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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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NASA NTRSDate not supplied

Computational Investigation of Oxidative Etch Pitting in FiberForm and Its Impact on Material Properties

Oxidation-driven carbon erosion does not occur uniformly but rather through the development of localized etch pits at active surface sites. These active sites form due to atomic defects on the carbon surface, making them significantly more reactive than the surrounding, non-defective areas. As a result, these sites are the first to react during ablation, leading to their removal. This process creates new defects in neighboring atoms, increasing their reactivity and causing localized carbon removal around these active sites. In this way, the highly reactive defective areas serve as nucleation points for the formation and growth of etch pits, which can have adverse effects on structural integrity of FiberForm. To better understand how these etch pits impact the material properties of carbon fiber microstructures, we have developed a new capability within the direct simulation Monte Carlo (DSMC) framework to capture the etch pit formation process. This capability, integrated into the DSMC code SPARTA (Stochastic Parallel Rarefied-gas Time-accurate Analyzer), models material removal in the presence of active sites, leading to the formation of etch pits. The current work focuses on studying the effects of these etch pits on the material properties of FiberForm, a widely used base material in thermal protection systems (TPS). The microstructure of virgin FiberForm, obtained via X-ray microtomography, is imported into SPARTA to generate the ablated geometries with etch pits. These modified microstructures are then analyzed using the Porous Microstructure Analysis (PuMA) software to compute various material properties, including elasticity, thermal conductivity, and permeability. We investigate the variation of these properties due to the complex surface topology changes caused by etch pit formation. Additionally, we compare the effects of pitting with the conventional model of shrinking fibers, traditionally used to simulate the ablation of carbon structures. Significant differences emerge between the two approaches. Consequently, this physically realistic model of material removal through etch pit formation offers improved accuracy in predicting the degradation of carbon-based TPS during oxidation. It also provides insights into other mechanisms, such as spallation, where chunks of material are removed into the flow due to etch pit growth. Ultimately, this model enhances our understanding of failure modes in these materials during ablation.

PuMA↗
NASA NTRS2003

High Temperature Permeability of Carbon Cloth Phenolic Composite

The carbon fiber phenolic resin composite material used for the RSRM nozzle insulator occasionally experiences problems during operation from pocketing or spalling-like erosion and lifting of plies into the char layer. This phenomenon can be better understood if the permeability of the material at elevated temperatures is well defined. This paper describes an experimental approach to determining high temperature permeability of the carbon phenolic material used as the RSRM nozzle liner material. Two different approaches were conducted independently using disk and bar type specimens with the designed permeability apparatus. The principle of the apparatus was to subject a test specimen to a high pressure differential and a heat supply and to monitor both the pressure and temperature variations resulting from gas penetration through the permeable wall between the two chambers. The bar types, especially designed to eliminate sealing difficulties at a high temperature environment, were directly exposed to real time temperature elevation from 22 C to 260 C during the test period. The disk types were pre-heat treated up to 300 C for 8 hours and cooled to room temperature before testing. Nonlinear variation of downstream pressure at a certain temperature range implied moisture release and matrix pyrolysis. Permeability was calculated using a semi-numerical model of quasi-steady state. The test results and the numerical model are discussed in the paper.

Park, O. Y.↗
NASA NTRS1985

Role of Hydrogen and Structure on CMSX-2

The goal was to characterize and understand the detailed effect of hydrogen on the tensile and fatigue behavior of single crystals of CMSX-2. Specimens were solutionized, air cooled, and then aged in one of two ways. The resultant macro and microstructure included a pronounced dendritic structure with numerous low angle boundaries in the interdendritic region and on the average a high level of porosity with a large variation in size and distribution. Hydrogen permeability and diffusivity in this material was found to be very low at room temperature. Hydrogen concentration studies on thin samples yielded values significantly higher than found for similar charging conditions in nickel and stainless steels. The tensile mechanical properties were found to depend on hydrogen concentration. SEM observations of the brittle subsurface zone revealed a strong correlation between crack initiation sites and voids just beneath the surface. The hollow and solid samples were compared to better understand the influence of increased charged volume on the fatigue behavior.

Baker, C. L.↗
NASA NTRS1984

Steady internal flow and aerodynamic loads analysis of shuttle thermal protection system

An analytical model for calculation of ascent steady state tile loading was developed and validated with wind tunnel data. The analytical model is described and results are given. Results are given for loading due to shocks and skin friction. The analysis included calculation of internal flow (porous media flow and channel flow) to obtain pressures and integration of the pressures to obtain forces and moments on an insulation tile. A heat transfer program was modified by using analogies between heat transfer and fluid flow so that it could be used for internal flow calculation. The type of insulation tile considered was undensified reusable surface insulation (RSI) without gap fillers, and the location studied was the lower surface of the orbiter. Force and moment results are reported for parameter variations on surface pressure distribution, gap sizes, insulation permeability, and tile thickness.

Petley, D. H.↗
NASA NTRS1997

Static Test for a Gravitational Force Coupled to Type 2 YBCO Superconductors

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cc. Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating type II, YBCO superconductor, with the percentage change (0.05 - 2.1 %) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10' was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field. Changes in acceleration were measured to be less than 2 parts in 108 of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between static superconductors and gravity.

Li, Ning↗
NASA NTRS1999

Granular Superconductors and Gravity

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

Noever, David↗
NASA NTRS2010

Material condition assessment with eddy current sensors

Eddy current sensors and sensor arrays are used for process quality and material condition assessment of conducting materials. In an embodiment, changes in spatially registered high resolution images taken before and after cold work processing reflect the quality of the process, such as intensity and coverage. These images also permit the suppression or removal of local outlier variations. Anisotropy in a material property, such as magnetic permeability or electrical conductivity, can be intentionally introduced and used to assess material condition resulting from an operation, such as a cold work or heat treatment. The anisotropy is determined by sensors that provide directional property measurements. The sensor directionality arises from constructs that use a linear conducting drive segment to impose the magnetic field in a test material. Maintaining the orientation of this drive segment, and associated sense elements, relative to a material edge provides enhanced sensitivity for crack detection at edges.

Goldfine, Neil J.↗
NASA NTRS1999

Test Status for Proposed Coupling of a Gravitational Force to Extreme Type II YBCO Ceramic Superconductors

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.

Noever, David↗
NASA NTRS1996

Permeation of protons, potassium ions, and small polar molecules through phospholipid bilayers as a function of membrane thickness

Two mechanisms have been proposed to account for solute permeation of lipid bilayers. Partitioning into the hydrophobic phase of the bilayer, followed by diffusion, is accepted by many for the permeation of water and other small neutral solutes, but transient pores have also been proposed to account for both water and ionic solute permeation. These two mechanisms make distinctively different predictions about the permeability coefficient as a function of bilayer thickness. Whereas the solubility-diffusion mechanism predicts only a modest variation related to bilayer thickness, the pore model predicts an exponential relationship. To test these models, we measured the permeability of phospholipid bilayers to protons, potassium ions, water, urea, and glycerol. Bilayers were prepared as liposomes, and thickness was varied systematically by using unsaturated lipids with chain lengths ranging from 14 to 24 carbon atoms. The permeability coefficient of water and neutral polar solutes displayed a modest dependence on bilayer thickness, with an approximately linear fivefold decrease as the carbon number varied from 14 to 24 atoms. In contrast, the permeability to protons and potassium ions decreased sharply by two orders of magnitude between 14 and 18 carbon atoms, and leveled off, when the chain length was further extended to 24 carbon atoms. The results for water and the neutral permeating solutes are best explained by the solubility-diffusion mechanism. The results for protons and potassium ions in shorter-chain lipids are consistent with the transient pore model, but better fit the theoretical line predicted by the solubility-diffusion model at longer chain lengths.

NASA Program Exobiology↗
NASA NTRS1982

Anion permselective membrane

The synthesis and fabrication of polymeric anion permselective membranes for redox systems are discussed. Variations of the prime candidate anion membrane formulation to achieve better resistance and/or lower permeability were explored. Processing parameters were evaluated to lower cost and fabricate larger sizes. The processing techniques to produce more membranes per batch were successfully integrated with the fabrication of larger membranes. Membranes of about 107 cm x 51 cm were made in excellent yield. Several measurements were made on the larger sample membranes. Among the data developed were water transport and transference numbers for these prime candidate membranes at 20 C. Other work done on this system included characterization of a number of specimens of candidate membranes which had been returned after service lives of up to sixteen months. Work with new polymer constituents, with new N.P.'s, catalysts and backing fabrics is discussed. Some work was also done to evaluate other proportions of the ingredients of the prime candidate system. The adoption of a flow selectivity test at elevated temperature was explored.

Hodgdon, R. B.↗
NASA NTRS1976

Graded-porosity heat-pipe wicks

To maximize the capacity of a nonarterial heat pipe, a wick is considered whose porosity is allowed to vary axially along its length. At every axial location the porosity is set no lower than required to maintain the wick in a nearly saturated state under the maximum heat-transport rate. The result is a wick whose permeability is everywhere as high as possible. The differential equation that governs the optimum porosity variation is solved numerically between a condenser-end boundary condition that just prevents a liquid slug or puddle in the vapor spaces and an evaporator-end boundary condition that just prevents circumferential groove dry-up. Experimental performance measurements for an ammonia heat pipe are presented.

Eninger, J. E.↗
NASA NTRS1994

Effect of nonzero surface admittance on receptivity and stability of compressible boundary layer

The effect of small-amplitude short-scale variations in surface admittance on the acoustic receptivity and stability of two-dimensional compressible boundary layers is examined. In the linearized limit, the two problems are shown to be related both physically and mathematically. This connection between the two problems is used, in conjunction with some previously reported receptivity results, to infer the modification of stability properties due to surface permeability. Numerical calculations are carried out for a self-similar flat-plate boundary layer at subsonic and low supersonic speeds. Variations in mean suction velocity at the perforated admittance surface can also induce receptivity to an acoustic wave. For a subsonic boundary layer, the dependence of admittance-induced receptivity on the acoustic-wave orientation is significantly different from that of the receptivity produced via mean suction variation. The admittance-induced receptivity is generally independent of the angle of acoustic incidence, except in a relatively narrow range of upstream-traveling waves for which the receptivity becomes weaker. However, this range of angles is precisely that for which the suction-induced receptivity tends to be large. At supersonic Mach numbers, the admittance-induced receptivity to slow acoustic models is relatively weaker than that in the case of the fast acoustic modes. We also find that purely real values for the surface admittance tend to have a destabilizing effect on the evolution of an instability wave over a slightly permeable surface. The limits on the validity of the linearized approximation are also assessed in one specific case.

Choudhari, Meelan↗
NASA NTRS1985

Lithologic and Structural Control on Slope Morphology in the Valles Marineris

Throughout the Valles Marineris scarp morphology varies as a function of lithology, structure and scarp height. In addition lithology is an important control on permeability and the relative importance of spring sapping processes. Geomorphic mapping of distinct subareas can be used to define the characteristic scarp forms. Distinct morphologic zones defined on the basis of regional variations in lithology are described. Lithology and tectonic history are shown to be the two most important factors controlling slope development. Regional variation in scarp morphology can be correlated with the orientation and density of fracture systems; scarp height and the presence of rejuvenated fault scarps; and the thickness and degree of exposure of presumably less competent, more permeable, water saturated crated plateau material in the chasmata scarps.

Patton, P. C.↗
NASA NTRS2000

RFI and SCRIMP Model Development and Verification

Vacuum-Assisted Resin Transfer Molding (VARTM) processes are becoming promising technologies in the manufacturing of primary composite structures in the aircraft industry as well as infrastructure. A great deal of work still needs to be done on efforts to reduce the costly trial-and-error methods of VARTM processing that are currently in practice today. A computer simulation model of the VARTM process would provide a cost-effective tool in the manufacturing of composites utilizing this technique. Therefore, the objective of this research was to modify an existing three-dimensional, Resin Film Infusion (RFI)/Resin Transfer Molding (RTM) model to include VARTM simulation capabilities and to verify this model with the fabrication of aircraft structural composites. An additional objective was to use the VARTM model as a process analysis tool, where this tool would enable the user to configure the best process for manufacturing quality composites. Experimental verification of the model was performed by processing several flat composite panels. The parameters verified included flow front patterns and infiltration times. The flow front patterns were determined to be qualitatively accurate, while the simulated infiltration times over predicted experimental times by 8 to 10%. Capillary and gravitational forces were incorporated into the existing RFI/RTM model in order to simulate VARTM processing physics more accurately. The theoretical capillary pressure showed the capability to reduce the simulated infiltration times by as great as 6%. The gravity, on the other hand, was found to be negligible for all cases. Finally, the VARTM model was used as a process analysis tool. This enabled the user to determine such important process constraints as the location and type of injection ports and the permeability and location of the high-permeable media. A process for a three-stiffener composite panel was proposed. This configuration evolved from the variation of the process constraints in the modeling of several different composite panels. The configuration was proposed by considering such factors as: infiltration time, the number of vacuum ports, and possible areas of void entrapment.

Loos, Alfred C.↗
NASA NTRS1978

Thirty-centimeter-diameter ion milling source

A 30-cm beam diameter ion source has been designed and fabricated for micromachining and sputtering applications. An argon ion current density of 1 mA/cu cm at 500 eV ion energy was selected as a design operating condition. The completed ion source met the design criteria at this operating condition with a uniform and well-collimated beam having an average variation in current density of + or - 5% over the center of 20 cm of the beam. This ion source has a multipole magnetic field that employs permanent magnets between permeable pole pieces. Langmuir probe surveys of the source plasma support the design concepts of a multipole field and a circumferential cathode to enhance plasma uniformity.

Robinson, R. S.↗
NASA NTRS2023

The Impact of Soft Magnetic Materials in Electrified Aircraft Applications

Electrical systems with high power and high power density are integral to many aerospace and energy applications. These systems, enabled by power electronics with wide bandgap semiconductor devices, require management of both efficiency/thermal aspects and electromagnetic interference that are problems specific to high power and high frequency applications, respectively. In addition to advanced active components, these applications also require passive components (inductors, capacitors, conductors) capable of operation under challenging conditions. This work surveys the state of the art of magnetic components and soft magnetic materials used as inductive cores. The wide variety of motor and converter topologies translates to a variety of requirements in the magnetics including mechanical properties, permeabilities, and frequency response. The scaling impact of material properties will be surveyed with respect to component performance and sizing, using both data from experiment and the published literature. Variations on simulations, both in lumped circuits and finite element models, will also be discussed as these are important aspects of the design phase of modern power electronics.

Alex Leary↗
NASA NTRS1986

Analysis of optically controlled microwave/millimeter wave device structures

The light-induced voltage and the change in the source-to-drain channel current under optical illumination higher than the semiconductor bandgap for GaAs MESFET, InP MESFET, Al0.3Ga0.7As/GaAs high electron mobility transistor (HEMT) and GaAs permeable base transistor (PBT) were analytically obtained. The GaAs PBT and GaAs MESFET have much higher sensitivity than InP MESFET. The Al0.3Ga0.7As/GaAs HEMT is observed to have the highest sensitivity. Variation in device parasitics due to optical illumination and its effect on the cutoff frequencies f sub T and f sub max are also investigated.

Simons, R. N.↗