Anti-loosening mechanism of pitch difference bolt nut connections based on Junker loosening test

Abstract

Bolt nut connections are essential elements and widely used in industry. The authors have verified that introducing a slight pitch difference between the bolt and the nut may improve the anti-loosening performance and fatigue life of the bolt nut connections. Besides, the effect of residual torque of pitch difference bolt-nut connections on the loosening resistance performance was discussed. In this study, the Junker loosening test was investigated experimentally and analytically to confirm the anti-loosening performance of pitch difference bolt nut connections directly. The FEA results are in good agreement with the experiments. It is confirmed that, for pitch difference bolt nut connections, the threads contact status is different from the common bolt nut connections, and the torque between the thread contact surface friction is the main reason of anti-loosening performance improvement of the pitch difference bolt nut connections. In addition, the results showed that if the pitch difference is large enough, the nut loosening angle equals the tightening angle for each vibration, and nut loosening does not occur. If the pitch difference is relatively small but just large enough to provide a prevailing torque, with increasing of the vibrations number of the nut, the loosening speed decreases gradually and finally the clamping force remains steady, which means the bolt nut connections retain anti-loosening performance to some extent.