Loosening accidents sometimes occur under several types of loadings such as winds, vibrations, earthquakes, impact loads and thermal changes. Recently, some studies have been conducted on the screw thread loosening in bolted joints under repeated transverse displacements. It is well known that bolted joints are easily loosened when repeated transverse loadings are applied [1]. In assembling bolted joints, double nut, spring plate washers and hexagon nuts with flange have been used. However, a few studies have been carried out on the loosening mechanism in bolted joints with the above parts for preventing the loosening. In the present paper, the effects of the double nut, spring plate washers and hexagon nuts with flange mentioned above are examined using FEM calculations. The experiments to measure the loosening in bolted joints were carried out using Junker’s testing machine for validation of the FEM calculations. As the results, it is seen that the loosening speed is the maximum when the hexagon nuts with flange is used. In addition, it is also observed that bolted joints in which almost nut parts for preventing loosening are applied are loosened easily in the FEM calculations. The amounts of loosening for bolted joints with double nut, spring plate washers and hexagon nuts with flange are in a fairly good agreement with the measured results. Discussion is made on the loosening mechanism of bolted joints with the above parts under repeated transverse displacements.

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