The mutually reinforcing mechanism of bolt loosening and thread fretting wear
Q1: Why do bolts suffer fretting wear in a vibrating environment?
A1: Repeated train vibration causes tiny relative slip on the thread contact surface between bolts and nuts, and contact peaks continuously friction and peel off, forming fretting wear. Metal powder generated by wear intensifies abrasive effect, rapidly destroying thread profile and expanding fitting clearance.
Q2: How does fretting wear accelerate bolt loosening?
A2: Wear reduces the roughness of thread contact surface, lowers friction coefficient and deteriorates preload retention capacity. Under vibration load, tiny slip gradually accumulates into macroscopic rotation, bolts loosen rapidly, preload is almost completely lost, and joint stiffness drops sharply.
Q3: Why are joint bolts more prone to such diseases than ordinary fastener bolts?
A3: Joint parts have strong impact and large vibration, complex bolt stress and larger fretting amplitude. At the same time, joint opening and closing movement aggravates thread relative slip and faster wear speed. Therefore, joint bolt loosening and thread slipping are far more than intermediate fastener bolts.
Q4: To what extent does thread wear lose fastening function?
A4: When the thread profile wear exceeds 1/5, damage to more than 2 consecutive buttons or obvious slipping occurs, the preload cannot be reliably transmitted. Even if forcibly tightened, it will loosen rapidly under vibration, which is a failure state and must be replaced immediately.
Q5: What measures can be taken to suppress fretting wear and loosening?
A5: Use anti-loosening structures such as lock nuts, self-locking washers and thread locking adhesives. Improve bolt installation torque accuracy to ensure sufficient preload. Retighten regularly and eliminate early loosening in time. Select wear-resistant and anti-corrosion bolts to extend the effective life of threads.