Research On The Loosening Failure Mechanism Of Threaded Fasteners Under Multi-Axis Random Vibration

With the rapid development of the aviation industry,the performance requirements of modern defense for missiles have become more stringent.The problem of missile damage caused by vibration has been paid more and more attention.The vibration environment caused by missile transportation and launch is random and complicated.Due to the limitations of the traditional one-axis random vibration test,people are more inclined to use the multi-axis random vibration test to screen the missile.For threaded fasteners in missiles,looseness is unavoidable in a multi-axis random vibration environment.With the advancement of science and technology,many scholars have carried out more research on the loosening of threaded fasteners under vibration conditions,and have achieved many results,but the research results are limited to the thread tightening under one-way simple harmonic vibration state.Firmware,theoretical research and tests related for loosening characteristics of threaded fasteners under three-axis random vibration.Therefore,in order to improve the reliability of high-strength threaded fastener connection in actual engineering,the research on the loose failure characteristics of threaded fasteners under multi-axis random vibration has theoretical research significance and engineering reference value.Therefore,this paper mainly uses the finite element analysis method to study the loose failure characteristics of small-sized high-strength screw joints in an electronic cabin.The main research contents of this paper are as follows.(1)The effectiveness of the simplified threaded MPC method is verified.Both the MPC method and the thread area method are simulation analysis ones for Simplified threaded connection structures.The advantages and disadvantages of the two methods are compared by simple bolt connection structure.It is found that the analysis results are similar,but the MPC method is convenient to operate and the calculation efficiency is higher.Therefore,the MPC method is adopted in the threaded connection structure of the cabin with a large number of units,and the accuracy of the pre-tightening method of the threaded connection is verified.(2)The necessity of triaxial random vibration research is certified.Taking the structure of an electronic cabin segment as the analysis object,the simplification,deletion and reconstruction of the detailed features of the complex cabin geometry model are carried out,and the finite element model of the cabin structure is established.Quantitative comparisons are made between the simulation results of the two excitations.It is found that the stress and acceleration responses on the connecting bolts of the three-axis simultaneous loading are larger,and the number of resonant modes excited is more.It confirms the correctness of the theoretical analysis results of one-axis and three-axis random vibrations.(3)The simulation analysis method of bolt loosening failure is explored and verified by experiments.The three-axis random vibration environment test of the computer circuit board in the electronic cabin is carried out on the three-axis vibration table,and the loosening phenomenon of the fixed bolt is monitored.Furthermore,the simulation of the loosening process of bolts in the same vibration environment is carried out in the finite element simulation software.The relationship between the bolt preload torque and the stress and strain response of the monitoring points during bolt loosening is obtained.The simulation results are basically consistent with the test results.T he rationality and feasibility of the finite element simulation method are verified.(4)The screw loosening mechanism under three-axis random vibration is studied.Taking the fastening screw in the key part of the electronic segment as an example,the screw loosening process under three-axis random vibration is simulated.According to the dynamic response characteristics of the screw,the screw loosening process is divided into three periods: stable period,transition period and loosening period,and reveals the mechanism of screw loosening under three-axis random vibration environment.Finally,three kinds of anti-loose suggestions are proposed for the screw connection characteristics in the electronic cabin.