Investigation of the formation of corrugation-induced rail squats based on extensive field monitoring

• Published in: International journal of fatigue 2018-07, Vol.112, p.94-105
• Main Authors: Deng, Xiangyun, Qian, Zhiwei, Li, Zili, Dollevoet, Rolf
• Format: Article
• Language: English
• Subjects: Brittle materials; Continual field monitoring; Corrugation; Crack initiation; Crack propagation; Fatigue life; Inclination; Materials fatigue; Monitoring; Rail squats; Rolling contact; Rolling contact fatigue (RCF); Sliding contact; Stress propagation; Tensile strength; Tensile stress; Welded joints
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2018.03.002

[Display omitted] •This work investigates the formation of rail squats induced by corrugations.•A five-year continual field monitoring was performed on a large number of squats.•Various stages of the whole life cycle of squats accompanied by cracks were captured and analyzed.•A squat development process from small depression to two-lung shape is presented.•The behaviors and mechanisms of the initiation and propagation of cracks are proposed. Rail squats originate from a number of sources, such as corrugations, indentations and welds. A five-year continual field monitoring study was performed on squats induced by corrugations. This study indicated that a small black depression formed at the corrugation under wheel-rail dynamic forces, and then, a primary crack typically initiated on the gauge side edge of the depression. Subsequently, the crack began to propagate in the rail surface in a U shape toward the gauge side in both the traffic direction and the opposite-traffic direction and into the rail toward the field side at an angle of approximately 20°. Rail inclination could influence the crack initiation location and propagation path. The geometry of the black squat depression was initially elliptical, and then, its edge followed the U-shaped cracking path as it grew. The squats turned into a kidney-like shape, typically with a U-shaped crack. Tensile stress likely led to the squat crack initiation and propagation. This cracking phenomenon and mechanism are analogous to the ring/cone crack formation of brittle materials under sphere-sliding contact. As the squats grew further, a ridge formed in the middle part of the depression, and an I-shaped crack appeared at this ridge due to the impact of the wheels. This process eventually led to two-lung-shaped mature squats, typically with a Y-shaped crack. The findings of this paper provide insight into the formation of rail squats.