights: • The NiTi-based composites were in-situ synthesized by SLM. • Ni{sub 4}Ti{sub 3} could tailor the phase transformation temperature of TiC/NiTi composites. • A three-dimensional stress field modeling of TiC/NiTi composites was established. • The relationship between growth of Ni{sub 4}Ti{sub 3} variants and cyclic stress was disclosed. - Abstract: NiTi-based composites were in-situ synthesized by selective laser melting (SLM) additive manufacturing technology with formation of a great many Ni{sub 4}Ti{sub 3} precipitates. The differential scanning calorimetry (DSC) were carried out to exhibit the similar phase transformation temperature (A{sub s} = 51.82 °C, A{sub f} = 94.02 °C, M{sub s} = 55.87 °C and M{sub f} = 18.93 °C) by comparing with that of SLM-fabricated equi-atomic NiTi alloy, which could be attributed to the compensation of Ni{sub 4}Ti{sub 3} precipitates for the effect of an addition of TiC particles. Three different Ni{sub 4}Ti{sub 3} precipitate variants ((111){sub R}//(1 1-bar 1-bar ){sub B2}, (111){sub R}//( 1-bar 1-bar 1){sub B2}, and (111){sub R}//( 1-bar 1 1-bar ){sub B2}) with various precipitate diameters were observed within SLM fabricated part, showing apparently selective growth behavior. By high-resolution transmission electron microscopy, severe lattice defects formed surrounding the smaller variant, while relatively intact lattice structure was found around the larger one, which indicated that high strain energy was produced in the interface between the matrix and the smaller variant. Furthermore, finite element simulation method was applied to disclose the evolution features of complicated cyclic stress during SLM processing of TiC/NiTi composites. By predicting, the main constraint mode within as-fabricated track was tensile stress effect. Based on the redistribution behavior of thermal stress and the coupling effect between the thermal stress and strain field induced by Ni{sub 4}Ti{sub 3} precipitate, the selective growth mechanism of Ni{sub 4}Ti{sub 3} variant was revealed.

36 MATERIALS SCIENCE↗