Fatigue spall initiation is one of the major modes of premature bearing failure. The spall initiation is often exacerbated by the presence of impurities in the near-surface region (∼400 μm) of the bearing raceways. Once a spall initiates, it can propagate rapidly, leading to abnormal bearing operation and possible catastrophic failure if not detected early. Testing performed at the University of Texas-Pan American (UTPA) has focused on ultrasonically scanned tapered roller bearings found to have inclusion content within 400 μm of the surface of the raceways. These bearings undergo accelerated service life tests in which spall initiation is detected and tracked over time while documenting spall growth. The work presented here provides several study cases that document the spall initiation and propagation on ultrasonically scanned tapered roller bearing components. Results show that spalls generally initiate on locations corresponding to sites of subsurface inclusions, and they grow many times their original size within relatively short operating periods. The study also shows that spalls tend to initiate and propagate at a faster rate on bearing cups (outer rings) than on cones (inner rings).

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