The failure mechanism of high DN value (bearing inner diameter multiply speed) bearing cage was analyzed. The results of roller bearing cage broken under the theory of ultra-high cycle fatigue showed that the method of designing of cage based on high cycle fatigue didn’t apply to high DN value cage. The stress causing fracture within over-long design life was far below fatigue limit of the material. The centrifugal stress caused by high speed contributed a lot to high DN value bearing cage fracture

and the main reason causing cage fracture was attributable to stress concentration because of the small pocket fillet. Therefore increasing pocket fillet and clean-up machining would help avoid cage fracture

and increase reliability of bearings.