Differential Strategy to High-Speed Inspection of Rails Via Passive Ultrasonic Monitoring

Abstract

This work presents an amplitude-imbalance identification approach to noncontact high-speed rail inspections. The passive monitoring utilizes an array of capacitive aircoupled ultrasonic transducers for data acquisition of ultrasonic-guided waves propagating in the rail. The excitation is generated by a combination of the test car’s wheel-rail friction and white noise generated by two additional actuators. The transfer function is reconstructed passively between two air-coupled sensors and transformed to the time domain by deconvolution. When discontinuities are present in the rail, the signature waveform in the time domain transfer function will change due to scattering. These changes in the amplitude of the reconstructed signal can be associated with the potential presence of a flaw. This method is referred to as the conventional approach to defect detection. However, tracking changes in one waveform is still subject to variability due to changing test conditions, different rail geometries, wear, poorer signal strength, and other rail anomalies that may be falsely flagged as defects. This paper presents a more robust defect detection strategy achieved by simultaneously assessing amplitude-related features from time signals of two sensors pairs probing adjacent segments of rail and using any significant mismatch as the indicator of an internal rail flaw in one of the two segments, hence, the differential strategy for defect detection. The performance of such a method in detecting flaws was assessed via receiver operating characteristic curves on data acquired from field tests at testing speeds of 40 mph conducted at the Transportation Technology Center Inc (TTCI) in Pueblo, CO.