Abstract
Bolt tightening is widely applied to the fastening of mechanical and structural elements. However, as various external forces act on machines and structures, fastened elements are displaced mutually and relatively, which loosens tightened bolts as the time passes. Prior occurrences indicate that bolt looseness like this has often incurred serious accidents. To counter the problem, the authors experimentally made a special washer that enlarged the displacement caused by a minimal looseness of tightened bolts by applying the principle of leverage to such an extent that the displacement can be visualized. The special washer, which displaces in accordance with the law of gravity as the looseness occurs, can construct the definite safety confirmation type.
