Effect of Thread Wear on Anti-Loosening Ability of Threaded Fastener under Vibration

In order to improve the anti-loosening ability of threaded fasteners under vibration, the anti-loosening abilities of the electro-zinc-plated fastener (EZP) and the electro-zinc-plated fastener treated by fine particle peening (FPP-EZP) were evaluated using a fastener transverse vibration apparatus. The surface damage and worn dimensions of the thread before and after testing were observed and measured using scanning electron microscopy. Then, a fastener stiffness model considering thread wear depth was used for numerical simulation of the effect of the wear depth on the threaded fastener preload. The test results show that the preload endurance limits of the EZP and FPP-EZP are respectively 2.8 kN and 2.0 kN, this suggests that the anti-loosening ability of the EZP is lower than that of the FPP-EZP. The observation results show severe damage on the thread surface for EZP, but no distinct damage on the FPP-EZP threads. The numerical simulation shows that the thread wear depth increases with the increase of the relative sliding distance between threads. Furthermore, the preload initially decreases nearly linearly with the increase in thread depth, and then rapidly. The thread wear can reduce the anti-loosening ability of threaded fasteners.