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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Torsional properties of hexagonal boron nitride nanotubes, carbon nanotubes and their hybrid structures: A molecular dynamics study

The torsional mechanical properties of hexagonal single-walled boron nitride nanotubes (SWBNNTs), single-walled carbon nanotubes (SWCNTs), and their hybrid structures (SWBN-CNTs) are investigated using molecular dynamics (MD) simulation. Two approaches - force approach and energy approach, are adopted to calculate the shear moduli of SWBNNTs and SWCNTs, the discrepancy between two approaches is analyzed. The results show that the shear moduli of single-walled nanotubes (SWNTs), including SWBNNTs and SWCNTs are dependent on the diameter, especially for armchair SWNTs. The armchair SWNTs show the better ability of resistance the twisting comparable to the zigzag SWNTs. The effects of diameter and length on the critical values of torque of SWNTs are obtained by comparing the torsional behaviors of SWNTs with different diameters and different lengths. It is observed that the MD results of the effect of diameter and length on the critical values of torque agrees well with the prediction of continuum shell model. The shear modulus of SWBN-CNT has a significant dependence on the percentages of SWCNT and the hybrid style has also an influence on shear modulus. The critical values of torque of SWBN-CNTs increase with the increase of the percentages of SWCNT. This phenomenon can be interpreted by the function relationship between the torque of different bonds (B-N-X, C-C-X, C-B-X, C-N-X) and the angles of bonds.

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

Optical and structural properties of Fe-doped SnO{sub 2} nanoparticles prepared by co-precipitation method

Today nanomaterials plays important role in every field, due to their unique mechanical, chemical and electrical properties which are completely different from the bulk materials. With reduction in the size of material its properties are dynamically changed. Semiconductor materials are widely used in electronic devices but in the field of optoelectronic these materials have some limitations. Tin oxide could be the material which could be used in these applications without limitations. Doped Tin Oxide is an oxygen deficient material which could be beneficial for transparent conducting oxide. Iron doped SnO{sub 2} prepared by co-precipitation method. Studies on structural properties of undoped and doped SnO{sub 2} were done by X-ray diffraction. The XRD results have shown that the size of the nanoparticles decreases with Fe doping down to 53nm. Optical Properties were studied by UV-visible spectroscopy. Band gap was found to decrease with increase in iron content in samples.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRSDate not supplied

An Investigation of the Dragonfly Mission Aeroshell/Parachute Dynamics through Subscale Drop Tests

The Dragonfly mission will place a rotorcraft/lander on Titan by 2034. The entry, descent, and landing system of the Dragonfly mission includes two parachutes: a drogue and a main. To provide needed data, subscale drop tests were used to conduct an experimental investigation of the aeroshell/parachute dynamics. The drop tests used a Disk-Gap-Band drogue parachute and two types of Ringslot main parachutes. All tests used a representative aeroshell which included the heatshield. All models were geometrically scaled to 16.7 percent. The model aeroshell had a diameter of 0.75 m. The model parachute nominal diameters were 0.9 m for the drogue and 2.78 m for the main. The aeroshell’s mass properties were dynamically scaled to simulate flight at an altitude of 4 km at Titan. This dynamic scaling allowed the conversion of model test results to full-scale Titan conditions. Onboard instrumentation on the aeroshell provided data on the rotation rates, from which the Euler angles were determined. Tests were conducted by lifting the models with a drone to an altitude of 350 m and dropping them inverted. Key results from these tests were: 1) the models were able to recover from the extreme inverted initial condition and settle to low-amplitude oscillations; 2) ninety nine percent of the time the oscillation amplitudes observed with the drogue parachute were 11.4 degrees or less; 3) ninety nine percent of the time the oscillation amplitudes observed with the 20 percent porosity main parachute were 15.4 degrees or less.

Parachutes↗
NASA NTRSDate not supplied

An Investigation of the Dragonfly Mission Aeroshell/Parachute Dynamics through Subscale Drop Tests

The Dragonfly mission will place a rotorcraft/lander on Titan by 2034. The entry, descent, and landing system of the Dragonfly mission includes two parachutes: a drogue and a main. To provide needed data, subscale drop tests were used to conduct an experimental investigation of the aeroshell/parachute dynamics. The drop tests used a Disk-Gap-Band drogue parachute and two types of Ringslot main parachutes. All tests used a representative aeroshell which included the heatshield. All models were geometrically scaled to 16.7 percent. The model aeroshell had a diameter of 0.75 m. The model parachute nominal diameters were 0.9 m for the drogue and 2.78 m for the main. The aeroshell’s mass properties were dynamically scaled to simulate flight at an altitude of 4 km at Titan. This dynamic scaling allowed the conversion of model test results to full-scale Titan conditions. Onboard instrumentation on the aeroshell provided data on the rotation rates, from which the Euler angles were determined. Tests were conducted by lifting the models with a drone to an altitude of 350 m and dropping them inverted. Key results from these tests were: 1) the models were able to recover from the extreme inverted initial condition and settle to low-amplitude oscillations; 2) ninety nine percent of the time the oscillation amplitudes observed with the drogue parachute were 11.4 degrees or less; 3) ninety nine percent of the time the oscillation amplitudes observed with the 20 percent porosity main parachute were 15.4 degrees or less.

Parachutes↗
DOE OSTI2019

Progress towards a phenomenological picture and theoretical understanding of glassy dynamics and vitrification near interfaces and under nanoconfinement

The nature of alterations to dynamics and vitrification in the nanoscale vicinity of interfaces-commonly referred to as "nanoconfinement" effects on the glass transition-has been an open question for a quarter century. We first analyze experimental and simulation results over the last decade to construct an overall phenomenological picture. Key features include the following: after a metrology- and chemistry-dependent onset, near-interface relaxation times obey a fractional power law decoupling relation with bulk relaxation; relaxation times vary in a double-exponential manner with distance from the interface, with an intrinsic dynamical length scale appearing to saturate at low temperatures; the activation barrier and vitrification temperature T-g approach bulk behavior in a spatially exponential manner; and all these behaviors depend quantitatively on the nature of the interface. We demonstrate that the thickness dependence of film-averaged T-g for individual systems provides a poor basis for discrimination between different theories, and thus we assess their merits based on the above dynamical gradient properties. Entropy-based theories appear to exhibit significant inconsistencies with the phenomenology. Diverse free-volume-motivated theories vary in their agreement with observations, with approaches invoking cooperative motion exhibiting the most promise. The elastically cooperative nonlinear Langevin equation theory appears to capture the largest portion of the phenomenology, although important aspects remain to be addressed. A full theoretical understanding requires improved confrontation with simulations and experiments that probe spatially heterogeneous dynamics within the accessible 1-ps to 1-year time window, minimal use of adjustable parameters, and recognition of the rich quantitative dependence on chemistry and interface. Published under license by AIP Publishing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser

Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H 2 O 2+ , D 2 O 2+ , and HDO 2+ , such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Thermal and Mechanical Properties of CO{sub 2}-Based Biodegradable Poly(cyclohexene carbonate)/Organically Modified Layered Zinc Phenylphosphonate Nanocomposites

A new sustainable composite material was fabricated using CO{sub 2}-based poly(cyclohexene carbonate) (PCHC) and organically modified layered zinc phenylphosphonate (m-PPZn) via a solution mixing process. Analysis by wide-angle X-ray diffraction (WAXD) showed that the interlayer spacing of the m-PPZn was enlarged to 30.4 Å. The morphology of the PCHC/m-PPZn nanocomposites was characterized by transmission electron microscopy and WAXD, which revealed that the layered materials were partially delaminated and randomly dispersed in the PCHC matrix. The enhancement of the dynamic mechanical properties of the 1 wt% PCHC/m-PPZn nanocomposite at 80 °C was approximately 114% relative to those of the neat PCHC matrix. The thermal properties of the PCHC/m-PPZn nanocomposites characterized using thermogravimetric analysis were substantially improved upon incorporation of m-PPZn. With the addition of 0.25 wt% m-PPZn into the PCHC matrix, the decomposition temperature associated with 10 wt% loss of the nanocomposites was substantially increased by approximately 24 °C compared with that of the PCHC matrix. The isothermal degradation data demonstrated that the activation energy of the composites was higher than that of the PCHC. This finding was attributed to the addition of m-PPZn to PCHC increasing the thermal energy required for degradation, thus inducing a reduction in the degradation rate and an increase in the residual weight for the PCHC/m-PPZn nanocomposites.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Expansion dynamics of femtosecond laser-induced plasmas: Influence of thermophysical plasma properties

This study investigates the expansion dynamics of femtosecond laser-induced plasmas, emphasizing the impact of plasma thermophysical properties and ambient gas composition. Through shadowgraphy experiments and multiphase computational fluid dynamics (CFD) simulations, the influence of parameters such as heat capacity, molecular weight, and thermal conductivity on plume morphology, shockwave evolution, and energy dissipation mechanisms is examined. A mixture multiphase model is implemented to capture the interaction between the plasma and the surrounding gas. Simulation results reveal that plasma expansion is strongly inertia-driven. Results show that differences in plasma properties and ambient conditions affect the shape and temperature distribution of the expanding plume. The early-stage dynamics are primarily dictated by pressure forces, whereas thermal and viscous effects play a growing role in the plume's behavior during later stages of expansion. The CFD findings show the necessity of accurate initial condition characterization, including crater geometry and plasma pressure and temperature, for reliable modeling of plasma evolution in laser ablation processes.

CFD modeling↗
DOE OSTI2014

Molecular Dynamics Simulations of Tri-n-butyl-phosphate/n-Dodecane Mixture: Thermophysical Properties and Molecular Structure

Molecular dynamics simulations of tri-n-butyl-phosphate (TBP)/n-dodecane mixture in the liquid phase have been carried out using two recently developed TBP force field models (J. Phys. Chem. B 2012, 116, 305) in combination with the all-atom optimized potentials for liquid simulations (OPLS-AA) force field model for n-dodecane. Specifically, the electric dipole moment of TBP, mass density of the mixture, and the excess volume of mixing were computed with TBP mole fraction ranging from 0 to 1. It is found that the aforementioned force field models accurately predict the mass density of the mixture in the entire mole fraction range. Commensurate with experimental measurements, the electric dipole moment of the TBP was found to slightly increase with the mole fraction of TBP in the mixture. Also, in accord with experimental data, the excess volume of mixing is positive in the entire mole fraction range, peaking at TBP mole fraction range 0.3 0.5. Finally, a close examination of the spatial pair correlation functions between TBP molecules, and between TBP and n-dodecane molecules, revealed formation of TBP dimers through self-association at close distance, a phenomenon with ample experimental evidence.

de Almeida, Valmor F↗
DOE OSTI2019

Sustainable Use of Chloroprene Rubber Waste as Blend Component with Natural Rubber, Epoxidized Natural Rubber and Styrene Butadiene Rubber

Recycling of rubber waste and finding the effective methods to extend its use are one of major challenges nowadays. The potential approach to reduce rubber waste is to blend it with virgin rubber, perhaps with synergistic advantages. In this study, chloroprene rubber waste (CRw) is used as blend component in binary blends with natural rubber (NR), epoxidized natural rubber with 50 mol% epoxidation level (ENR50), and styrene butadiene rubber (SBR). The effects of blend ratio [95/5, 85/15, 75/25, 65/35 and 50/50 (phr/phr)] on the properties were studied. The results indicate that CRw prolongs scorch and curing times, due to the differences in unsaturation contents and cure incompatibility. The maximum torque (M{sub H}), minimum torque (M{sub L}), and torque difference (M{sub H}–M{sub L}) in all cases increased with CRw content in the blend. Because CRw has a crosslink precursor, crosslink density also increased with CRw content. This is clearly confirmed by the combination of swelling resistance, crosslink density and dynamic mechanical properties observed. SEM micrographs showed mostly rough surface and tearing areas for low CRw contents in the blends. The blends also showed less crack paths with increasing CRw content over 50 phr. Further increase in CRw content obviously enhanced the thermal stability of the blends, with elevated decomposition temperatures in TGA results.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electrochemical Control of the Ultrafast Lattice Response of a Layered Semimetal

The unique layer-stacking in two-dimensional (2D) van der Waals materials facilitates the formation of nearly degenerate phases of matter and opens novel routes for the design of low-power, reconfigurable functional materials. Electrochemical ion intercalation between stacked layers offers a promising approach to stabilize bulk metastable phases and to explore the effects of extreme carrier doping and strain. However, in situ characterization methods to study the structural evolution and dynamical functional properties of these intercalated materials remains limited. Here a novel experimental platform is presented capable of simultaneously performing electrochemical lithium-ion intercalation and multimodal ultrafast characterization of the lattice using both electron diffraction and nonlinear optical techniques. Using the layered semimetal WTe 2 as a model system, the interlayer shear phonon mode that modulates stacking between 2Dlayers is probed, showing that small amounts of lithiation enhance the amplitude and lifetime of the phonon, contrary to expectations. This results from the dynamically fluctuating and anharmonic structure between nearly degenerate phases at room temperature, which can be stabilized by electronic carriers accompanying the inserted lithium ions. At high lithiation, the T d ’ structure emerges and quenches the phonon response. This work defines new approaches for using electrochemistry to engineer the dynamic structure of 2D materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Evaluation of a fiber-coupled x-ray diffraction detector for dynamic compression experiments

The long-term x-ray diffraction (XRD) detector scheme compatible with Z-containment experiments will involve conversion of the diffracted x-rays to optical light, which will be transported away from the Z-Dynamic Materials Properties (DMP) load and detected on a fast-gated camera. In this so-called DIffraction SCintillator Optic (DISCO) scheme , the scintillator is coupled to a long, coherent imaging fiber bundle using a custom lens system with high numerical aperture. In addition, the DISCO diagnostic incorporates time-gating to allow measurement only during the short time window of the x-ray pulse in which XRD occurs, thereby significantly reducing unwanted background generated by the Z-DMP load. Dynamic compression experiments were performed at the Chama target chamber to evaluate the DISCO diagnostic . Specifically, a Zr sample was laser-shocked with the Chaco laser while the Z-Beamlet (ZBL) laser was used to generate x-rays, which enabled time-gated 6.7-keV XRD patterns from the compressed Zr sample to be obtained.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Size effects on the structural, electronic, and optical properties of (5,0) finite-length carbon nanotube: An ab-initio electronic structure study

We use density functional computations to study the zero temperature structural, electronic, magnetic, and optical properties of (5,0) finite carbon nanotubes (FCNT), with length in the range of 4–44 Å. It is found that the structural and electronic properties of (5,0) FCNTs, in the ground state, converge at a length of about 30 Å, while the excited state properties exhibit long-range edge effects. We discuss that curvature effects enhance energy gap of FCNTs, in contrast to the known trend in the periodic limit. It is seen that compensation of curvature effects in two special small sizes may give rise to spontaneous magnetization. The obtained cohesive energies provide some insights into the effects of environment on the growth of FCNTs. The second-order difference of the total energies reveals an important magic size of about 15 Å. The optical and dynamical magnetic responses of the FCNTs to polarized electromagnetic pulses are studied by time dependent density functional theory. The results show that the static and dynamic magnetic properties mainly come from the edge carbon atoms. The optical absorption properties are described in terms of local field effects and characterized by Casida linear response method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1986

Hybrid deployable/erectable solar dynamic box truss system

The design of a hybrid deployable/erectable solar dynamic box truss power generation system for the initial operation capability (IOC) of the Space Shuttle is examined. An organic Rankine cycle heat engine for IOC solar power generation is studied. The design configuration is a simple parabolic concentration where the receiver is located in the focal plane with its aperture at the focal point. The relationship between concentrator size and collection efficiency is analyzed. The geometry of the deployable graphite/epoxy box truss ring and the reflective panels of the system are described. Mass properties and dynamic analyses are performed to evaluate the center of gravity location and moments of inertia characteristics of the energy conversion subsystem (ECS). The deployable/erectable truss is applicable for large IR space telescopes and center and offset fed ECSs.

Coyner, J. V., Jr.↗
NASA NTRS2023

Dragonfly: A Case Study in Dynamic Stability Characterization

Next decade, the Dragonfly probe will enter Titan’s atmosphere on a mission to explore and characterize its unique and complex organic chemistry. In contrast to Mars entry missions, where the challenge is to slow down in its tenuous atmosphere before impacting the surface, Titan’s thick atmosphere provides generous drag. However, Titan has its own unique EDL challenges. Among these challenges is the long time (on the order of 90 minutes!) the vehicle will need to descend unguided through flow regimes where blunt-body entry probes are known to be dynamically unstable. This elongated timeline, both prior to drogue parachute deployment, and during the ensuing descent, has the potential to allow adverse dynamic instability properties to produce large amplitude oscillations in angle-of-attack. This, in-turn may lead to non-compliance in vehicle attitude requirements for EDL events such as parachute deployment, and lander release, or in the most extreme case, tumbling of the aeroshell and near-assured loss of mission.

EDL↗
NASA NTRS1991

Adaptive control of interface by temperature and interface profile feedback in transparent multi-zone crystal growth furnace

The objective of this research is to control the dynamics of multizone programmable crystal growth furnaces. Due to the inevitable heat exchange among different heating zones and the transient nature of the process, the dynamics of multizone furnaces is time varying, distributed, and therefore complex in nature. Electrical power to heating zones and the translational speed of the ampoule are employed as inputs to control the dynamics. Structural properties of the crystal is the ultimate aim of this adaptive control system. These properties can be monitored in different ways. Following an order of complexity, these may include: (1) on line measurement of the material optical properties such as the refractive index of crystal; (2) on line x-ray imaging of the interface topology; (3) on line optical quantification of the interface profile such as the determination of concavity or convexity of the interface shape; and (4) on line temperature measurement at points closest to the material such as measurements of the ampoule's outside and inside surface temperatures. The research performed makes use of the temperature and optical measurements, specified in (3) and (4) as the outputs of furnace dynamics. However, if the instrumentation is available, the proposed control methodology can be extended to the measurements listed in (1) and (2).

Batur, Celal↗
NASA NTRS2023

Dragonfly: A Case Study in Dynamic Stability Characterization

Next decade, the Dragonfly probe will enter Titan’s atmosphere on a mission to explore and characterize its unique and complex organic chemistry. In contrast to Mars entry missions, where the challenge is to slow down in its tenuous atmosphere before impacting the surface, Titan’s thick atmosphere provides generous drag. However, Titan has its own unique EDL challenges. Among these challenges is the long time (on the order of 90 minutes!) the vehicle will need to descend unguided through flow regimes where blunt-body entry probes are known to be dynamically unstable. This elongated timeline, both prior to drogue parachute deployment, and during the ensuing descent, has the potential to allow adverse dynamic instability properties to produce large amplitude oscillations in angle-of-attack. This, in-turn may lead to non-compliance in vehicle attitude requirements for EDL events such as parachute deployment, and lander release, or in the most extreme case, tumbling of the aeroshell and near-assured loss of mission.

EDL↗
DOE OSTI2019

Investigation of dynamic fracture behavior of additively manufactured Al-10Si-Mg using high-speed synchrotron X-ray imaging

The dynamic tensile properties of additively manufactured (AM) and cast Al-10Si-Mg alloy were disccused using high-speed synchrotron X-ray imaging coupled with a modified Kolsky bar apparatus. A controlled tensile loading (strain rate ≈ 750 s -1 ) was applied using the Kolsky bar apparatus and the deformation and fracture behavior were recorded using the high-speed X-ray imaging setup. The CT and high-speed imaging results worked together to identify the location of the critical flaw and to capture the dynamics of crack propagation. In all experiments, the critical flaw was located on the surface of each specimen. The AM specimens displayed significantly higher crack propagation speed, yield strength, ultimate tensile strength, strain hardening coefficient, and yet lower ductility compared to the cast specimens under dynamic tension. Although the strength values were higher for the AM specimens, the critical mode I stress intensity factors were comparable for both specimens. The microstructures of the samples were characterized by synchrotron X-ray computed tomography (CT) and scanning electron microcopy. The correlation between the dynamic fracture behavior of the samples and the microstructure of the samples is analyzed and discussed.

36 MATERIALS SCIENCE↗