Dynamic railroad inspection using the laser-air hybrid ultrasonic technique

In recent years, remote non-contact NDE techniques have been sought in an effort to improve railroad related inspection operations. More specifically, efforts have been aimed at increasing the inspection coverage and performing dynamic inspections for railroad tracks and wheels. Throughout most of the 20th century, dynamic inspections of railroad tracks have been developed and performed, however, the coverage of these techniques is limited to the rail head. Additionally, a number of critical flaws, such as VSH and TDD, can be difficult to detect with the dynamic inspection techniques that are available to the railroad industry today. No method is available for wayside dynamic inspections of railroad wheels. Laser, air-coupled, and water jet ultrasound transduction are the only methods that can comply with the restriction imposed by the nature of railroad operations. These restrictions include, but are not limited to, the following: q The NDE methods must be a non-contact inspection method. q The NDE methods must operate from a distance at least 0.5 in (12.5 mm) and as much as 8 in (203 mm) from the surface of the interrogated part. q The technique must tolerate the geometry of the rail track and wheel. q The technique must be capable of interrogating dirty, rusty, eroded, rough, and curved surfaces of the railroad steel. q All components of the apparatus must remain above the running surface of the rail (for track inspections), and clear of the path of the moving train (for wheel inspections). q The technique must be tolerant of the ambient vibrations of a moving train.