Tooth Interior Fatigue Fracture — computational and material aspects

The hypothesis of the gear failure mode Tooth Interior Fatigue Fracture (TIFF), i.e. a fatigue crack is initiated in the interior of the tooth, is analysed by numerical simulations using FEM and the critical plane fatigue initiation criterion according to Findley. The residual stress profile in the gear is simulated and calibrated versus a neutron diffraction residual stress measurement. Fatigue properties are determined experimentally and are taken to vary with depth in the numerical analysis. In addition, the effect of shot peening is included. The analysis shows that a TIFF-crack is initiated approximately mid-height of the tooth and slightly below the case-core boundary. Furthermore, the analysis shows that TIFF is more pronounced in idlers than in single stage gears.