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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Probing iron in Earth’s core with molecular-spin dynamics

Dynamic compression of iron to Earth-core conditions is one of the few ways to gather important elastic and transport properties needed to uncover key mechanisms surrounding the geodynamo effect. Herein, a machine-learned ab initio derived molecular-spin dynamics (MSD) methodology with explicit treatment for longitudinal spin-fluctuations is utilized to probe the dynamic phase-diagram of iron. This framework uniquely enables an accurate resolution of the phase-transition kinetics and Earth-core elastic properties, as highlighted by compressional wave velocity and adiabatic bulk moduli measurements. In addition, a unique coupling of MSD with time-dependent density functional theory enables gauging electronic transport properties, critically important for resolving geodynamo dynamics.

58 GEOSCIENCES↗
NASA NTRS1979

Acoustic plane waves normally incident on a clamped panel in a rectangular duct

The theory of acoustic plane wave normally incident on a clamped panel in a rectangular duct is developed. The coupling theory between the elastic vibrations of the panel (plate) and the acoustic wave propagation in infinite space and in the rectangular duct is considered. The partial differential equation which governs the vibration of the panel (plate) is modified by adding to its stiffness (spring) forces and damping forces, and the fundamental resonance frequency and the attenuation factor are discussed. The noise reduction expression based on the theory is found to agree well with the corresponding experimental data of a sample aluminum panel in the mass controlled region, the damping controlled region, and the stiffness controlled region. All the frequency positions of the upward and downward resonance spikes in the sample experimental data are identified theoretically as resulting from four cross interacting major resonance phenomena: the cavity resonance, the acoustic resonance, the plate resonance, and the wooden back panel resonance.

Unz, H.↗
DOE OSTI2025

Sound Velocities in Vanadium Reveal Complex Elastic Behavior at High Pressures

Compressional (VP) and shear (VS) wave velocities of polycrystalline vanadium were measured simultaneously up to 11.5 GPa at room temperature using ultrasonic interferometry in a multi-anvil press. Complex softening behavior in VS and resulting shear moduli are discovered, possibly revealing a precursor to the reported phase transition within 30–60 GPa. The current data enables a comprehensive assessment of the elastic and mechanical properties of vanadium at high pressures, including bulk and shear moduli, Young’s modulus, Poisson’s ratio, and Pugh’s ratio. Through fitting to the 3rd-order finite strain equations, the elastic moduli and their pressure derivatives were determined to be K S0 = 151 (2) GPa, G 0 = 46.9 (8) GPa, K$^{’}_{S0}$ = 3.47 (5), and G$^{’}_{0}$ = 0.62 (1). These experimental results allow us to compare with and benchmark the existing Steinberg–Guinan models for extrapolations to extreme pressure and temperature conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Effect of a hypergravity environment on cortical bone elasticity in rats

There is considerable interest in determining whether hypergravity can be used as a countermeasure for microgravity-induced bone loss. This study was conducted on 20 immature male rats in order to investigate possible elastic adaptations of cortical bone in rapidly growing rats exposed to chronic hypergravity. Ten rats were continuously centrifuged for 14 days at twice gravitational acceleration (2G) on a 12.75 foot radius centrifuge and 10 rats concurrently acted as stationary controls. The effect of hypergravity on the elastic characteristics of cortical bone was quantified via ultrasonic wave propagation. Propagation velocities of longitudinal and shear waves were measured through cubic cortical specimens from the posterior femoral diaphyses. Density was measured with an Archimedes' technique. The orthotropic elastic properties were calculated and used to compare the difference between groups. Results showed an average increase in both the Young's moduli (Eii, + 2.2%) and shear moduli (Gij, + 4.3%) with a statistically significant increase only in G12 (+15.7%, P = 0.046). The ratio of transverse to axial strain (Poisson's ratio, nuij) demonstrated statistically significant changes in nu12, nu21, nu13, and nu31 (P < 0.05). These findings suggest that although slight elastic changes were incurred via a hypergravity environment, the treatment level or duration in this study do not dramatically perturb the normal elastic behavior of cortical bone and that dramatic biomechanical differences noted in previous studies were due more to structural changes than material elasticity changes. Hypergravity applied post facto to a microgravity environment would offer further illucidation of this method as treatment for a degenerative spaceflight experience.

Non-NASA Center↗
NASA NTRS1982

Analysis of long-period seismic waves excited by the May 18, 1980, eruption of Mount St. Helens - A terrestrial monopole

The eruption of Mount St. Helens on May 18, 1980, excited long-period seismic waves, and high-quality digital seismograms were recorded. The present investigation is concerned with the results of detailed analyses of Rayleigh and Love waves excited by this eruption. Since the elastic response of the earth is very accurately known, it is possible to retrieve the source parameters of this unique event from observations at far-field. It is shown that the source can be represented by a nearly horizontal single force. The conducted analysis is concerned with only long-period characteristics of the source. The short-period behavior of the source is difficult to determine from surface waves because the available knowledge of the earth's response is less accurate than at long periods.

Kanamori, H.↗
DOE OSTI2025

Inelastic deformation of diamond single crystals shock compressed to multimegabar stresses: Wave profile calculations

As the archetypal strong solid, the response of diamond shock compressed to multimegabar stresses is important for fundamental science and for numerical simulations of wave profiles for applications in high energy density physics experiments. Previous experiments and analysis have shown that the commonly used hydrodynamic assumption is invalid for diamond shock compressed to stresses below melt and an elastic–inelastic description is needed. Here, we present a phenomenological material model for calculating wave profiles in shock compressed diamond single crystals that incorporates this description. Also, to support the modeling effort, we carried out wave profile measurements on shock compressed diamond single crystals at the Sandia Z facility to augment previous measurements. Wave profiles for [100] and [111] diamond calculated using the material model provide a good match to the elastic–inelastic response (observed two-wave structure) measured at ∼325 and ∼360 GPa. Furthermore, the calculated peak stresses for single (overdriven) waves provide a good match to the measured Hugoniot states for stresses reaching ∼700 GPa, which is near melting conditions. The present results show that the diamond single crystal response at multimegabar shock stresses is characteristic of a brittle solid—pressure-dependent strength and strength loss due to inelastic deformation.

Deformation↗
DOE OSTI2024

Fast Seismic Anomalies Under Continents Explained by the Delaminated Lower Continental Crust—Implications From High Pressure‐Temperature Elasticity of Jadeite

Seismic tomography has shown that the shear wave velocities (Vs) under continents, especially under cratons, are extremely fast at 100–200 km depth, which is difficult to explain by low temperatures or high Mg#. Alternatively, delaminated eclogitic lower continental crust has been proposed to account for these fast seismic anomalies. However, the thermoelastic properties of jadeite which constitutes up to 60–80 mol% of clinopyroxene in the potentially delaminated lower continental crust are not well constrained. In this study, we measured the single-crystal elasticity of jadeite by Brillouin spectroscopy under simultaneous high pressure and temperature conditions for the first time. We found that the temperature dependence of Vs of jadeite is extremely small if not negligible. The seismic velocities of the potentially delaminated lower continental crusts were subsequently modeled and found to match the widely observed fast seismic anomalies under cratons between 100 and 200 km depth.

Geology↗
NASA NTRS1972

Soil mechanical properties at the Apollo 14 site.

The Apollo 14 lunar landing provided a greater amount of information on the mechanical properties of the lunar soil than previous missions. Measurements on core-tube samples and the results of transporter track analyses indicate that the average density of the soil in the Fra Mauro region is in the range from 1.45 to 1.60 g/cu cm. The soil strength appears to be higher in the vicinity of the site of the Apollo 14 lunar surface experiments package, and trench data suggest that strength increases with depth. Lower-bound estimates of soil cohesion give values of 0.03 to 0.10 kN/sq m, which are lower than values of 0.35 to 0.70 kN/sq m estimated for soils encountered in previous missions. The in situ modulus of elasticity, deduced from the measured seismic-wave velocity, is compatible with that to be expected for a terrestrial silty fine sand in the lunar gravitational field.

Mitchell, J. K.↗
NASA NTRS1983

Eikonal phase shift analyses of carbon-carbon scattering

A high-energy double-folding optical potential approximation to the exact nucleus-nucleus multiple-scattering series is used in determining eikonal phase shifts for carbon-carbon scattering at 204.2, 242.7, and 288.6 MeV. The double-folding potentials are derived by folding the energy-dependent free nucleon-nucleon interaction with densities for the projectile and target; these latter are obtained by unfolding the finite nucleon charge density from harmonic-well carbon charge distributions. The charge parameters for these distributions are taken from the results of electron scattering experiments. Predictions are made for total, reaction, and elastic differential cross sections using standard partial wave analysis for the scattering of identical particles and are then compared with recent experimental results. Excellent agreement is obtained despite the absence of arbitrarily adjusted parameters in the theory.

Townsend, L. W.↗
NASA NTRS1985

Vibrational Stabilization of Flexible Structures

It has been demonstrated that a high frequency excitation (HFE) field significantly changes the fundamental properties of mechanical systems. The most important contribution of HFE is the stiffening effect of an elastic continuum in the direction of the wave vector. This effect allows control of stiffness in any selected direction by the corresponding changes in the intensity of HFE. This new approach can be effective for large flexible space structures. Such an approach may prove to be very practical in the sense that large structures need to be made as flimsy as possible for low cost under ordinary situations. However, for certain operations such as development, orbital transfer, docking, and other circumstances, it would be vital to have a means of temporarily stiffening certain structural members. If the structure was designed to meet these occasional loads without temporary stiffening, it would be considerably more massive and more expensive.

Zak, M.↗
NASA NTRS1989

Adhesive bond evaluation using phase sensitive detection techniques

Quadrature phase detection techniques have been used to monitor the amplitude and phase of a toneburst ultrasonic wave normally reflected from adhesively-bonded steel/rubber interface. The measured phase change values of the reflected signals were found to correlate with variations in sample preparation. It was determined that measured phase shift changes were larger for samples with weaker bonds as manifested by smaller measured values of the applied tensile loads at failure. A model calculation which incorporates the concept of interfacial strength into the usual problem of wave propagation in multi-layered isotropic elastic media was used to deduce a bond-quality parameter from an experimentally measured phase shift.

Smith, Alphonso C.↗
NASA NTRS1995

The Schwinger Variational Method

Variational methods have proven invaluable in theoretical physics and chemistry, both for bound state problems and for the study of collision phenomena. The application of the Schwinger variational (SV) method to e-molecule collisions and molecular photoionization has been reviewed previously. The present chapter discusses the implementation of the SV method as applied to e-molecule collisions. Since this is not a review of cross section data, cross sections are presented only to server as illustrative examples. In the SV method, the correct boundary condition is automatically incorporated through the use of Green's function. Thus SV calculations can employ basis functions with arbitrary boundary conditions. The iterative Schwinger method has been used extensively to study molecular photoionization. For e-molecule collisions, it is used at the static exchange level to study elastic scattering and coupled with the distorted wave approximation to study electronically inelastic scattering.

Huo, Winifred M.↗
NASA NTRS1992

Evaluation of microcrack thermal shock damage in ceramics: Modeling and experiment

In this paper we present an experimental and theoretical study of the effect of microcrack damage on ceramic properties. For the experimental investigation, ceramic samples of aluminum oxide and reaction bonded silicon nitride (RBSN) are used. Thermal shock treatment from different temperatures up to 1000 C is applied to produce the microcracks. Both surface and bulk ultrasonic wave methods are used to correlate the change of elastic constants to microstructural degradation and to determine the change in elastic anisotropy induced by microcrack damage. For the theoretical investigation, damage mechanics, which relates microstructural damage to material service life and mechanical failure, is used. The change in elastic properties due to microcrack damage calculated from the theoretical model is compared with the experimental results for determination of the applicability of damage theory. It is shown that two independent experimental methods (bulk wave and surface wave) give the same results for shear moduli of damaged ceramics. The experimental results aagree reasonably well with the moduli predicted from the cracked solid model.

Chu, Y. C.↗
NASA NTRS1995

Low Frequency Guided Plate Waves Propagation in Fiber Reinforced Composites

Conventional destructive techniques for the determination of the elastic stiffness constants of composite materials can be costly and often inaccurate. Reliable nondestructive evaluation methods for monitoring the integrity of composite materials and structures are needed. Guided wave propagation in isotropic plate have been studied. Studies on the low frequency symmetric guide waves are presented.

applied mechanics and materials plate wave propaga↗
NASA NTRS1983

Volume integrals associated with the inhomogeneous Helmholtz equation. Part 1: Ellipsoidal region

Problems of wave phenomena in fields of acoustics, electromagnetics and elasticity are often reduced to an integration of the inhomogeneous Helmholtz equation. Results are presented for volume integrals associated with the Helmholtz operator, nabla(2) to alpha(2), for the case of an ellipsoidal region. By using appropriate Taylor series expansions and multinomial theorem, these volume integrals are obtained in series form for regions r 4' and r r', where r and r' are distances from the origin to the point of observation and source, respectively. Derivatives of these integrals are easily evaluated. When the wave number approaches zero, the results reduce directly to the potentials of variable densities.

Fu, L. S.↗