Abstract
The transverse vibration test of bolts has been designed with adoption of the fatigue tester to study the features of the loosening life of bolts. Firstly, the transverse vibration frequency has been changed, the effects of the amplitudes of displacement, velocity, and acceleration on the loosening life of bolts have been compared, and it has been confirmed that the transverse displacement amplitude is the main factor that affects bolt loosening in low-frequency vibration. Secondly, the loosening degree of the bolts preloaded standard under five displacement amplitude grades has been monitored and the bolt loosening situation has been expressed through the residual preload-vibration times curve. The data of each stage of residual preload under each displacement amplitude were summarized, and the displacement-life (D-N) curve of bolt loosening under different loosening situations (percentage of residual preload) which is referred to the material fatigue life S-N curve was drawn. Finally, the accumulation mechanism of bolt loosening has been studied and the linear accumulation model of bolt loosening has been set up through designing variable amplitude vibration tests at high-low and low-high displacement stages. Results show that, through the bolt loosening D-N curve, it can be found out that the bolt loosening life curve and the material fatigue life curve are with features of double line and high- and low-cycle boundary under the logarithmic coordinate. Linear accumulation of bolt loosening is with similar principle of linear damage accumulation of material fatigue. Therefore, the bolt loosening life can be predicted through bolt displacement-loosening life (D-N) curve attained from the experiment and the established linear accumulation model of bolt loosening.
Highlights
In engineering application, it is very common for bolts to loosen when vibrating. e fatigue failure caused by the inadequate bolt tension is the main form of bolt vibration failure
In the vibration test “from small to big,” it can be found that the residual preload decreases significantly after the change of the vibration amplitude, which is due to the rapid fracture of bolts after the change, which decreases the residual preload to the minimum, as shown in Figure 12. e residual preload had decreased to 70% before the rapid fracture happened
The similarities of the bolt vibration loosening and fatigue were studied through tests and the bolt loosening was studied through the fatigue research
Summary
It is very common for bolts to loosen when vibrating. e fatigue failure caused by the inadequate bolt tension is the main form of bolt vibration failure. E bolt loosening life can be predicted effectively if a rule of bolt loosening life is found by using the method for studying fatigue properties of materials (such as S-N curve) It is of great guidance significance for the design and practical production and maintenance of bolt connection. Rough this experiment, Junker obtained the relationship among relative displacement between the clamped pieces, transverse (vertical to the bolt axis) force, and the axial residual preload applied to the bolt. He proposed that the influence of the transverse (vertical to the bolt axis) load or displacement on bolt loosening is the biggest. When reciprocating transverse vibration ±S happens to plane B and makes the resultant force of the inertial force and the component of gravity force along
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