Fracture failure analysis on swivel nut of 30CrMnSiA steel in aircraft

In this work, the cracks of HB4-49-14CdD swivel nut in aircraft were found and analyzed by macroscopic observation, morphology testing and metallographic examination. In order to figure out the cause of cracks, manufacturing and assembling process were investigated, and finite element method was used to simulate the tightening process. The results showed that overload tightening torque lead to the fracture and failure of swivel nut.