Fatigue Damage to Fishplate and Bolts Due to Rail Joint Collapse
Q1: Why does joint collapse cause obvious bending of fishplates?
A1: Collapse forms a step at the joint, generating strong impact when wheels pass, and subjecting the middle of the fishplate to huge bending moment. Under repeated impact, the fishplate gradually undergoes plastic bending and arching, worsening joint fitting. Bending deformation further aggravates stress concentration, promotes fatigue crack initiation, and may eventually lead to fishplate fracture.
Q2: Why do joint bolts suffer more frequent fatigue fracture in collapsed sections?
A2: Impact subjects bolts to repeated combined tension and bending loads, greatly increasing stress amplitude. The opening and closing of joints exposes bolts to continuous dynamic tension, leading to rapid accumulation of fatigue damage. The more severe the collapse, the stronger the impact, and the more likely bolts are to suffer brittle or fatigue fracture at the root or thread section.
Q3: How does joint collapse accelerate the failure of under-rail pads?
A3: Strong impact causes instantaneous overload of pads at joints, sharply increasing compression deformation and resulting in permanent crushing and cracking. Vibration aggravates pad wear and aging, leading to rapid loss of elasticity. After pad failure, joint stiffness further decreases and collapse becomes more obvious, forming a vicious circle.
Q4: Why is joint collapse on heavy-haul lines far more harmful than on ordinary lines?
A4: Heavy-haul axle loads are large, impact energy is doubled, and the dynamic load generated by collapse is extremely high. Fishplates and bolts may suffer severe fatigue damage in a short time, even fracture due to one-time impact overload. Joint collapse also aggravates rail end crushing, greatly shortening the service life of equipment.
Q5: What fastener problems need to be paid attention to simultaneously when rectifying joint collapse?
A5: During collapse rectification, inspect fishplates for deformation and cracks, and replace damaged parts in a timely manner. Retighten or replace fatigued bolts to restore preload. Replace crushed and failed pads to restore joint stiffness. Adjust rail gaps simultaneously to eliminate additional stress. Strengthen monitoring after rectification to prevent recurrence of collapse and fastener damage.