Tooth flank fracture – An applied fatigue study of case hardened bevel gears

Abstract

A material model for carburized CrNiMo steel and an advanced shear stress intensity, multiaxial fatigue criterion against surface and subsurface fatigue in bevel gears have been developed and presented in earlier publications. This study assesses the accuracy of the proposed methodology by comparing it to load-controlled bevel gear tests at varying hardening layer thicknesses. The dominant failure mode was wheel-initiated tooth flank fracture. Fractographic analysis by means of scanning electron microscopy revealed a severely elongated MgO-Al2O3 cluster in the only pinion-initiated tooth flank fracture. By correlating the calculated material utilizations and the number of cycles to failure, a reiterated lifetime factor is presented. The refined methodology is shown to be capable to differentiate between and accurately predict pitting and subsurface fatigue under well-defined test conditions.