Fracture Analysis of Lug Boss of Engine Bearing Outer Ring

There was a metal filing alarm during the test run of engine, and the lug boss of the No.4 bearing outer ring was found fractured after the overhaul. Visual observation and the stereoscopic microscope were used to analyze the appearance and marks of the bearing outer ring, the scanning electron microscope was used to analyze the fracture, the material structure and the hardness of the outer ring were examined. The results show that the fracture property of the lug boss of the No.4 bearing outer ring is fatigue. The fatigue fracture is due to the assembly interference, which caused by the improper size and shape coordination between lug boss and reef groove. This kind of failures can be prevented by increasing the depth of groove, and chamfering the lug boss of the bearing outer ring instead of groove, which avoid the assembly interference.