Mechanisms of squat initiation and propagation on rail surfaces

Squats are recognized as an important rail track issue and occur in many railway networks across the world. Consequently, squats exacerbate the deterioration of track and some vehicle components. Associated excessive noise and vibration have increased the complaints against the rail operators. The area of squat initiation is still a matter of controversy. Research efforts have included possible relationships between the narrow and brittle white etching layers (WELs) observed on rail surfaces and squat formation in rails. However, based on current literature, the nature of WELs and their formation mechanisms are not fully understood, as is their relationship to the squat formation. In order to implement a more effective preventive and early corrective management strategy, it is critical to determine the root causes of squat defects and understand the mechanism of squat initiation and subsequent crack propagation on the rail surface.