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  • Other Sources  (1,588)
  • MECHANICAL ENGINEERING  (1,586)
  • Physics
  • 2005-2009  (2)
  • 1980-1984  (858)
  • 1975-1979  (728)
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  • 1
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    Volcanic inflation of Mount Hokkaido-Komagatake, Japan, determined from a dense Global Positioning System array (2005)
    In:  Geophys. Res. Lett., Amsterdam, Schweizerbart'sche Verlagsbuchhandlung, vol. 32, no. 20, pp. 693-711, pp. L20304, (ISSN 0016-8548, ISBN 3-510-50045-8)
    Details
    Publication Date: 2005
    Keywords: Volcanology ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Geodesy ; GRL ; 1036 ; Geochemistry: ; Magma ; chamber ; processes ; (3618) ; 8419 ; Volcanology: ; Volcano ; monitoring ; (7280) ; 8439 ; Physics ; and ; chemistry ; of ; magma ; bodies ; 8434 ; Magma ; migration ; and ; fragmentation
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Volcano-earthquake interaction at Mauna Loa volcano, Hawaii (2006)
    In:  J. Geophys. Res., Washington, D.C., AGU, vol. 111, no. B5, pp. 1669-1675, pp. B05204, (ISSN: 1340-4202)
    Details
    Publication Date: 2006
    Keywords: Volcanology ; Seismicity ; USA ; static ; elastic ; Stress ; JGR ; volcano ; spreading ; dike ; intrusion ; 8414 ; Volcanology: ; Eruption ; mechanisms ; and ; flow ; emplacement ; 8415 ; Intra-plate ; processes ; (1033, ; 3615) ; 8425 ; Effusive ; volcanism ; 8439 ; Physics ; and ; chemistry ; of ; magma ; bodies ; 8488 ; Volcanic ; hazards ; and ; risks ; TWALTER
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Impact tensile testing of wires (1976)
    In:  CASI
    Details
    Publication Date: 2006-08-09
    Description: The test consists of fixing one end of a wire specimen and allowing a threaded falling weight to strike the other. Assuming the dynamic stress in the wire to be a function only of its strain, energy considerations show for negligible wire inertia effects that the governing dynamic stress-strain law can be determined directly from impact energy vs. wire elongation data. Theoretical calculations are presented which show negligible wire inertia effects for ratios of wire mass to striking mass of the order of .01 or less. The test method is applied to soft copper wires and the dynamic stress-strain curve so determined is found to be about 30 percent higher than the corresponding static curve.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 1; p 319-326
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  • 4
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    Numerical determination of the transmissibility characteristics of a squeeze film damped forced vibration system (1976)
    In:  CASI
    Details
    Publication Date: 2006-08-09
    Description: Numerical solutions of the governing equations of motion of a liquid squeeze film damped forced vibration system were carried out to examine the feasibility of using a liquid squeeze film to cushion and protect large structures, such as buildings, located in areas of high seismic activity. The mathematical model used was that for a single degree of freedom squeeze film damped spring mass system. The input disturbance was simulated by curve fitting actual seismic data with an eleventh order Lagranging polynomial technique. Only the normal component of the seismic input was considered. The nonlinear, nonhomogeneous governing differential equation of motion was solved numerically to determine the transmissibility over a wide range of physical parameters using a fourth-order Runge-Kutta technique. It is determined that a liquid squeeze film used as a damping agent in a spring-mass system can significantly reduce the response amplitude for a seismic input disturbance.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 1; p 327-338
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  • 5
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    Experimental investigation of dynamic characteristics of turbine generators and low-tuned foundations (1979)
    In:  CASI
    Details
    Publication Date: 2006-07-02
    Description: Turbine generator (T-G) units with low tuned concrete foundations were investigated experimentally during both startup and normal operating conditions. The dynamic response of the turbine generators and their foundation systems were characterized by resonance curves obtained during the startup transient and by vibration mode shapes at the normal operating condition. No severe resonance at the fundamental frequencies of the system was observed. The deflection or displacement of the foundation pedestal does not lead to unacceptable T-G vibration. The experimental results are compared and discussed with some previous theoretical studies.
    Keywords: MECHANICAL ENGINEERING
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 3; p 69-77
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  • 6
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    Evaluation of rotor-bearing system dynamic response to unbalance (1979)
    In:  CASI
    Details
    Publication Date: 2006-07-02
    Description: The vibration environment within air conditioner rotating machinery referred to as an air cycle machine (ACM) was investigated to effectively increase ACM reliability. To assist in the selection of design changes which would result in improved ACM performance, various design modifications were incorporated into a baseline ACM configuration. For each design change, testing was conducted with the best balance achieveable (baseline) and with various degrees of unbalance. Relationships between unbalance (within the context of design changes) and the parameters associated with design goals were established. The results of rotor dynamics tests used to establish these relationships are presented.
    Keywords: MECHANICAL ENGINEERING
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 3; p 41-53
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  • 7
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    Improved techniques of parallel gap welding and monitoring (1984)
    In:  CASI
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    Publication Date: 2006-02-14
    Description: Welding programs which show that parallel gas welding is a reliable process are discussed. When monitoring controls and nondestructive tests are incorporated into the process, parallel gap welding becomes more reliable and cost effective. The panel fabrication techniques and the HAC thermal cycling test indicate reliable product integrity. The design and building of automated tooling and fixturing for welding are discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Space Photovoltaic Res. and Technol. 1983; p 228-234
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  • 8
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    Tribology (1982)
    In:  CASI
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    Publication Date: 2006-04-12
    Description: The adhesion, friction, and wear properties of materials are reviewed and some of the factors influencing these properties are discussed. The forms of lubrication and types of lubricants will also be discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Langley Research Center Advan. Mater. Technol.; p 391-410
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  • 9
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    Incipient failure detection (IFD) of SSME ball bearings (1982)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Because of the immense noise background during the operation of a large engine such as the SSME, the relatively low level unique ball bearing signatures were often buried by the overall machine signal. As a result, the most commonly used bearing failure detection technique, pattern recognition using power spectral density (PSD) constructed from the extracted bearing signals, is rendered useless. Data enhancement techniques were carried out by using a HP5451C Fourier Analyzer. The signal was preprocessed by a Digital Audio Crop. DAC-1024I noise cancelling filter in order to estimate the desired signal corrupted by the backgound noise. Reference levels of good bearings were established. Any deviation of bearing signals from these reference levels indicate the incipient bearing failures.
    Keywords: MECHANICAL ENGINEERING
    Type: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 20 p
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  • 10
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    A clamp mechanism for deployable three-ton payloads (1981)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: The requirements, capabilities, and unique design features of the instrument payload subsystem payload clamp assembly (PCA) are presented. The PCA is designed to have the flexibility to accommodate a wide payload range varying from 0.5 m to 3 m in diameter and from 500 kg to 3000 kg mass. This is achieved by modular clamp design in connection with replaceable struts. The design features include clamping of payload in a statically determined way and actuation of clamp latches by means of single linear actuator via ropes. The vibration and TV environmental conditions for the mechanism are extremely severe. A structural and prototype model was built. Test results of the operating characteristic are presented. In addition, problems of tribology are highlighted.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center The 15th Aerospace Mech. Symp.; p 375-390
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  • 11
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    An antenna pointing mechanism for large reflector antennas (1981)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: An antenna pointing mechanism for large reflector antennas on direct broadcasting communication satellites was built and tested. After listing the requirements and constraints for this equipment the model is described, and performance figures are given. Futhermore, results of the qualification level tests, including functional, vibrational, thermovacuum, and accelerated life tests are reported. These tests were completed successfully.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center The 15th Aerospace Mech. Symp.; p 253-261
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  • 12
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    A drive unit for the instrument pointing system (1981)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: The requirements, capabilities, and unique design features of the instrument pointing system drive units (DU) are presented. The DU's are identical for all three gimbal axes (elevation, cross elevation, and azimuth) and provide alternating rotation of shaft versus the housing of + or - 180 deg. The design features include: two ball bearing cartridges using cemented carbide balls coated with TiC a layer; redundant brushless torque motors and resolvers; a load by-pass mechanism driven by a dc torque motor to off-load the bearings during ascent/descent, ground transportation, and to provide an emergency breaking capability; and cabling over each gimbal axis by means of cable follow-up consisting of 13 signal and 15 power flat band cable loops. Test results of disturbance torque characteristics are presented.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center The 15th Aerospace Mech. Symp.; p 263-278
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  • 13
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    An antenna fine pointing mechanism (1981)
    In:  CASI
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    Publication Date: 2006-01-16
    Description: SOFA, a device designed for the highly accurate 2 axis pointing of antenna or any feature installed on a spacecraft is described. The major characteristic of this system is complete freedom from friction and wear out, resulting in numerous advantages, such as outstanding precision, virtually endless service life, high simplicity, and reliability. The sizing method is described and performances are analyzed. The results from analogue simulations are presented. A functional model of the electrical and mechanical parts was built and subjected to on ground tests using a 2 axis platform simulating the spacecraft's motions. The results obtained are thoroughly in keeping with the predictions and simulations. Various possible applications of the SOFA system are mentioned.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center The 15th Aerospace Mech. Symp.; p 235-252
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  • 14
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    A mechanical drive for retractable telescopic masts (1981)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: Test results on the mechanical drive have indicated that the system is capable of deploying a typical telescopic mast under ambient conditions. The design can be considered for a wide range of space applications since, in theory, there is no limit to the number of tubes that can be deployed. The mechanical system offers a number of advantages over a gas driven system, such as the ability to retract and also provide a significant mass saving.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center The 15th Aerospace Mech. Symp.; p 205-217
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  • 15
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    Test evaluation of shock buffering concept for hydrodynamic ram induced by yawing projectile impacting a simulated integral fuel tank (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: A concept for containing the shock inputs due to hydrodynamic ram caused by an impacting projectile within a fuel cell is discussed. This is to provide a buffering layer of foam, flexible, rigid or a combination thereof, which is sealed from the liquid. A program is described in which this buffering concept was tested. The effectiveness of a novel muzzle-mounted, 'tumble', test device is shown.
    Keywords: MECHANICAL ENGINEERING
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 1; p 141-170
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  • 16
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    Mass drivers. 3: Engineering (1979)
    In:  CASI
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    Publication Date: 2006-01-12
    Description: The last of a series of three papers by the Mass-Driver Group of the 1977 Ames Summer Study is presented. It develops the engineering principles required to implement the basic mass-driver. Optimum component mass trade-offs are derived from a set of four input parameters, and the program used to design a lunar launcher. The mass optimization procedures is then incorporated into a more comprehensive mission optimization program called OPT-4, which evaluates an optimized mass-driver reaction engine and its performance in a range of specified missions. Finally, this paper discusses, to the extent that time permitted, certain peripheral problems: heating effects in buckets due to magnetic field ripple; an approximate derivation of guide force profiles; the mechanics of inserting and releasing payloads; the reaction mass orbits; and a proposed research and development plan for implementing mass drivers.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Ames Res. Center Space Resources and Space Settlements; p 119-157
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  • 17
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    Mass drivers. 1: Electrical design (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: A mass driver is an electrical device used to accelerate payloads of any material to a high velocity. Small vehicles (called buckets) containing superconducting coils carry the payloads. These buckets are accelerated by pulsed magnetic fields, timed by information on their position, and are guided by induced magnetic fields set up in a surrounding guideway. Upon reaching the correct velocity, the buckets release their payloads, then they are slowed for recirculation to be reused. A rationale is presented that leads to a relatively simple and near-optimum design, as well as basic programs for calculating acceleration. The transverse oscillation frequencies are found to be invariant to guideway transverse dimensions.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Ames Res. Center Space Resources and Space Settlements; p 87-100
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  • 18
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    Tribology experiment (1981)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A two-dimensional concept for Spacelab rack 7 was developed to study the interaction of liquid lubricants and surfaces under static and dynamic conditions in a low-gravity environment fluid wetting and spreading experiments of a journal bearing experiments, and means to accurately measure and record the low-gravity environment during experimentation are planned. The wetting and spreading process of selected commercial lubricants on representative surface are to the observes in a near-zero gravity environment.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center Spacecraft Dyn. as Related to Lab. Expt. in Space; p 58-60
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  • 19
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    An experimental design for total container impact response modeling at extreme temperatures (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: An experimental design (a drop test) was developed to test the effects of confinement upon cushions. The drop test produced consistent corner void cushion data from which mathematical models were developed. A mathematical relationship between temperature and drop height was found.
    Keywords: MECHANICAL ENGINEERING
    Type: Shock and Vibration Inform. Center The Shock and Vibration Bull., Pt. 1; p 101-107
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  • 20
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    Mass drivers. 2: Structural dynamics (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: Various structural and dynamical problems related to both small-scale forces between the drive coils and within the bucket structure as well as the overall combined large-scale dynamical interaction of the bucket stream and MDRE (Mass Drive Reaction Engine) structure are examined. The large-scale dynamics appear weakly stable. Finally, MDRE operation in an inverse-square-law gravitational field is discussed and the required curved shape of the guideway is computed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Ames Res. Center Space Resources and Space Settlements; p 101-118
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  • 21
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    Minimum energy control of a class of electrically driven vehicles (1978)
    In:  CASI
    Details
    Publication Date: 2006-03-02
    Description: Theoretical and experimental results are obtained in the investigation of a minimum energy control problem associated with a class of electrically driven vehicles. Analytical results are obtained by making several justifiable approximations in the dynamical equations of the plant, the performance index of which is related to the minimization of system energy consumption for any required control action. The control problem of interest is simplified and solved by using Bellman's invariant imbedding technique. The optimality of the resulting control law is compared with those of the bang-bang control law, which is the exact solution for the case of speed-setting control action, and the classical control laws under identical conditions. A stochastic optimization problem is then formulated and solved by using Bellman's dynamic programming technique. The resulting control law is mechanized for a particular vehicle configuration which is simulated in the laboratory.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA, Washington Fourth Inter-Center Control Systems Conf.; p 387-421
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  • 22
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    Robotic fruit harvester (1982)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Technol. Appl. Team; p 15
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  • 23
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    What is EHD (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: The life of many highly loaded machine elements relies on the formation of a very thin elastohydrodynamic (EHD) oil film between surfaces in motion. Its formation results from the combination of a remarkable set of circumstances rarely appreciated. This article endeavors to explain the mechanism of elastohydrodynamic lubrication with simple physical concepts that are easy to understand.
    Keywords: MECHANICAL ENGINEERING
    Type: Lubrication Engineering; 31; June 197
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  • 24
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    Variable polarity plasma arc welding on the Space Shuttle external tank (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Variable polarity plasma arc (VPPA) techniques used at NASA's Marshall Space Flight Center for the fabrication of the Space Shuttle External Tank are presentedd. The high plasma arc jet velocities of 300-2000 m/s are produced by heating the plasma gas as it passes through a constraining orifice, with the plasma arc torch becoming a miniature jet engine. As compared to the GTA jet, the VPPA has the following advantages: (1) less sensitive to contamination, (2) a more symmetrical fusion zone, and (3) greater joint penetration. The VPPA welding system is computerized, operating with a microprocessor, to set welding variables in accordance with set points inputs, including the manipulator and wire feeder, as well as torch control and power supply. Some other VPPA welding technique advantages are: reduction in weld repair costs by elimination of porosity; reduction of joint preparation costs through elimination of the need to scrape or file faying surfaces; reduction in depeaking costs; eventual reduction of the 100 percent-X-ray inspection requirements. The paper includes a series of schematic and block diagrams.
    Keywords: MECHANICAL ENGINEERING
    Type: Welding Journal (ISSN 0043-2296); 63; 27-35
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  • 25
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    Two-phase turbine staging (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Two-phase turbines would be useful in Rankine cycles using low-quality or saturated-liquid working fluids. The chief problem is low efficiency due to slip losses in nozzles and due to liquid impact and friction losses in rotors. To raise efficiency, a staging method was tested in which the first stage operated at high speed with low relative liquid velocity, and the second stage recovered the first-stage exit energy. The theoretical efficiency for an experimental turbine operating with Refrigerant-22 was raised from 55 percent to 66 percent, and the measured efficiency was raised from 52 percent to 57 percent.
    Keywords: MECHANICAL ENGINEERING
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  • 26
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    DOE/NASA Automotive Stirling Engine Project Overview 83 (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An overview of the DOE/NASA Automotive Stirling Engine Project is presented. The background and objectives of the project are reviewed. Project activities are described and technical progress and status are presented and assessed. Prospects for achieving the objective 30 percent fuel economy improvement are considered good. The key remaining technology issues are primarily related to life, reliability and cost, such as piston rod seals, and low cost heat exchanges. Previously announced in STAR as N83-27924
    Keywords: MECHANICAL ENGINEERING
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  • 27
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    An analysis of temperature effect in a finite journal bearing with spatial tilt and viscous dissipation (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The analysis presented herein deals with the evaluation of the pressure, velocity, and temperature profiles in a finite-length plane journal bearing. The geometry of the case under study consists of a spatially tilted shaft. The two-dimensional Reynolds equation accounts for the variation of the clearance gap h with x and z and is used to model the pressure field. The latter is solved for a variety of shaft tilt angles and then used to calculate the two-dimensional flow field. Finally, the flow field is used in the energy equation to solve for the film temperature profile, when the effect of viscous dissipation is taken into account.
    Keywords: MECHANICAL ENGINEERING
    Type: ASLE Transactions; 27; 405-412;
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  • 28
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    Influence of unbalance on the nonlinear dynamical response and stability of flexible rotor-bearing systems (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In this paper, some of the effects of unbalance on the nonlinear response and stability of flexible rotor-bearing systems is presented from both a theoretical and experimental standpoint. In a linear system, operating above its stability threshold, the amplitude of motion grows exponentially with time and the orbits become unbounded. In an actual system, this is not necessarily the case. The actual amplitudes of motion may be bounded due to various nonlinear effects in the system. These nonlinear effects cause limit cycles of motion. Nonlinear effects are inherent in fluid film bearings and seals. Other contributors to nonlinear effects are shafts, couplings and foundations. In addition to affecting the threshold of stability, the nonlinear effects can cause jump phenomena to occur at not only the critical speeds, but also at stability onset or restabilization speeds.
    Keywords: MECHANICAL ENGINEERING
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  • 29
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    Ceramics potential in automotive powerplants (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The paper addresses the potential that ceramic materials can play an important role in future automotive powerplants - both advanced heat engines and advanced battery systems. A number of related experimental programs are reviewed including ceramics for gasoline and diesel piston engines, gas turbine and Stirling Engines and sodium-sulfur batteries. A strong integrated program to develop ceramics technology is recommended.
    Keywords: MECHANICAL ENGINEERING
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  • 30
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    Into mesh lubrication of spur gears with arbitrary offset oil jet. I - For jet velocity less than or equal to gear velocity (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analysis was conducted for into mesh oil jet lubrication with an arbitrary offset and inclination angle from the pitch point for the case where the oil jet velocity is equal to or less than pitch line velocity. The analysis includes the case for the oil jet offset from the pitch point in the direction of the pinion and where the oil jet is inclined to intersect the common pitch point. Equations were developed for the minimum oil jet velocity required to impinge on the pinion or gear and the optimum oil jet velocity to obtain the maximum impingement depth.
    Keywords: MECHANICAL ENGINEERING
    Type: ASME; 713-718
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  • 31
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    Special cases of friction and applications (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two techniques for reducing friction forces are presented. The techniques are applied to the generalized problem of reducing the friction between kinematic pairs which connect a moveable link to a frame. The basic principles are: (1) Let the moveable link be supported by two bearings where the relative velocities of the link with respect to each bearing are of opposite directions. Thus the resultant force (torque) of friction acting on the link due to the bearings is approximately zero. Then, additional perturbation of motion parallel to the main motion of the moveable link will require only a very small force; (2) Let the perturbation in motion be perpendicular to the main motion. Equations are developed which explain these two methods. The results are discussed in relation to friction in geared couplings, gyroscope gimbal bearings and a rotary conveyor system. Design examples are presented.
    Keywords: MECHANICAL ENGINEERING
    Type: ASME; 256-260
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  • 32
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    Why ceramic engines? (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Oil is still a problem for the U.S. and its allies. Transportation uses 61 percent of U.S. oil and its share is increasing, so more efficient technology should be concentrated there. Trucks' share of oil use is increasing because they are already much more efficient than autos. The primary truck opportunities are streamlining, more efficient engines, and shifting freight to railroads. More efficient engines are possible using ceramics to allow elimination of cooling systems and better use of waste exhaust heat. A 60 percent improvement seems possible if ceramics can be made tough enough and durable enough.
    Keywords: MECHANICAL ENGINEERING
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 5; 281-284
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  • 33
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    Gas bearings (1980)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The present work deals with the fundamentals of gas lubrication theory, which forms the foundation of all analytical design tools for gas bearings. Most of the hard lessons learned in the past are outlined with reference to dry contact, debris ingestion, sliding speed, and chemical stability of lubricant. The mathematical theory of gas lubrication is described for scaling rules in thin-film viscous flow, momentum conservation, mass conservation, energy conservation, isothermal gas bearing theory, coupling effects, and global bearing characteristics. Particular attention is given to the governing differential equations for common bearing configurations. Also discussed are representative solutions of self-acting gas bearings, externally pressurized bearings, and time-dependent effects.
    Keywords: MECHANICAL ENGINEERING
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  • 34
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    Adhesion and friction of transition metals in contact with non-metallic hard materials (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: (Previously announced in STAR as N81-28233)
    Keywords: MECHANICAL ENGINEERING
    Type: Wear; 77; Apr. 1
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  • 35
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    The transfer of polytetrafluoroethylene studied by X-ray photoelectron spectroscopy (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: A polytetrafluoroethylene (PTFE) sphere of radius 4.8 mm was rubbed against nickel and S-Monel at speeds from 0.94 to 94 mm/s and at loads from 0.19 to 3.9 N. The transfer film of PTFE on the metal was examined with X-ray photoelectron spectroscopy. In all cases the film was found to be indistinguishable from bulk PTFE. A trace of metal fluoride was observed whether the rubbing took place on oxidized or atomically clean metal. The film was of the order of a molecule thick for the entire range of loads and did not increase with repeated passes over the same rubbed area. An erratic increase in thickness at rubbing speeds above 10 mm/s was taken as evidence of random transfer of bulk material.
    Keywords: MECHANICAL ENGINEERING
    Type: Wear; 66; Feb. 16
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  • 36
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    A practical magnetic bearing (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A small compact magnetic bearing design developed and tested features a bearing capable of supporting over ten times its own weight, dimensioned 8 cm diam by 3.75 cm, with rare-earth cobalt magnets. Only 1% of the device payload figures as part of the magnetic suspension. The design is servoed in two axes and exhibits inherent stability in three more degrees of freedom, with full rotational freedom in the desired axis. Capacitive radial gap sensing allows stiff servoing of the rotation axis. Differential sensing and EM control linearize control functions. Low power drain, simple fabrication and assembly, and larger clearances than in air bearings or ball bearings are reported
    Keywords: MECHANICAL ENGINEERING
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  • 37
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    An estimation of the effect of fluid inertia on the performance of the plane inclined slider thrust bearing with particular regard to turbulent lubrication (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Keywords: MECHANICAL ENGINEERING
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  • 38
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    Nonlinear flap-lag axial equations of a rotating beam (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: It is possible to identify essentially four approaches by which analysts have established either the linear or nonlinear governing equations of motion for a particular problem related to the dynamics of rotating elastic bodies. The approaches include the effective applied load artifice in combination with a variational principle and the use of Newton's second law, written as D'Alembert's principle, applied to the deformed configuration. A third approach is a variational method in which nonlinear strain-displacement relations and a first-degree displacement field are used. The method introduced by Vigneron (1975) for deriving the linear flap-lag equations of a rotating beam constitutes the fourth approach. The reported investigation shows that all four approaches make use of the geometric nonlinear theory of elasticity. An alternative method for deriving the nonlinear coupled flap-lag-axial equations of motion is also discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: AIAA Journal; 15; June 197
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  • 39
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    Industrialization of the ion plating process (1976)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A new process referred to as ion plating by induction heating (IPIH) is described, which combines the advantages of both ion plating and induction heating. The IPIH apparatus consists of the specimen (cathode) to be coated and the evaporation heating source, which is a ceramic crucible containing the metal to be heated. The specimen is an internal part of the high-voltage ceramic-metal vacuum feedthrough and is connected to the negative terminal of the high-voltage power supply, the positive terminal of the power supply being grounded. The plating conditions are the same as those most commonly used in industrial ion plating. A number of metals - such as nickel, iron, platinum - which were practically impossible to deposit by resistance heating evaporation can now be effectively evaporated and deposited to any desired thickness. Excellent adherence is observed for many metals deposited on various metal surfaces in thicknesses from 0.15 to 50 microns, regardless of the materials selected for coating and substrate.
    Keywords: MECHANICAL ENGINEERING
    Type: Research/Development; 27; Oct. 197
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  • 40
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    Ion beam texturing (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A microscopic surface texture was created by sputter-etching a surface while simultaneously sputter-depositing a lower sputter yield material onto the surface. A xenon ion-beam source was used to perform the texturing process on samples as large as 3-cm diameter. Textured surfaces have been characterized with SEM photomicrographs for a large number of materials including Cu, Al, Si, Ti, Ni, Fe, stainless steel, Au, and Ag. A number of texturing parameters are studied including the variation of texture with ion-beam powder, surface temperature, and the rate of texture growth with sputter etching time.
    Keywords: MECHANICAL ENGINEERING
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  • 41
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    Simplified solution for elliptical-contact deformation between two elastic solids (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A linear regression by the method of least squares is made on the geometric variables that occur in the equation for elliptical-contact deformation. The ellipticity and the complete elliptic integrals of the first and second kind are expressed as a function of the x,y-plane principal radii. The ellipticity was varied from 1 (circular contact) to 10 (a configuration approaching line contact). The procedure for solving these variables without the use of charts or a high-speed computer would be quite tedious. These simplified equations enable one to calculate easily the elliptical-contact deformation to within 3 percent accuracy without resorting to charts or numerical methods.
    Keywords: MECHANICAL ENGINEERING
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  • 42
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    Lateral forces induced by a misaligned roller (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The magnitude of the lateral force induced by a roller, misaligned in its direction of travel is considered. Consequences of the induced lateral forces and examples of wheel suspension designs are given.
    Keywords: MECHANICAL ENGINEERING
    Type: The Deep Space Network; p 253-257
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  • 43
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    Spherical artifacts on ferrograms (1976)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: In the past, hollow spheres detected on ferrograms have been interpreted as being due to fretting, abrasion, cavitation erosion, and fatigue-related processes. Here it is reported that such spheres were found to result from the fact that a routine grinding operation on a steel plate was carried out about 20 feet away from the ferrograph. A similar grinding operation was performed on a piece of low carbon steel a few feet from the ferrograph, and after a few minutes of grinding, the resulting ferrogram contained thousands of particles of which more than 90% were spherical. Because of the widespread occurrence of ordinary grinding operations, it seems prudent that those utilizing the ferrograph be cognizant of this type of artifact.
    Keywords: MECHANICAL ENGINEERING
    Type: Wear; 37; Apr. 197
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  • 44
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    Long term technology development program (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In the Advanced Adiabatic Development program, the following technology were identified as critical: piston development for oil-less, adiabatic engine; positive displacement compounding and charge system; experimental evaluation of the preheat concept; combustion system with positive ignition assist; and ceramic manufacturing technology. Of these five areas, ceramic manufacturing technology is the pacing item, and is already being addressed by several organizations. Therefore the four remaining areas need immediate attention. Since the lead time involved in engine development and production is long, this technology development should be done concurrently with the AAD engine development. A four year program is outlined which will simultaneously study these first four areas. This program requires two test rigs; one single cylinder adiabatic engine; and one multicylinder adiabatic turbocompound engine.
    Keywords: MECHANICAL ENGINEERING
    Type: Advan. Automotive Diesel Assessment Program; 7 p
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  • 45
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    A.A.D. engine noise evaluation (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A critique of the various characteristics of engine design influencing noise and attempts to indicator areas where attention is required to obtain noise acceptable engine for automobiles are discussed. It was concluded that the engine has a potential to be quiet beccause a ion rated speed is chosen. Problems with high gas pressure, the fuel injection pump, and the expander/compressor are discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 29 p
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  • 46
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    Screw expander for light duty diesel engines (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Preliminary selection and sizing of a positive displacement screw compressor-expander subsystem for a light-duty adiabatic diesel engine; development of a mathematical model to describe overall efficiencies for the screw compressor and expander; simulation of operation to establish overall efficiency for a range of design parameters and at given engine operating points; simulation to establish potential net power output at light-duty diesel operating points; analytical determination of mass moments of inertia for the rotors and inertia of the compressor-expander subsystem; and preparation of engineering layout drawings of the compressor and expander are discussed. As a result of this work, it was concluded that the screw compressor and expander designed for light-duty diesel engine applications are viable alternatives to turbo-compound systems, with acceptable efficiencies for both units, and only a moderate effect on the transient response.
    Keywords: MECHANICAL ENGINEERING
    Type: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 46 p
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  • 47
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    Thermal and mechanical analysis of major components for the advanced adiabatic diesel engine (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The proposed design for the light duty diesel is an in-line four cylinder spark assisted diesel engine mounted transversely in the front of the vehicle. The engine has a one piece cylinder head, with one intake valve and one exhaust valve per cylinder. A flat topped piston is used with a cylindrical combustion chamber recessed into the cylinder head directly under the exhaust valve. A single ceramic insert is cast into the cylinder head to insulate both the combustion chamber and the exhaust port. A similar ceramic insert is cast into the head to insulate the intake port. A ceramic faceplate is pressed into the combustion face of the head to insulate the face of the head from hot combustion gas. The valve seats are machined directly into the ceramic faceplate for the intake valve and into the ceramic exhaust pot insert for the exhaust valve. Additional ceramic applications in the head are the use of ceramic valve guides and ceramic insulated valves. The ceramic valve guides are press fit into the head and are used for increased wear resistance. The ceramic insulated valves are conventional valves with the valve faces plasma spray coated with ceramic for insulation.
    Keywords: MECHANICAL ENGINEERING
    Type: Advan. Automotive Diesel Assessment Program; 65 p
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  • 48
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    Advanced automotive diesel engine system study (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A conceptual study of an advanced automotive diesel engine is discussed. The engine concept selected for vehicle installation was a supercharged 1.4 liter, 4 cylinder spark assisted diesel of 14:1 compression ratio. A compounding unit consisting of a Lysholm compressor and expander is connected to the engine crankshaft by a belt drive. The inlet air charge is heated by the expander exhaust gas via a heat exchanger. Four levels of technology achievement on the selected engine concept were evaluated, from state-of-the-art to the ideal case. This resulted in the fuel economy increasing from 53.2 mpg to 81.7 mpg, and the 0-60 mph time decreasing from 17.6 seconds to 10.9 seconds.
    Keywords: MECHANICAL ENGINEERING
    Type: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 18 p
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  • 49
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    A study of the Armstrong Whitworth swing beam engine for automotive application (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The introduction of ceramics to those parts suffering high thermal loading was successfully demonstrated, and there is no question that the 100 kw (134 hp) naturally aspirated engine of the future will be developed to produce up to 300 kw (402 hp) by the application of turbocharging or its equivalent. However, at the 60 - 80 kw (80 - 107 hp) size needed for the economic automotive engine, scaling down the 300 kw (402 hp) is beset by the laws of scale. The conventional four stroke diesel was not shown to be successful at the small high speed engine size. The opposed piston two stroke engine does not suffer the same laws of scale and engines in the low power range have already been marketed successfully. The half liter/cylinder Armstrong Whitworth Swing Beam Engine is the latest to be designed with the automotive market in mind. Its low noise structure and balanced linkage system coupled with advantages for easy start and potential use of low grade fuels, derived from its variable compression ratio and slow piston motion, qualifies it for the application.
    Keywords: MECHANICAL ENGINEERING
    Type: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 3 p
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  • 50
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    Roller crosshead analysis (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analysis of the frictional behavior of a roller crosshead configuration is given. This configuration consists of a piston which carries at the wristpin position a roller of large diameter which can roll on the cylinder liner surfaces. A preliminary assessment is given of whether the roller can roll on the cylinder liner without skidding, and what, if any, are the tribological implications of this approach to a dry lubricated design. The rotational speed of the roller must change during the stroke if it is not to slip on the cylinder liner. The maximum value of angular acceleration occurs at top dead center and bottom dead center. If the traction force on the rim of the roller, which is the product of the normal force due to piston side load and the coefficient of friction, is not sufficient to drive the roller through the necessary angular acceleration, sliding will occur. At 1,000 rpm, it appears that there will be a definite area of slip near each end of the stroke. The length of the area of slip may be of the order of 1/8 inch at each of these points.
    Keywords: MECHANICAL ENGINEERING
    Type: Advan. Automotive Diesel Assessment Program; 9 p
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  • 51
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    Advanced Automotive Diesel Assessment Program, executive summary (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The objectives of this analytical study were: to select one advanced automotive diesel engine (AAD) concept which would increase the tank mileage of a 3,000 pound passenger car from the present 35 mpg to at least 52 mpg; to identify long term component research and development work required to bring the selected concept to fruition; and to prepare a development strategy that will bring the selected concept to a prototype testing phase. Cummins Engine Company has completed this study. The selected concept is a 4 stroke cycle, direct injection, spark assisted, advanced adiabatic diesel engine with positive displacement compounding plus expander and part load air preheating. The engine does not use a liquid coolant nor liquid lubricants. It is a 4 cylinder, in-line, 77 mm bore x 77 mm stroke, 1.434 liters displacement engine weighing 300 lb, and rated at 70 BHP at 3000 rpm. Installation dimensions are 621 mm length x 589 mm width x 479 mm height (24.4 inch x 22 inch x 18.9 inch).
    Keywords: MECHANICAL ENGINEERING
    Type: Advan. Automotive Diesel Assessment Program p; 59 p
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  • 52
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    Detailed performance analysis of the A.A.D. - concept B (1983)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New concepts for engine performance improvement are seen through the adoption of heat regeneration techniques; advanced methods to enhance the combustion; and higher efficiency air handling machinery, such as the positive displacement helical screw expander and compressor. Each of these concepts plays a particular role in engine performance improvement. First regeneration has a great potential for achieving higher engine thermal efficiency through the recovery of waste energy. Although the concept itself is not new (this technique is used in the gas turbine), the application to reciprocating internal combustion engines is quite unusual and presents conceptual difficulties. The second important area is better control of the combustion process in terms of heat transfer characteristics, combustion products, and heat release rate. The third area for performance improvement is in the adoption of high efficiency air handling machinery. In particular, positive displacement helical expander and compressor exhibit an extremely high efficiency over a wide range of operating conditions.
    Keywords: MECHANICAL ENGINEERING
    Type: Advan. Automotive Diesel Assessment Program; 46 p
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  • 53
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    NASA transmission research and its probable effects on helicopter transmission design (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Transmissions studied for application to helicopters in addition to the more conventional geared transmissions include hybrid (traction/gear), bearingless planetary, and split torque transmissions. Research is being performed to establish the validity of analysis and computer codes developed to predict the performance, efficiency, life, and reliability of these transmissions. Results of this research should provide the transmission designer with analytical tools to design for minimum weight and noise with maximum life and efficiency. In addition, the advantages and limitations of drive systems as well as the more conventional systems will be defined.
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  • 54
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    Feasibility analysis of a spiral groove ring seal for counter-rotating shafts (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: MECHANICAL ENGINEERING
    Type: Journal of Aircraft (ISSN 0021-8669); 21; 618-622
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  • 55
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    Pivoting and slip in an angular contact bearing (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Pivoting slips are calculated for the ball-race and ball-ball contacts in a retainerless bearing. The calculation is kinematic, ignoring all inertial loadings. Pure spin and uniform precession of the balls are considered. Pivoting slip magnitudes are compared with several other kinds of slip which were previously reported in an R4 size bearing. Previously announced in STAR as N83-26079
    Keywords: MECHANICAL ENGINEERING
    Type: ASLE Transactions; 27; 259-262
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  • 56
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    Elastic model of the traction behavior of two traction lubricants (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the analysis of rolling-sliding concentrated contacts, such as gears, bearings and traction drives, the traction characteristics of the lubricant are of prime importance. The elastic shear modulus and limiting shear stress properties of the lubricant dictate the traction/slip characteristics and power loss associated with an EHD contact undergoing slip and/or spin. These properties can be deducted directly from the initial slope m and maximum traction coefficient micron of an experimental traction curve. In this investigation, correlation equations are presented to predict m and micron for two modern traction fluids based on the regression analysis of 334 separate traction disk machine experiments. The effects of contact pressure, temperature, surface velocity, ellipticity ratio are examined. Problems in deducing lubricant shear moduli from disk machine tests are discussed. Previously announced in STAR as N83-20116
    Keywords: MECHANICAL ENGINEERING
    Type: ASLE Transactions; 27; 129-137;
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  • 57
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    Bonding procedure for Teflon seals (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Material and bonding procedures designed for use as seals at the National Transonic Facility at the NASA Langley Research Center are presented. Teflon TFE was chosen for its ability to withstand pressures of up to 130 psi and temperatures ranging from -320 to 150 F, in addition to tolerances of 0.074 in. and having a movement allowance of 0.75 in. during transient cycles. Since some of the seals are 14 in. in diameter, Teflon sheets had to be sliced and bonded together after machining to size, resulting in seals with circular, oval, straight, and rectangular cross sections. Step-by-step preparation procedures are provided, and it is noted that the scarf joints performed as predicted during tests.
    Keywords: MECHANICAL ENGINEERING
    Type: Astronautics and Aeronautics; 20; Sept
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  • 58
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    Ball bearing lubrication: The elastohydrodynamics of elliptical contacts (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The history of ball bearings is examined, taking into account rollers and the wheel in the early civilizations, the development of early forms of rolling-element bearings in the classical civilizations, the Middle Ages, the Industrial Revolution, the emergence of the precision ball bearing, scientific studies of contact mechanics and rolling friction, and the past fifty years. An introduction to ball bearings is presented, and aspects of ball bearing mechanics are explored. Basic characteristics of lubrication are considered along with lubrication equations, the lubrication of rigid ellipsoidal solids, and elastohydrodynamic lubrication theory. Attention is given to the theoretical results for fully flooded elliptical hydrodynamic contacts, the theoretical results for starved elliptical contacts, experimental investigations, the elastohydrodynamics of elliptical contacts for materials of low elastic modulus, the film thickness for different regimes of fluid-film lubrication, and applications.
    Keywords: MECHANICAL ENGINEERING
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  • 59
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    Adhesion and friction of single-crystal diamond in contact with transition metals (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An investigation was conducted to examine the adhesion and friction of single-crystal diamond in contact with various transition metals and the nature of metal transfer to diamond. Sliding friction experiments were conducted with diamond in sliding contact with the metals yttrium, titanium, zirconium, vanadium, iron, cobalt, nickel, tungsten, platinum, rhenium and rhodium. All experiments were conducted with loads of 0.05 to 0.3 N, at a sliding velocity of 0.003 m per minute, in a vacuum of 10 to the -8th Pa, at room temperature, and on the (111) plane of diamond with sliding in the 110 line type direction. The results of the investigation indicate that the coefficient of friction for diamond in contact with various metals is related to the relative chemical activity of the metals in high vacuum. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to the surface of diamond in sliding.
    Keywords: MECHANICAL ENGINEERING
    Type: Applications of Surface Science; 6; 1980
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  • 60
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    Practical small-scale explosive seam welding (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A small-scale explosive seam welding process has been developed that can significantly contribute to remote metal joining operations under hazardous or inaccessible conditions, such as nuclear reactor repair and assembly of structure in space. This paper describes this explosive seam welding process in terms of joining principles, variables, types of joints created, capabilities, and applications. Very small quantities of explosive in a ribbon configuration are used to create narrow (less than 0.5 inch), long-length, uniform, hermetically sealed joints that exhibit parent metal properties in a wide variety of metals, alloys, and combinations. The practicality of this process has been demonstrated by its current acceptance, as well as its capabilities that are superior in many applications to the universally accepted joining processes, such as mechanical fasteners, fusion and resistance welding, and adhesives. Previously announced in STAR as N83-24896
    Keywords: MECHANICAL ENGINEERING
    Type: (ISSN 0025-6501)
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  • 61
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    Dynamic stiffness characteristics of high eccentricity ratio bearings and seals by perturbation testing (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The complex behavior of cylindrical bearings and seals that are statically loaded to eccentricities in excess of 0.7 are examined. The stiffness algorithms as a function of static load are developed from perturbation methodology by empirical modeling.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 481-501
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  • 62
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    Damping capacity of a sealed squeeze film bearing (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The advantages of incorporating an open-ended or weakly-sealed squeeze-film bearing in a flexible support structure simulating an aero-engine assembly were examined. Attention is given to empirically modelling the hydrodynamics of the more usual tightly-sealed squeeze-film bearing, with a view to assessing its damping performance.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 407-428
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  • 63
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    Influence of stationary components on unsteady flow in industrial centrifugal compressors (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An experimental investigation was performed to determine the characteristics of the onset and the growth of rotating nonuniform flow in a standard low specific speed stage, normally utilized in high pressure applications, in relation to change of stationary component geometry. Four configurations, differing only in the return channel and crossover geometry were tested on an atmospheric pressure open loop test rig. Experimental results make conspicious the effect of return channel geometry and give the possibility of shifting the unstable zone onset varying such geometry. An attempt was made to interpret the experimental results in the Emmons - Stenning's rotating stall theory.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 429-480
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  • 64
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    Squeeze-film dampers for turbomachinery stabilization (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A technique for investigating the stability and damping present in centrally preloaded radially symmetric multi-mass flexible rotor bearing systems is presented. In general, one needs to find the eigenvalues of the linearized perturbation equations, though zero frequency stability maps may be found by solving as many simultaneous non-linear equations as there are dampers; and in the case of a single damper, such maps may be found directly, regardless of the number of degrees of freedom. The technique is illustrated for a simple symmetric four degree of freedom flexible rotor with an unpressurized damper. This example shows that whereas zero frequency stability maps are likely to prove to be a simple way to delineate multiple solution possibilities, they do not provide full stability information. Further, particularly for low bearing parameters, the introduction of an unpressurized squeeze film damper may promote instability in an otherwise stable system.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 391-406
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    Design of electromagnetic bearing for vibration control of flexible transmission shaft (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Recently magnetic bearings were proposed by several researchers and shown to be viable on a variety of rotor assemblies. The design and construction of such a bearing, which employs features hitherto not used by other workers is examined. These include an original approach to the design of the electromagnets and their amplifiers, and to software in a digital control system, to condition the control signals so as to make the magnets appear to be linear and uncoupled. The resulting system is used to control a rotor-bearing assembly, whose speed range covers two flexural-critical speeds.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 351-364
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  • 66
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    Effects of fluid inertia and turbulence on force coefficients for squeeze film dampers (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The effects of fluid inertia and turbulence on the force coefficients of squeeze film dampers are investigated analytically. Both the convective and the temporal terms are included in the analysis of inertia effects. The analysis of turbulence is based on friction coefficients currently found in the literature for Poiseuille flow. The effect of fluid inertia on the magnitude of the radial direct inertia coefficient (i.e., to produce an apparent added mass at small eccentricity ratios, due to the temporal terms) is found to be completely reversed at large eccentricity ratios. The reversal is due entirely to the inclusion of the convective inertia terms in the analysis. Turbulence is found to produce a large effect on the direct damping coefficient at high eccentricity ratios. For the long or sealed squeeze film damper at high eccentricity ratios, the damping prediction with turbulence included is an order of magnitude higher than the laminar solution.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 365-390
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  • 67
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    Analysis for leakage and rotordynamic coefficients of surface roughened tapered annular gas seals (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: In order to soften the effects of rub, the smooth stators of turbine gas seals are sometimes replaced by a honeycomb surface. This deliberately roughened stator and smooth rotor combination retards the seal leakage and may lead to enhanced rotor stability. However, many factors determine the rotordynamic coefficients and little is known as to the effectiveness of these honeycomb seals under various changes in the independent seal parameters. An analytical-computational method to solve for the rotordynamic coefficients of this type of compressible-flow seal is developed. The governing equations for surface roughned tapered annular gas seals are based on a modified Hirs' turbulent bulk flow model. A perturbation analysis is employed to develop zeroth and first-order perturbation equations. These equations are numerically integrated to solve for the leakage, pressure, density, and velocity for small motion of the shaft about the centered position. The resulting pressure distribution is then integrated to find the corresponding rotor-dynamic coefficients.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 341-350
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  • 68
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    Analysis and testing for rotordynamic coefficients of turbulent annular seals with different, directionally homogeneous surface-roughness treatment for rotor and stator elements (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A theory is presented, based on a simple modification of Hirs' turbulent lubrication equations, to account for different but directionally-homogeneous surface roughness treatments for the rotor and stator of annular seals. The theoretical results agree with von Pragenau's predictions that a damper seal which uses a smooth rotor and a rough stator yields more net damping than a conventional seal which has the same roughness for both the rotor and stator. Experimental results for four stators confirm that properly-designed roughened stators yield higher net damping values and substantially less leakage than seals with smooth surfaces. The best seal from both damping and leakage viewpoints uses a round-hole-pattern stator. Initial results for this stator suggest that, within limits, seals can be designed to yield specified ratios of stiffness to damping.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 313-340
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  • 69
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    Identification of dynamic coefficients of annular turbulent seals (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An identification procedure to determine dynamic coefficients of annular turbulent seals in turbopumps is presented. Measurements were carried out at a built test rig with two symmetrical arranged seals. A rigid rotating shaft is surrounded by an elastically supported housing, which is excited by impact forces. The relative radial motion between the rotating parts and the housing, respectively between the seal surfaces, is measured by displacement pick-ups and from the time signals complex frequency response functions can be calculated. Finally an analytical model, depending on the seal parameters, is fitted to the measured data, to find the dynamic coefficients.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 295-312
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  • 70
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    Preliminary investigation of labyrinth packing pressure drops at onset of swirl-induced rotor instability (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Backward and forward subsynchronous instability was observed in a flexible model test rotor under the influence of swirl flow in a straight-through labyrinth packing. The packing pressure drop at the onset of instability was then measured for a range of operating speeds, clearances and inlet swirl conditions. The trend in these measurements for forward swirl and forward instability is generally consistent with the short packing rotor force formulations of Benchert and Wachter. Diverging clearances were also destabilizing and had a forward orbit with forward swirl and a backward orbit with reverse swirl. A larger, stiff rotor model system is now being assembled which will permit testing steam turbine-type straight-through and hi-lo labyrinth packings. With calibrated and adjustable bearings in this new apparatus, direct measure of the net destabilizing force generated by the packings can be made.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 281-294
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  • 71
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    An iwatsubo-based solution for labyrinth seals - comparison with experimental results (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The basic equations are derived for compressible flow in a labyrinth seal. The flow is assumed to be completely turbulent in the circumferential direction where the friction factor is determined by the Blasius relation. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order pressure distribution is found by satisfying the leakage equation while the circumferential velocity distribution is determined by satisfying the momentum equation. The first-order equations are solved by a separation of variables solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients. The results of this analysis are compared to published test results.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 257-280
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  • 72
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    Prediction of force coefficients for labyrinth seals (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The development of a linear model for the prediction of labyrinth seal forces and on its comparison to available stiffness data is presented. A discussion of the relevance of fluid damping forces and the preliminary stages of a program to obtain data on these forces are examined. Fluid-dynamic forces arising from nonuniform pressure patterns in labyrinth seal glands are known to be potentially destablizing in high power turbomachinery. A well documented case in point is that of the space Shuttle Main Engine turbopumps. Seal forces are also an important factor for the stability of shrouded turbines, acting in that case in conjunction with the effects of blade-tip clearance variations.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 235-256
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  • 73
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    Analysis of dynamic characteristics of fluid force induced by labyrinth seal (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Flow patterns of the labyrinth seal are experimentally investigated for making a mathematical model of labyrinth seal and to obtain the flow induced force of the seal. First, the flow patterns in the labyrinth chamber are studied on the circumferential flow using bubble and on the cross section of the seal chamber using aluminum powder as tracers. And next, the fluid force and its phase angle are obtained from the measured pressure distribution in the chamber and the fluid force coefficients are derived from the fluid force and the phase angle. Those are similar to the expression of oil film coefficients. As a result, it is found that the vortices exist in the labyrinth chambers and its center moves up and down periodically. The pressure drop is biggest in the first stage of chambers and next in the last stage of chambers.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 211-234
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  • 74
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    Experimental investigation of lateral forces induced by flow through model labyrinth glands (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The lateral forces induced by flow through model labyrinth glands were investigated. Circumferential pressure distributions, lateral forces and stiffness coefficients data obtained are discussed. The force system is represented as a negative spring and a tangential force orthogonal to eccentricity. The magnitude of these forces are dependent on eccentricity, entry swirl, rotor peripheral velocity and seal size. A pressure equalization chamber at midgland tests should in significantly reduced forces and stiffness coefficients.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 187-210
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  • 75
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    Theoretical approach to labyrinth seal forces - cross-coupled stiffness of a straight-through labyrinth seal (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Two kinds of three dimensional flows in a labyrinth seal, a jet flow and a core flow, are considered and theoretical equations are set up concerning the motion of each flow. The pressure distribution within the labyrinth is calculated, when the rotor shaft makes a small displacement from the center line of the casing, keeping parallel with it. The theoretical values of cross coupled stiffness obtained by integrating the pressure under different labyrinth geometries and operating conditions through these formulas are compared with the experimental data.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 173-186
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  • 76
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    Two-dimensional unsteady analysis of fluid forces on a whirling centrifugal impeller in a volute (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Destabilizing fluid forces on a whirling centrifugal impeller rotating in a volute were observed. A quasisteady analysis neglecting shed vorticity or an unsteady analysis without a volute does not predict the existence of such destabilizing fluid forces on a whirling impeller. The effects of a volute and the shed vorticity are considered. We treat cases when an impeller with an infinite number of vanes rotates with a constant velocity omega and its center whirls with a constant eccentric radius epsilon and a constant whirling velocity psi. It is assumed that: (1) the number of the vanes is so large that the impeller can be treated as an actuator impeller in which the flow is perfectly guided; (2) flow is inviscid, incompressible and two dimensional; (3) the eccentricity epsilon is so small that unsteady components can be linearized; (4) vorticity is transported on a prescribed mean flow, the operating point is near design flow rate; and (5) the volute can be represented by a curved plate.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 161-172
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  • 77
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    Hydrodynamic impeller stiffness, damping, and inertia in the rotordynamics of centrifugal flow pumps (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The lateral hydrodynamic forces experienced by a centrifugal pump impeller performing circular whirl motions within several volute geometries were measured. The lateral forces were decomposed into: (1) time averaged lateral forces and (2) hydrodynamic force matrices representing the variation of the lateral forces with position of the impeller center. It is found that these force matrices essentially consist of equal diagonal terms and skew symmetric off diagonal terms. One consequence of this is that during its whirl motion the impeller experiences forces acting normal and tangential to the locus of whirl. Data on these normal and tangential forces are presented; it is shown that there exists a region of positive reduced whirl frequencies, within which the hydrodynamic forces can be destablizing with respect to whirl.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 137-160
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  • 78
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    Hydraulic forces on a centrifugal impeller undergoing synchronous whirl (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: High speed centrifugal rotating machinery with large vibrations caused by aerodynamic forces on impellers was examined. A method to calculate forces in a two dimensional orbiting impeller in an unbounded fluid with nonuniform entering flow was developed. A finite element model of the full impeller is employed to solve the inviscid flow equations. Five forces acting on the impeller are: Coriolis forces, centripetal forces, changes in linear momentum, changes in pressure due to rotation and pressure changes due to linear momentum. Both principal and cross coupled stiffness coefficients are calculated for the impeller.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 123-136
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  • 79
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    Lateral fluid forces acting on a whirling centrifugal impeller in vaneless and vaned diffuser (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Fluid forces on a rotating centrifugal impeller in whirling motion were studied. A two dimensional impeller installed in a parallel-walled vaneless and vaned diffuser whirled on a circular orbit with various positive and negative angular velocities. It is shown that the fluid forces exert a damping effect on the rotor in most operating conditions, but become excitatory when the impeller operates at very low partial discharge while rotating far faster than the whirl speed. The fluid forces were expressed in terms of mass, damping and stiffness matrices. Impellers with the same geometry and whirl condition are calculated. Quantitative agreement is obtained especially in positive whirl.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 109-122
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  • 80
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    Internal hysteresis experienced on a high pressure syn gas compressor (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A vibration instability phenomenon experienced in operating high pressure syn gas centrifugal compressors in two ammonia plants is described. The compressors were monitored by orbit and spectrum analysis for changes from baseline readings. It is found that internal hysteresis was the major destabilizing force; however, the problem was further complicated by seal lockup at the suction end of the compressor. A coupling lockup problem and a coupling fit problem, which frettage of the shaft, are also considered as contributors to the self excited vibrations.
    Keywords: MECHANICAL ENGINEERING
    Type: Rotordynamic Instability Problems in High-Performance Turbomachinery; p 97-108
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  • 81
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    Experimental on-stream elimination of resonant whirl in a large centrifugal compressor (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Resonant whirl condition during operation of a multi-stage centrifugal compressor at higher than anticipated speeds and loads was reported. The condition was diagnosed by a large scale computerized Machinery Condition Monitoring System (MACMOS). This computerized system verified that the predominant subsynchronous whirl frequency locked in on the first resonant frequency of the compressor rotor and did not vary with compressor speed. Compressor stability calculations showed the rotor system had excessive hearing stiffness and inadequate effective damping. An optimum bearing design which was developed to minimize the unbalance response and to maximize the stability threshold is presented.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 81-95
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  • 82
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    Control of rotordynamic instability in a typical gas turbine's power system (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The effect of rotor internal friction on the system's stability was studied when operated above the first critical speed. This internal friction is commonly caused by sliding press fits or sliding splines. Under conditions of high speed and low bearing damping, these systems will occassionally whirl at a frequency less than the shaft's rotational speed. This subsynchronous precession is a self excited phenomenon and stress reversals are created. This phenomenon was observed during engine testing. The reduction of spline friction and/or the inclusion of squeeze film damping have controlled the instability. Case history and the detail design of the squeeze film dampers is discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 53-80
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  • 83
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    Experiences with nonsynchronous forced vibration in centrifugal compressors (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The high subsynchronous vibrations which are often forced vibrations caused by flow instabilities, such as stage stall were examined. Modifications to improve the rotor stability by changing the bearings or seals have little effects on the subsynchronous vibrations. Understanding of the differences between forced vibrations and self excited vibrations to properly diagnose the problem and to correct it, is recommended. A list of characteristics of the two types of subsynchronous vibration is presented.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 37-52
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  • 84
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    Subsynchronous vibrations in a high pressure centrifugal compressor: A case history (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Two distinct aerodynamically excited vibrations in a high pressure low flow centrifugal compressor are documented. A measured vibration near 21% of running speed was identified as a nonresonant forced vibration which results from rotating stall in the diffuser; a measured vibration near 50% of running speed was identified as a self excited vibration sustained by cross coupling forces acting at the compressor wheels. The dependence of these characteristics on speed, discharge pressure, and changes in bearing design are shown. The exciting mechanisms of diffuser stall and aerodynamic cross coupling are evidenced. It is shown how the rotor characteristics are expected to change as a result of modifications. The operation of the compressor after the modifications is described.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 17-36
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  • 85
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    Full load testing in the platform module prior to tow-out: A case history of subsynchronous instability (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An electric motor driven centrifugal compressor to supply gas for further compression and reinjection on a petroleum production platform in the North Sea was examined. The compressor design, raised concerns about susceptibility to subsynchronous instability. Log decrement, aerodynamic features, and the experience of other compressors with similar ratios of operating to critical speed ratio versus gas density led to the decision to full load test. Mixed hydrocarbon gas was chosen for the test to meet discharge temperature restrictions. The module was used as the test site. Subsynchronous vibrations made the compressor inoperable above approximately one-half the rated discharge pressure of 14500 kPa. Modifications, which includes shortening the bearing span, change of leakage inlet flow direction on the back to back labyrinth, and removal of the vaned diffusers on all stages were made simultaneously. The compressor is operating with satisfactory vibration levels.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 1-16
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  • 86
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    Structural Optimization in automotive design (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Although mathematical structural optimization has been an active research area for twenty years, there has been relatively little penetration into the design process. Experience indicates that often this is due to the traditional layout-analysis design process. In many cases, optimization efforts have been outgrowths of analysis groups which are themselves appendages to the traditional design process. As a result, optimization is often introduced into the design process too late to have a significant effect because many potential design variables have already been fixed. A series of examples are given to indicate how structural optimization has been effectively integrated into the design process.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Langley Research Center Recent Experiences in Multidisciplinary Analysis and Optimization, Part 1; 16 p
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  • 87
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    Inherent Problems in Designing Two-Failure Tolerant Electromechanical Actuators (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An electromechanical ac-powered rotary actuated four-bar linkage system for rotating the Shuttle/Centaur deployment adapter is described. The essential features of the deployment adapter rotation system (DARS) are increased reliability for mission success and maximum practical hazard control for safety. The requirements, concept development, hardware configuration, quality assurance provisions, and techniques used to meet two-fault tolerance requirements are highlighted. The rationale used to achieve a degree of safety equivalent of that of two-failure tolerance is presented. Conditions that make this approach acceptable, including single failure point components with regard to redundancy versus credibility of failure modes, are also discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 155-170
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  • 88
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    Design and test of a low-temperature liner driver/rate controller (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The design and testing of a force/rate control device used to deploy an Earth shield on an orbiting satellite is described. Test experience, failure modes, and applications are emphasized.
    Keywords: MECHANICAL ENGINEERING
    Type: The 18th Aerospace Mech. Symp.; p 65-77
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  • 89
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    A passively controlled appendage deployment system for the San Marco D/L spacecraft (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The analytical simulation of deployment dynamics of these two axis concepts as well as the evolution of practical designs for the add on deployable inertia boom units is described. With the boom free to swing back in response to Coriolis forces as well as outwards in response to centrifugal forces, the kinematics of motion are complex but admit the possibility of absorbing deployment energy in frictional or other damping devices about the radial axis, where large amplitude motions can occur and where the design envelope allows more available volume. An acceptable range is defined for frictional damping for any given spin rate. Inadequate damping allows boom motions which strike the spacecraft; excessive damping causes the boom to swing out and latch with damaging violence. The acceptable range is a design parameter and must accommodate spin rate tolerance and also the tolerance and repeatability of the damping mechanisms.
    Keywords: MECHANICAL ENGINEERING
    Type: The 18th Aerospace Mech. Symp.; p 29-48
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  • 90
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    Evolution from a hinge actuator mechanism to an antenna deployment mechanism for use on the European large communications satellite (L-SAT/OLYMPUS) (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The evolution of an Antenna Deployment Mechanism (ADM) from a Hinge Actuator Mechanism (HAM) is described as it pertains to the deployment of large satellite antennas. Design analysis and mechanical tests are examined in detail.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 79-91
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  • 91
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    Unified Analysis for Antenna Pointing and Structural Errors. Part 1. Review (1983)
    In:  CASI
    Details
    Publication Date: 2014-09-10
    Description: A necessary step in the design of a high accuracy microwave antenna system is to establish the signal error budget due to structural, pointing, and environmental parameters. A unified approach in performing error budget analysis as applicable to ground-based microwave antennas of different size and operating frequency is discussed. Major error sources contributing to the resultant deviation in antenna boresighting in pointing and tracking modes and the derivation of the governing equations are presented. Two computer programs (SAMCON and EBAP) were developed in-house, including the antenna servo-control program, as valuable tools in the error budget determination. A list of possible errors giving their relative contributions and levels is presented.
    Keywords: MECHANICAL ENGINEERING
    Type: The Telecommun. and Data Acquisition Rept.; p 40-59
    Format: text
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  • 92
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    Status of Understanding for Seal Materials (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: Material selection for mainshaft face and ring seals, labyrinth seals, accessory gearbox face seals, and lip seals are discussed in light of tribology requirements and a given seal application. Carbon graphite has been found to be one of the best sealing materials and it is widely used in current gas turbine mainshaft and accessory gearbox seals. Its popularity is due to its unique combination of properties which consists of dimensional stability, corrosion resistance, low friction, good self lubricating characteristics, high thermal conductivity and low thermal expansion, the latter two properties combining to provide good thermal shock resistance. A brief description of the seals and the requirements they must meet are discussed to provide insight into the limitations and advantages of the seals in containing the lubricant. A forecast is made of the operational requirements of main shaft and gearbox seals for advanced engines and candidate materials and coatings that may satisfy these advanced engine requirements.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 811-829
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  • 93
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    Status of Understanding for Gear Materials (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: A wide variety of gear materials is available today for the gear designer. The choice of which material to use should be based on the requirements of the application and will include the operating conditions of load, speed, and temperature in addition to reliability, weight, noise limitation, accuracy, and cost. In aircraft applications such as helicopters, V/STOL aircraft, and turboprops, the dominant factors to be considered are reliability and weight. The following gear materials are reviewed herein with an emphasis upon mechanical properties, cost, and durability: plastics, nonferrous metals, copper alloys, iron alloys, metal powders, and steels.
    Keywords: MECHANICAL ENGINEERING
    Type: Tribology in the 80's, vol. 2; p 795-809
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  • 94
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    Sputtering as a Technique for Applying Tribological Coatings (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: Friction and wear-induced mechanical failures may be controlled to extend the life of tribological components through the interposition of selected solid materials between contacting surfaces. Thin solid films of soft and hard materials are appropriate to lower friction and enhance the wear resistance of precision tribo-elements. Tribological characteristics of thin hard coats deposited on a variety of ferrous and non-ferrous substrates were tested. The thin hard coats used were titanium nitride films deposited by reactive magnetron sputtering of metallic titanium. High contact stress, low speed tests showed wear rate reductions of one or more magnitude, even with films a few micrometers in thickness. Low contact stress, high speed tests carried out under rather severe test conditions showed that thin films of TiN afforded significant friction reduction and wear protection. Thin hard coats were shown to improve the friction and wear performance of rolling contacts. Satisfactory film-to-substrate adhesion strengths can be obtained with reactive magnetron sputtering. X-ray diffraction and microhardness tests were employed to assess the effectiveness of the sputtering technique.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 753-772
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  • 95
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    Micro-elastohydrodynamic Lubrication (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: Conventional elastohydrodynamics, which is based on assumption of smooth surfaces, is reviewed to show its insufficiency for explaining the failure processes in these contacts. For conditions approaching failure, lubrication breakdown occurs locally at asperity contacts where the lubrication behavior is controlled by microelastohydrodynamic lubrication (micro-EHL). The film formation mechanisms in micro-EHL conjunctions is described. The level of film thickness due to normal approach and sliding of a single asperity and due to asperity-asperity collision between two asperities is assessed. Possible influence of the micro-EHL to incipient scuffing failure, surface crack propagation and wear are discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 615-639
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  • 96
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    Transient EHL Effects in Starved Ball Bearings (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: The independent variables used in most calculations for EHL film thickness in ball bearings involve lubricant properties, contact elasticity, load, and bearing kinematics. The calculations are for steady state, and they give a time constant film thickness. Four distinct processes in starved ball bearings which are explained by assuming a time varying film thickness are shown. The four processes and another transient EHL effect which does not involve the thickness of the film are described. A simple model allows direct calculation of several of the thickness transients.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 641-649
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  • 97
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    Real Surface Effects in Elastohydrodynamic Lubrication (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: The real effects in electrohydrodynamic lubrication (EHL,) are discussed and the role of stochastic roughness superimposed on the nominal solid boundaries is considered. The full film EHL regime where incipient asperity contact bears a negligible fraction of the load is analyzed. Flow, from which an averaged Reynolds equation can be formed, is nonetheless modified by the amplitude and texture of the roughness patterns. It is found that only two extra parameters are needed, the rms surface height and the ratio of the correlation lengths in the two principal roughness directions. In a lowest order perturbation expansion of these flow factors in powers of the ratio of rms roughness to nominal film thickness, no other properties of the roughness appear. The factors describing Poiseuille flow are separable into the sum of two single surface flow factors which means that a combination of a single equivalent rough surface versus an ideal smooth surface is found. For flow entrained by slip velocity the factors separate instead into a difference of single surface factors and it becomes significant which of the two surfaces carries the equivalent roughness. Applications of the averaged Reynolds equation based on the flow factor method to the EHL line contact problem are discussed. The partial EHL regime is considered where comparable load fractions are carried by the hydrodynamic film and by incipient mechanical contact. An extension of the method into this regime by combining it with asperity contact models appears most encouraging.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 595-614
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  • 98
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    Non-steady State Effects in EHL (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: Lubricated machine elements are subjected to cyclic variations of load and speed, particularly in reciprocating machinery. Squeeze film action plays an important role in preserving satisfactory lubricating films in many cases in which the entraining velocities fall to zero during each cycle, as in the reciprocating seal and synovial joints. The essential features of combined entraining and normal motion for hydrodynamic and elastohydrodynamic conditions are described. It is shown that very small squeeze film velocities lead to substantial hydrodynamic action. A squeeze film lubrication between spheres or cylinders and a plane is reviewed by an analysis of ankle joint lubrication. It is shown that elastohydrodynamic lubrication might be encountered in the conjunction between a piston ring and cylinder liner and that combined entraining and squeeze film action is important. The 2 stroke Diesel engine shows that variations in squeeze film velocity throughout the conjunction, associated with time rates of change of elastic deformation, must be considered in a full elastohydrodynamic lubrication analysis.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 579-592
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  • 99
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    Lubricant Rheology in Concentrated Contacts (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: Lubricant behavior in highly stressed situtations shows that a Newtonian model for lubricant rheology is insufficient for explanation of traction behavior. The oil film build up is predicted by using a Newtonian lubricant model except at high slide to roll ratios and at very high loads, where the nonNewtonian behavior starts to be important already outside the Hertzian contact area. Static and dynamic experiments are reported. In static experiments the pressure is applied to the lubricant more than a million times longer than in an EHD contact. Depending on the pressure-temperature history of the experiment the lubricant will become a crystallized or amorphous solid at high pressures. In dynamic experiments, the oil is in an amorphous solid state. Depending on the viscosity, time scale, elasticity of the oil and the bearing surfaces, the oil film pressure, shear strain rate and the type of lubricant, different properties of the oil are important for prediction of shear stresses in the oil. The different proposed models for the lubricant, which describe it to a Newtonian liquid, an elastic liquid, a plastic liquid and an elastic-plastic solid.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 555-572
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  • 100
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    Elastohydrodynamic Lubrication. Status of Understanding (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: The development of elastohydrodynamic lubrication which was divided into three main stages is discussed. The first stage is the development of the idealized form of elastohydrodynamic lubrication, where the surfaces are smooth, the fluid behavior is assumed to be Newtonian, and isothermal considerations are assumed. The complete spectrum of contact geometries contact materials and lubricant availability are presented. The second state of development incorporates the effects of a nonNewtonian fluid model, thermal effects, and surface roughness effects into the elastohydrodynamic lubrication model developed in stage one. Recent developments in this stage are presented. The third stage considers the items considered in stage two, the lubrication of real surfaces in their operating environments is examined.
    Keywords: MECHANICAL ENGINEERING
    Type: Tribology in the 80's, vol. 2; p 507-531
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