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At least 289 records · Page 16

All sources NASA NTRS DOE OSTI

NASA NTRS1974

Quantum mechanical streamlines. I - Square potential barrier

Exact numerical calculations are made for scattering of quantum mechanical particles hitting a square two-dimensional potential barrier (an exact analog of the Goos-Haenchen optical experiments). Quantum mechanical streamlines are plotted and found to be smooth and continuous, to have continuous first derivatives even through the classical forbidden region, and to form quantized vortices around each of the nodal points. A comparison is made between the present numerical calculations and the stationary wave approximation, and good agreement is found between both the Goos-Haenchen shifts and the reflection coefficients. The time-independent Schroedinger equation for real wavefunctions is reduced to solving a nonlinear first-order partial differential equation, leading to a generalization of the Prager-Hirschfelder perturbation scheme. Implications of the hydrodynamical formulation of quantum mechanics are discussed, and cases are cited where quantum and classical mechanical motions are identical.

Hirschfelder, J. O.↗

NASA NTRS1976

Resizing procedure for optimum design of structures under combined mechanical and thermal loading

An algorithm is reported for resizing structures subjected to combined thermal and mechanical loading. The algorithm is applicable to uniaxial stress elements (rods) and membrane biaxial stress members. Thermal Fully Stressed Design (TFSD) is based on the basic difference between mechanical and thermal stresses in their response to resizing. The TFSD technique is found to converge in fewer iterations than ordinary fully stressed design for problems where thermal stresses are comparable to the mechanical stresses. The improved convergence is demonstrated by example with a study of a simplified wing structure, built-up with rods and membranes and subjected to a combination of mechanical loads and a three dimensional temperature distribution.

Adelman, H. M.↗

NASA NTRS1975

Fracture mechanics correlation of boron/aluminum coupons containing stress risers

The mechanical behavior of boron/aluminum near stress risers has been studied and reported. This effort was directed toward defining the tensile behavior of both unidirectional and (0/ plus or minus 45) boron/aluminum using linear elastic fracture mechanics (LEFM). The material used was 5.6-mil boron in 6061 aluminum, consolidated using conventional diffusion bonding techniques. Mechanical properties are reported for both unidirectional and (0/ plus or minus 45) boron/aluminum, which serve as control data for the fracture mechanics predictions. Three different flawed specimen types were studied. In each case the series of specimens remained geometrically similar to eliminate variations in finite size correction factors. The fracture data from these tests were reduced using two techniques. They both used conventional LEFM methods, but the existence of a characteristic flaw was assumed in one case and not the other. Both the data and the physical behavior of the specimens support the characteristic flaw hypothesis. Cracks were observed growing slowly in the (0/ plus or minus 45) laminates, until a critical crack length was reached at which time catastrophic failure occurred.

Adsit, N. R.↗

NASA NTRS1977

Opto-mechanical subsystem with temperature compensation through isothemal design

An opto-mechanical subsystem for supporting a laser structure which minimizes changes in the alignment of the laser optics in response to temperature variations is described. Both optical and mechanical structural components of the system are formed of the same material, preferably beryllium, which is selected for high mechanical strength and good thermal conducting qualities. All mechanical and optical components are mounted and assembled to provide thorough thermal coupling throughout the subsystem to prevent the development of temperature gradients.

Goodwin, F. E.↗

NASA NTRS1977

Mechanical processess affecting differentiation of protolunar material

Mechanisms prior to lunar formation are sought to account for the loss of volatiles, the depletion of iron, and the enrichment of plagioclase. Some of the same mechanisms are necessary to account for achondritic, stony-iron, and iron meteorites. Collisions seem marginally capable of providing the heat to accomplish the differentiation into iron, magnesian silicates, and plagioclase. Once this differentiation is accomplished, the subsequent mechanical history should have been sufficient to sort material according to composition in the protolunar circumterrestrial cloud. Effects operating include the correlation of body size with mechanical strength; the lesser ability of the cloud to trap the larger, denser infalling bodies; the more rapid drawing into the Earth of the larger moonlets; and the higher energy orbits for dominantly plagioclase smaller pieces broken off by collision.

Kaula, W. M.↗

NASA NTRS1977

Fly-away restraint pin mechanism for the Army's PATRIOT missile system

The development of the longitudinal restraint mechanism for the PATRIOT missile system is reviewed. Two approaches for the restraint pin design are discussed: an initial ordnance mechanism, and a passive fly-away mechanism. Because of reliability problems and a desire to reduce cost the fly-away restraint mechanism was chosen.

Knight, F. W.↗

NASA NTRS1978

Impetus of composite mechanics on test methods for fiber composites

Significant contributions of the three major areas of composite mechanics to the development of test methods are illustrated with selected examples. The areas of composite mechanics include composite micromechanics, composite macromechanics, and laminate theory. The examples can be considered to be representative of the contribution of composite mechanics to the development of composite test methods. The specific examples describe contributions such as criteria for selecting resin matrices for improved composite strength, the 10 deg off-axis tensile test, procedures for configuring hybrids, and the concept of 'reduced bending rigidities'. The pertinent composite mechanics equations associated with each contribution are given and supplemented by tabular and/or graphical data which illustrate the significance of the contribution.

Chamis, C. C.↗

NASA NTRS1978

Lubrication and failure mechanisms of molybdenum disulfide films. 2: Effect of substrate roughness

An optical microscope was used to study the lubrication and failure mechanisms of rubbed MoS2 films applied to three substrate surface finishes; polished, sanded, and sandblasted as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrate was rough, flat plateaus were created during run-in and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and as deposit sites for wear debris. In moist air the failure mechanism was the transformation of metallic colored MoS2 films to a black, powdery material that was found by X-ray diffraction to be alpha iron, MoO3, and possibly FeMoO3. In dry argon the failure mechanism was the gradual depletion of MoS2 from the contact region by transverse flow, and the wear debris on the track at failure was alpha iron, residual MoS2, and possibly FeS.

Fusaro, R. L.↗

NASA NTRS1979

Tests of a protective shell passive release mechanism for hypersonic wind-tunnel models

A protective shell mechanism for wind tunnel models was developed and tested. The mechanism is passive in operation, reliable, and imposes no new structural design changes for wind tunnel models. Methods of predicting the release time and the measured loads associated with the release of the shell are given. The mechanism was tested in a series of wind tunnel tests to validate the removal process and measure the pressure loads on the model. The protective shell can be used for wind tunnel models that require a step input of heating and loading such as a thin skin heat transfer model. The mechanism may have other potential applications.

Puster, R. L.↗

NASA NTRS1979

Mechanical property degradation of graphite/polyimide composites after exposure to moisture or shuttle orbiter fluids

The effects of moisture exposure on the mechanical properties of graphite polyimide systems are presented. The mechanism of the degradation and the magnitude of the affect associated with specific mechanical properties is investigated. An experimental effort involving exposure to selected environmental variables and subsequent mechanical property testing and analysis is included.

Lisagor, W. B.↗

NASA NTRS1979

Mechanics of intraply hybrid composites - Properties, analysis and design

A mechanics theory is developed for predicting the physical thermal, hygral and mechanical properties (including various strengths) of unidirectional intraply hybrid composites (UIHC) based on unidirectional properties of the constituent composites. Procedures are described which can use this theory in conjunction with composite mechanics computer codes and general purpose structural analysis finite element programs for the analysis/design of structural components made from intraply hybrid angleplied laminates (IHAL). Comparisons with limited data show that this theory predicts mechanical properties of UIHC and flexural stiffnesses of IHAL which are in good agreement with experimental data. The theory developed herein makes it possible to design and optimize structural components from IHAL based on a large class of available constituent fibers.

Chamis, C. C.↗

NASA NTRS1980

Mechanisms of UK radiometers flown on Nimbus 5 and 6 with particular reference to bearings, pivots and lubrication

The mechanisms incorporated in the vertical sounding infrared radiometry experiments which were launched on Nimbus 5 in 1972 and on Nimbus 6 in 1975 are discussed. Both use dry lubricants. The Nimbus 5 radiometer includes a rotating chopper driven via a carbon fiber-acetal resin gearwheel. The driving motor runs at 2000 rpm and has completed over 7 x 10 to the 9th power revolutions. Four gear driven filter wheels powered by stepper motors have each completed 2 x 10 to the 8th power changes. The input calibration mirror mechanism and its field of view compensation mechanisms are also described. All 25 ball races used in the experiment are of the film transfer type. The Nimbus 6 radiometer includes two cells. Each contains a piston supported on diaphragm springs and driven electromagnetically. The pistons are 6 cm in diameter with a stroke of 1 cm and are driven at their mechanical resonant frequency of approx. 15 Hz. The calibrating mirrors rotate periodically to view a target. The support pivots are synthetic sapphire ring stones with separate end thrust stones. The problems of mounting these stones to withstand vibration loads is described.

Hadley, H.↗

NASA NTRS1980

Mechanical energy output of the 5 September 1973 flare

The mechanical energy flux of observed macroscopic mass plasma motions in the solar flare of Sept. 5, 1973, is estimated. Consideration is given to the cool eruptive material in the eruptive filament and large surge as revealed by H alpha observations, the moving emission front seen in Ca II as well as H alpha, the piston-driven shock and mass ejection coronal transient observed in radio spectra and flare core motions, and mechanical energy estimates of 5.6 x 10 to the 29th to 8.9 x 10 to the 30th, 9.0 x 10 to the 29th, 2 x 10 to the 30th (thermal) and 10 to the 31st (magnetic), and 9 x 10 to the 24th erg are obtained, respectively, in agreement with previous estimates. It is concluded that the mechanical energy of large-scale mass motions dominates the radiative output of the flare by more than two orders of magnitude, and that a significant portion of the mechanical energy is in the form of magnetic flux delivered to interplanetary space.

Webb, D. F.↗

NASA NTRS1980

Effect of Substrate Surface Finish on the Lubrication and Failure Mechanisms of Molybdenum Disulfide Films

An optical microscope was used to study the lubrication and failure mechanisms of rubbed (burnished) MoS2 films applied to three substrate surface finishes - polished, sanded, and sandblasted - as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrates were rough, flat plateaus were created during 'run in' and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and a deposit site for wear debris. In moist air, the failure mechanism was the transformation of metallic colored MoS2 films to a black, powdery material that was found by X ray diffraction to consist primarily of alpha iron and MoO3 powders. In dry argon, the failure mechanism was the gradual depletion of the MoS2 film from the contact region by transverse flow. Analysis of the wear debris on the wear track at failure showed it consisted mainly of alpha iron and some residual MoS2. No molybdenum oxides were found.

Fusaro, R. L.↗

NASA NTRS1981

Drive mechanism for the shuttle orbiter/external tank propellant disconnect

The Space Shuttle design required development of a large, 0.43-m (17-in.) nominal diameter separable disconnect for the liquid hydrogen and liquid oxygen propellant lines at the orbiter-to-external-tank interface. The disconnect must provide for shutoff of the propellant flow area by simultaneous action of two rotary flapper valves (orbiter and external tank) prior to disconnect separation. In the case of pneumatic system failure, the rotary flapper valves are closed automatically through mechanical interlocking linkage during disconnect separation. The mechanism must meet requirements while accommodating changes in bearing clearances and linkage geometry over a wide temperature range from ambient to 20.37 K (-423°F). The mechanical design of the separable disconnect, kinematics of the drive mechanism, and the analysis and test methods used to verify proper operation and qualification for the Space Shuttle dynamic environments are presented.

E. Thomas↗

NASA NTRS1981

Effect of substrate surface finish on the lubrication and failure mechanisms of molybdenum disulfide films

An optical microscope was used to study the lubrication and failure mechanisms of rubbed (burnished) MoS2 films applied to three substrate surface finishes - polished, sanded, and sandblasted - as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrate was rough, flat plateaus were created during 'run-in' and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and a deposit site for wear debris. In moist air, the failure mechanism was the transformation of metallic-colored MoS2 films to a black, powdery material that was found by X-ray diffraction to consist primarily of alpha-iron and MoO3 powders. In dry argon, the failure mechanism was the gradual depletion of the MoS2 film from the contact region by transverse flow. Analysis of the wear debris on the wear track at failure showed it consisted mainly of alpha-iron and some residual MoS2. No molybdenum oxides were found.

Fusaro, R. L.↗

NASA NTRS1981

Aspects of the mechanisms of smoke generation by burning materials

An investigation of smoke generation during the burning of natural and synthetic solid materials (relevant to fire safety problems), under simulated fire conditions, is presented. Smoke formation mechanisms, including flaming and nonflaming combustion, are reviewed, and the complex physical, chemical, and electrical processes, important in smoke particulate production, are identified. With reference to the smoke formation mechanisms, measured experimental data are discussed, and include effects of ventilation gas temperature, dependence on material composition, and chemical analysis of smoke particulates. Significant differences in smoke characteristics are observed between flaming and nonflaming conditions, which is attributed to specific differences in controlling mechanisms and resultant ways leading to particulate formation. The effects of polymer substrate properties and effects of additives for a given substrate on smoke properties are also discussed in terms of basic processes. It is shown that many of the measured trends can be interpreted by considering postulated mechanisms of particulate formation.

Bankston, C. P.↗

NASA NTRS1981

Degradation Mechanisms in Aluminum Matrix Composites: Alumina/Aluminum and Boron/Aluminum

The effects of fabrication and long term thermal exposure (up to 10,000 hours at 590 K) on two types of aluminum matrix composites were examined. An alumina/aluminum composite, was made of continuous alpha Al2O3 fibers in a matrix of commercially pure aluminum alloyed with 2.8% lithium. The mechanical properties of the material, the effect of isothermal exposure, cyclic thermal exposure, and fatigue are presented. Two degradation mechanisms are identified. One was caused by formation of a nonstoichiometric alumina during fabrication, the other by a loss of lithium to a surface reaction during long term thermal exposure. The other composite, boron/aluminum, made of boron fibers in an aluminum matrix, was investigated using five different aluminum alloys for the matrices. The mechanical properties of each material and the effect of isothermal and cyclic thermal exposure are presented. The effects of each alloy constituent on the degradation mechanisms are discussed. The effects of several reactions between alloy constituents and boron fibers on the composite properties are discussed.

Olsen, G. C.↗