Fatigue Life Calculation Formula

The fatigue life (basic rating life) is the number of revolutions (or number of hours at constant speed) which 90% of a sufficiently large quantity of apparently identical ball bearings will complete or exceed before the first evidence of fatigue develops. The calculations are made according to DIN ISO 281.

Basic rating life in hours is calculated as follows:

The influence of load on the life is only to be taken into consideration in the above life equation. If the ball bearings listed in this catalogue are used for conventional bearing purposes, this life calculation will be sufficient.

As the life calculation only takes material fatigue as a cause of failure the calculated life will only correspond with the actual life of the ball bearing if the following requirements are fulfilled:

1. Sufficient lubrication is guaranteed during the whole running time.
2. The loads and speeds used in the calculation correspond with the actual operating conditions.
3. Contamination of ball bearing and lubricant is avoided.

Y = dynamic axial load factor