Abstract
It is common experience that threaded fastenings can be loosened by vibration even though they are initially tight.
In order to know the mechanism of the relaxation of threaded fastenings, the experiments were carried out by using a newly designed "repeated load test machine", on which the bolt to be tested was tightened on the seats.
The tightening force were measured by strain gauge pasted on the bolt tee tested.
As the experimental result, the mechanism of the relaxation of threaded fastening was clarified to some extent and the authors recommend the value of 0. 20. 5 for the coefficient of friction between bolt and nut.
Furthermore, the relaxing characteristic of threaded fastening under repeated load was formulized by some theoretical considerations.
