Reason of double planetary gear broken teeth

The double planetary gear on the electric wheel of a certain type of mining car broke during operation. The reason for the fracture of the planetary gear was analyzed using methods such as macroscopic observation, scanning electron microscopy analysis, metallographic examination, and hardness testing. The results show that the typical fatigue fracture characteristics were observed at the broken teeth of the planetary gear. The crack source was located approximately 2 mm from the subsurface of the tooth root. There was a large-sized spindle shaped alumina inclusion parallel to the tooth width direction at the crack source, where the crack initiated and expanded, ultimately led to gear fracture.