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  • MACHINE ELEMENTS AND PROCESSES  (27)
  • ELECTRONICS  (1)
  • 1970-1974  (28)
  • 1
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    The Backup-Gilbert method and its application to the electrical conductivity problem (1972)
    In:  CASI
    Details
    Publication Date: 2006-03-12
    Description: The theory of Backus and Gilbert gives a technique for solving the general linear inverse problem. Observational error and lack of data are shown to reduce the reliability of the solution in different ways: the former introduces statistical uncertainties in the model, while the latter smooths out the detail. Precision can be improved by sacrificing resolving power, and vice versa, so that some compromise may be made between the two in choosing the best model. Nonlinear inverse problems can be brought into the domain of the theory by linearizing about a typical solution. The inverse problem of electrical conductivity in the mantle is used to illustrate the Backus-Gilbert technique; an example of the tradeoff diagram is given.
    Keywords: ELECTRONICS
    Type: NASA. Ames Res. Center Math. of Profile Inversion; 8 p
    Format: text
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  • 2
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    Elastohydrodynamic film thickness formula based on X-ray measurements with a synthetic paraffinic oil (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An empirical elastohydrodynamic film thickness formula for heavily loaded contacts based upon X-ray film thickness measurements made with a synthetic paraffinic oil is presented. The deduced relation was found to adequately reflect the high load dependence exhibited by the measured minimum film thickness data at high Hertizian contact stresses, that is, above 1.04 x 10 to the ninth N/sq m (150,000 psi). Comparisons were made with the numerical results from a theoretical isothermal film thickness formula. The effects of changes in contact geometry, material, and lubricant properties on the form of the empirical model are also discussed.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-7502 , E-7041
    Format: application/pdf
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  • 3
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    Effect of lubricant extreme pressure additives on rolling element fatigue life (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The effects of surface active additives on rolling-element fatigue life were investigated with the five-ball fatigue tester at conditions where classical subsurface initiated rolling-element fatigue is the sole mode of failure. Test balls of AISI 52100, AISI M-50, and AISI 1018 were run with an acid-treated white oil containing either 2.5 percent sulfurized terpene, 1 percent didodecyl phosphite, or 5 percent chlorinated wax. In general, it was found that the influence of surface active additives was detrimental to rolling-element fatigue life. The chlorinated-wax additive significantly reduced fatigue life by a factor of 7. The base oil with the 2.5 percent sulfurized-terpene additive can reduce fatigue life by as much as 50 percent. No statistical change in fatigue life occurred with the base oil having the 1 percent didodecyl-phosphite additive. The additives used with the base oil did not change the ranking of the bearing steels where rolling-element fatigue life was of subsurface origin.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-7383 , E-7337
    Format: application/pdf
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  • 4
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    Comparative lubrication studies of OH-58A tail rotor drive shaft bearings (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Comparative lubrication tests were run with OH-58A helicopter tail rotor drive shaft bearings. The tests were run in an outdoor environment with ambient temperatures ranging from 10 to 75 F. Dust was periodically applied to the bearings to simulate field conditions. The cause of bearing failure was associated with dust penetration. Rotor shaft failure was found to be caused by the shaft rotating in the standard rubber collar due to seizure of the bearings. Bearings with a positive rubbing seal having a MIL-G-81322 grease produced lives greater than with bearings having labyrinth seals and a mineral oil paste lubricant. An elongated collar prevented failure of the rotor shaft during bearing seizure. In a limited test, installation of tail boom shrouds over the bearings which excluded dust and water resulted in bearing lives in excess of 1800 hours or 1200 hours greater than the current 600 hours TBO, regardless of the lubricant-bearing combination used.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TM-X-68118 , E-7054
    Format: application/pdf
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  • 5
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    Reevaluation of the stress-life relation in rolling-element bearings (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Four groups of 12.7 millimeter diameter vacuum-degassed AISI 52100 balls were tested, each at a maximum Hertz stress in the range of 4.5 times 10 to 9th power to 6.0 times 10 to 9th power N/m2. Tests were run in the five-ball fatigue tester at a contact angle of 30 deg and a shaft speed of 10,000 rpm. The 10 percent fatigue lives at the four stress levels indicated that fatigue life is inversely proportional to maximum Hertz stress raised to the power of 12. This result agrees with a survey of the literature which suggests that a stress-life exponent of approximately 12 is typical of vacuum-processed bearing steels rather than the exponent of 9 which has been generally accepted by the bearing industry.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-6745 , E-6768
    Format: application/pdf
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  • 6
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    Rolling-element fatigue life of silicon nitride balls (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The five-ball fatigue tester was used to evaluate silicon nitride as a rolling-element bearing material. Results indicate that hot-pressed silicon nitride running against steel may be expected to yield fatigue lives comparable to or greater than those of bearing quality steel running against steel at stress levels typical rolling-element bearing application. The fatigue life of hot-pressed silicon nitride is considerably greater than that of any ceramic or cermet tested. Computer analysis indicates that there is no improvement in the lives of 120-mm-bore angular--contact ball bearings of the same geometry operating at DN values from 2 to 4 million where hot-pressed silicon nitride balls are used in place of steel balls.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-7794 , E-7219
    Format: application/pdf
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  • 7
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    Effect of residual stresses induced by prestressing on rolling element fatigue life (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A mechanical prestress cycle suitable to induce compressive stress beneath the surface of the inner race of radially loaded 207-size bearings was determined. Compressive residual stress in excess 0.69 x 10 to the 9th power N/sq m (100,000 psi), as measured by X-ray diffraction, were induced at the depth of maximum shearing stress. The prestress cycle consisted of running the bearings for 25 hours at 2750 rpm at a radial load which produced a maximum Hertz stress of 3.3 x 10 to the 9th power N/sq m (480,000 psi) at the contact of the inner race and the heaviest loaded ball. Bearings subjected to this prestress cycle and subsequently fatigue tested gave a 10 percent fatigue life greater than twice that of a group of baseline bearings.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-6995 , E-6922
    Format: application/pdf
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  • 8
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    Rolling-element fatigue lives of through hardened bearing materials (1971)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Hardness and fatigue tests of steel bearing alloys
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TM-X-67874 , E-5687
    Format: application/pdf
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  • 9
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    Elastohydrodynamic film thickness measurements with advanced ester, fluorocarbon, and polyphenyl ether lubricants to 589 K (600 F) (1971)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Elastohydrodynamic (EHD) film thicknesses have been measured, by means of an X-ray technique, under conditions that closely simulate the ball-race contact in advanced turbine engine thrust bearings. The experiments were conducted with a rolling-disk machine using disks which yield a contact zone similar to that in the actual bearing. Both the rolling and spinning motions of the ball relative to the race were simulated by the apparatus. Four lubricants were evaluated at temperatures to 600 F and maximum Hertz stresses to 350,000 psi. The X-ray film thickness data correlated well with observations of surface distress (or lack thereof) in full-scale bearing tests with the same lubricants under similar conditions of temperature and load. The predicted variation of film thickness with speed and viscosity as verified, although the magnitude of measured film thickness was generally one-half to one-third of predicted values. An effect of stress greater than predicted was consistently observed in the higher stress range.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-6608 , E-6440
    Format: application/pdf
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  • 10
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    Evaluation of electron-beam welded hollow balls for high-speed ball bearings (1970)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Rolling element fatigue tests of hollow and solid electron beam welded ball bearings
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TM-X-52779
    Format: application/pdf
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