Design of Rail Temperature Force and Fastening System Stress Matching
Q1: How are temperature forces transmitted and distributed in the fastening system?
A1: Rails elongate and produce compressive stress at high temperatures, and contract with tensile stress at low temperatures. These longitudinal forces are transmitted through the rail base to clips and clamps, then to sleepers via bolts and spikes. Temperature forces are relatively uniform in straight sections but more complex in curves due to additional lateral forces. Insufficient fastening stiffness causes rail crawling, while excessive restraint may result in clip fracture or sleeper damage.
Q2: Why are fatigue fractures of clips more likely in high-temperature seasons?
A2: Rail compressive stress increases significantly at high temperatures, with strong longitudinal elongation tendency, requiring greater clamping force and longitudinal resistance from clips. Under sustained high stress, internal stress amplitude rises, and superposed train vibration easily induces fatigue cracks at arc transition zones. Meanwhile, high temperature slightly reduces steel yield strength, weakening clip deformation resistance and further increasing fracture risk.
Q3: What harm does excessive temperature force cause to fishplates and joint bolts?
A3: Temperature forces create additional longitudinal forces at rail joints, subjecting fishplates to greater tension, compression and shear. Excessive pressure may cause joint bulging, while excessive tension tends to break bolts. Under temperature cycling, bolt forces fluctuate repeatedly, accelerating fatigue damage such as thread elongation, fracture or fishplate hole-edge cracking, severely impairing joint integrity.
Q4: How do temperature differences in different regions affect fastening system configuration?
A4: In northern regions with large temperature differences, rail temperature forces vary widely, requiring higher-resistance clips and firmer anchoring to prevent track buckling. In southern regions with smaller temperature differences, longitudinal resistance can be appropriately reduced while meeting basic stability. Mountainous and elevated sections affected by wind and temperature shall also have strengthened clip torque and pad stiffness.
Q5: How to adapt to temperature force changes through operation and maintenance?
A5: Intensify fastener inspection during seasonal transitions, focusing on retightening clips and joint bolts. Set reasonable rail gaps to release part of temperature stress. Strengthen displacement monitoring in long rail sections and adjust timely when crawling occurs. Increase inspection frequency under extreme high or low temperatures, promptly handling loose and deformed components to maintain the fastening system in good stress condition.