A tractor trailer's front wheel separated from the axle, traveled across the median and struck an oncoming vehicle, resulting in a fatality. A metallurgical failure analysis was requested on the truck's front axle, several wheel bearings, the left front wheel hub, brake drum and brake shoe. The failure analysis was limited to a visual inspection only.
After visual and microscopic examination the possible causes of the bearing failure were:
- Improper wheel bearing installation – The truck had traveled a small number of miles since bearing installation.
- Improper/inadequate lubrication – The testimony of the driver also supported the theory that wheel bearing lubrication was properly maintained and inspected.
Latent product defect – The driver testified he neither heard nor felt anything unusual prior to the incident, indicating the bearing failure was a sudden and unexpected event. A latent defect in the subject bearing would have increased in size propagating by metal fatigue.
Failure of the subject bearing and loss of the left front steering axle wheel was probably the result of a latent defect in the subject front axle wheel bearing.
Photograph A Failed wheel bearing inner race showing lack of lubrication.