How to improve bolt fatigue strength
Fatigue failure is a common failure mode for high-strength bolts, regardless of complex loads. As early as 1980, some experts studied the failure of 200 cases of bolted connections, of which more than 50% were fatigue failure. Improving the fatigue resistance of high-strength bolts is critical.
Fatigue fracture of bolts has the following characteristics:
1. The maximum stress of fatigue fracture is much lower than the strength limit of the material
under static stress, even lower than the yield limit.
2. The fatigue fractures are all brittle fractures without obvious plastic deformation.
3. Fatigue fracture is the result of accumulation of microscopic damage to a certain extent.
For bolts, the failure modes are mainly plastic deformation of the threaded part and fatigue
fracture of the screw, among which:
65% of the damage occurs in the first thread connected to the nut;
20% of the damage occurs at the transition between the thread and the polished rod;
15% of the damage occurred at the transition fillet between the bolt head and the screw.