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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 127 records · Page 7

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NASA NTRS1983

A microprocessor-based position control system for a telescope secondary mirror

The pointing requirements for the Shuttle IR Telescope Facility (SIRTF), which consists of an 0.85-m cryogenically cooled IR telescope, call for an image stability of 0.25 arcsec. Attention is presently given to a microprocessor-based position control system developed for the control of the SIRTF secondary mirror, employing a special control law (to minimize energy dissipation), a precision capacitive position sensor, and a specially designed power amplifier/actuator combination. The microprocessor generates the command angular position and rate waveforms in order to maintain a 90 percent dwell time/10 percent transition time ratio independently of chop frequency or amplitude. Performance and test results of a prototype system designed for use with a demonstration model of the SIRTF focal plane fine guidance sensor are presented.

Lorell, K. R.↗

NASA NTRS2008

The Effects of Heat Treatment and Microstructure Variations on Disk Superalloy Properties at High Temperature

The effects of heat treatment and resulting microstructure variations on high temperature mechanical properties were assessed for a powder metallurgy disk superalloy LSHR. Blanks were consistently supersolvus solution heat treated and quenched at two cooling rates, than aged at varying temperatures and times. Tensile, creep, and dwell fatigue crack growth tests were then performed at 704 C. Gamma' precipitate microstructures were quantified. Relationships between heat treatment-microstructure, heat treatment-mechanical properties, and microstructure-mechanical properties were assessed.

Gabb, Timothy P.↗

NASA NTRS2019

Demonstration Testing for Ground Servicing of the Commercial Crew Vehicle Emergency Breathing Air Assembly

The new Commercial crew vehicle (CCV) Breathing Air Assembly (CEBAA) is a Composite Overwrapped Pressure Vessel (COPV) filled with high-pressure air, which is designed to provide portable emergency breathing air for up to five crew in the event of an ammonia leak aboard the International Space Station (ISS). Industrially, several common methods of delivering breathing air exist; however, ground processing constraints and flight requirements necessitate the more unusual approach of servicing a COPV with high purity gaseous nitrogen and oxygen serially to achieve a specific mixture of breathing air at approximately 4000 PSIA. A dwell period allows the gases to mix before sampling for composition verification. The novelty of this approach led to concerns about acceptable gas mixing and the ability to deliver accurate gas compositions. Tests examining mixing rate over a series of post-servicing dwell periods were conducted to determine the optimal time for achieving a homogeneous mixture. Further testing was conducted to examine process accuracy using temperature-pressure load criteria to target a specific concentration of oxygen and nitrogen. Test results show that while some stratification of nitrogen and oxygen was observed, a seven-day dwell is adequate time to achieve an acceptable level of mixing, and that existing ground support equipment can accurately service CEBAA COPVs to the required temperature, pressure and composition for flight.

Active Thermal↗

NASA NTRS2019

Demonstration Testing for Ground Servicing of the Commercial Crew Vehicle Emergency Breathing Air Assembly

The new Commercial crew vehicle (CCV) Emergency Breathing Air Assembly (CEBAA) is a Composite Overwrapped Pressure Vessel (COPV) filled with high-pressure air, which is designed to provide portable emergency breathing air for up to five crew in the event of an ammonia leak aboard the International Space Station (ISS). Industrially, several common methods of delivering breathing air exist; however, ground processing constraints and flight requirements necessitate the more unusual approach of servicing a COPV with high purity gaseous nitrogen and oxygen serially to achieve a specific mixture of breathing air at approximately 4000 PSIA. A dwell period allows the gases to mix before sampling for composition verification. The novelty of this approach led to concerns about acceptable gas mixing and the ability to deliver accurate gas compositions. Tests examining mixing rate over a series of post-servicing dwell periods were conducted to determine the optimal time for achieving a homogeneous mixture. Further testing was conducted to examine process accuracy using temperature-pressure load criteria to target a specific concentration of oxygen and nitrogen. Test results show that while some stratification of nitrogen and oxygen was observed, a seven-day dwell is adequate time to achieve an acceptable level of mixing, and that existing ground support equipment can accurately service CEBAA COPVs to the required temperature, pressure and composition for flight.

Active Thermal↗

NASA NTRS1980

Evaluation of the cyclic behavior of aircraft turbine disk alloys, part 2

Several nickel-base aircraft turbine disk superalloys were evaluated at 650 C for resistance to fatigue crack initiation and propagation under cyclic and cyclic/dwell conditions. Controlled strain low cycle fatigue (LCF) and controlled load crack propagation tests were performed and results utilized to provide a direct comparison among the alloys. Tests were performed on selected alloys to evaluate the effects of hold times, mean stresses, stress-dwell cycle types, inert environment, and contractor test methods. At the lower total strain ranges of interest, the alloys exhibited generally increasing initiation life with increasing tensile strength for both cyclic (0.33 Hz) and cyclic/dwell (900-sec hold per cycle) conditions. Rank order of the alloys by LCF initiation life changed substantially at higher strain ranges, approaching the rank order expected from monotonic tensile ductilities. The effect of the 900 sec (15 min) hold time fatigue life varied significantly from alloy to alloy. Generally, the higher-strength, finer-grained alloys exhibited more significant reductions in fatigue life due to the dwell. The effects of mean strain were found to be negligible and the effects of mean stress were pronounced. At high strain ranges the mean stress was near zero and did not contribute to reduction in life. At low strain ranges, however, mean stresses were large and significant reductions in LCF lives occurred.

Cowles, B. A.↗

NASA NTRS1983

VAS applications at Colorado State University

The application of the VAS program is outlined. The initial assessments of VAS radiometer and satellite performance were satisfactory; and VAS operations were smoothly carried out by the NESS SOCC and associated processing and retransmission facilities. The availability of advanced image processing systems, previous studies with the geosynchronous European Space Agency Meteorological Satellite (Meteosat), and the polar orbiter multichannel radiance data enabled the progress of the application. The VAS data are implemented as these data are received in the real time VISSR mode, and as dwell sounding (DS) and multispectral imaging (MSI) radiances on magnetic tapes.

Kruidenier, M.↗

NASA NTRS1992

A distributed clients/distributed servers model for STARCAT

STARCAT, the Space Telescope ARchive and CATalogue user interface has been along for a number of years already. During this time it has been enhanced and augmented in a number of different fields. This time, we would like to dwell on a new capability allowing geographically distributed user interfaces to connect to geographically distributed data servers. This new concept permits users anywhere on the internet running STARCAT on their local hardware to access e.g., whichever of the 3 existing HST archive sites is available, or get information on the CFHT archive through a transparent connection to the CADC in BC or to get the La Silla weather by connecting to the ESO database in Munich during the same session. Similarly PreView (or quick look) images and spectra will also flow directly to the user from wherever it is available. Moving towards an 'X'-based STARCAT is another goal being pursued: a graphic/image server and a help/doc server are currently being added to it. They should further enhance the user independence and access transparency.

Pirenne, B.↗

NASA NTRS1983

Low strain, long life creep fatigue of AF2-1DA and INCO 718

Two aircraft turbine disk alloys, GATORIZED AF2-DA and INCO 718 were evaluated for their low strain long life creep-fatigue behavior. Static (tensile and creep rupture) and cyclic properties of both alloys were characterized. The cntrolled strain LCF tests were conducted at 760 C (1400 F) and 649 C (1200 F) for AF2-1DA and INCO 718, respectively. Hold times were varied for tensile, compressive and tensile/compressive strain dwell (relaxation) tests. Stress (creep) hold behavior of AF2-1DA was also evaluated. Generally, INCO 718 exhibited more pronounced reduction in cyclic life due to hold than AF2-1DA. The percent reduction in life for both alloys for strain dwell tests was greater at low strain ranges (longer life regime). Changing hold time from 0 to 0.5, 2.0 and 15.0 min. resulted in corresponding reductions in life. The continuous cycle and cyclic/dwell initiation failure mechanism was predominantly transgranular for AF2-1DA and intergranular for INCO 718.

Thakker, A. B.↗

NASA NTRS2016

Viscoplastic Characterization of Ti-6-4: Experiments

As part of a continued effort to improve the understanding of material time-dependent response, a series of mechanical tests have been conducted on the titanium alloy, Ti-6Al-4V. Tensile, creep, and stress relaxation tests were performed over a wide range of temperatures and strain rates to engage various amounts of time-dependent behavior. Additional tests were conducted that involved loading steps, overloads, dwell periods, and block loading segments to characterize the interaction between plasticity and time-dependent behavior. These data will be used to characterize a recently developed, viscoelastoplastic constitutive model with a goal toward better estimates of aerospace component behavior, resulting in improved safety.

mechanical properties↗

NASA NTRS1985

Time composite sounding

In the time composite sounding mode, the Vertical Atmospheric Sounder (VAS) data is collected in a series of images of one spin each rather than in the dwell sound mode where single lines are repeatedly scanned. A drawback of the time composite method is temporal smearing of the data, but to compensate this there is also the chance that shifting cloud patterns will permit better spatial coverage. Time composite sounding was performed for a single case study, June 14, 1984. Four, ten minute single spin swaths were processed. The principal conclusion was that the time composite results were at least equivalent to the conventional dwell sounding results, despite the fact that compositing was done in a less than optimum way because of software limitations.

Hayden, C.↗

NASA NTRS1998

Liquid Motion Experiment Flight Test Results

The Liquid Motion Experiment (LME), designed to study the effects of liquid motion in rotating tanks, was flown on STS 84. LME was essentially a spin table that created a realistic nutation motion of scale-model tanks containing liquid. TWo spherical and two cylindrical transparent tanks were tested simultaneously, and three sets of such tanks were employed to vary liquid viscosity, fill level, and propellant management device (PMD) design. All the tanks were approximately 4.5 inches diameter. The primary test measurements were the radial and tangential torques exerted on the tanks by the liquid. Resonant frequencies and damping of the liquid oscillations were determined by sine sweep tests. For a given tank shape, the resonant frequency depended on fill level. For the cylindrical tanks, the resonances had somewhat different frequencies for the tangential axis (0.55 to 0.75 times spin rate) and the radial axis (0.73 to 0.78 times spin rate), and the tangential axis resonance agreed more closely with available analytical models. For the spherical tanks, the resonant frequencies were between 0.74 to 0.77 times the spin rate and were the same for the tangential and radial axes. The damping coefficients varied from about I% to 3% of critical, depending on tank shape, fill level, and liquid viscosity. 'Me viscous energy dissipation rates of the liquid oscillations were determined from sine dwell tests. The LME energy dissipation rates varied from 0.3 to 0.5 times the estimates obtained from scaling previous ground tests and spacecraft flight data. The PNDs sometimes enhanced the resonances and energy dissipation rates and sometimes decreased them, which points out the need to understand better the effects of PMD on liquid motion as a function of PMD and tank design.

Chato David J.↗

NASA NTRS1975

Modal test - Measurement and analysis requirements

Data from the Viking Orbiter Modal Test Program are used to illustrate modal test measurement and analysis requirements. The test was performed using a multiple shake dwell technique where data were acquired one channel at a time and recorded on paper tape. Up to ten shakers were used simultaneously, with a complete set of data consisting of 290 strain-gage readings and 125 accelerometer readings. The data analysis provided information sufficient to minimize errors in the data. The list of analyses in order of value is orthogonality, residual mass, frequency sweep, data checks to assure good test data, multilevel trends, global kinetic energy, and global strain energy.

Wada, B. K.↗

NASA NTRS2003

Heat Treatment Devices and Method of Operation Thereof to Produce Dual Microstructure Superalloys Disks

A heat treatment assembly and heat treatment methods are disclosed for producing different microstructures in the bore and rim portions of nickel-based superalloy disks, particu- larly suited for gas turbine applications. The heat treatment assembly is capable of being removed from the furnace and disassembled to allow rapid fan or oil quenching of the disk. For solutioning heat treatments of the disk, temperatures higher than that of this solvus temperature of the disk are used to produce coarse grains in the rim of each disk so as to give maximum creep and dwell crack resistance at the rim service temperature. At the same time, solution temperature lower than the solvus temperature of the disk are provided to produce fine grain in the bore of the disk so as to give maximum strength and low cycle fatigue resistance.

John Gayda↗

NASA NTRSDate not supplied

Investigation of Liquid Fuel Injection Processes in a Rotating Detonation Combustor using Megahertz Planar Laser-Induced Fluorescence Imaging

Direct imaging of liquid fuel injection is performed within an optically accessible rotating detonation combustor (RDC) using planar laser-induced fluorescence (PLIF) to spatio-temporally resolve the highly dynamic spray characteristics at rates up to 1 MHz. The RDC is operated on air and hydrogen to sustain a stable, cyclically propagating detonation wave with cycle periods of up to ∼250 μs. One of the hydrogen fuel injection sites is replaced with a liquid jet to introduce a diesel spray as a fuel surrogate to enable tracer-free fluorescence excitation using the 355 nm third-harmonic output of a burst-mode Nd:YAG laser. The time-resolved PLIF measurements reveal the evolution of the highly unsteady spray, including the dwell period after the arrival of the detonation wave, the jet recovery, breakup and entrainment into the supersonic crossflow of air, propagation into the detonation chamber, and interaction with the detonation wave. Following passage of the detonation wave, the spray characteristics reveal significant changes in the momentum flux ratio between the liquid and air streams, altering the jet trajectory and temporarily halting fuel delivery to the detonation channel. This temporary cessation of fuel spray injection into the combustor is quantified, along with the fill rate as a function of time. As the injection system recovers, the fuel spray eventually returns to a quasi-steady position prior to the arrival of the detonation wave, allowing qualitative comparisons with theoretical jet trajectories for a range of air mass-flux conditions. These data, enabled by ultra-high-speed PLIF imaging, represent some of the first detailed measurements for characterizing and quantifying the interactions of liquid jets and detonations in an operating RDC.

Propulsion↗

NASA NTRSDate not supplied

Investigation of Liquid Fuel Refill Dynamics in a Rotating Detonation Combustor using Megahertz Planar Laser-Induced Fluorescence

Propulsion↗

NASA NTRS1994

Microstructurally based variations on the dwell fatgue life of titanium alloy IMI 834

An experimental study was undertaken to determine the role of microstructure on the fatigue life reduction observed in titanium alloy IMI 834 under dwell loading conditions. The wave forms compared were a trapezoid with 15 and 30 second hold times at the maximum test load and a baseline, 10 Hertz, haversine. The stress ratio for both loading wave forms was 0.10. The fatigue loading of each specimen was conducted in a vacuum within a scanning electron microscope chamber which minimized the possibility that the laboratory environment would adversely affect the material behavior. Two microstructural conditions were investigated in the experimental program. The first involved standard 'disk' material with equiaxed alpha in a transformed beta matrix. The second material was cut from the same disk forging as the first but was heat treated to obtain a martensitic alpha prime microstructure. Tensile tests were performed prior to the onset of the fatigue loading portion of the study, and it was determined that the yield strengths of the specimens from both material conditions were within ten percent. The maximum fatigue loads were chosen to be 72 percent of the average yield strength for both materials as determined from the tensile tests. It was found that the cycles to failure from the 10 Hertz loading wave form were reduced by a factor of approximately five when the loading was changed to the trapezoidal wave form for the standard 'disk' material. The fatigue life reduction for the martensitic structure under identical test conditions was approximately 1.75. The improvement observed with the martensitic structure also was accompanied by an increase in overall fatigue life for the wave forms tested. This paper will review the results and conclusions of this effort.

Thomsen, Mark L.↗

NASA NTRS2003

The Effect of Stabilization Treatments on Disk Alloy CH98

Gas turbine engines for future subsonic transports will probably have higher pressure ratios which will require nickelbase superalloy disks with 1300 to 1400 F temperature capability. Several advanced disk alloys are being developed to fill this need. One of these, CH98, is a promising candidate for gas turbine engines and is being studied in NASA s Advanced Subsonic Technology (AST) program. For large disks, residual stresses generated during quenching from solution heat treatments are often reduced by a stabilization heat treatment, in which the disk is heated to 1500 or 1600 F for several hours followed by a static air cool. The reduction in residual stress levels lessens distortion during machining of disks. However, previous work on CH98 has indicated that stabilization treatments can also decrease creep capability. In this study, a systematic variation of stabilization temperature and time was investigated to determine its effect on 1300 F tensile and, more importantly, creep behavior. Dwell crack growth rates were also measured for selected stabilization conditions. As these advanced disk alloys may be given a supersolvus solution or a subsolvus solution heat treatment for a given application, it was decided that both options would be studied.

Gayda, John↗

NASA NTRS2013

Implementation of Speed Variation in the Structural Dynamic Assessment of Turbomachinery Flow-Path Components

During the design of turbomachinery flow path components, the assessment of possible structural resonant conditions is critical. Higher frequency modes of these structures are frequently found to be subject to resonance, and in these cases, design criteria require a forced response analysis of the structure with the assumption that the excitation speed exactly equals the resonant frequency. The design becomes problematic if the response analysis shows a violation of the HCF criteria. One possible solution is to perform "finite-life" analysis, where Miner's rule is used to calculate the actual life in seconds in comparison to the required life. In this situation, it is beneficial to incorporate the fact that, for a variety of turbomachinery control reasons, the speed of the rotor does not actually dwell at a single value but instead dithers about a nominal mean speed and during the time that the excitation frequency is not equal to the resonant frequency, the damage accumulated by the structure is diminished significantly. Building on previous investigations into this process, we show that a steady-state assumption of the response is extremely accurate for this typical case, resulting in the ability to quickly account for speed variation in the finite-life analysis of a component which has previously had its peak dynamic stress at resonance calculated. A technique using Monte Carlo simulation is also presented which can be used when specific speed time histories are not available. The implementation of these techniques can prove critical for successful turbopump design, as the improvement in life when speed variation is considered is shown to be greater than a factor of two.

Brown, Andrew M.↗