Abstract：The purpose of this paper is to study the variation law of threaded joints loosening under transverse vibration, and examine the mechanical behavior during the loosening process. A single-bolted and single-lap joint structure was adopted as the research specimen. Based on this structure, a preload degradation model for bolted connections was developed.Subsequently, the friction torque and friction shear models of the bearing surface and thread surface were established. After that, the friction-shear model of the bearing surface and the thread surface caused by the additional bending moment is also established. Thereafter, the impacts of vibration amplitude, thread pitch and initial preload on the variation of bolt preload were analyzed, and the failure mechanism of bolt loosening is explored through case studies. In the end, a transverse vibration test bed was designed and fabricated, and the preload decline curves under different parameters were obtained, which verified the rationality of the theoretical model between the loosening factors and the preload. The results indicate that when the loosening torque exceeds the combined friction torque of the bolt head's bearing surface and the threaded surface, the bolt reaches the critical condition for loosening. The friction torque between the bearing surface of the bolt head and the thread pair's surface decreases when the vibration amplitude increases. And when the vibration amplitude reaches the critical value, the loosening of the bolt will be further accelerated. The greater the initial preload of the bolt, the more difficult it is to reach the critical condition of bolt loosening, and the slower the preload decay. Under the same conditions, the larger the vibration amplitude and thread pitch, the faster the preload declines.
2025, Vol. 46 
