FEM Stress Analysis and Design for Bolted Circular Flange Joints Under Tensile Loading

In designing a bolted joint, it is necessary to know a ratio of increment Ft in axial bolt force to an external tensile loading W, that is, the load factor φ=Ft/W. In our previous paper, the new formulation for obtaining the value of the load factor φ for a bolted joint in which two hollow cylinders and two T-shape flanges were clamped was proposed by introducing the tensile spring constant Kpt for clamped parts. Then, the values of the load factor of bolted joint obtained from our formulation are shown to be in a fairly good agreement with the experimental values. In the present paper, the mechanical characteristics of bolted circular flange joints are analyzed by Finite Element Method (FEM) and axi-symmetrical theory of elasticity such as the load factor, the contact stress distributions at the interfaces and a load when a separation occurs at the interfaces. For verification of the analyses, experiments were carried out to measure the load factor, the maximums stress and a load when a separation occurs. In the analyses, the effect of the bolt pitch circle diameter D on the value of the load factor is examined. The numerical results of the load factor are fairly coincided with the experimental results. As the results, it is found that the load factor decreases as the bolt pitch circle diameter D increases and that the value of the load factor is less than 0.1. It is also found that the load when the interfaces start to separate decreases as the value of D increases. Based on the obtained results, a design method for the bolted circular flange joints under tensile loadings is demonstrated, that is, the method how to determine the bolt nominal diameter, bolt strength grade, the bolt preload for the external tensile loading are described.