Do Load Peaks Cause Breakage, Plastic Deformation or Cracks in Case-Hardened Gears?

Apart from the continuous load over the lifetime, load peaks are critical for the capacity of a gearing. This article focuses on the maximally bearable load peaks in case-hardened gears. The ISO 6336 calculation guideline assesses the load capacity at a low number of load alternations (N less than 100 to 1000). The criterion is crack initiation. However, industrial experience shows that unallowably high plastic deformation can occur even in case-hardened gears. In some cases the allowable deformation is reached at such low load levels that cracks do not yet occur. In order to investigate these problems and improve the calculation method, the institute of the authors carried out a research project in cooperation with the industrial research association “Forschungsvereinigung Antriebstechnik” (FVA; Frankfurt/Main, Germany). This article sums up the theoretical and practical work and a calculation procedure derived from the results. During the project it became evident that the current guidelines need to be amended. For the experimental analyses materials of varying core hardness were used. In addition, the load capacity was tested for a variety of addendum modifications and tooth root fillet radii. Analysis criteria were: breakage, cracking, and plastic deformation. A universal relationship between deformation limit and crack initiation was found.Copyright © 2003 by ASME