Analysis And Experimental Study On Loosening Characteristics Of Bolted Connections

As a common fastening means,bolt connection structure is widely used in various mechanical structures,especially in the field of Aeronautics and Astronautics.The quality of the bolt connection structure is very important to the overall performance of the mechanical equipment.Loosening is one of the main forms of the failure of the bolt connection structure,which will lead to the gradual decrease of the clamping force between the joints,even the failure of the whole bolt connection,and cause a major accident.Therefore,it is very important to study the loosening of the threaded connection structure for the engineering practice.This paper focuses on the loosening of bolt connection bolts,mainly from the load analysis of the bolt connection structure,the loosening finite element analysis and the loosening test to explore the loosening mechanism of the bolt connection structure,and a series of research work has been carried out.The specific work and main thesis of the paper are as follows:(1)First,the load distribution and loosening behavior of the bolt connection structure are theoretically studied.Through the theoretical calculation of the axial load distribution and the loosening torque of the bolt structure,the influence factors of the bolt loosening are qualitatively explored.(2)Secondly,a finite element simulation analysis method for loosening of the bolt connection structure is proposed by using the angle method to appl y the preload.The finite element simulation analysis of the loosening of the bolt connection structure under the transverse vibration is carried out.It is found that in the initial stage of transverse vibration,the decrease of preload is mainly due to plastic deformation of materials;there is no obvious relative sliding between the meshing threads,but the joint rotation caused by the elastic torsion deformation of the bolt,and points out that the joint which characterizing the elastic torsion deformation of the bolt is fast and slow to distinguish the loosening period of the material and the period of loosening of the structure.(3)Thirdly,various factors influencing the loosening of bolt are simulated,and the influence of each factor is analyzed.The large initial preload,the large friction coefficient of the support surface,the small friction coefficient of the screw thread,and the small aperture gap of the bolt rod are more favorable to the loosening of the bolt connection structure.(4)Finally,the bolt loosening test bench was designed and established,and the bolt loosening test was carried out.The accuracy of the simulation method was verified by comparing the test results and simulation results,which could provide reference for the bolt loosening test and research work in the future.