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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
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 OSTI2022

Effects of surface treatments on ABS mechanical properties from fused filament fabrication

This paper examines the influence of surface treatments on the mechanical properties of acrylonitrile butadiene styrene (ABS) samples printed by fused filament fabrication (FFF). Prior efforts have applied brushing, painting, solvent dipping, infiltration, and vapor smoothing as post-processing surface treatments to improve the mechanical properties of FFF components. Additionally, because FFF can produce components with undesirable surface roughness, mechanical abrasion, epoxy coating, and acetone treatment may increase tensile strength by decreasing stress concentrations. Ridged surface texture may provide desirable tribological or handling properties. Based on these opportunities, this paper investigates abrasive media blasting, epoxy coating, acetone immersion, and ridged texturing surface treatments on the tensile strength and other mechanical properties of FFF ABS samples. ASTM D638-14 Type-I samples were printed, treated on all sample sides, and tested. From tensile tests, the elastic modulus, tensile strength, and fracture strain for both the untreated and treated ABS samples were calculated. For each sample, the surface finish and fracture macromorphology were observed with optical microscopy and the roughness values for the surface finish were calculated from profilometer data. Furthermore, samples were submerged in water and weighed periodically to measure mass changes due to water absorption. From surface profilometry and optical miscopy data, mechanical media blasting, epoxy coating, and immersion in all concentrations of acetone decreased surface roughness. Overall, on average, grit blasting with large beads and epoxy coating led to 2.6% and 1.2% increases in tensile strength, respectively; immersion in 40% acetone led to a 1.9% increase in tensile strength while treatment in 60% and 80% acetone decreased tensile strength by 4.9% and 1.9%, respectively. The study concludes that only grit blasting with large beads, immersion in 60% acetone, and the ridged texture significantly affected the tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effects of the background plasma temperature on the current filamentation instability

The effects of thermal anisotropy of background plasma on the current-filamentation instability (CFI) in an asymmetric counterstreaming system are investigated with a fully relativistic kinetic model. It is found that both the temperature and the thermal anisotropy of the background plasma play important roles in the development of the CFI. It is also pointed out that the thermal anisotropy of the background plasma dominates over the space charge effect in suppressing the CFI. A parametric study of the CFI is presented in the context of fast ignition. A new way to suppress CFI and its detrimental effects on the fast electron beam divergence has been proposed. The results of the analytical estimations are verified by 2D3V particle-in-cell simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Synthesis of SiO{sub 2}/β-SiC/graphite hybrid composite by low temperature hot filament chemical vapor deposition

β-SiC thin films were synthesized directly on graphite by hot filament chemical vapor deposition at low temperature. SiH{sub 4} diluted in hydrogen was employed as the silicon source, while graphite was functioned as both substrate and carbon source for the as-grown β-SiC films. X-ray diffraction and Fourier transform infrared analysis indicate that SiO{sub 2}/β-SiC/graphite hybrid composite was formed after post annealing treatment, and its crystalline quality can be remarkably improved under optimized annealing conditions. The possible growth mechanism was proposed based on in situ etching of graphite by reactive hydrogen radicals at the atomic level.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Comment on “Motion of a helical vortex filament in superfluid {sup 4}He under the extrinsic form of the local induction approximation” [Phys. Fluids 25, 085101 (2013)]

We comment on the paper by Van Gorder [“Motion of a helical vortex filament in superfluid {sup 4}He under the extrinsic form of the local induction approximation,” Phys. Fluids 25, 085101 (2013)]. We point out that the flow of the normal fluid component parallel to the vortex will often lead into the Donnelly–Glaberson instability, which will cause the amplification of the Kelvin wave. We explain why the comparison to local nonlinear equation is unreasonable, and remark that neglecting the motion in the x-direction is not reasonable for a Kelvin wave with an arbitrary wavelength and amplitude. The correct equations in the general case are also derived.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Infrared pulse characterization using four-wave mixing inside a few cycle pulse filament in air

We demonstrate a four-wave mixing (FWM) technique to measure near- and mid-infrared (IR) laser pulse shapes in time domain. Few cycle 800 nm laser pulses were synchronized with the IR pulse and focused colinearly to generate a plasma filament in air. Second harmonic radiation around 400 nm was generated through FWM, with a yield proportional to the IR pulse intensity. Excellent signal to noise ratio was observed from 2.1 μm to 18 μm. With proper phase stabilization of the IR beam, this technique is a promising step toward direct electric field sensing of near-IR pulses in air.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Compact 180-kV Marx generator triggered in atmospheric air by femtosecond laser filaments

We developed a compact Marx generator triggered in atmospheric air by a single femtosecond laser beam undergoing filamentation. Voltage pulses of 180 kV could be generated with a subnanosecond jitter. The same laser beam was also used to initiate simultaneously guided discharges up to 21 cm long at the output of the generator.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Comment on “General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation” [Phys. Fluids 26, 065105 (2014)]

Van Gorder considers a formulation of the local induction approximation, which allows the vortex to move in the direction of the reference axis [“General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation,” Phys. Fluids 26, 065105 (2014)]. However, in his analytical and numerical study he does not use it. A mistake in the torsion of a helical vortex is also corrected.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Four-photon parametric mixing and interaction between filaments

Recently energy exchange between two filaments crossing at small angle and with power slightly above the critical for self-focusing P{sub cr} was experimentally demonstrated. In this paper we present a model describing the process of this transfer through degenerate four-photon parametric mixing. Our model confirms the experimental results that the direction of energy exchange depends on the relative transverse velocity (incident angle), laser intensity and initial distance between the pulses (relative initial phase)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Nonlinear dynamics of the ion Weibel-filamentation instability: An analytical model for the evolution of the plasma and spectral properties

We present a predictive model of the nonlinear phase of the Weibel instability induced by two symmetric, counter-streaming ion beams in the non-relativistic regime. This self-consistent model combines the quasilinear kinetic theory of Davidson et al. [Phys. Fluids 15, 317 (1972)] with a simple description of current filament coalescence. It allows us to follow the evolution of the ion parameters up to a stage close to complete isotropization, and is thus of prime interest to understand the dynamics of collisionless shock formation. Its predictions are supported by 2-D and 3-D particle-in-cell simulations of the ion Weibel instability. The derived approximate analytical solutions reveal the various dependencies of the ion relaxation to isotropy. In particular, it is found that the influence of the electron screening can affect the results of simulations using an unphysical electron mass.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Photoelectron emission from metal surfaces induced by VUV-emission of filament driven hydrogen arc discharge plasma

Photoelectron emission measurements have been performed using a filament-driven multi-cusp arc discharge volume production H{sup −} ion source (LIISA). It has been found that photoelectron currents obtained with Al, Cu, Mo, Ta and stainless steel (SAE 304) are on the same order of magnitude. The photoelectron currents depend linearly on the discharge power. It is shown experimentally that photoelectron emission is significant only in the short wavelength range of hydrogen spectrum due to the energy dependence of the quantum efficiency. It is estimated from the measured data that the maximum photoelectron flux from plasma chamber walls is on the order of 1 A per kW of discharge power.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Hydrogen atom temperature measured with wavelength-modulated laser absorption spectroscopy in large scale filament arc negative hydrogen ion source

The velocity distribution function of hydrogen atoms is one of the useful parameters to understand particle dynamics from negative hydrogen production to extraction in a negative hydrogen ion source. Hydrogen atom temperature is one of the indicators of the velocity distribution function. To find a feasibility of hydrogen atom temperature measurement in large scale filament arc negative hydrogen ion source for fusion, a model calculation of wavelength-modulated laser absorption spectroscopy of the hydrogen Balmer alpha line was performed. By utilizing a wide range tunable diode laser, we successfully obtained the hydrogen atom temperature of ∼3000 K in the vicinity of the plasma grid electrode. The hydrogen atom temperature increases as well as the arc power, and becomes constant after decreasing with the filling of hydrogen gas pressure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Particles trajectories in magnetic filaments

The motion of a particle in a spatially harmonic magnetic field is a basic problem involved, for example, in the mechanism of formation of a collisionless shock. In such settings, it is generally reasoned that particles entering a Weibel generated turbulence are trapped inside it, provided their Larmor radius in the peak field is smaller than the field coherence length. The goal of this work is to put this heuristic conclusion on firm ground by studying, both analytically and numerically, such motion. A toy model is analyzed, consisting of a relativistic particle entering a region of space occupied by a spatially harmonic field. The particle penetrates the magnetic structure in a direction aligned with the magnetic filaments. Although the conclusions are not trivial, the main result is confirmed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Nonlinear bubble nucleation and growth following filament and white-light continuum generation induced by a single-shot femtosecond laser pulse into dielectrics based on consideration of the time scale

Bubble nucleation and growth following plasma channeling (filament) and white-light continuum in liquid irradiated by a single-shot fs-pulse were experimentally investigated with close observation of the time scale. Making full use of a new confocal system and time-resolved visualization techniques, we obtained evidence suggestive of a major/minor role of the non-linear/thermal effects during the fs-pulse-induced bubble's fountainhead (10{sup −13} s) and growth (10{sup −7} s), which was never observed with the use of the ns-pulse (i.e., optic cavitation). In this context, the fs-pulse-induced bubble is not an ordinary optic cavitation but rather is nonlinear-optic cavitation. We present the intrinsic differences in the dominant-time domain of the fs-pulse and ns-pulse excitation, and intriguingly, a mere hundred femtoseconds' excitation predetermines the size of the bubble appearing several microseconds after irradiation. That is, the nucleation happens temporally beyond a six-order-of-magnitude difference.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Robust authentication through stochastic femtosecond laser filament induced scattering surfaces

We demonstrate a reliable authentication method by femtosecond laser filament induced scattering surfaces. The stochastic nonlinear laser fabrication nature results in unique authentication robust properties. This work provides a simple and viable solution for practical applications in product authentication, while also opens the way for incorporating such elements in transparent media and coupling those in integrated optical circuits.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Study of the thermal properties of filaments for 3D printing

Various materials are used for 3D printing, most commonly Acrylonitrile butadiene styrene (ABS), Polylactic acid (PLA), Polyethylene (PET) and Polypropylene (PP). These materials differ mainly in their melting point, which significantly influences the properties of the final products. Filaments are melted in the print head during the printing process. The temperature range is from 150 °C to 250 °C depending on the technology used. The optimum temperature for the cooling substrate on which printing is carried out is chosen so as to ensure uniform cooling and deformation. It generally varies between (40 – 100) °C. From the above it is clear that both temperatures can significantly affect the properties of the printed 3D object. It is therefore important to determine the thermal parameters (thermal conductivity, specific heat and thermal diffusivity) of the materials used across the entire range of temperatures. For evaluating the properties of different types of PLA materials, the step transient method was used, which allows determination of all required parameters using a fractal heat transfer model.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Features of the electron density dynamics in the filamentation of femtosecond laser radiation in air at elevated pressure

The electron density in the plasma channel of a femtosecond filament in air at pressures from 1 to 7 atm is measured at different instants, starting from the ionisation onset and up to several hundreds of picoseconds after it. The initial electron density is found to increase sharply in the pressure range of 3 – 4 atm. The plasma channel diameter is found to decrease with an increase in pressure from 3 to 7 atm. (extreme laser radiation: physics and fundamental applications)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Broadening and shift of emission lines in a plasma of filaments generated by a tightly focused femtosecond laser pulse in air

We study the broadening and shift of N I (λ = 746.8 nm) and O I ( λ = 777.4 nm) lines in a plasma of filaments generated by a tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). It is shown that the dynamic Stark effect makes a major contribution to the broadening and shift of the N I line (λ = 746.8 nm). It is found that amplified spontaneous emission of a regenerative amplifier and post-pulses break the LS coupling for the O I 3p {sup 5}P energy level, lead to the generation of side bands related to the Rabi splitting of levels and result in pulsed emission of the first positive system of N{sub 2}. (paper)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗