A bolt connection is widely used to put things together. Since a bolt screw has a valley shape, it is well known the stress concentration occurs there. Therefore, from fatigue point of view, in order to design the structure with bolt connection, it is very important to predict stress at a bolt screw of the structure accurately, especially stress amplitude under operating condition.

The example introduces the method to predict stress amplitude at a bolt screw of machine structure under operating condition and including nonlinear phenomena such as contact and plastic behavior as well as axial force and shape of thread of a bolt with practical computer cost.

The example states "Sub-modeling Analysis" so-called "Zooming Analysis", which has a feature that analysis starts from linear transient response analysis then moves to nonlinear structural analysis including contact and plastic behaviors in zooming model of the hot-spot.

This analytical process makes it possible to simulate the deformation of a bolt screw under operating condition properly and to keep the low computational cost.

Regardless loading or unloading on a bolt connection, the following output of the analysis indicates stress amplitude increases at a bolt point even though stress at a bolt point is low comparing to one at a start point of a bolt engagement, which tells a bolt point has a disadvantage for fatigue strength.