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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 253 records · Page 14

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NASA NTRS1982

Compression behavior of unidirectional fibrous composite

The longitudinal compression behavior of unidirectional fiber composites is investigated using a modified Celanese test method with thick and thin test specimens. The test data obtained are interpreted using the stress/strain curves from back-to-back strain gages, examination of fracture surfaces by scanning electron microscope, and predictive equations for distinct failure modes including fiber compression failure, Euler buckling, delamination, and flexure. The results show that the longitudinal compression fracture is induced by a combination of delamination, flexure, and fiber tier breaks. No distinct fracture surface characteristics can be associated with unique failure modes. An equation is described which can be used to extract the longitudinal compression strength knowing the longitudinal tensile and flexural strengths of the same composite system.

Sinclair, J. H.↗

NASA NTRS1982

Changes in the UV spectrum of HD 4174

It is noted that the symbiotic-like object HD 4174 (EG And) exhibits the optical spectrum of an M2 giant star, but also shows Balmer and nebular line emission. The first UV spectrum showed an intense far UV emission line spectrum typical of many symbiotic stars. A 470 day binary or pulsation period for this system, based on the changing strength and velocity of the H alpha emission. Preliminary indications are that the H alpha and far UV continuum are eclipsed near phase 0.6 (at maximum H alpha redshift), but that the correlation for the emission lines remains unclear and requires additional observations.

Stencel, R. E.↗

NASA NTRS1983

Compressive behavior of unidirectional fibrous composites

The longitudinal compressive behavior of unidirectional fiber composites was investigated by using the Illinois Institute of Technology Research Institute (IITRI) test method with thick and thin test specimens. The test data obtained are interpreted by means of stress/strain curves from back-to-back strain gages, examination of fracture surfaces by scanning electron microscope, and predictive equations for distinct failure modes including fiber compression failure. Euler buckling, delamination, and flexure. The results show that longitudinal compressive fracture is induced by a combination of delamination, flexure, and fiber tier breaks. No distinct fracture surface characteristics can be associated with unique failure modes. An equation is described that can be used to extract the longitudinal compressive strength from the longitudinal tensile and flexural strengths of the same composite system.

Sinclair, J. H.↗

NASA NTRS1985

Tethers for Mars space operations

A tether-mediated transport system is proposed in which mass may be transferred between the Martian surface, Mars orbit, and open space, using the orbital momentum of Phobos and Deimos. The performance and materials strength requirements of a prototype tether system are studied with attention given to: tether dynamics effects during different stages of operation; micrometeoroid impact effects; replacement of tether segments; and contingency methods in case of tether failure. A schematic diagram of the proposed tether transportation system is provided.

Penzo, P. A.↗

NASA NTRS1986

Some comments on passive microwave measurement of rain

It is argued that because microwave radiation interacts much more strongly with hydrometeors than with cloud particles, microwave measurements from space offer a significant chance of making global precipitation estimates. Over oceans, passive microwave measurements are essentially attenuation measurements that can be very closely related to the rain rate independently of the details of the drop-size distribution. Over land, scattering of microwave radiation by the hydrometeors, especially in the ice phase, can be used to estimate rainfall. In scattering, the details of the drop-size distribution are very important and it is therefore more difficult to achieve a high degree of accuracy. The SSM/I (Special Sensor Microwave Imager), a passive microwave imaging sensor that will be launched soon, will have dual-polarized channels at 85.5 GHz that will be very sensitive to scattering by frozen hydrometeors. Other sensors being considered for the future space missions would extend the ability to estimate rain rates from space. The ideal spaceborne precipitation-measurement system would use the complementary strengths of passive microwave, radar, and visible/infrared measurements.

Wilheit, Thomas T.↗

NASA NTRS1987

Chromospherically active stars. III - HD 26337 = EI Eri: An RS CVn candidate for the Doppler-imaging technique

Spectroscopic observations of the chromospherically active G5 IV single-lined binary HD 26337 = EI Eri are presented. An orbital period of 1.94722 days is found for the star. It has moderately strong Ca II H and K emission and strong ultraviolet emission features, while H-alpha is a weak absorption feature that is variable in strength. The inclination of the system is 46 + or - 12 deg, and the unseen secondary is probably a late K or early M dwarf. The v sin i of the primary is 50 + or - 3 km/s, resulting in a minimum radius of 1.9 + or - 0.1 solar radius. The star is within the required limits for Doppler imaging. The primary is close to filling its Roche lobe, resulting in a strong constraint that the mass ratio is 2.6 or greater, with a primary mass of at least 1.4 solar mass. The distance to the system is estimated at 75 pc.

Fekel, Francis C.↗

NASA NTRS1988

Flexibilized copolyimide adhesives

Two copolyimides, LARC-STPI and STPI-LARC-2, with flexible backbones were processed and characterized as adhesives. The processability and adhesive properties were compared to those of a commercially available form of LARC-TPI. Lap shear specimens were fabricated using adhesive tape prepared from each of the three polymers. Lap shear tests were performed at room temperature, 177 C, and 204 C before and after exposure to water-boil and to thermal aging at 204 C for up to 1000 hours. The three adhesive systems possess exceptional lap shear strengths at room temperature and elevated temperatures both before and after thermal exposure. LARC-STPI, because of its high glass transition temperature provided high lap shear strengths up to 260 C. After water-boil, LARC-TPI exhibited the highest lap shear strengths at room temperature and 177 C, whereas the LARC-STPI retained a higher percentage of its original strength when tested at 204 C. These flexible thermoplastic copolyimides show considerable potential as adhesives based on this study and because of the ease of preparation with low cost, commercially available materials.

Progar, Donald J.↗

NASA NTRS1988

NESSUS/EXPERT - An expert system for probabilistic structural analysis methods

An expert system (NESSUS/EXPERT) is presented which provides assistance in using probabilistic structural analysis methods. NESSUS/EXPERT is an interactive menu-driven expert system that provides information to assist in the use of the probabilistic finite element code NESSUS/FEM and the fast probability integrator. NESSUS/EXPERT was developed with a combination of FORTRAN and CLIPS, a C language expert system tool, to exploit the strengths of each language.

Millwater, H.↗

NASA NTRS1988

Models of the quasar population. II - The effects of dust obscuration

A model for dust obscuration is proposed to account for the apparent lack of high-redshift quasars which are assumed to be obscured by dust in intervening galaxies. The distribution function for the optical depth as a function of redshift is constructed and used to determine the expected properties of quasars. The apparent magnitude distribution at three points is used to fit the model. Optical results are given for the comoving number density, redshift distribution, and mean color excess. If the theory is correct, evidence for dust may be seen in quasar spectra and a correlation between quasar continuum slopes and strength of metal line absorption systems should be observed.

Heisler, Julia↗

NASA NTRS1989

A model for including thermal conduction in molecular dynamics simulations

A technique is introduced for including thermal conduction in molecular dynamics simulations for solids. A model is developed to allow energy flow between the computational cell and the bulk of the solid when periodic boundary conditions cannot be used. Thermal conduction is achieved by scaling the velocities of atoms in a transitional boundary layer. The scaling factor is obtained from the thermal diffusivity, and the results show good agreement with the solution for a continuous medium at long times. The effects of different temperature and size of the system, and of variations in strength parameter, atomic mass, and thermal diffusivity were investigated. In all cases, no significant change in simulation results has been found.

Wu, Yue↗

NASA NTRS1989

AMTEC recirculating test cell component testing and operation

Alkali metal thermoelectric converter operation in a recirculating test cell (RTC), which requires a small electromagnetic pump (EM) and a high-temperature beta-double-prime alumina-solid-electrolyte (BASE)-to-metal seal, is discussed. The design of a pump and an active metal braze seal and the initial operation of a cell using these components are described. The pump delivered 0.25 cu cm/min against a 28-psia head. A braze seal system was selected after shear strength tests of Ta or Nb brazed to BASE by a variety of fillers including TiCuNi, TiNi, and TiNiCr. The TiCuNi filler was chosen for environment cell testing and showed no failure or observable degradation after short-term tests up to 1055 K. The pump and the Nb/TiCuNi/BASE seal were used in a test that demonstrated all the operational functions of the RTC for the first time. An increase in the radiation reduction factor at constant input power was observed, indicating that the condenser was being wet by sodium resulting in an increased reflectivity.

Underwood, M. L.↗

NASA NTRS1993

Probabilistic material degradation under high temperature, fatigue, and creep

A methodology has been developed and embodied in two computer codes for quantitatively characterizing the material strength degradation of aerospace propulsion system structural components that are subjected to various random effects over the course of their service lives. The codes, PROMISS and PROMISC, constitute a material-resistance model that is used in the NESSUS aerospace structural-reliability program. NESSUS addresses the service life-reducing effects of high temperature, mechanical fatigue, and creep.

Boyce, L.↗

NASA NTRS1994

GPS tracking of TOPEX/POSEIDON: Results and implications

A reduced dynamic filtering strategy that exploits the unique geometric strength of the Global Positioning System (GPS) to minimize the effects of force model errors has yielded orbit solutions for TOPEX/POSEIDON which appear accurate to better than 3 cm (1 sigma) in the radial component. Reduction of model error also reduces the geographic correlation of the orbit error. With a traditional dynamic approach, GPS yields radial orbit accuracies of 4-5 cm, comparable to the accuracy delivered by satellite laser ranging and the Doppler orbitography and radio positioning integrated by satellite (DORIS) tracking system. A portion of the dynamic orbit error is in the Joint Gravity Model-2 (JGM-2); GPS data from TOPEX/POSEIDON can readily reveal that error and have been used to improve the gravity model.

Bertiger, W. I.↗

NASA NTRS2004

Vibration-Based Method Developed to Detect Cracks in Rotors During Acceleration Through Resonance

In recent years, there has been an increasing interest in developing rotating machinery shaft crack-detection methodologies and online techniques. Shaft crack problems present a significant safety and loss hazard in nearly every application of modern turbomachinery. In many cases, the rotors of modern machines are rapidly accelerated from rest to operating speed, to reduce the excessive vibrations at the critical speeds. The vibration monitoring during startup or shutdown has been receiving growing attention (ref. 1), especially for machines such as aircraft engines, which are subjected to frequent starts and stops, as well as high speeds and acceleration rates. It has been recognized that the presence of angular acceleration strongly affects the rotor's maximum response to unbalance and the speed at which it occurs. Unfortunately, conventional nondestructive evaluation (NDE) methods have unacceptable limits in terms of their application for online crack detection. Some of these techniques are time consuming and inconvenient for turbomachinery service testing. Almost all of these techniques require that the vicinity of the damage be known in advance, and they can provide only local information, with no indication of the structural strength at a component or system level. In addition, the effectiveness of these experimental techniques is affected by the high measurement noise levels existing in complex turbomachine structures. Therefore, the use of vibration monitoring along with vibration analysis has been receiving increasing attention.

Sawicki, Jerzy T.↗

NASA NTRS2006

Adaptive Engine Technologies for Aviation CO2 Emissions Reduction

Adaptive turbine engine technologies are assessed for their potential to reduce carbon dioxide emissions from commercial air transports.Technologies including inlet, fan, and compressor flow control, compressor stall control, blade clearance control, combustion control, active bearings and enabling technologies such as active materials and wireless sensors are discussed. The method of systems assessment is described, including strengths and weaknesses of the approach. Performance benefit estimates are presented for each technology, with a summary of potential emissions reduction possible from the development of new, adaptively controlled engine components.

Mercer, Carolyn R.↗

NASA NTRS2010

Robonaut 2 (R2) Overview

This slide presentation reviews the development and uses of the second robot designed to work in space. The presentation reviews the motivation for developing Robonaut, the cooperative commercial relationship with General Motors, the evolution design of Robonaut Robonaut 2 improvements over the first robonaut (R1), Robonaut 2's hand dexterity, finger impedance control, tactile system, finger haptics, arm control, strength, neck movement and head sensors, human interaction, and the controller. Also the plans for use on board the International Space Station are reviewed. The patent for the Phalange Tactile Load Cell is included.

Diftler, Myron↗

NASA NTRS2017

Proton Testing: Opportunities, Pitfalls and Puzzles

Although proton SEE testing can place constraints on some heavy-ion SEE susceptibilities, it is important to quantify residual risk that protons may not reveal all SEE susceptibilities in a system. We examine the relative strengths and limitations of proton and heavy-ion SEE testing and how these may be affected by technology scaling and high-Z materials in the device.

Protons↗

NASA NTRS2018

Robots and Robots and More

Over the course of this year I worked on several projects across different departments, from physical robots at Swamp Works, to automated robots running functional tests on launch critical Graphical User Interfaces (GUIs). My overarching project this year was designing a new automated testing framework. It began with becoming familiar with the existing automated testing framework, which used image matching to perform programmatic GUI testing. After writing a few dozen tests with the existing framework, I was able to identify the strengths and weaknesses of the system and begin the search for another tool to replace it. I ended up selecting an open source library, which I modified to fit both National Aeronautics and Space Administration (NASA) requirements and those of the specific Computer Software Configuration Item (CSCI) I worked on. After the new framework was feature-rich enough to meet the team requirements, I helped roll out the changes, managed the transition to the new framework, and directed continuing automation work in regards to the library. The result was a comprehensive new way of efficiently testing the GUI that was robust enough to handle small changes to the GUI itself. Additionally, for approximately six weeks I worked on rebuilding, repairing, and updating the software of four "Swarmie" robots for a NASA event. By the close of the six weeks, the four robots were operational and had improved obstacle detection software that solved a faulty stop signal issue that the robots were experiencing.

Siegel, Alex↗