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  • 1975-1979  (11)
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Year
  • 1
    facet.materialart.
    Unknown
    What is EHD (1975)
    In:  Other Sources
    Details
    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
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Unknown
    Analysis of a heat transfer device for measuring film coefficients (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A heat transfer device consisting of a heated rotating cylinder in a bath was analyzed for its effectiveness to determine heat transfer coefficient of fluids. A time dependent analysis shows that the performance is insensitive to the value of heat transfer coefficient with the given rig configuration.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-X-71809 , E-8156
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Unknown
    Effect of starvation on film thickness and traction under elastohydrodynamic rolling and sliding conditions (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Traction measurements under starved elastohydrodynamic conditions were obtained for a point-contact geometry. Simultaneous measurements of the film thickness and the location of the inlet lubricant boundary were made. Optical interferometry was used to measure film thickness. The thickness of a starved film for combined rolling and sliding conditions varies with the location of the inlet boundary in the same way as previously found for pure rolling conditions. When the fluid velocity distribution is calculated in the inlet region by a Reynolds lubrication analysis, backflow is seen to occur over a portion of the inlet region. Backflow is essential for the establishment of a flooded condition. The location of certain fluid velocity conditions within the inlet region, as suggested in the literature, does not adequately describe the onset of starvation. For the same slide-roll ratio a starved film was observed to possess greater traction than a flooded film. Traction measurements under starved conditions were also compared with those under flooded conditions for equivalent shear rates in the Hertzian region. When the shear rates within the Hertzian region were low and the film was severely starved, the measured tractions were lower than expected. This may be due to large shear stresses developed by the large pressure gradients that are generated in the inlet region when it is severely starved.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TN-D-8087 , E-8412
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Unknown
    Elastohydrodynamic film thickness measurements of artificially produced surface dents and grooves (1978)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Elastohydrodynamic (EHD) film thickness measurements using optical interferometry were made of artificially produced dents and grooves under rolling and sliding conditions. These measurements are compared to stylus traces of the dent and groove profiles to determine the local deformation associated with micro-EHD pressure generation. The surface geometry associated with the dents and grooves became intimately involved in the lubrication process itself, creating local pressure variations that substantially deformed the local surface geometry, particularly under sliding conditions. The rolling results implied surface initiated fatigue, and the sliding results showed clearly the EHD surface interactions that must occur prior to scuffing failure.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-78949 , E-9693 , Joint Lubrication Conf.; Oct 24, 1978 - Oct 26, 1978; Minneapolis, MN; United States
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  • 5
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    Unknown
    Influence of debris dent on EHD lubrication (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Film thickness measurements associated with a debris dent have been made with interferometry under static and dynamic conditions. The presence of a debris dent alters the shape of the inlet region so that the local film thickness at the leading edge of the dent can become substantially lower than the trailing edge. The pressure modifications associated with these local EHD effects are in line with the frequent occurrence of surface initiated fatigue spalls originating at the trailing edge of debris dents. The effectiveness of the EHD mechanism in reducing the stress concentrations at the shoulders of the dent is related to inlet dimensions and dent size.
    Keywords: MECHANICAL ENGINEERING
    Type: ASLE PREPRINT 76-LC-1A-3 , Lubrication Conference; Oct 05, 1976 - Oct 07, 1976; Boston, MA; US
    Format: text
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  • 6
    facet.materialart.
    Unknown
    Influence of debris dent on EHD lubrication (1975)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Film thickness measurements associated with a debris dent have been made with interferometry under static and dynamic conditons. The presence of a debris dent alters the shape of the inlet region so that the local film thickness at the leading edge of the dent can become substantially lower than the trailing edge. The pressure modifications associated with these local elastohydrodynamic (EHD) effects are in line with the frequent occurrence of surface initiated fatigue spalls originating at the trailing edge of debris dents. The effectiveness of the EHD mechanism in reducing the stress concentrations at the shoulders of the dent is related to inlet dimensions and dent size.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-X-73457 , E-8690 , Joint Lubrication Conf.; Oct 05, 1976 - Oct 07, 1976; Boston
    Format: application/pdf
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  • 7
    facet.materialart.
    Unknown
    Elastohydrodynamic film thickness measurements of artificially produced surface dents and grooves (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Elastohydrodynamic (EHD) film thickness measurements using optical interferometry have been made of artificially produced dents and grooves under rolling and sliding conditions. These measurements are compared to stylus traces of the dent and groove profiles to determine the local deformation associated with micro-EHD pressure generation. The surface geometry associated with the dents and grooves is seen to become intimately involved in the lubrication process itself, creating local pressure variations that substantially deform the local surface geometry, particularly under sliding conditions. The rolling results have implications concerning surface initiated fatigue and the sliding results show clearly the EHD surface interactions that must occur prior to scuffing failure.
    Keywords: MECHANICAL ENGINEERING
    Type: ASLE PREPRINT 78-LC-1A-1 , American Society of Lubrication Engineers and American Society of Mechanical Engineers, Joint Lubrication Conference; Oct 24, 1978 - Oct 26, 1978; Minneapolis, MN
    Format: text
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  • 8
    facet.materialart.
    Unknown
    Elastohydrodynamic film thickness measurements of artificially produced nonsmooth surfaces (1979)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Optical interferometry is used to measure the elastohydrodynamic (EHD) film thickness associated with artificially produced nonsmooth surfaces. The nonsmooth surfaces are produced by modifying the surfaces of highly-polished balls with irregularities in the form of multiple grooves and dents. By closely spacing these irregularities it is possible not only to produce depressions on the surface of the balls but also to generate pseudo asperities. The average roughness wavelength of this artificially-produced, nonsmooth, surface approximates the average fundamental roughness wavelength found on surfaces of some mechanical elements operating under concentrated contact. By comparing the measured film thickness profiles to the stylus traces of the irregularities, it was possible to observe the local deformations associated with micro-EHD pressure generation. In both pure rolling and pure sliding conditions the artificially-produced asperities are deformed and complete separation exists between them and the mating surface. Such findings demonstrate the importance of local surface topography and resulting micro-EHD effects on the film thickness between rough surfaces in concentrated contact. Sliding data are presented which demonstrate a severe constriction, caused by the irregularities, at the exit of the Hertzian region.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-79214 , E-9977 , Joint Lubrication Conf.; Oct 16, 1979 - Oct 18, 1979; Dayton, OH; United States
    Format: application/pdf
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  • 9
    facet.materialart.
    Unknown
    Diagnostics of wear in aeronautical systems (1979)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Maintenance costs associated with the transmissions and drive train greatly increase the maintenance burden and failure risk. Detection measurements fall under two general categories of vibration and particle detectors. The latter are more amenable to tracking wear. Wear debris analysis can supply a great deal of information such as: particle concentration, rate of change in concentration, composition, particle size and shape, principal metals, etc. It is not economically feasible to monitor all variables. At least one role of the lubrication and wear specialist is to provide guidance in selecting the most appropriate variables to monitor.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-79185 , E-052 , State-of-the-Art Symp. on Corrosion and Wear; Jun 04, 1979 - Jun 06, 1979; Washington, DC; United States
    Format: application/pdf
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  • 10
    facet.materialart.
    Unknown
    Elastohydrodynamic film thickness measurements of artificially-produced nonsmooth surfaces (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Optical interferometry is used to measure the elastohydrodynamic (EHD) film thickness associated with artificially produced, nonsmooth surfaces. The nonsmooth surfaces are produced by modifying the surfaces of highly-polished balls with irregularities in the form of multiple grooves and dents. By closely spacing these irregularities, it is possible not only to produce depressions on the surface of the balls but also to generate pseudo asperities. The average roughness wavelength of this artificially-produced, nonsmooth surface approximates the average fundamental roughness wavelength found on surfaces of some mechanical elements operating under concentrated contact. By comparing the measured film thickness profiles to the stylus traces of the irregularities, it is possible to observe the local deformations associated with micro-EHD pressure generation. In both pure rolling and pure sliding conditions, the artificially-produced 'asperities' are deformed and complete separation exists between them and the mating surface. Such findings demonstrate the importance of local surface topography and resulting micro-EHD effects on the film thickness between rough surfaces in concentrated contact. In addition, sliding data are presented which demonstrate a severe constriction, caused by the irregularities, at the exit of the Hertzian region.
    Keywords: MECHANICAL ENGINEERING
    Type: ASLE PREPRINT 79-LC-1A-3 , Lubrication Conference; Oct 16, 1979 - Oct 18, 1979; Dayton, OH
    Format: text
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    NASA TECHNICAL REPORTS
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