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  • 1
    Electronic Resource
    Electronic Resource
    Genetic correlation and response to selection in simulated populations (1970)
    Springer
    Theoretical and applied genetics 40 (1970), S. 157-162 
    Details
    ISSN: 1432-2242
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary One of two quantitative traits was selected and correlated response in the other trait was measured in each of 30 generations for models of additive genes and of complete dominance. Each trait was controlled by 48 loci with equal effects, segregating independently from frequencies of 0.5 in the initial generation. Intensity of selection regulated the number of offspring from randomly mating 24 males and 24 females each generation. Three each of genetic correlations between traits, intensities of selection, and amounts of environmental variation were simulated. In the additive model correlated responses of the unselected trait to selection of the primary trait agreed closely with responses expected from theoretical considerations. In the model of complete dominance, responses of genotypic means of the unselected trait to selection of the primary trait in opposite directions were quite symmetrical for the first few generations but became distinctly asymmetrical in later generations. With little selection, response was fairly linear but became distinctly curvilinear as intensity of selection increased and environmental variance decreased. Between 15th and 30th generations some gains in the correlated trait to the 15th generation were lost.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00282696
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Genetic correlation and response to selection in simulated populations (1970)
    Springer
    Theoretical and applied genetics 40 (1970), S. 106-110 
    Details
    ISSN: 1432-2242
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Effects of truncation selection of a primary trait upon genetic correlation between the primary trait and an unselected secondary trait were observed during 30 generations. Populations were 24 male and 24 female parents per generation randomly mated with replacement, the number of offspring set by intensity of selection. Each trait was controlled by genes with equal effects and complete dominance segregating independently from starting frequencies of 0.5 at each of 48 loci. Three levels each of genetic correlation, selection, and environmental variation were simulated. Genetic correlation decreased faster under more intense selection by lower than by upper truncation but behaved similarly in both by remaining near initial level when as many as one-half of the offspring were saved for parents. Truncation selection decreased genetic correlation in the offspring selected to be parents whether selection was by upper or lower truncation. Estimates of genetic correlation from covariances between phenotypes of parent and offspring were erratic for both directions of selection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00997001
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    Paper (German National Licenses)
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  • 3
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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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  • 4
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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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  • 5
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    Method of making rolling element bearings (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method is described of making rolling elements by forming low mass cores having either hollow centers or being of a low mass material. The low mass cores are plated and heat treated to provide hard surfaces on the rolling elements. After grinding to the proper diameter the rolling elements are assembled between races to form a hearing.
    Keywords: GENERAL
    Format: application/pdf
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  • 6
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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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  • 7
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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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  • 8
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    Common bearing material has highest fatigue life at moderate temperature (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: AISI 52100, a high carbon chromium steel, has the longest fatigue life of eight bearing materials tested. Fatigue lives of the other materials ranged from 7 to 78 percent of the fatigue life of AISI 52100 at a temperature of 340 K (150 F).
    Keywords: MATERIALS
    Type: LEW-11592
    Format: application/pdf
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  • 9
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    Series-hybrid bearing - An approach to extending bearing fatigue life at high speeds (1971)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Fluid film bearing of hybrid device consists of orifice compensated annular thrust bearing and self-acting journal bearing. In series hybrid bearing, both ball bearing and annular thrust bearing carry full system thrust load, but two bearings share speed. Operation of system is stable and automatically fail-safe.
    Keywords: MACHINERY
    Type: LEW-11152
    Format: application/pdf
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  • 10
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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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