Residual stress of flash-butt welded rail and its influence on critical initial flaw size and fatigue life

Flash-butt welding is widely used in the construction of long, continuous railway lines and for replacing defective rails. During welding, residual stresses develop in the welded joints due to localized temperature variations and thermo-mechanical stresses. Moreover, flaws may form on the weld surface during the welding process or in corrosive environments. If a flaw exceeds the critical initial flaw size (CIFS), it can propagate under repeated wheel loads, leading to rail fracture when it reaches the critical flaw size (CFS). This study employed 3D thermal elastic-plastic finite element analysis (FEA) to investigate the mechanisms of residual stress formation in flash-butt welded rail. The stress intensity factor range (K) for a semi-circular crack at the rail foot was calculated using 3D linear-elastic FEA, with crack size incrementally increased until K reached both the threshold (Kth) and critical value (KC), determining CIFS and CFS. The study also estimated fatigue crack propagation life by calculating the number of cycles required for the crack to grow from CIFS to CFS. Results demonstrated that residual stress formation was influenced by changes in the thermal expansion coefficient, strain, and elastic modulus with temperature. The calculated cooling temperatures and residual stresses aligned with experimental results. Moreover, welded rails exhibited a larger CIFS than unwelded rails due to residual stress effects. These findings provide valuable guidelines for determining residual stress and CIFS in flash-butt welded rail, offering insights into maintaining flash-butt welded rails and improving welding processes to enhance rail durability.