数値解析による遠心力を受けるボルト締結体の力学特性の評価

抄録

  Bolted joints used in rotary machines, such as electric generators, are commonly subjected to high centrifugal forces. When rotary machines are used in a way that repeats running and shut-down conditions, a fair level of stress amplitude occurs in the threaded portions of bolted joints. The magnitude of stress amplitude increases as the rotational speed is increased, which may lead to fatigue failure of the joint. To avoid such fatal accidents and provide effective guidelines for designing rotary machines, it is necessary to clarify the fundamental mechanical behavior of bolted joints under centrifugal forces.

  In this paper, using the three-dimensional finite element method and elementary theory of solid mechanics, the mechanical behavior of bolted joints subjected to centrifugal forces is comprehensively studied. In this process, emphasis is placed on the maximum stress amplitude and the rotational speed that causes the complete separation of the interface and lowers the joint strength. It is found that the maximum stress amplitude occurs at the first bolt thread root, and it shows a steep increase when the contact between clamped parts is almost lost. It is also shown that the elementary theory of solid mechanics on compound cylinders can be successfully applied to estimate the aforementioned critical rotational speed.