Railroad Rails Containing Electrode-Induced Pitting From Pressure Electric Welding

The Federal Railroad Administration (FRA) routinely conducts investigations of railroad accidents to determine causation and any contributing factors to help the railroad industry implement corrective measures that may prevent similar incidents in the future. Over the past decade, FRA has investigated multiple broken rail accidents in which fractures in the rail web were identified. The common features observed in the recovered rail fragments from these accidents included welds and spots or burn marks on the web, indicating that the rails were joined together by pressure electric welding. Pressure electric welding uses a welding head that clamps around two opposing rail ends, pressing an electrode on each rail, then hydraulically pulling the rail ends together while arcing current through the electrodes into the rails, causing them to essentially melt together to form a continuous rail. Based on the similarities observed in the web fractures, FRA rail integrity specialists hypothesized that stray (i.e. inadvertent and unwanted) arcing during pressure electric welding can result in the formation of burns or pits on the rail where it makes contact with the electrodes. Moreover, these electrode-induced pits behave as stress raisers (also referred to as stress concentrations). Fatigue cracks often develop at locations of stress concentration. Once a fatigue crack initiates, the localized stress encourages the growth of the crack, which may potentially lead to rail failure. This paper describes the forensic evaluations of three railroad rails containing electrode-induced pitting. These evaluations include: magnetic particle inspection to nondestructively detect cracks emanating from the pitting; fractography to study the fracture surfaces of the cracks; metallography to study the microstructure; analysis of chemical composition; and measurements of tensile mechanical properties and fracture toughness of rail steel. Moreover, the results of these evaluations confirm the hypothesis postulated by FRA that stray arcing during pressure electric welding can cause electrode-induced pitting.

Analytical Modeling of Residual Stress in Railroad Rails Using Critically Refracted Longitudinal Ultrasonic Waves With COMSOL Multiphysics Module

Assessment of residual stresses in railroad rails without destructing the material plays a vital role in rail road safety. Ultrasonic testing is a commonly used nondestructive technique to determine the stresses in any structure. Ultrasonic stress evaluation technique is based on acoustoelastic effect which refers to the changes in the speed of the elastic wave propagation in a structure undergoing static elastic deformations. Critically refracted longitudinal (LCR) waves can be used as the propagating waves because it is a bulk wave and can reflect the surface and subsurface characteristics by the wave property linked to material elasticity. In this paper, a COMSOL Multiphysics module-based Finite Element Method (FEM) model is developed and numerical simulations are carried out for critically refracted longitudinal wave propagation in a railroad rail head for residual stresses. The time travel data results from this FEM Model are validated with reported experimental results.