Research On The Self-loosening Mechanism Of Blind Hole Bolted Joints Under Shear Excitation

Bolted joints are commonly used fasteners in mechanical equipment which has the advantage of simple structure,convenient assembly and economic applicability.Due to vibration impact and other factors,the bolted joints failed in the actual working conditions which cause great safety hazards.Therefore,domestic and foreign scholars have carried out a series of studies on the self-loosening behavior of bolted joints.At present,the research of bolted joints is focused on the bolt/nut connection structure,but there is less research on blind hole bolted joints structure.This paper studied the self-loosening behavior of blind hole bolted joints under shear excitation,and the fatigue life of blind-hole bolted joints is analyzed and verified,these have important guiding significance for the practical application of blind-hole bolted joints.In this paper,a device for loosening test of blind hole bolted joints is designed,and the self-loosening behavior of blind hole bolted joints is studied under shear excitation.The dynamic response and loosening curve of blind hole bolted joints are discussed under different parameters.The damage morphology of thread contact interface was analyzed,and the fretting behavior of the contact surface is discussed in depth.The loosening mechanism of the blind hole bolted joints is further revealed under shear excitation.The finite element method was used to simulate the blind hole bolted joints.The change rule of contact state between threaded interfaces is studied and analyzed with the test results.The main conclusions of this paper are as follows:(1)The dynamic response of blind-hole bolted joints shows that the relative slip of the threaded contact interface decreases with the increase of preload,and the micro-slip phenomenon of the threaded contact interface changes from local slip to complete slip with the increase of load amplitude.(2)The results of damage morphology analysis of the threaded contact interface show that the damage defects are discontinuous due to the uneven distribution of load on the contact interface.The damage of thread contact interface is a complex phenomenon which includes fatigue wear,adhesion wear,oxidation wear and abrasive wear.(3)The self-loosening process of blind hole bolted joints can be divided into three stages: firstly,due to the need of testing machine to gradually load to the set load,the axial force of bolts appears light microwave vibration;secondly,because of the removal of asperities on the thread contact interface and plastic deformation of materials,the axial force of bolts drops rapidly;finally,due to fretting wear at the contact interface that the axial force of bolts decreases slowly.(4)The results of finite element analysis show that the relative slip amplitude and friction dissipation energy decrease with the increase of preload.With the increase of the load amplitude,the wear phenomenon of the thread contact interface becomes more serious,which leads to the increase of friction dissipation energy.