Finite Element Analysis of the Load Factor and New Design Method for Bolted Joints Consisting of Dissimilar Hollow Cylinders Under Tensile Loads

In designing a bolted joint consisting of dissimilar hollow cylinders, the load factor (the ratio of an increment in axial bolt force to an external tensile load) is important. However, no researches on the characteristics of bolted joints consisting of dissimilar joint members have been conducted. In this paper, the effects of load application positions, the ratio b/a of the outside diameter to the inside diameter of dissimilar hollow cylinders, Young's modulus ratio between the dissimilar hollow cylinders on the load factor, and a load when the interface separation starts are examined using finite element method (FEM) calculations. As a result, it is found that the values of the load factor decrease as the ratio b/a increases, and the load application position approaches the interfaces, while the value of the load factor is independent of the bolt preload. For verification of the FEM calculations, experiments to measure the load factor and a load when the interfaces start to separate were carried out. The FEM results are fairly coincident with the experimental results. It is found that the value of the load factor is less than 0.15 for steel and aluminum joints, it is less than 0.1 for steel and steel joints, and it is less than 0.2 for aluminum and aluminum joints, where the bolt material is steel in this study. Finally, using the obtained load factor, a new design method for bolted joints with dissimilar hollow cylinders is demonstrated for determining the nominal diameter of bolt, the bolt strength grade, a target tightening torque, and a target bolt preload. Additionally, in the design procedure, an issue if a washer should be inserted or not inserted is discussed as well as determination of bolt preload.