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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Mechanical end joint system for structural column elements

A mechanical end joint system, useful for the transverse connection of strut elements to a common node, comprises a node joint half with a semicircular tongue and groove, and a strut joint half with a semicircular tongue and groove. The two joint halves are engaged transversely and the connection is made secure by the inherent physical property characteristics of locking latches and/or by a spring-actioned shaft. A quick release mechanism provides rapid disengagement of the joint halves.

Bush, H. G.↗
NASA NTRS1981

A negative feedback mechanism for the long-term stabilization of the earth's surface temperature

It is suggested that the partial pressure of carbon dioxide in the atmosphere is buffered, over geological time scales, by a negative feedback mechanism, in which the rate of weathering of silicate minerals (followed by deposition of carbonate minerals) depends on surface temperature, which in turn depends on the carbon dioxide partial pressure through the greenhouse effect. Although the quantitative details of this mechanism are speculative, it appears able to partially stabilize the earth's surface temperature against the steady increase of solar luminosity, believed to have occurred since the origin of the solar system.

Walker, J. C. G.↗
NASA NTRS1980

Mode and mechanisms of plateau uplifts

The mode and mechanisms of plateau uplifts are reported, based on discussions which occurred as part of a conference on plateau uplifts sponsored by the Inter-Union Commission on Geodynamics and the Lunar and Planetary Institute. Major plateaus and high plains of the world are discussed with emphasis on the Colorado Plateau, which possesses a shield-like crust 45 km thick and occupies most of eastern Utah and parts of Colorado, Arizona, and New Mexico. Several uplift mechanisms are described, including thermal expansion due to a deep mantle plume or hot spot, and hydration reactions such as serpentinization. It is concluded that uplifts are most commonly associated with either subduction and its direct effects, or deep-seated thermal disturbances.

Mcgetchin, T. R.↗
NASA NTRS1981

Fracture and failure: Analyses, mechanisms and applications; Proceedings of the Symposium, Los Angeles, CA, March 17-20, 1980

Papers are presented on the application of fracture mechanics to spacecraft design, fracture control applications on the Space Shuttle reaction control thrusters, and an assessment of fatigue crack growth rate relationships for metallic airframe materials. Also considered are fracture mechanisms and microstructural relationships in Ni-base alloy systems, the use of surface deformation markings to determine crack propagation directions, case histories of metallurgical failures in the electronics industry, and a failure analysis of silica phenolic nozzle liners.

Tung, P. P.↗
NASA NTRS1981

An excitation mechanism for the free 'core nutation'

The earth is believed to possess a free nutational mode due to its rotating, elliptical, fluid core, with an eigenfrequency of approximately (1 + 1/460) cycle per sidereal day as seen from the sidereally rotating earth. This free 'core nutation' has not yet been undisputably observed. Furthermore, there has been considerable doubt that any known mechanism could excite this mode to an observable level. It is shown here that diurnal atmospheric and oceanic loading of the earth's surface provides an efficient excitation mechanism which depends critically on the physical damping of the mode. Possible effects of the mode on geodetic measurements are discussed. The effects of 'wobble' and 'nutation' on astrometric observations are also considered.

Sasao, T.↗
NASA NTRS1982

The mechanics of fatigue in composite laminates

A status report is presented for the development of the mechanics of fatigue in composite materials. A concensus is noted on the need to construct mechanics treatments on the basis of precisely defined damage states which are both characteristic of the material and independent of as many extensive variables, such as load history, as possible. This approach is in keeping with the use of a single crack as the characteristic damage state in homogeneous materials, which has provided a well defined and precise boundary value problem that can be used in the description and prediction of damaged material response. The utility of stress redistribution concepts in determining residual strength, stiffness, and life in composite laminates is also recognized.

Reifsnider, K. L.↗
NASA NTRS1982

Alterations in heat loss and heat production mechanisms in rat exposed to hypergravic fields

A review of studies investigating the thermal response of rats exposed to hypergravic fields well below maximum tolerance levels is presented. It is concluded that several lines of evidence indicate that the neural switching network for temperature regulation and cardiovascular channeling of blood flow is transiently affected during the first hour a rat is exposed to hypergravity. Moreover, even after one hour of exposure, when the core temperature has fallen several degrees, shivering and nonshivering thermogenesis are not fully activated. Only after prolonged exposure to hypergravic fields do heat production mechanisms recover sufficiently to bring the core temperature back to a normal level. Thus, the data indicate a more rapid recovery of effector mechanisms for heat loss than for heat production.

Horowitz, J. M.↗
NASA NTRS1980

Stress accumulated mechanisms on strike-slip faults

The tectonic framework causing seismicity on the San Andreas and North Anatolian faults can be understood in terms of plate tectonics. However, the mechanisms responsible for the distribution of seismicity in space and time on these faults are poorly understood. The upper part of the crust apparently behaves elastically in storing energy that is released during an earthquake. The relatively small distances from the fault in which stress is stored argue in favor of a plate with a thickness of 5-10 km. The interaction of this plate with a lower crust that is behaving as a fluid damps the seismic cycling in distances of the order of 10 km from the fault. Low measured heat flow also argues in favor of a thin plate with a low stress level on the fault. Future measurements of stress, strain, and heat flow should help to provide a better understanding of the basic mechanisms governing the behavior of strike-slip faults.

Turcotte, D. L.↗
NASA NTRS1984

Retention Mechanism for Spinning Objects

Mechanism enables controlled release of two rotating objects. Mechanism applicable to some kinds of motor starters, drive shafts, or other drive systems released while rotating.

Cloyd, R. A.↗
NASA NTRS1982

Influence of cobalt, tantalum, and tungsten on the microstructure and mechanical properties of superalloy single crystals

The influence of Co, Ta, and W on the microstructure and mechanical properties of nickel base super-alloy single crystals was investigated. A matrix of alloys was based on Mar-M 247 stripped of C, B, Zr, and Hf. The microstructures of the alloys were examined using optical and electron microscopy, phase extraction, X-ray diffraction, and differential thermal analysis. Tensile and creep-rupture tests were performed at 1000 C. An increase in tensile and creep strength resulted when Co was removed from alloys containing high refractory metal contents, but Co effects were negligible for alloys with lower refractory metal levels. In the composition range studied, W was more effective than Ta in increasing the creep resistance. The mechanical properties are discussed in relation to the microstructures of the alloys.

Nathal, M. V.↗
NASA NTRS1982

Mechanical properties of low tantalum alloys

The mechanical property behavior of equiaxed cast B-1900 + Hf alloy as a function of tantalum content was studied. Tensile and stress rupture characterization was conducted on cast to size test bars containing tantalum at the 4.3% (standard level), 2.2% and 0% levels. Casting parameters were selected to duplicate conditions used to prepare test specimens for master metal heat qualification. The mechanical property results as well as results of microstructural/phase analysis of failed test bars are presented.

Kortovich, C. S.↗
NASA NTRS1983

Dynamic Mechanical Properties of N-Phenylnadimide Modified PMR Polyimide Composites

The rheological behavior of newly developd Celion 6000/N-phenylnadimide modified PMR polyimide and PMR-15 composites was investigated. The dynamic mechanical properties were correlated with the structure of N-phenylnadimide modified PMR polyimides. The storage modulus (G'), loss modulus (G''), and loss tangent (tan delta) of four composite systems were measured over a temperature range from -150 to 400 C. Three well defined peaks were seen in the regions of 360, 100, and -120 C, corresponding to the alpha, beta, and gamma relaxations, respectively, of the matrix resins. The activation energies of the alpha, beta, and gamma relaxations were estimated to be 232, 60, and 14 kcal/mole, respectively, for PMR-15. Addition of N-phenylnadimide to the PMR-15 composition lowered the glass transition temperature and the activation energies of PMR-15 polyimide. The dynamic mechanical data appear to be consistent with the formation of a copolymer from N-phenylnadimide and a PMR-15 prepolymer.

Pater, R. H.↗
NASA NTRS1982

The effects of Ni, Mo, Ti and Si on the mechanical properties of Cr free Mn steel (Fe-25Mn-5Al-2C)

The FeMnAlC alloys may hold potential as Cr-free replacements for high strategic material iron base superalloys, but little is known about their intermediate temperature (650 C to 870 C) mechanical properties. The effects of alloying elements on the mechanical properties of model FeMnAlC alloys were studied. Results showed that modified FeMnAlC alloys had promising short term, intermediate temperature properties but had relatively poor stress rupture lives at 172 MPa and 788 C. Room temperature and 788 C tensile strength of FeMnAlC alloys were better than common cast stainless steels. Changes in room temperature tensile and 788 C tensile strength and ductility, and 788 C stress rupture life were correlated with changes in Ni, Mo, Ti, and Si levels due to alloying effects on interstitial carbon levels and carbide morphology. Fe-25Mn-5Al-2C had a very poor stress rupture life at 172 MPa and 788 C. Addition of carbide-forming elements improved the stress rupture life.

Schuon, S. R.↗
NASA NTRS1983

Polarizer mechanism for the space telescope faint object spectrograph

The polarizer mechanism for the Space Telescope Faint Object Spectrograph is described. This device will allow spectropolarimetric measurements of faint astronomical objects. The mechanism employs a unique arrangement to meet functional requirements in a compact package and with only one actuator. Detailed tolerance analysis and a variety of tests indicate that the polarizer is capable of accurate and reliable performance.

Thulson, M. D.↗
NASA NTRS1983

The evolution of a release-engage mechanism for use on the orbiter

The Release-Engage Mechanism (REM) is designed to secure a deployable payload in the orbiter during launch and to enable the payload to be released, deployed, and reattached for re-entry. This paper presents the following: (1) the initial design concepts of the Release-Engage Mechanism; (2) the problems encountered during assembly, (3) the abnormalities that occurred during vibration testing, (4) the incompatibility of the Remote Manipulator System and REM operation, and (5) the resulting modifications to the REM that assured its successful performance on two Shuttle flights.

Calvert, J.↗
NASA NTRS1983

A procedure for combining acoustically induced and mechanically induced loads (first passage failure design criterion)

The combined load statistics are developed by taking the acoustically induced load to be a random population, assumed to be stationary. Each element of this ensemble of acoustically induced loads is assumed to have the same power spectral density (PSD), obtained previously from a random response analysis employing the given acoustic field in the STS cargo bay as a stationary random excitation. The mechanically induced load is treated as either (1) a known deterministic transient, or (2) a nonstationary random variable of known first and second statistical moments which vary with time. A method is then shown for determining the probability that the combined load would, at any time, have a value equal to or less than a certain level. Having obtained a statistical representation of how the acoustic and mechanical loads are expected to combine, an analytical approximation for defining design levels for these loads is presented using the First Passage failure criterion.

Crowe, D. R.↗
NASA NTRS1983

Comparative evaluation of gas-turbine engine combustion chamber starting and stalling characteristics for mechanical and air-injection

The effectiveness of propellant atomization with and without air injection in the combustion chamber nozzle of a gas turbine engine is studied. Test show that the startup and burning performance of these combustion chambers can be improved by using an injection during the mechanical propellant atomization process. It is shown that the operational range of combustion chambers can be extended to poorer propellant mixtures by combined air injection mechanical atomization of the propellant.

Dyatlov, I. N.↗
NASA NTRS1982

Statistical mechanics of dilute liquid mixtures of He3 in He4

The Woo-Tan-Massey quantum-mechanical theory of dilute mixtures of He-3 in liquid He-4 is extended to incorporate superfluid flow. Then statistical-mechanical principles are employed to find explicit formulas for thermodyanmic and hydrodynamic properties of mixtures, such as internal energy, free energy, entropy, pressure, chemical potential, and normal-fluid and superfluid densities. This paper is the first in a planned series that applies methods originally developed for pure liquid He-4 to dilute mixtures as a means of establishing a comprehensive theory that includes a theoretical bridge between a microscopic description of the mixtures and a hydrodynamic two-fluid model. Ultimately effects of applied electric and magnetic fields on dilute solutions are also planned to be treated.

Jackson, H. W.↗