Tooth Flank Fracture – Design Process for a New Test Gearing and First Test Results

Tooth flank fracture (TFF) is a gear fatigue failure mode. TFF differs from tooth root breakage and pitting in that the crack emerges below the hardened case of the active flank. However, like tooth root breakage, it leads to a total breakdown of the gears in contact and often in severe failure of the entire transmission. TFF recently has occurred more frequently, especially in larger sized gears. This makes it all the more important to investigate TFF failures. In order to avoid TFF in the future, a calculation method, that must be applicable in the design phase is needed and should be widely verified by experimental results. For the systematic investigation of TFF, smaller sized test gears are used. So far, only test gears for TFF with a center distance of 200 mm are commonly used. Although the gears are significantly smaller than those used in the relevant industrial applications, extensive experimental investigations still result in high costs. A smaller sized test gearing with a center distance of 91.5 mm would reduce the costs of manufacturing the test gears significantly and also offer more testing capabilities based on the use of standardized FZG back-to-back gear test rigs. Based on the experimental results of the test gears with a center distance of 200 mm, a calculation approach (ISO/TS 6336-4) was developed in the FVA 556 I research project. In this work, this practical approach is used to design a smaller sized test gearing with a center distance of 91.5 mm. The test gear pairing is tested with a back-to-back test rig and initial test results are shown and discussed. In addition, results of further investigations regarding microstructure, hardness and residual stresses are presented.

Authors: Daniel Müller, Thomas Tobie, and Karsten Stahl 

ISBN: 978-1-64353-097-0