A modelling approach for considering material and structural properties in the calculation of local tooth root endurance limit of case hardened gears

Gear and gearbox design require reliable strength numbers to calculate the tooth root load carrying capacity. These values can be determined directly by experiments on the one hand, which is often associated with considerable effort and costs, or, on the other hand, with the aid of established calculation standards, such as ISO 6336‑3. This is based on reference values for strength parameters for various heat treatment and manufacturing processes, such as case hardening. To further increase the precision of the calculation of the tooth root endurance limit of case hardened gears, this paper presents an extended approach considering actual material and structural properties after manufacturing, some of which are currently not yet directly included in standard calculations. For this purpose, an existing calculation approach for the formation of cracks in the tooth root area was adapted, applied and validated with experimental test results in the pulsator test rig on the tooth root load carrying capacity. It can be shown that the calculation results are in good accordance with the experimental results and that the approach is fundamentally suitable for determining the tooth root endurance limit of case hardened gears.