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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 NTRS1983

Stress studies in EFG

Stress distributions were calculated for a creep law to predict a rate of plastic deformation. The expected reduction in stresses is obtained. Improved schemes for calculating growth system temperature distributions were evaluated. Temperature field modeling examined the possibility of using horizontal temperature gradients to influence stress distribution in ribbon. The defect structure of 10 cm wide ribbon grown in the cartridge system was examined. A new feature is identified from an examination of cross sectional micrographs. It consists of high density dislocation bands extending through the ribbon thickness. A four point bending apparatus was constructed for high temperature study of the creep response of silicon, to be used to generate defects for comparison with as grown defects in ribbon. The feasibility of laser interferometric techniques for sheet residual stress distribution measurement is examined. The mathematical formalism for calculating residual stress from changes in surface topology caused by an applied stress in a rectangular specimen was developed, and the system for laser interferometric measurement to obtain surface topology data was tested on CZ silicon.

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NASA NTRS1987

Progress in optical strain measurement system development

A laser speckle strain measurement system has been built and tested for the NASA Lewis Research Center. The system is based on a speckle shift technique, which automatically corrects for error due to rigid body motion, and provides a near real time measure of strain. The first stage of a multiphase effort to develop an optical strain gauge capable of mapping in two dimensions the strain on the surface of a hot specimen is discussed. The objectives of this first phase have been to provide a noncontact, one-dimensional, differential strain gauge for experimental purposes, and to determine the maximum open air temperature limit of the system.

Lant, Christian T.↗

NASA NTRS1987

Optical strain measurement system development, phase 1

A laser speckle, differential strain measurement system was built and tested for future applications in hostile environments. One dimensional electronic correlation of speckle pattern movement allows a quasi-real time measure of strain. The system was used successfully to measure uniaxial strain reaching into plastic deformation of a test specimen, at temperatures ranging to 450 C. A resolution of 16 microstrain is given by the photodiode array sensor pitch and the specimen to sensor separation. The strain measurement limit of the gauge is determined by air density perturbations causing decorrelation of the reference and shifted speckle patterns, and may be improved by limiting convective flow in the immediate vicinity of the test specimen.

Lant, Christian T.↗

NASA NTRS1988

Study of optical output couplers for submillimeter wavelength backward-wave oscillators (BWO's)

The machining of slow wave structures for high frequency backward-wave oscillators (BWO) is extremely difficult beyond 1 THz. Recently a microfabrication technique using photolithography and ion-beam assisted etching has been used to construct a prototype BWO operating at 200 to 265 GHz. The output coupler for such tubes remains a problem. Waveguides do not exist or are very lossy at the frequencies of interest (300 to 2000 GHz). This paper discusses several scaled experiments of optical output couplers for submillimeter BWOs. Various designs of planar antennas (Vivaldi horns) and lens-feed systems (Hyperhemispherical lens) were constructed and tested between 20 and 100 GHz using a spectrum analyzer. The lens system was also tested at 337 GHz using a CO2 pumped FIR laser.

Cook, Jerry D.↗

NASA NTRS1989

Study of optical output couplers for submillimeter wavelength backward-wave oscillators (BWO's)

Several scaled experiments of optical output couplers for submillimeter backward-wave oscillators (BWOs). Various designs of planar antennas (Vivaldi horns) lens-feed systems (hyperhemispherical lens) were constructed and tested between 20 and 100 GHz using a spectrum analyzer. The lens system was also tested at 337 GHz using a CO2 pumped FIR laser. It is found that Vivaldi horns have unsatisfactory resonances, perhaps because the horns studied were relatively short. Several techniques to maximize and flatten the frequency response of these horns are presented. The results suggest that alternate coupling schemes are superior to Vivaldi horns.

Cook, Jerry D.↗

NASA NTRS1991

One GHz digitizer for space based laser altimeter

This is the final report for the research and development of the one GHz digitizer for space based laser altimeter. A feasibility model was designed, built, and tested. Only partial testing of essential functions of the digitizer was completed. Hybrid technology was incorporated which allows analog storage (memory) of the digitally sampled data. The actual sampling rate is 62.5 MHz, but executed in 16 parallel channels, to provide an effective sampling rate of one GHz. The average power consumption of the one GHz digitizer is not more than 1.5 Watts. A one GHz oscillator is incorporated for timing purposes. This signal is also made available externally for system timing. A software package was also developed for internal use (controls, commands, etc.) and for data communication with the host computer. The digitizer is equipped with an onboard microprocessor for this purpose.

Staples, Edward J.↗

NASA NTRS1992

The e-Beam Sustained Laser Technology for Space-based Doppler Wind Lidar

An overview is presented of GEC Avionics activities relating to the Spaceborne Doppler Wind Lidar. In particular, the results of design studies into the use of an e-beam sustained CO2 laser for spaceborne applications, and experimental work on a test bed system are discussed.

Brown, M. J.↗

NASA NTRS1992

Fiber optic-based laser vapor screen flow visualization systems for aerodynamic research in larger-scale subsonic and transonic wind tunnels

The design, installation, and application of the NASA laser vapor screen (LVS) flow visualization systems developed by 10-foot high speed tunnel and 8-foot transonic pressure tunnel are discussed. Sufficient quantity of water is injected into the wind tunnel diffuser section to increase the relative humidity and promote condensation of the water vapor in the flow field about the model. Vortex-dominated flows are illuminated with an intense sheet of laser light. Fiber optics are used to deliver the laser beam through the plenum shell that surrounds the test section of each facility and to the light sheet-generating optics positioned in the ceiling window of the test section. Operational experience indicates that fiber optic-based systems are safe, reliable, and capable of proving high-quality off-surface flow visualization in larger scale subsonic and transonic wind tunnels.

Erickson, Gary E.↗

NASA NTRS1993

Nondestructive analysis and development

This final report summarizes the achievements of project #4 of the NASA/UCF Cooperative Agreement from January 1990 to December 1992. The objectives of this project are to review NASA's NDE program at Kennedy Space Center (KSC) and recommend means for enhancing the present testing capabilities through the use of improved or new technologies. During the period of the project, extensive development of a reliable nondestructive, non-contact vibration technique to determine and quantify the bond condition of the thermal protection system (TPS) tiles of the Space Shuttle Orbiter was undertaken. Experimental modal analysis (EMA) is used as a non-destructive technique for the evaluation of Space Shuttle thermal protection system (TPS) tile bond integrity. Finite element (FE) models for tile systems were developed and were used to generate their vibration characteristics (i.e. natural frequencies and mode shapes). Various TPS tile assembly configurations as well as different bond conditions were analyzed. Results of finite element analyses demonstrated a drop in natural frequencies and a change in mode shapes which correlate with both size and location of disbond. Results of experimental testing of tile panels correlated with FE results and demonstrated the feasibility of EMA as a viable technique for tile bond verification. Finally, testing performed on the Space Shuttle Columbia using a laser doppler velocimeter demonstrated the application of EMA, when combined with FE modeling, as a non-contact, non-destructive bond evaluation technique.

Moslehy, Faissal A.↗

NASA NTRS1995

High-Temperature Optical Window Design

A high-temperature optical window is essential to the optical diagnostics of high-temperature combustion rigs. Laser Doppler velocimetry, schlieren photography, light sheet visualization, and laser-induced fluorescence spectroscopy are a few of the tests that require optically clear access to the combustor flow stream. A design was developed for a high-temperature window that could withstand the severe environment of the NASA Lewis 3200 F Lean Premixed Prevaporized (LPP) Flame Tube Test Rig. The development of this design was both time consuming and costly. This report documents the design process and the lessons learned, in an effort to reduce the cost of developing future designs for high-temperature optical windows.

Roeloffs, Norman↗

NASA NTRS1998

In-Space Transportation with Tethers

The annual report covers the research conducted on the following topics related to the use of spaceborne tethers for in-space transportation: ProSEDS tether modeling (current collection analyses, influence of a varying tether temperature); proSEDS mission analysis and system dynamics (tether thermal model, thermo-electro-dynamics integrated simulations); proSEDS-tether development and testing (tether requirements, deployment test plan, tether properties testing, deployment tests); and tethers for reboosting the space-based laser (mission analysis, tether system preliminary design, evaluation of attitude constraints).

Lorenzini, Enrico↗

NASA NTRS1998

Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier Coatings

Thick thermal barrier coating systems in a diesel engine experience severe thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) during engine operation. In this paper, the mechanisms of fatigue crack initiation and propagation in a ZrO2-8wt% Y2O3 thermal barrier coating, under simulated engine thermal LCF and HCF conditions, are investigated using a high power CO2 laser. Experiments showed that the combined LCF-HCF tests induced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. Lateral crack branching and the ceramic/bond coat interface delaminations were also facilitated by HCF thermal loads, even in the absence of severe interfacial oxidation. Fatigue damage at crack wake surfaces, due to such phenomena as asperity/debris contact induced cracking and splat pull-out bending during cycling, was observed especially for the combined LCF-HCF tests. It is found that the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. The failure associated with HCF process, however, is mainly associated with a surface wedging mechanism. The interaction between the LCF, HCF and ceramic coating creep, and the relative importance of LCF and HCF in crack propagation are also discussed based on the experimental evidence.

Zhu, Dongming↗

NASA NTRS2002

Exotic Molecules in Space: A Coordinated Astronomical Laboratory and Theoretical Study

This report details the work of NASA grant NAG5-9379 which is concerned with the discovery and characterization of new astrophysical molecules. Numerous papers have been or will be published on the laboratory detection of 21 molecules of astrophysical interest, nearly all not previously observed, and nearly all of astrophysical interest as plausible candidates for the interstellar gas and circumstellar shells. Also of interest include the laboratory detection of of optical molecular band exactly coinciding in frequency with the strongest and most widely studied optical diffuse interstellar band which remains an enigma in astrophysical spectroscopy. A new laser spectrometer has been developed and is now undergoing testing.

Thaddeus, Patrick↗

NASA NTRS2001

Membrane Vibration Studies Using a Scanning Laser Vibrometer

This paper summarizes on-going experimental work at NASA Langley Research Center to measure the dynamics of a 1.016 m (40 in.) square polyimide film Kapton membrane. A fixed fully automated impact hammer and Polytec PSV-300-H scanning laser vibrometer were used for non-contact modal testing of the membrane with zero-mass-loading. The paper discusses the results obtained by testing the membrane at various tension levels and at various excitation locations. Results obtained by direct shaker excitation to the membrane are also discussed.

Gaspar, James L.↗

NASA NTRS2003

Response Surface Methods for Spatially-Resolved Optical Measurement Techniques

Danehy, P. M.↗

NASA NTRS2003

Response Surface Methods For Spatially-Resolved Optical Measurement Techniques

Response surface methods (or methodology), RSM, have been applied to improve data quality for two vastly different spatially-resolved optical measurement techniques. In the first application, modern design of experiments (MDOE) methods, including RSM, are employed to map the temperature field in a direct-connect supersonic combustion test facility at NASA Langley Research Center. The laser-based measurement technique known as coherent anti-Stokes Raman spectroscopy (CARS) is used to measure temperature at various locations in the combustor. RSM is then used to develop temperature maps of the flow. Even though the temperature fluctuations at a single point in the flowfield have a standard deviation on the order of 300 K, RSM provides analytic fits to the data having 95% confidence interval half width uncertainties in the fit as low as +/- 30 K. Methods of optimizing future CARS experiments are explored. The second application of RSM is to quantify the shape of a 5-meter diameter, ultra-lightweight, inflatable space antenna at NASA Langley Research Center. Photogrammetry is used to simultaneously measure the shape of the antenna at approximately 500 discrete spatial locations. RSM allows an analytic model to be developed that describes the shape of the majority of the antenna with an uncertainty of 0.4 mm, with 95% confidence. This model would allow a quantitative comparison between the actual shape of the antenna and the original design shape. Accurately determining this shape also allows confident interpolation between the measured points. Such a model could, for example, be used for ray tracing of radio-frequency waves up to 95 GHz. to predict the performance of the antenna.

Danehy, P. M.↗

NASA NTRS2004

Controller of the Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna mission is a planned gravitational wave detector consisting of three spacecraft in heliocentric orbit. Laser interferometry is used to measure distance fluctuations between test masses aboard each spacecraft to the picometer level over a 5 million kilometer separation. The Disturbance Reduction System comprises the pointing and positioning control of the spacecraft, electrostatic suspension control of the test masses, and point-ahead and acquisition control. This paper presents a control architecture and design for the Disturbance Reduction System to meet the stringent pointing and positioning requirements. Simulations are performed to demonstrate the feasibility of the proposed architecture.

Hyde, T. T.↗

NASA NTRS2003

Spin Testing for Durability Began on a Self-Tuning Impact Damper for Turbomachinery Blades

NASA and Pratt & Whitney will collaborate under a Space Act Agreement to perform spin testing of the impact damper to verify damping effectiveness and durability. Pratt & Whitney will provide the turbine blade and damper hardware for the tests. NASA will provide the facility and perform the tests. Effectiveness and durability will be investigated during and after sustained sweeps of rotor speed through resonance. Tests of a platform wedge damper are also planned to compare its effectiveness with that of the impact damper. Results from baseline tests without dampers will be used to measure damping effectiveness. The self-tuning impact damper combines two damping methods-the tuned mass damper and the impact damper. It consists of a ball located within a cavity in the blade. This ball rolls back and forth on a spherical trough under centrifugal load (tuned mass damper) and can strike the walls of the cavity (impact damper). The ball s rolling natural frequency is proportional to the rotor speed and can be designed to follow an engine-order line (integer multiple of rotor speed). Aerodynamic forcing frequencies typically follow these engineorder lines, and a damper tuned to the engine order will most effectively reduce blade vibrations when the resonant frequency equals the engine-order forcing frequency. This damper has been tested in flat plates and turbine blades in the Dynamic Spin Facility. During testing, a pair of plates or blades rotates in vacuum. Excitation is provided by one of three methods--eddy-current engine-order excitation (ECE), electromechanical shakers, and magnetic bearing excitation. The eddy-current system consists of magnets located circumferentially around the rotor. As a blade passes a magnet, a force is imparted on the blade. The number of magnets used can be varied to change the desired engine order of the excitation. The magnets are remotely raised or lowered to change the magnitude of the force on the blades. The other two methods apply force to the rotating shaft itself at frequencies independent of the rotor speed. During testing, blade vibration is monitored with strain gauges and laser displacement probes.

Duffy, Kirsten↗