The interface stress distributions in scarf adhesive joints with dissimilar adherends under static tensile loadings are analyzed using two-dimensional and three-dimensional finite element calculations. The effects of the adherends and adhesive Young's modulus, the scarf angle and the adhesive thickness on the interface stress distributions are examined. In addition, the joint strength is predicted using the interface stress distributions based on the maximum principal stress theory. It is found that when the scarf angle is around 60˚, the singular stress at the edges of the interfaces is minimum in the 3-Dimensional FEM calculations. Furthermore, it is noticed that the strength of the joints with dissimilar adherends is smaller than that of the joints with similar adherends. For verification of the FEM calculations, the strains in the adherends and the joint strengths were measured in the experiments. The measured strains are in fairly good agreement with those obtained from FEM calculations. Also, the measured joint strength is fairly consistent with the calculated results.
Bolted flange connections for wind power generations and chemical plants are subjected to repeated bending moments due to wind and earthquake loads. It is known empirically that the bolts loosening in the bolted connections occur. Thus, it is necessary to examine the bolt loosening in the bolted flange connections under repeated bending moments. The objective of the present paper is to clarify the mechanism of bolt loosening in bolted flange connections subjected to repeated bending moments and to discuss on a solution for preventing the loosening of the bolted flange connections subjected to repeated bending moments, too. The loosening mechanism of the bolted flange connections is examined using the FEM calculations and the experiments. In the loosening experiments using the specified hexagon nuts, it is observed that the loosening of the bolts in the connection occurs due to the permanent-set of the bolts and the movement of the bearing surfaces in the flange due to the external bending moment. In the FEM calculation, it is examined that the bolt loosening in the bolted flange connections qualitatively. In addition, it is found that as the bolt preload increase, the bolt loosening decreases. From the FEM results and the experimental results, it is found that the most effective part for preventing the loosening of the bolted flange connection is the eccentric nut.
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 loadings. It is well known that bolted joints are easily loosened when repeated transverse loadings are applied. While, in assembling bolted joints, the contact surfaces between a bolt head/nut and a clamped part are inclined geometrically. However, a lot of researches have dealt with the bolted joints in which the bearing surfaces are perfectly contacted without the inclined surfaces. Thus, it is necessary to examine the incline of the bearing surfaces on the loosening in bolted joint. A lot of parts for preventing the loosening have been proposed and sold at market. Among these parts, the authors have demonstrated that eccentric nuts are especially expected to be the solution for preventing the loosening of the joints under repeated transverse loadings. However, a few studies have been carried out on the loosening and loosening mechanism in bolted joints with inclined bearing surface and the effective solution for preventing loosening of bolted joint with the inclined bearing surfaces under the repeated transverse loadings. Thus, it is necessary to examine the effect of the incline at the bearing surfaces on the loosening and to evaluate the solutions for preventing loosening of the bolted joints with the inclined bearing surfaces. In this study, the effect of the incline at the bearing surfaces on the loosening is examined using FEM calculations. In the FEM calculations, the incline angle at the bearing surfaces is changed as 0, 2 and 3 degree, respectively. The experiments to measure the loosening in bolted joints were carried out using Junker’s testing machine to validities of the FEM calculations for revealing the effect of the loosening in the joints with the inclined bearing surfaces. In addition, nut parts for preventing the loosening in bolted connections with the inclined bearing surface under repeated transverse loadings are examined using the FEM calculations. As the result, it is seen that the loosening increases as the angle of incline increases. In addition, it is observed that bolted joints in which almost nut parts for preventing loosening are applied are loosened easily while the eccentric nut does not loosened. Discussion is made on the loosening mechanism in bolted joints under repeated transverse loadings.
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