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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Thermal Expansion Studies of Selected High Temperature Thermoelectric Materials

Radioisotope thermoelectric generators (RTGs) generate electrical power by converting the heat released from the nuclear decay of radioactive isotopes (typically plutonium-238) into electricity using a thermoelectric converter. RTGs have been successfully used to power a number of space missions and have demonstrated their reliability over an extended period of time (tens of years) and are compact, rugged, radiation resistant, scalable, and produce no noise, vibration or torque during operation. System conversion efficiency for state-of-practice RTGs is about 6% and specific power less than or equal to 5.1 W/kg. Higher specific power would result in more on-board power for the same RTG mass, or less RTG mass for the same on-board power. The Jet Propulsion Laboratory has been leading, under the advanced thermoelectric converter (ATEC) project, the development of new high-temperature thermoelectric materials and components for integration into advanced, more efficient RTGs. Thermoelectric materials investigated to date include skutterudites, the Yb14MnSb11 compound, and SiGe alloys. The development of long-lived thermoelectric couples based on some of these materials has been initiated and is assisted by a thermo-mechanical stress analysis to ensure that all stresses under both fabrication and operation conditions will be within yield limits for those materials. Several physical parameters are needed as input to this analysis. Among those parameters, the coefficient of thermal expansion (CTE) is critically important. Thermal expansion coefficient measurements of several thermoelectric materials under consideration for ATEC are described in this paper. The stress response at the interfaces in material stacks subjected to changes in temperature is discussed, drawing on work from the literature and project-specific tools developed here. The degree of CTE mismatch and the associated effect on the formation of stress is highlighted.

silicon germanium↗
NASA NTRS1977

Work function determination of promising electrode materials for thermionic converters

Work performed on this contract was primarily for the evaluation of selected electrode materials for thermionic energy converters. The original objective was to characterize selected nickel based superalloys up to temperatures of 1400 K. It was found that an early selection, Inconel 800 produced a high vapor pressure which interfered with the vacuum emission measurements. The program then shifted to two other areas. The first area was to obtain emission from the superalloys in a cesiated atmosphere. The cesium plasma helps to suppress the vaporization interference. The second area involved characterization of the Lanthanum-Boron series as thermionic emitters. These final two areas resulted in three journal publications which are attached to this report.

Jacobson, D.↗
NASA NTRS2000

Testing and Selection of Fire-Resistant Materials for Spacecraft Use

Spacecraft fire-safety strategy emphasizes prevention, mostly through the selection of onboard items classified accord- ing to their fire resistance. The principal NASA acceptance tests described in this paper assess the flammability of materials and components under "worst-case" normal-gravity conditions of upward flame spread in controlled-oxygen atmospheres. Tests conducted on the ground, however, cannot duplicate the unique fire characteristics in the nonbuoyant low-gravity environment of orbiting spacecraft. Research shows that flammability an fire-spread rates in low gravity are sensitive to forced convection (ventilation flows) and atmospheric-oxygen concentration. These research results are helping to define new material-screening test methods that will better evaluate material performance in spacecraft.

Friedman, Robert↗
NASA NTRS1980

Relative toxicity testing of spacecraft materials. 2: Aircraft materials

The relative toxicity of thermodegradation (pyrolysis/combustion) products of aircraft materials was studied. Two approaches were taken to assess the biological activity of the pyrolysis/combustion products of these materials: (1) determine the acute lethality to rats from inhalation of these pyrolysates and (2) examine the tendency for sublethal exposure to the pyrolysates to disrupt behavioral (shock avoidance) performance of exposed rats. The ralative importance of lethality vs. behavioral effects in selection of a material may be dictated by whether or not individuals potentially exposed to such products, would have an opportunity to escape if they were behaviorally capable of doing so. If so, the second parameter would assume greater importance, but if not the first parameter may be of much greater importance in selecting materials.

Lawrence, W. H.↗
NASA NTRS1984

Breakway friction and dynamic friction/wear measurements of various ceramic materials from 25 C (75 F) to 650 C (1200 F)

This report describes the results of a program designed to evaluate the breakaway friction and dynamic friction/wear characteristics of materials having potential for use as load bearing components in a high-performance high-temperature heavy duty diesel engine. Ten candidate materials were selected, six of which were evaluated under all possible material combinations as both stationary as well as moving breakaway specimens. The remaining materials were evaluated either in the static mode against themselves and all other materials, or against themselves only. Experiments were performed at five temperatures up to 650 C (1200 F) and unit pressures of 700 kPa (100 lb/sq in.), 3500 kPa (500 lb/sq in.), and 7000 kPa (1000 lb/sq in.). Experimental results indicate that under dynamic conditions, four of the ten materials exhibited good to excellent friction/wear characteristics in various material combinations. These materials were: titanium carbide, silicon nitride, silicon carbide (reaction sintered), and Refel (SiC).

Boes, D. J.↗
NASA NTRS1991

Impact response of composite materials

Composite materials composed of carbon fibers and resin matrices offer great promise in reducing the weight of aerospace structures. However they remain extremely vulnerable to out of plane impact loads, which lead to severe losses in strength and stiffness. The results of an experimental program, undertaken to investigate the low velocity impact damage tolerance of composite materials is presented. The objectives were to identify key neat resin/composite properties that lead to enhancement of composite impact damage tolerance and to find a small scale test that predicts compression after impact properties of panels. Five materials were selected for evaluation. These systems represented different classes of material behavior such as brittle epoxy, modified epoxies, and amorphous and semicrystalling thermoplastics. The influence of fiber properties on the impact performance was also studied in one material, i.e., in polyether ether ketone (PEEK). Several 24 and 48 ply quasi-isotropic and 24 ply orthotropic laminates were examined using an instrumented drop weight impactor. Correlations with post impact compression behavior were made.

Tiwari, S. N.↗
NASA NTRS2018

Space Environmental Effects on Additively Manufactured Materials

Space simulations including thermal vacuum, atomic oxygen, and ultraviolet radiation were performed to study the durability of various additively manufactured materials. In addition to ground simulations, additively manufactured materials were selected for a one-year flight on the Materials on International Space Station Experiment (MISSE) Flight Facility. The space environment is composed of atomic oxygen, ultraviolet radiation, protons, electrons, meteoroid/space debris impacts, thermal cycling, and hard vacuum. An improved UV sensor is also discussed.

Finckenor, M. M.↗
NASA NTRS1981

Aerothermodynamic design feasibility of a Mars aerocapture/aeromaneuver vehicle

Lifting aerodynamic configurations have been screened and selected for the Mars aerocapture mission that (1) meet the geometric packaging requirements of the various payloads and the Space Shuttle cargo bay and (2) provide the aerodynamic performance characteristics required to obtain the atmospheric exit steering accuracy and the parachute deployment conditions desired. Hypersonic heat transfer and aerodynamic loads to the vehicle in the CO2 atmosphere are evaluated. Contemporary low density ablative thermal protection materials were selected that meet all the atmospheric entry requirements and provide a minimum mass solution. Results are presented of the aerodynamic configuration and thermal protection materials screening and selection. It is concluded that the aerothermodynamic design of this concept is feasible using state-of-the-art technology.

Florence, D. E.↗
NASA NTRS1990

The effect of thermal damage on the mechanical properties of polymer regrinds

Reprocessed polymers are subjected to high processing temperatures that result in the breakdown of molecular chains and changes in the molecular structures. These phenomena are reflected in the mechanical properties of materials. Practically every regrind is seen as a new material. These experiments deal with the molding, regrinding, and reprocessing of test specimens for the study of their mechanical properties. The comparative test data from each recycled material would give students an insight of the molecular structures and property degradation. Three important rheological and mechanical properties such as melt flow, impact strength, and flexural strength are to be determined. These properties play key roles in the selection of engineering materials. The material selected for demonstration was Makrolon 3000L, a polycarbonate thermoplastic from Bayer AG. The thermal degradation due to repeated processing is reflected in the decrease in molecular weight and breakdown of molecular chains causing increase in melt flow. The Izod-impact resistance and the flexural strength deteriorate gradually.

Kundu, Nikhil K.↗
NASA NTRS1974

Effect of gravity on liquid phase sintering

The unique conditions offered by the earth orbital environment in material processing involving both solid and liquid phases, such as liquid phase sintering, were studied. An experimental development program involving both test and theoretical work was initiated. Experimental work using material combinations selected such that maximum information about the effect of gravity can be derived has been conducted. Wetting of the solid phase by the liquid during sintering is an important phenomenon in liquid phase sintering, and gravity has influence on both capillary phenomenon and density segregation; hence, material combinations were selected such that these two effects can be suitably studies. The experimental work is meant to form the basis for similar comparative work done under low-g conditions. The part of the model dealing with the capillary phenomenon, as related to liquid phase sintering and the effect of gravity on it, suggest that gravity will have negligible effect on the Bond number and that the cohesive force is dependent on both the amount of liquid phase and the angle of contact.

Mookherji, T.↗
NASA NTRS1936

A comparison of corrosion-resistant steel (18 percent chromium - 8 percent nickel) and aluminum alloy (24st)

In the selection of materials for aircraft application, it is not enough to make the selection on a strength-weight basis alone. A strength-weight comparison is significant but other factors must be considered, for while a material with a high ratio of strength to weight may be perfectly satisfactory for one use, it may be totally unfitted for another. It is essential, among other things, that the probable nature, magnitude, and direction of the principal stresses be given special consideration. The following analysis has therefore been made with this in mind. An attempt has been made to cover insofar as possible the major, but not all the points, that a designer would consider in the use of "18-8", as it is commonly referred to, and 24ST aluminum alloy, as applied to aircraft. 24ST was selected for this comparison as it has practically replaced 17ST for aircraft construction and it appears to have the best combination of properties of the alloys now available for this purpose. The cost of fabrication has not been considered.

Sullivan, J E↗
NASA NTRS2013

Investigation of Methods for Selectively Reinforcing Aluminum and Aluminum-Lithium Materials

Several studies have indicated that selective reinforcement offers the potential to significantly improve the performance of metallic structures for aerospace applications. Applying high-strength, high-stiffness fibers to the high-stress regions of aluminum-based structures can increase the structural load-carrying capability and inhibit fatigue crack initiation and growth. This paper discusses an investigation into potential methods for applying reinforcing fibers onto the surface of aluminum and aluminum-lithium plate. Commercially-available alumina-fiber reinforced aluminum alloy tapes were used as the reinforcing material. Vacuum hot pressing was used to bond the reinforcing tape to aluminum alloy 2219 and aluminum-lithium alloy 2195 base plates. Static and cyclic three-point bend testing and metallurgical analysis were used to evaluate the enhancement of mechanical performance and the integrity of the bond between the tape and the base plate. The tests demonstrated an increase in specific bending stiffness. In addition, no issues with debonding of the reinforcing tape from the base plate during bend testing were observed. The increase in specific stiffness indicates that selectively-reinforced structures could be designed with the same performance capabilities as a conventional unreinforced structure but with lower mass.

Bird, R. Keith↗
NASA NTRS1989

High-temperature LDV seed particle development

The feasibility of developing a method for making monodisperse, unagglomerated spherical particles greater than 50 nm in diameter was demonstrated. Carbonaceous particles were made by pyrolyzing ethylene with a pulsed CO2 laser, thereby creating a non-equilibrium mixture of carbon, hydrogen, hydrocarbon vapors, and unpyrolyzed ethylene. Via a complex series of reactions, the carbon and hydrocarbon vapors quickly condensed into the spherical particles. By cooling and dispersing them in a supersonic expansion immediately after their creation, the hot newly-formed spheres were prevented from colliding and coalescing, thus preventing the problem of agglomeration which as plagued other investigators studying laser-simulated particle formation. The cold particles could be left suspended in the residual gases indefinitely without agglomerating. Their uniform sizes and unagglomerated nature were visualized by collecting the particles on filters that were subsequently examined using electron microscopy. It was found the mean particle size can be coarsely controlled by varying the initial ethylene pressure, and can be finely controlled by varying the fluence (energy/unit area) with which the laser irradiates the gas. The motivating application for this research was to manufacture particles that could be used as laser Doppler velocimetry (LDV) seeds in high-temperature high-speed flows. Though the particles made in this program will not evaporate until heated to about 3000 K, and thus could serve as LDV seeds in some applications, they are not ideal when the hot atmosphere is also oxidizing. In that situation, ceramic materials would be preferable. Research performed elsewhere has demonstrated that selected ceramic materials can be manufactured by laser pyrolysis of appropriate supply gases. It is anticipated that, when the same gases are used in conjunction with the rapid cooling technique, unagglomerated spherical ceramic particles can be made with little difficulty. Such particles would also be valuable to manufacturers of ceramic or abrasive products, and this technique may find its greatest commercial potential in those areas.

Frish, Michael B.↗
NASA NTRS1990

A phenomenological model of coating/substrate adhesion and interfacial bimetallic peeling stress in composite mirrors

Adhesion and interfacial stress between metal films and structural composite material substrates is discussed. A theoretical and conceptual basis for selecting coating materials for composite mirror substrates is described. A phenomenological model that interrelates cohesive tensile strength of thin film coatings and interfacial peeling stresses is presented. The model serves as a basis in determining gradiated materials response and compatibility of composite substrate and coating combinations. Parametric evaluation of material properties and geometrical factors such as coating thickness are used to determine the threshold stress levels for maintaining adhesion at the different interfaces.

Mcelroy, Paul M.↗
NASA NTRS1986

Amphibious Airplane

The airplane pictured is the new Air Shark I, a four-place amphibian that makes extensive use of composite materials and cruises at close to 200 miles per hour under power from a 200-horsepower engine. Air Shark I is a "homebuilt" airplane, assembled from a kit of parts and components furnished by Freedom Master Corporation, Satellite Beach, Florida. The airplane incorporates considerable NASA technology and its construction benefited from research assistance provided by Kennedy Space Center (KSC) In designing the Shark, company president Arthur M. Lueck was able to draw on NASA's aeronautical technology bank through KSC's computerized "recon" library. As a result of his work at KSC, the wing of the Air Shark I is a new airfoil developed by Langley Research Center for light aircraft. In addition, Lueck opted for NASA-developed "winglets," vertical extensions of the wing that reduce drag by smoothing air turbulence at the wingtips. The NASA technology bank also contributed to the hull design. Lueck is considering application of NASA laminar flow technology-means of smoothing the airflow over wing and fuselage-to later models for further improvement of the Shark's aerodynamic efficiency. A materials engineer, Lueck employed his own expertise in designing and selecting the materials for the composite segments, which include all structural members, exposed surfaces and many control components. The materials are fiber reinforced plastics, or FRP They offer a high strength-to-weight ratio, with a nominal strength rating about one and a half times that of structural steel. They provide other advantages: the materials can be easily molded into finished shapes without expensive tooling or machining, and they are highly corrosion resistant. The first homebuilt to be offered by Freedom Master, Air Shark I completed air and water testing in mid-1985 and the company launched production of kits.

Source record↗
NASA NTRS2001

Apparatus and process for freeform fabrication of composite reinforcement preforms

A solid freeform fabrication process and apparatus for making a three-dimensional reinforcement shape. The process comprises the steps of (1) operating a multiple-channel material deposition device for dispensing a liquid adhesive composition and selected reinforcement materials at predetermined proportions onto a work surface; (2) during the material deposition process, moving the deposition device and the work surface relative to each other in an X-Y plane defined by first and second directions and in a Z direction orthogonal to the X-Y plane so that the materials are deposited to form a first layer of the shape; (3) repeating these steps to deposit multiple layers for forming a three-dimensional preform shape; and (4) periodically hardening the adhesive to rigidize individual layers of the preform. These steps are preferably executed under the control of a computer system by taking additional steps of (5) creating a geometry of the shape on the computer with the geometry including a plurality of segments defining the preform shape and each segment being preferably coded with a reinforcement composition defining a specific proportion of different reinforcement materials; (6) generating programmed signals corresponding to each of the segments in a predetermined sequence; and (7) moving the deposition device and the work surface relative to each other in response to these programmed signals. Preferably, the system is also operated to generate a support structure for any un-supported feature of the 3-D preform shape.

Yang, Junsheng↗