Proof of concept of wayside railroad wheel inspection using a laser-air hybrid ultrasonic technique

Non-destructive inspection of railroad wheels is performed in maintenance shops, where wheels are removed and inspected individually. No technique is yet available to the railroad industry to perform wayside inspections of wheels on a moving train. The characteristics of laser and air-coupled ultrasound are discussed to justify the use of a laser-air hybrid ultrasonic technique. Laser generation of ultrasound is combined with air-coupled detection to provide a flexible non-contact and remote technique that would enable the railroad industry to perform wayside inspections of moving railroad wheels. The present paper describes Proof of Concept set-up and results of the experiments performed at the Transportation Technology Center facilities, in Pueblo, Colorado. Sensors are used to detect the position of the wheel, drive a two-position mirror to direct the laser beam to one of two test stations and trigger the laser when the wheel is in position for detection. Wheels are inspected for subsurface shattered rim cracks, thermal fatigue cracks along the tread and the flange areas of the wheel. Analysis is based on the time domain radio frequency (RF) signal and time-frequency wavelet transforms. The experimental results are promising, indicating that dynamic wayside inspections are possible with the laser-air hybrid ultrasonic technique.