1989 Volume 55 Issue 518 Pages 2611-2617
The stress distribution in a bolted joint and the pressure distribution on the bearing surface of a hexagonal flange nut have been examined by the three-dimensional photoelastic experiment. The experiment shows that the stress distribution in a bolted joint is axially asymmetrical, because the screw part has an axiasymmetrical shape. The pressure distribution on the bearing surface of hexagonal flange nuts has the asymmetry corresponding to that stated above. The radial distribution of the bearing surface pressure concentrates at the inner part of the flange, while the pressure on the bearing surface at the outer part of the flange is reduced to almost zero. Namely, the pressure on the bearing surface of the hexagonal flange nuts is not uniformly distributed. In the case of a nut having some part without the thread, i. e, an improved nut with the skirt, the peripheral portion of the nut can bear the load pressure which has uniform distribution in all directions of circular angles. Thus the cause of loosening due to asymmetrical distribution of pressure on the bearing surface is eliminated.