A standardizable approach for Tooth Flank Fracture

Abstract

AbstractUltrasonic scanning of large spiral bevel gears and the subsequent fracture analyses of early-stage tooth flank fractures imply a mode II crack initiation under surface-parallel, orthogonal shear stresses. An iteration of the Dang Van criterion is presented that focuses exclusively on surface-parallel material planes, yielding a standardizable approach for the study of tooth flank fracture in spiral bevel gears. It is shown that Dang Van’s shear stress amplitude and maximum hydrostatic stress along a surface-perpendicular path can adequately be described by the Hertzian orthogonal shear stress amplitude and Lang’s compressive residual stress. The fatigue properties along the same path are estimated from Thomas’ hardness model and augmented by ISO-inspired lifetime, size and conversion factors. The article closes with a comparison between the commonly used Witzig-Boiadjiev, Hertter-Wirth, DNV subsurface fatigue and the herein proposed, rationalized Dang Van criterion.