Influence of Residual Stress on Critical Initial Flaw Size in Flash–Butt Welded Rail

Flaws can develop on the weld surface of a rail during welding 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. This study employed 3D thermo-elastic-plastic finite element analysis (FEA) to simulate the residual stress in a flash-butt welded rails made of R260 rail steel. Under 4-point bending, the stress intensity factor range ([Formula: see text]) for a semi-circular crack at the rail foot was calculated using 3D linear-elastic FEA. The crack size was increased until [Formula: see text] reached the threshold value ([Formula: see text]), determining the CIFS. For small cracks, compressive residual stress at the rail foot’s outer edge counteracted tensile stress, preventing crack propagation. In contrast, larger cracks extended into the tensile residual stress region near the middle of the rail foot, promoting crack opening and reducing fatigue resistance. The study showed that welded rails have a larger CIFS than unwelded ones due to the influence of compressive residual stress at the rail foot’s outer edge. These findings provide valuable guidelines for determining CIFS, maintaining flash-butt welded rails made of R260 rail steel, and improving the welding process to enhance rail durability.