Lubricant-Crack Interaction, Origin of Pitting, and Fatigue of Drivers and Followers

Abstract

A mechanical model for lubricated elastic solids weakened by cracks is studied. The model is used to explain mechanisms of surface and subsurface originated contact fatigue. Subsurface and surface cracks are considered including the interaction of lubricant with elastic solids within cavities of surface cracks. The adequate boundary conditions for the crack displacement jumps and normal stress applied to crack faces within the surface crack cavities fully or partially filled with lubricant as well as for subsurface cracks arc used. These boundary conditions include conditions that: prevent crack faces from overlapping, describe multiple surface crack cavities fully or partially filled with lubricant etc. Numerical results for surface and subsurface cracks are discussed, and numerical and asymptotic results for small subsurface cracks are compared. It is shown that stress intensity factors for surface cracks may be two orders of magnitude higher than those for subsurface cracks. Based on the crack analysis it is shown that pitting has predominantly subsurface origin. Moreover, an explanation of the difference in fatigue behavior of followers and drivers is presented. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002