Microgeometrical influences on micropitting fatigue damage: multi-scale analysis

Abstract

Effective prediction methods are needed by engineers to design parts used in fatigue conditions. In gears, surface fatigue damage is observed at two scales: pitting and micropitting. These two phenomena occur in response to the variation of the local loading on the contact zone between teeth. The loading is influenced by the shape of the teeth and their surface roughness, which induces stress raisers. The pertinent geometrical parameters that determine fatigue lifetime need to be identified, and in this situation improved knowledge is still required. In the current study, seven parameters are used to define a generic tooth roughness profile. The transient mechanical loading acting on this rough tooth in rolling/sliding contact with a smooth tooth is obtained using elastohydrodynamic code. The stress time history is determined by integration so that pitting and micropitting can be predicted using the Crossland fatigue criterion. The ana- lyses were applied to results obtained for 32CrMoV13 quenched and tempered steel for about 50 variations of the generic roughness profile parameters. It was found that pitting (at the position of the maximum Hertzian shear stress) is influenced by four of the parameters, the extent to which the von Mises equivalent stress exceeds the material yield stress in the zone where micropitting occurs is influenced by two parameters, and the fatigue lifetime is influenced by three parameters.