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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Durability of foam insulation for LH2 fuel tanks of future subsonic transports

In connection with the potential short-supply of petroleum based fuels, NASA has initiated investigations concerning the feasibility of aircraft using as fuel hydrogen which is to be stored in liquid form. One of the problems to be solved for an operation of such aircraft is related to the possibility of a suitable storage of the liquid hydrogen. A description is presented of an experimental study regarding the suitability of commercially available organic foams as cryogenic insulation for liquid hydrogen tanks under extensive thermal cycling typical of subsonic airline type operation. Fourteen commercially available organic foam insulations were tested. The thermal performance of all insulations was found to deteriorate with increased simulated flight cycles. Two unreinforced polyurethane foams survived over 4200 thermal cycles (representative of approximately 15 years of airline service) without evidence of structural deterioration. The polyurethane foam insulations also exhibited excellent thermal performance.

Sharpe, E. L.↗
NASA NTRS1978

A low cost, durable anti-reflective film for solar collectors

The physics of reflection reduction by thin films is briefly reviewed. Current techniques for the production of anti-reflective coatings are surveyed with respect to their applicabilities to solar panel covers. Techniques for the production of suitable anti-reflection coatings based on acid-hardened sodium silicate solutions are presented along with optical data for both acid-leached and silicate coatings

Pastirik, E. M.↗
NASA NTRS1979

Durability of foam insulation for LH2 fuel tanks of future subsonic transports

Organic foams were tested to determine their suitability for insulating liquid hydrogen tanks of subsonic aircraft. The specimens, including nonreinforced foams and foams with chopped glass reinforcements, flame retardants, and vapor barriers, were scaled to simulate stress conditions in large tanks. The tests were conducted within aluminum tank compartments filled with liquid hydrogen and the boil-off rate was used as the criterion of thermal performance. It was found that while all insulations deteriorated with increased cycles, two nonreinforced polyurethane foams showed no structural deterioration after 4200 thermal cycles (equivalent to 15 years of airline service). It was also found that fiberglass reinforcement and flame retardants impaired thermal performance and reduced useful life of the foams. Vapor barriers enhanced structural integrity without any deterioration in thermal properties.

Sharpe, E. L.↗
NASA NTRS1981

Turbine blade tip durability analysis

An air-cooled turbine blade from an aircraft gas turbine engine chosen for its history of cracking was subjected to advanced analytical and life-prediction techniques. The utility of advanced structural analysis techniques and advanced life-prediction techniques in the life assessment of hot section components are verified. Three dimensional heat transfer and stress analyses were applied to the turbine blade mission cycle and the results were input into advanced life-prediction theories. Shortcut analytical techniques were developed. The proposed life-prediction theories are evaluated.

Mcknight, R. L.↗
NASA NTRS1981

Advanced oxide dispersion strengthened sheet alloys for improved combustor durability

Burner design modifications that will take advantage of the improved creep and cyclic oxidation resistance of oxide dispersion strengthened (ODS) alloys while accommodating the reduced fatigue properties of these materials were evaluated based on preliminary analysis and life predictions, on construction and repair feasibility, and on maintenance and direct operating costs. Two designs - the film cooled, segmented louver and the transpiration cooled, segmented twin Wall - were selected for low cycle fatigue (LCF) component testing. Detailed thermal and structural analysis of these designs established the strain range and temprature at critical locations resulting in predicted lives of 10,000 cycles for MA 956 alloy. The ODs alloys, MA 956 and HDA 8077, demonstrated a 167 C (300 F) temperature advantage over Hastelloy X alloy in creep strength and oxidation resistance. The MA 956 alloy was selected for mechanical property and component test evaluations. The MA 956 alloy was superior to Hastelloy X in LCF component testing of the film cooled, segmented louver design.

Henricks, R. J.↗
NASA NTRS1979

Study of fatigue durability of advanced composite materials under conditions of accelerated loading

The effect of temperature on the tension-tension fatigue life of the T300/5208 graphite/epoxy angle-ply laminate system was investigated in an effort to develop an acceptable and reliable method of accelerated loading. Typical S log sub 10 N curves were determined experimentally at 25 C, 75 C, and 115 C. The time-temperature superposition principle was employed to find the shift factors of uniaxial fatigue strength, and a general linear equation of S log sub 10 N for shifting purpose was established. The combined techniques of cyclic creep measurements and optical microscopy upon fatigue failure allow some assessment of the possible physical basis of S log 10 N curve shifting. Before fatigue, the laminates at all test temperatures and stress levels undergo a unique damage mechanism during fatigue loading. It is concluded that an accelerated loading method is feasible.

Shih, H. M.↗
NASA NTRS1982

Accelerated fatigue durability of a high performance composite

The fatigue behavior of multidirectional graphite-epoxy laminates was analyzed theoretically and experimentally in an effort to establish an accelerated testing methodology. Analysis of the failure mechanism in fatigue of the laminates led to the determination of the failure mode governing fracture. The nonlinear, cyclic-dependent shear modulus was used to calculate the changing stress field in the laminate during the fatigue loading. Fatigue tests were performed at three different temperatures: 25 C, 74 C, and 114 C. The prediction of the S-N curves was made based on the artificial static strength artificial static strength at a reference temperature and the fatigue functions associated with them. The prediction of an S-N curve at other temperatures was performed using shifting factors determined for the specific failure mode. For multidirectional laminates, different S-N curves at different temperatures could be predicted using these shifting factors. Different S-N curves at different temperatures occur only when the fatigue failure mode is matrix dominated. It was found that whenever the fatigue failure mode is fiber dominated, temperature, over the range investigated, had no influence on the fatigue life. These results permit the prediction of long-time, low temperature fatigue behavior from data obtained in short time, high temperature testing, for laminates governed by a matrix failure mode.

Rotem, A.↗
NASA NTRS1981

High temperature durable catalyst development

A program has been carried out to develop a catalytic reactor capable of operation in environments representative of those anticipated for advanced automotive gas turbine engines. A reactor consisting of a graded cell honeycomb support with a combination of noble metal and metal oxide catalyst coatings was built and successfully operated for 1000 hr. At an air preheat temperature of 740 K and a propane/air ratio of 0.028 by mass, the adiabatic flame temperature was held at about 1700 K. The graded cell monolithic reaction measured 5 cm in diameter by 10.2 cm in length and was operated at a reference velocity of 14.0 m/s at 1 atm. Measured NOx levels remained below 5 ppm, while unburned hydrocarbon concentrations registered near zero and carbon monoxide levels were nominally below 20 ppm.

Snow, G. C.↗
NASA NTRS1981

Photovoltaic module hot spot durability design and test methods

As part of the Jet Propulsion Laboratory's Low-Cost Solar Array Project, the susceptibility of fat-plate modules to hot-spot problems is investigated. Hot-spot problems arise in modules when the cells become back-biased and operate in the negative-voltage quadrant, as a result of short-circuit current mismatch, cell cracking or shadowing. The details of a qualification test for determining the capability of modules of surviving field hot-spot problems and typical results of this test are presented. In addition, recommended circuit-design techniques for improving the module and array reliability with respect to hot-spot problems are presented.

Arnett, J. C.↗
NASA NTRS1982

Turbine engine materials durability research

High temperature environmental attack of dollar intensive turbine components reduces turbine efficiency and can limit life. The mechanisms of alloy and coating attack and the effects of interaction with the environment on mechanical behavior. This base of understanding provides the foundation for developing life prediction methods and identifying strategies for controlling attack. Subjects discussed in detail include oxidation and new developments in thermal barrier coating research.

S. R. Levine↗
NASA NTRS1985

Designing for fiber composite structural durability in hygrothermomechanical environment

A methodology is described which can be used to design/analyze fiber composite structures subjected to complex hygrothermomechanical environments. This methodology includes composite mechanics and advanced structural analysis methods (finite element). Select examples are described to illustrate the application of the available methodology. The examples include: (1) composite progressive fracture; (2) composite design for high cycle fatigue combined with hot-wet conditions; and (3) general laminate design.

Chamis, C. C.↗
NASA NTRS1986

Digital Control of Durability-Testing Burner Rigs

Report describes hardware and software that implement hybrid digital control of two Jet A-1 fueled, mach-0.3 burners from startup to completion of preset number of hot-corrosion/flame-durability cycle tests of materials at 1,652 degree F (900 degree C). Surface temperatures controlled more precisely than before.

Deadmore, D. L.↗
NASA NTRS1985

Encapsulant selection and durability testing experience

The Flat Plate Solar Array Project (FSA) has established technically challenging cost and service life goals for photovoltaic modules. These goals are a cost of $70 sq m and an expected 30 years of service life in an outdoor weathering environment. out of the cost goal, $14 sq m is allocated for encapsulation materials, which includes the cost of a structural panel. At FSA's inception in 1975, the cumulative cost of encapsulation materials in popular use, such as room temperature vulcanized (RTV) silicones, aluminum panels, etc., greatly exceeded $14/sq m. Accordingly, it became necessary to identify and/or develop new materials and new material technologies to achieve the goals. Many of these new materials are low cost polymers that satisfy module engineering and encapsulation processing requirements but unfortunately are not intrinsically weather stable. This necessitates identifying lifetime and/or weathering deficiencies inherent in these low cost materials and developing specific approaches to enhancing weather stability.

Cuddihy, E. F.↗
NASA NTRS1985

Designing for fiber composite structural durability in hygrothermomechanical environments

A methodology is described which can be used to design/analyze fiber composite structures subjected to complex hygrothermomechanical environments. This methodology includes composite mechanics and advanced structural analysis methods (finite element). Select examples are described to illustrate the application of the available methodology. The examples include: (1) composite progressive fracture; (2) composite design for high cycle fatigue combined with hot-wet conditions; and (3) general laminate design.

Chamis, C. C.↗
NASA NTRS1987

More Durable Tracks for Heavy Vehicles

Tie bars instead of threaded fasteners make track throwing less likely. Proposed undercarriage for tank or bulldozer has flanged edges to prevent rocks and other road debris from getting caught in track drive and damaging or casting off track. Improved track has no threaded fasteners to be loosened by road shock and vibration. Continuous chain of floating guide bars articulated at web junctions. Pins replace bolted connections. Guide bars and flanges on vehicle keep out stones.

Collins, Earl R., Jr.↗
NASA NTRS1987

Design of Fiber Composites for Structural Durability

Hygrothermomechanical effects analyzed by computers. Computational methodology developed and available at NASA Lewis Research Center to design and analyze fiber-composite structures subjected to complex hygrothermomechanical environments. Includes composite mechanics and advanced finited-element structural-analysis methods. Methodology applied to such problems as progressive fracture of composite material, design of composite material for cycle fatigue combined with hot and wet conditions, and general composite-laminate configurations.

Chamis, Christos C.↗
NASA NTRS1986

On the thermal durability of solar prominences, or how to evaporate a prominence

The thermal disappearance of solar prominences under strong perturbations due to wave heating, Ohmic heating, viscous heating or conduction was investigated. Specifically, how large a thermal perturbation is needed to destroy a stable thermal equilibrium was calculated. It was found that the prominence plasma appears to be thermally very rugged. Its cold equilibrium may most likely be destroyed by either strong magnetic heating or conduction in a range of parameters which is relevant to flares.

Malherbe, J. M.↗