Research On Self-loosening Behavior Of Two Bolted Joints Under Eccentric Excitation

As important connecting pieces in mechanical equipment,the bolted joints are easy to loosening in vibration environment,which has restricted the development of high-security,high-reliability and long-life for mechanical joining structures.Self-loosening behavior of bolted joints has been the focus of research at home and abroad,in view of its importance.Currently,researches on the self-loosening behavior of bolted joints are concentrate on the self-loosening under axial excitation and shear excitation.However,in the actual project,the bolted joints also bear the eccentric excitation,but few research on it.This paper focuses on the study of self-loosening behavior of two kinds of bolted joints under eccentric excitation.This study will not only enriches the theoretical system of self-loosening mechanism,but also has important significance in solving the problem of self-loosening of bolted joints and expanding the practical application of fretting tribology.Based on the design and manufacture of the bolt loosening test rig,the loosening tests of bolted joints subjected to eccentric excitation have been carried out.According to the evolution curves of the axial force of the bolt,the self-loosening behavior of bolted joints under eccentric excitation was investigated.After the tests,the damage of threads was analyzed,and the influences of fretting behavior between the contact threads on self-loosening of bolted joints were discussed in depth,and the self-loosening mechanism of bolted joints had been revealed in details.In addition,finite element analysis software ABAQUS was used to analyze the contact stress,the slip amplitude and the dissipated friction energy.The experimental results were further explained and verified.The main obtained results are as follows:(1)The self-loosening process of the bolted joints can be divided into two stages:Firstly,because of the removal of asperities on the contact surfaces and the plastic deformation,the axial force of the bolt drops rapidly.Secondly,because of the fretting wear of contact surface,the axial force of the bolt drops slowly.Damage morphology analysis shows that the wear mechanism of contact threads is delamination,abrasive wear,adhesive wear and oxidation wear.It is an extremely complex wear behavior.(2)It is found that the eccentric distance,the amplitude of excitation and the preload have a significant impact on the self-loosening behavior of two bolted joints.For L-bolted joints,with the increase of the eccentric distance and the amplitude of excitation,the loosening degree increases gradually,the loosening degree increases gradually,and with the increase of the preload,the loosening degree decreases gradually.For T-bolted joints,whenthe factors of the self-loosening are symmetrically distributed,the loosening degree of the left and right sides of the T-bolted joints is basically the same,but when the factors of the self-loosening are asymmetrically distributed,the loosening degree of the left and right sides of the T-bolted joints are different.The specific performance is: with the increase of the eccentric distance,the loosening degree increases,and with the increase of the preload,the loosening degree decreases.(3)The numerical analysis results: For L-bolted joints,the dissipated friction energy increases with the increase of the eccentric distance and the amplitude of excitation,and decreases with the increase of the preload.For T-bolted joints,when the factors of the self-loosening are symmetrically distributed,the dissipated friction energy of the two bolted joints is approximately equal;but when the factors of the self-loosening are asymmetrically distributed,the dissipated friction energy increases with the increase of the eccentric distance,and decreases with the increase of the preload.