Fracture and fatigue crack growth analyses on a weld-repaired railway rail

Abstract

Although repair by arc welding is a well-known method for damaged rail surface recovery due to its ease of application, the method is vulnerable to the creation of cracks. In this study, a series of failure analyses and crack growth analyses were carried out on a fractured weld-repaired rail to determine the cause of the rail failure and the effect of residual stress on the crack growth rate. For this purpose, the residual stress profiles of rails under various conditions were obtained by both sectioning the physical rail and simulating the weld-repair process of the rail using the finite element method. Subsequently, the fatigue crack growth in the weld-repaired rail was simulated by assuming that a semi-elliptical crack was initiated at the boundary between the weld pool and heat-affected zone. From these analyses, it was found that weld defects, such as porosity, lamella line cracks, and quick transitions in material hardness and microstructure, especially at the boundaries, could be the causes of the crack initiation. The crack growth rate was strongly influenced by the magnitude of the residual stress, while it was significantly increased in the presence of high tensile residual stress at the rail head due to the weld repair. Therefore, reducing the tensile stress magnitude and increasing the compressive stress magnitude in the rail head is crucial to solving this problem in railway rail weld repair.