Early interferometric detection of rolling contact fatigue induced micro-cracking in railheads

In the world of rail travel, unplanned track maintenance constitutes disruption and negatively impacts customer satisfaction. To maintain railway networks it is necessary to plan maintenance before it becomes critical, preferably by at least a year. A major concern in railway quality is the occurrence of micro-cracks in railhead surfaces, due to rolling contact fatigue. When these cracks are superficial, no more than about a millimeter in depth, the railhead lifetime can be increased by grinding or polishing. However, the deeper the cracks are, the sooner they will grow beyond a depth that can be managed by polishing. Current inspection techniques are able to detect millimeter sized cracks, but no smaller. We present a new technique for the detection of cracks in railheads, which is able to detect cracks of 20-100 µm depth optically, by way of broadband, spatially incoherent optical coherence tomography. Detection of micro-cracks at an earlier stage of development and the study of their progression will aid in advance planning and scheduling of maintenance.