Analysis of Screw Fastener Loosening and Development of Evaluation Method.

Abstract

The inherent fault of screw fasteners is that they loosen. Loosening occurs most rapidly when vibration is applied at right angles to the bolt axis. In this paper, the mechanisms of loosening are discussed. A new loosening test method, which is designed based on the mechanism of loosening, is proposed. This method was employed to evaluate the claims of some supposedly antiloosening nuts and parts. The conclusions are as follows. (1) There are two main causes of loosenig. The first is torsion of the bolt due to slipping at the clamped threaded area. The second is the release of torsion during the slipping process at the bottom surface of the nut. (2) The method is useful in analyzing the mechanism of loosening, and also in evaluating the ability to prevent loosening. (3)Some supposedly antiloosening nuts and parts are effective only under limited conditions.