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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Creep fatigue life prediction for engine hot section materials (isotropic): Two year update

Requirements for increased durability of gas turbine hot section components have placed a greater degree of importance on accurate structural analysis and life prediction. Various life prediction approaches for high temperature applications were investigated. Basic models were selected and developed for simple-cycle, isothermal loading conditions. Models will be developed which address thermomechanical cycling, multiaxial conditions, cumulative loading, environmental effects, and cyclic mean stress. Verification tests of models will be conducted on an alternate material and coating system.

Moreno, V.↗
NASA NTRS1987

Strength characterization of yttria/alumina-doped sintered silicon nitride

The flexural strength of yttria/alumina-doped sintered silicon nitride (Ford Material-RM 20) was measured as a function of temperature (20 to 1400 deg C), applied stress and time. Flexural stress rupture testing at 800 and 1000 deg C indicated that the material can sustain 344 MPa and 276 MPa, respectively, without failure, for a limited time (less than or equal to 100 h). The RM 20 material was susceptible to both oxidation and early stages of creep deformation at temperatures above 1000 deg C and displayed extensive creep deformation and degradation in strength above 1300 deg C.

Govila, R. K.↗
NASA NTRS1988

Elevated temperature durability of ceramic materials

Fast fracture, stress rupture, and cyclic high temperature durability characterizations have been conducted for advanced silicon carbide and silicon nitride ceramics applicable to gas turbine hot section components. The fast fracture and stress rupture tests were conducted in four-point flexure at temperatures of up to 1540 C; the durability tests involved cycling specimens to temperatures of 1370 C and air quenching at 200 C for up to 3500 hrs. Materials with further reliability improvements are noted to be required for gas turbine hot section component applications.

Lindberg, Laura J.↗
NASA NTRS1989

Fracture characteristics of balloon films

An attempt was made to determine the failure modes of high altitude scientific balloons through an investigation of the fracture characteristics of the thin polyethylene films. Two films were the subject of the evaluation, Winzen Int.'s Stratafilm SF-85 and Raven Industries' Astro-E. Research began with an investigation of the film's cold brittleness point and it's effect on the ultimate strength and elasticity of the polyethylene film. A series of preliminary investigations were conducted to develop an understanding of the material characteristics. The primary focus of this investigation was on the notch sensitivity of the films. Simple stress strain tests were also conducted to enable analysis employing fracture toughness parameters. Studies were conducted on both film types at 23 C (room temperature), -60 C, -90 C, and -120 C.

Portanova, Marc A.↗
NASA NTRS1990

Dependence of the microwave radar cross section on ocean surface variables - Comparison of measurements and theory using data from the Frontal Air-Sea Interaction Experiment

The purpose of this investigation was to study the ability of theoretical radar cross section (RCS) models to predict the absolute magnitude of the ocean radar cross section under a wide variety of sea and atmospheric conditions. The dependence of the RCS on wind stress (as opposed to wind speed) was also studied. An extensive amount of experimental data was acquired during the Frontal Air-Sea Interaction Experiment. Measurements across an ocean front demonstrated that the vertical polarization and horizontal polarization radar cross section were more strongly dependent on wind stress than on wind magnitude. Current theoretical models for the RCS, based on stress, were tested with this data. In situations where the Bragg scattering theory does not agree with the measured radar cross section (magnitude and angle dependence), revisions are hypothesized and evaluated.

Weissman, David E.↗
NASA NTRS1953

Structural efficiencies of various aluminum, titanium, and steel alloys at elevated temperatures

Efficient temperature ranges are indicated for two high-strength aluminum alloys, two titanium alloys, and three steels for some short-time compression-loading applications at elevated temperatures. Only the effects of constant temperatures and short exposure to temperature are considered, and creep is assumed not to be a factor. The structural efficiency analysis is based upon preliminary results of short-time elevated-temperature compressive stress-strain tests of the materials. The analysis covers strength under uniaxial compression, elastic stiffness, column buckling, and the buckling of long plates in compression or in shear.

COLUMNS, STRUCTURAL↗
NASA NTRS1956

Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures

This report describes the results of a comprehensive study of plastic deformation of aluminum single crystals over a wide range of temperatures. The results of constant-stress creep tests have been reported for the temperature range from 400 degrees to 900 degrees F. For these tests, a new capacitance-type extensometer was designed. This unit has a range of 0.30 inch over which the sensitivity is very nearly linear and can be varied from as low a sensitivity as is desired to a maximum of 20 microinches per millivolt with good stability. Experiments were carried out to investigate the effect of small amounts of prestraining, by two different methods, on the creep and tensile properties of these aluminum single crystals. From observations it has been concluded that plastic deformation takes place predominantly by slip which is accompanied by the mechanisms of kinking and polygonization.

Johnson, R D↗
NASA NTRS1994

Evaluation of bonded boron/epoxy doublers for commercial aircraft aluminum structures

An 18 month laboratory test and stress analysis program was conducted to evaluate bonded boron/epoxy doublers for repairing cracks on aluminum aircraft structures. The objective was to obtain a core body of substantiating data which will support approval for use on commercial transports of a technology that is being widely used by the military. The data showed that the doublers had excellent performance.

Belason, Bruce↗
NASA NTRS1995

Operational characteristics of a 200 C LC parallel resonant circuit

Research efforts are currently underway at the NASA Lewis Research Center to design and demonstrate an inverter capable of operating with a baseplate temperature of 200 C. In support of this project, various electrical components including capacitors, inductors, transformers, cables, and semiconductor switches are being developed or evaluated for integration into the inverter. In this work, a parallel LC resonant circuit was constructed and evaluated under simultaneous electrical and thermal stressing. The tests were performed in the temperature range of 25 to 200 C with an applied voltage of up to 90 V, 20 kHz. The individual components were comprised of high temperature film capacitors and powder core inductors developed in-house. The circuit was characterized in terms of the component currents and case temperatures as well as frequency of resonance as a function of applied bias and temperature. The results obtained, which have indicated good functional stability up to 200 C, are presented and discussed.

Baumann, Eric D.↗
NASA NTRS1995

Bend Properties of Sapphire Fibers at Elevated Temperatures: Bend Survivability - 1

The effect of temperature on the bend radius that a c-axis-oriented sapphire fiber can withstand was determined for fibers of various diameter. Bend stress rupture tests were performed for times of 1-100 h and temperatures of 300-1700 C. Fibers would survive the bend test undeformed, would fracture or would deform. The bend survival radius was determined to be the radius above which no fibers fractured or deformed for a given time-temperature treatment. It was found that the ability of fibers to withstand curvature decreases substantially with time and increasing temperature and that fibers of smaller diameter (46-83 micron) withstood smaller bend radii than would be expected from just a difference in fiber diameter when compared with the bend results of the fibers of large diameter (144 micron). This was probably due to different flaw populations, causing high temperature bend failure for the tested sapphire fibers of different diameters.

Morscher, Gregory N.↗
NASA NTRS1997

Time/Temperature Dependent Tensile Strength of SiC and Al2O3-Based Fibers

In order to understand and model the thermomechanical behavior of fiber-reinforced composites, stress-rupture, fast-fracture, and warm-up rupture studies were conducted on various advanced SiC and Al2O3-based fibers in the,temperature range from 20 to 1400 C in air as well as in inert environments. The measured stress-rupture, fast fracture, and warm-up rupture strengths were correlated into a single master time/temperature-dependent strength plot for each fiber type using thermal activation and slow crack growth theories. It is shown that these plots are useful for comparing and selecting fibers for CMC and MMC reinforcement and that, in comparison to stress rupture tests, the fast-fracture and warm-up tests can be used for rapid generation of these plots.

Yun, Hee Mann↗
NASA NTRS1998

Stressed-Oxidation Lifetime of Different SiC Fiber, CVI Matrix SiC Minicomposites in Air

The stressed-oxidation lifetime properties of several minicomposites composed of single fiber tows with a CVI SiC matrix were compared. The minicomposites were made up of Nicalon(Tm) and Hi-Nicalon(Tm) SiC fibers with carbon or BN interphases. Constant load stress-rupture tests were performed between 600 and 13000 C in air for all of the minicomposite systems. Cyclic load testing was performed on the Hi-Nicalon minicomposite systems. The factors controlling the different lifetime behaviors: fiber rupture properties, interphase oxidation, fiber degradation, and fiber-matrix bonding, are discussed in light of different minicomposite constituents. All of the systems were subject to intermediate temperature embrittlement. The Hi-Nicalon fiber, BN interphase system, performed the best for constant load conditions. For cyclic load conditions, both the BN- interphase and C-interphase minicomposites displayed poor, but different failure behavior.

Morscher, Gregory N.↗
NASA NTRS2000

Slow Crack Growth Behavior and Life/Reliability Analysis of 96 wt % Alumina at Ambient Temperature With Various Specimen/Loading Configurations

Extensive constant stress-rate testing for 96 wt % alumina was conducted in room-temperature distilled water using four different specimen/loading configurations: rectangular beam test specimens under four-point uniaxial flexure, square plate test specimens in ring-on-ring biaxial flexure, square plate test specimens in ball-on-ring biaxial flexure, and dog-boned tensile test specimens in pure tension. The slow crack growth (SCG) parameter n was almost independent of specimen/loading configurations, in either four-point uniaxial flexure, ring-on-ring biaxial flexure, ball-on-ring biaxial flexure, or pure tension, ranging from n = 35 to 47 with an average value of n = 41.1 +/- 4.5. The prediction of fatigue strength/reliability based on the four-point uniaxial flexure data by using the CARES/Life design code as well as a simple PIA model was in good agreement with both the ring-on-ring biaxial and the ball-on-ring biaxial flexure data. A poor prediction using the PIA model was observed for the dog-boned tensile test specimens, presumably due to different flaw population involved in the tensile test specimens.

Choi, Sung R.↗
NASA NTRS2004

Effect of gravity on the caloric stimulation of the inner ear

Robert Barany won the 1914 Nobel Prize in medicine for his convection hypothesis for caloric stimulation. Microgravity caloric tests aboard the 1983 SpaceLab 1 mission produced nystagmus results that contradicted the basic premise of Barany's convection theory. In this paper, we present a fluid structural analysis of the caloric stimulation of the lateral semicircular canal. Direct numerical simulations indicate that on earth, natural convection is the dominant mechanism for endolymphatic flow. However, in the microgravity environment of orbiting spacecraft, where buoyancy effects are mitigated, an expansive convection becomes the sole mechanism for producing endolymph motion and cupular displacement. Transient 1 g and microgravity case studies are presented to delineate the different dynamic behaviors of the 1 g and microgravity endolymphatic flows. The associated fluid-structural interactions are also analyzed based on the time evolution of cupular displacements.

Labyrinth/anatomy & histology/physiology↗
NASA NTRS2003

Oxidation of Carbon Fibers in Water Vapor Studied

T-300 carbon fibers (BP Amoco Chemicals, Greenville, SC) are a common reinforcement for silicon carbide composite materials, and carbon-fiber-reinforced silicon carbide composites (C/SiC) are proposed for use in space propulsion applications. It has been shown that the time to failure for C/SiC in stressed oxidation tests is directly correlated with the fiber oxidation rate (ref. 1). To date, most of the testing of these fibers and composites has been conducted in oxygen or air environments; however, many components for space propulsion, such as turbopumps, combustors, and thrusters, are expected to operate in hydrogen and water vapor (H2/H2O) environments with very low oxygen contents. The oxidation rate of carbon fibers in conditions representative of space propulsion environments is, therefore, critical for predicting component lifetimes for real applications. This report describes experimental results that demonstrate that, under some conditions, lower oxidation rates of carbon fibers are observed in water vapor and H2/H2O environments than are found in oxygen or air. At the NASA Glenn Research Center, the weight loss of the fibers was studied as a function of water pressure, temperature, and gas velocity. The rate of carbon fiber oxidation was determined, and the reaction mechanism was identified.

Opila, Elizabeth J.↗
NASA NTRS2006

Effect of 16-Day Spaceflight on the Morphology of Thick-Toed Geckos (Pachydactylus Bibronii Smith, 1846)

There are grounds to believe that space flown experiments on thick-toed geckos may help solve the problem of floatation of vertebrates in microgravity. Geckos of this species carry on the lower surface of their toes numerous setae, which allow them to remain attached to any surfaces regardless of the gravitational effects. Experiments were performed on 5 animals in each of the following groups: flight, basal, synchronous and laboratory controls. 32 hours after a 16- day flight the animals were euthanazed and examined using traditional histology and X-ray microtomography. Body mass losses were 10% in the flight animals, 7.4% in the synchronous controls, and 12.3% in the laboratory controls. Since the flight and synchronous animals were kept at 15-19 C, whereas the laboratory controls - at 26-28 C, it can be inferred that environmental temperatures impacted animal metabolism no less than flight induced stress. Blood tests of the flown animals showed a 12% decrease of erythrocytes and a 40% decrease of dark-nuclear granulocytes, with the number of light-nuclear granulocytes remaining unchanged. In the small intestine the number of goblet cells increased allowing them to occupy a large portion of the cyptal surface. Enhanced secretion was accompanied by the appearance of dead intestinal cells in the lumen. Clusters of degraded hepatocytes were found at the liver edges of flight animals. Signs of liver involution were similar to the changes produced by alcohol consumption but did not spread to its central part. In the heart, insignificant hypertrophy and excessive blood supply that still remained within the physiological norm were detected. No significant changes were found in the pancreas, lungs, nervous systems or the snouts of the flown animals, but the volume of their gallbladders was greater than in controls. The epithelium of toe pads of the flight animals became thinner. Histological examination of the humerus did not demonstrate significant mineral losses. However, X-ray microtomography showed changes in the trabecular structure in the subepyphyseal zone of bones in flight animals compared to the controls. In summary, all the changes detected in the flight animals were adaptive. Therefore, geckos of this species can be used as an animal model for morphological studies in longer-duration space flights.

Gulimova, V. I.↗
NASA NTRS2008

Low-Cost, Large C-SiC Blisk Fabrication

C-SiC composites offer unique properties for propulsion applications. However, fabrication of low-cost, thick, large scale C-SiC disk for integrally bladed disk (blisk) applications has not been established yet. MER has demonstrated a new process to address this issue. Polymer-based processing was employed for interfacial coatings, consolidation and densification. Up to 40" O.C., 2" thick C-SiC composite processing was established, yielding in excess of 1.8 g/cu cm density. Computer tomography (CT) scans on the 40" O.D., 2" thick C-SiC disk showed no visible delamination, and good density uniformity. Stress-rupture testing in air was conducted at 2200 F, 2400 F and 2550 F.

Kowbel, W.↗