3.0 MW fan blade bolt is cracked

and obvious fatigue arc can be seen on its fracture surface.The breaking position is at the bottom of the bolt thread

and the final fatigue area is small

which is judged to be low-stress fatigue crack.A series of tests such as SEM & EDS

chemical composition

tensile properties and impact are carried out to compare the broken bolts and intact bolts.No obvious abnormality is found

and it is determined that the fatigue cause of the failed bolts is not directly related to the material of the parts itself.It can be seen from the stress analysis of bolts that the joints of bolts and nuts are stressed and become the initiation zone of fatigue cracks.When the bolt is subjected to alternating load

fatigue cracks occur at the stress concentration of the bolt

and eventually spread along the maximum direction of stress

resulting in fatigue crack.