| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 773952 | Engineering Failure Analysis | 2014 | 8 Pages |
•The fracture property and reasons of worm gear connecting bolts were studied.•The fracture of the bolts was two-way bending fatigue fracture.•There was a big gap between the bolt and bolt hole was the main fracture reason.•Surface decarburization and local stress concentration accelerated the fracture.•The study can provide reference to prevent similar failure reoccurring.
The worm gear connecting bolts of refueling machines of a nuclear power plant, with implementing standard of ANSI/ASME B18.3 and ASTM A574-08 and strength grade of 10.9, fractured at the thread neck position after running for about 10 years, and means such as macro examination, chemical compositions analysis, hardness testing, metallographic examination and fracture analysis, were used to analyze the fracture property and reasons of the bolts. The results show that the fracture of the bolts is due to two-way bending fatigue fracture. Surface decarburization of the bolts and stress concentration at the bolt thread neck decreased the fatigue strength of this position and resulted in the initiation of fatigue cracks. By comprehensive analysis and stress estimating, it was concluded that the main reason for fracture of the bolts is that there was a big gap between the bolts and the bolt holes, which resulted in fatigue fracture of the worm gear connecting bolts.
