A certain type of aircraft is inspected during use

it is found that exhaust valve motor fixed bearing has suspected crack. After the cleaning

the dye penetrant inspection finds penetrative cracks. The bearing material grade is АЛ34（domestically produced grade is ZL116）

the heat treatment requirement is σ

b

≥294 MPa

and the surface treatment requirements are anodizing sulfuric acid and dichromate filling/priming. The bearing is above the engine compartment and is subject to relatively large vibrations. Through the observation of the fault bearing appearance

stereo inspection

microscopic observation

energy spectrum analysis

metallographic examination

hardness test and other tests

it is concluded that the bearing has fatigue crack

and the main cause of fatigue is stress concentration. Due to the existence of welding defects

the cracks expand rapidly

which is the direct cause of the formation of fatigue cracks.According to the analysis results

a effective method is given to improve the fatigue resistance of the bearing parts and avoid the recurrence of faults. And prevention advice is also put forward.