Study on self-loosening mechanism of bolted joint under rotational vibration

The self-loosening failure of bolt connection will bring a series of problems. Sakai first proposed the self-loosening theory of fixed nut and free bolt head under rotational vibration. Based on this theory, this paper proposed a more extensive self-loosening theoretical criterion under the boundary condition of free nut and free bolt head under rotational vibration. The theoretical analysis shows that there are two forms of self-loosening failure under the new boundary conditions, which are the bolt head self-loosening failure and the nut self-loosening failure. Combining with the finite element analysis, it is shown that the proposed self-loosening theory is in good agreement with the simulation results. It is concluded that the self-loosening mechanism of the first case is caused by the complete slipping of the bolt head bearing surface and the thread surface. In the second case, the self-loosening is caused by the complete slipping of the thread surface and nut bearing surface. Local slipping does not cause loosening failure, which is different from the loosening mechanism under transverse vibration. Finally, the influence of several factors on bolt loosening is studied. The results show that the vibration amplitude and initial preload have great influence on bolt loosening, while the vibration frequency has little effect on bolt loosening. •Proposing the theoretical prediction for bolted joint self-loosening on the free boundary conditions of bolt head and nut•Two forms of loosening failure are revealed: bolt head loosening; nut loosening.•The three-dimensional self-loosening failure mechanism map is drawn to more intuitively reveal the failure mechanism.•Fine finite element mode of bolted joint considering the helical thread and the hexahedral element is established to verify the new theory.•Complete slipping in the contact surface is the main reason for self-loosening under the rotational vibration.