ADVANCEMENT OF SPUR GEAR DESIGN TECHNOLOGY
Final rept. 29 Jun 1965-28 Jul 1966
GENERAL MOTORS CORP INDIANAPOLIS IN ALLISON GAS TURBINE DIV
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The investigation of four geometric variables indicated that the endurance strength was significantly affected by changes in pitch diameter and pressure angle. These effects were in some instances greater than those predicted by bending stress calculations. The effects of fillet size and fillet configuration--full form or protuberance--were not significant with respect to the endurance strength of the configurations tested. Stress calculations did not accurately consider the fillet configuration. A basic material strength curve for carburized AMS-6265 was established by R. R. Moore specimens. This strength curve correlated very closely with the AGMA method of calculating stress. By averaging all fatigue test data points, a design SN curve was established. For design purposes, a 1-percent failure endurance strength of 102,000 p.s.i. was also established. Of the five strength formulas investigated, the AGMA bending strength formula provides the most accurate method for assessment of spur gear tooth bending strength. The limited dynamic testing conducted indicated that a dynamic factor for lightweight aircraft gears should be considered for applications with a pitch line velocity over 8000 feetminute. A centrifugal speed factor is necessary for high pitch line velocity applications. A modification is required to the Dolan-Broghamer stress concentration factor used in the AGMA formula to consider tooth geometry more accurately. The AGMA formula modified to incorporate a centrifugal speed, a high speed dynamic factor, and to use R. R. Moore material strength data will produce an accurate estimate of gear tooth bending stress and life.
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