Crack path and regularities for ball-bearing fracture in the very high cycle fatigue regime

The process of fatigue spalling in the rings of ball bearings at durability exceeding 10 cycles under in-service loading conditions is analyzed on the basis of fractography and the slices prepared in radial planes of rings. The cracks are shown to originate at subsurface from carbides inherent in the bearing steel or inclusions permissible by sizes for the material. Subsequently, the development of cracks perpendicular to the ring raceway surface takes place similarly as in the VHCF regime with the elliptical “fish-eye” formation. The subsequent crack growth was demonstrated step-by-step up to the ring material fragment separation. The total crack path by alternating stops of propagation and new crack nucleation under conditions of mixed-mode I+II+III mechanisms with the crack branching was discussed. In the final stage, the crack grows towards the ring raceway and either appears on the raceway surface or coalesce with a similar adjacent crack followed by fatigue spalling formation.