Proceedings of 4th International Conference on Fracture Fatigue and Wear, FFW 2015, Ghent University, Belgium, 27-28 August 2015The high strength bolts and nuts are widely used in various fields. In this study the effect of slight
pitch difference is considered when the nut pitch is αμm larger than the bolt pitch. In the first place, the fatigue experiment is conducted with varying pitch difference. The results show that the fatigue life is
extended to about 1.5 times by introducing the suitable pitch difference under the high stress amplitude.
Next, the detail observation is performed on the fractured specimens including the fractured positions and
the crack configurations. It is found that the fractured positions and the crack distributions vary depending on the pitch difference. Finally, to clarify the improvement mechanism of the fatigue strength, the finite element method is applied to calculate the stress amplitude and mean stress at each bolt threads, and the
incomplete threads at the nut ends are also considered to obtain the accurate analytical results