Crack path and regularities for ball-bearing fracture in the very high
cycle fatigue regime
Abstract
The process of fatigue spalling in the rings of ball bearings at
durability exceeding 10 8 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.