Research On Self-Loosening Behavior And Numerical Simulation Of Steel Threaded Joints Under Axial Vibration

Threaded joints are widely used in all kinds of mechanical components, and are very important to the performance of the mechanical equipment. Self-Loosening of bolted joints, which means the clamping force of thread joined structures decreases continuously under vibration environment, is a serious safety hidden danger. Currently, researches on the loosening of threaded joints were concentrated on the loosening problems due to harmonic shear loads, while existing reports about loosening of screwed joints under axial vibration were mainly based on theoretical derivation. Fretting damage often occurs between fastening mating screw contact surfaces of bolted joints under axial vibration, which can cause phenomena such as loosening and scuffing of screw connection, but few study were focused on this factor. This paper concentrated on the effect of plastic deformation and fretting wear in the loosening process provides an important theoretical significance for understanding of the self-loosening mechanism of threaded joints. Also, it offers an important reference value for resistance to loosening of threaded joints in engineering.Based on the design and manufacture of the bolt loading device, the fatigue tests of self-loosening of threaded joints under axial vibration have been carried out. By analyzing the plastic deformation of bolt and the fretting damage of screw contact, the loosening mechanism of threaded joints were explored and influence of both axial load and pre-tightening torque were discussed. Then finite element analysis software ABAQUS was used to simulate thread joined structure and the experimental phenomena were explained further in this part from the following aspects:equivalent stress, contact state and cumulative plastic deformation. The research results were mainly as follows:(1) The self-loosening process of threaded joints under axial vibration can be divided into two stages:firstly, the clamping force decreased greatly due to the cyclic plastic deformation of the materials; secondly, the clamping force reduced slowly caused by fretting wear between contact threads. The wear mechanism of contact threads was mainly adhesive wear, abrasive wear, fatigue wear and oxidative wear, which was a very complicated wear behavior.(2) The loosening degree of threaded joints increased with the increase of axial load and decreased with the increase of pre-tightening torque; the clamping force decreased obviously, however, the breakaway torque had no obvious change compared to the pre-tightening torque.(3) Stress and plastic deformation of different working threads were obtained through finite element analysis, and the equivalent stress, contact state and cumulative plastic deformation of the first working thread under different axial load and pre-tightening torque were discussed to explain the experimental phenomena.