Rail contact stress real-time monitoring using ultrasound reflectometry

The rail stress is vital to lifespan, safety of rail tracks and riding comfort, among which the wheel-rail contact stress is a determining factor to wear, damage, cracks and failure of both wheel and rail. The wheel-rail contact system has been investigated and simulated for years, and a variety of methods have been developed for stress determination, but there is still no robust measuring technique for accurate real-time online stress characterization. The ultrasonic reflectometry technique has been proven successfully in characterizing various static machine-element contacts. The general process is firstly, an ultrasonic wave is emitted through a material that is either fully or partially reflected at an interface. The reflected waveform is then measured and information about the contact can be extracted from the A-Scan. The contact interface mechanism is modelled using a quasi-static spring approach. In this paper, an ultrasound reflectometry measuring method was introduced for rail contact stresses determination, and a set of ultrasonic tools were developed in order to take measurements under various situations. Wheel-rail contact stresses were profoundly investigated. Static contact stresses of normal wheel-rail contact under different normal loads were measured using ultrasonic focusing probe, high resolution images of contact stress distribution were obtained from measurements. Dynamic wheel-rail contact stresses were characterized using array of ultrasonic elements. A pitch-catch measuring technique was introduced for dynamic contact stress measurements, and specific ultrasonic arrays were designed and made for different mounting places. Measurements were taken under different normal loads, and stress distribution image were plotted from the measurements.