Semi-metal and non-metal gaskets (spiral wound, joint sheet, etc.) are well known that their stress-strain curve shows strong nonlinearity and hysteresis. These characteristics should be considered, when we analyze the behavior of a bolted flange joint. Regarding the analysis of bolted flange joints, authors had proposed a simplified modeling method of gasket stress-strain curve for FEM analysis in the previous PVP conferences. The method approximates the nonlinearity of gasket stress-strain relation using two different linear elastic moduli in loading and unloading, respectively. This paper provides that the comparison of computed results due to the simplified analysis and the ones due to accurate nonlinear analysis that uses a nonlinear-hysteresis gasket model. This paper also proposes the guidance to determine the two linear elastic moduli for the simplified modeling. Since the simplified analysis gives a good approximation, we conclude that the method is very useful for the analysis of bolted flange joints, especially in design stage of pressure vessel flanges or piping flanges.
Bolted joints have been used in mechanical structures. However, loosening accidents sometimes happen under several types of loadings. Recently, some studies have been conducted on the screw thread loosening in bolted joints. It is verified that bolted joints are loosened when transverse repeated loadings are applied. A lot of parts for preventing the loosening in the joints have been proposed. Among these parts, eccentric nut is especially expected to be the solution for preventing the loosening. Some studies on no rotational loosening in bolted joints under thermal changes have also conducted. However, few studies on rotational screw thread loosening in bolted joints have conducted. In our previous study, mechanism of rotational screw thread loosening in bolted joint under repeated temperature changes was examined. However, the difference in the loosening mechanism between the FEM results and the experimental results was substantial. In this study, the effect of the incline at the bearing surfaces was taken into consideration on the loosening. In addition, the loosening in the bolted joint with the eccentric nut under repeated temperature changes was examined using finite element method (FEM) calculations. Discussion is made on the mechanism and a solution of rotational screw thread loosening in the bolted joints under the repeated temperature changes. The results show that a reduction in axial bolt force was increased when the incline at the bearing surfaces was taken into consideration and the eccentric nut was shown for preventing the bolt loosening.
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