Abstract
The bolts and nuts are widely used in various field s as an important joining machine element. To ensure the structure safety, a lot of special bolts and nuts were studied previously, and most of the researches focus on the anti-loosening performance. It is known that failures usually happen at the root of the first bolt thread, where the maximum stress concentration occurs. The previous experimental results showed that the fatigue strength may be improved under suitable pitch error existing between bolt and nut. However, the effect of the pitch difference on the stress and stress amplitude at each bolt thread has not been clarified. In this paper, at the first place, the fatigue experiment was performed with varying the pitch difference. The fatigue lives and fracture positions of different specimens were discussed. Then, the finite element method was applied to simulate the fatigue experiment and the stress status at the roots of bolt threads was obtained. As a result, it is found that when the stress amplitude is over the fatigue limit, the fatigue life of the bolt can be extended by introducing pitch difference.
