4. The static check, which is a different failure
Fatigue life assumes the bearing turns. A bearing that is stationary, or barely moving, under a large load fails another way entirely: the balls press permanent flats into the races. Brinelling. Once that has happened the bearing is noisy and rough forever, however good its calculated life was.
P0 = X0 Fr + Y0 Fa
s0 = C0P0ISO 281
C₀ is the basic static load rating, a separate catalogue number, defined by a permanent deformation of 0.0001 of the rolling element diameter. P₀ never falls below Fr.
| Requirement | s₀ |
|---|---|
| Quiet running, high precision | ≥ 2 |
| Normal running | ≥ 1 |
| Coarse, noise not a concern | ≥ 0.5 |
When the static check governs. A robot joint that holds a payload
stationary for hours, a crash into an end stop, a machine lifted by its shaft during installation.
None of those appear in the fatigue calculation at all, and all of them can ruin a bearing that
passes it comfortably.