Dynamic railroad inspection using the laser-air hybrid ultrasonic technique

Abstract

Laser-Air Hybrid Ultrasonic Technique (LAHUT) combines laser generation with air-coupled detection of ultrasound. The technique is non-contact and has the characteristic of operating from remote distances. Acoustic wave laser-generation apparatus can be metres away from the interrogated surface while air-coupled detection standoff can be on the order of several centimetres. The technique has the unique capability of interrogating structural materials in their true industrial environment. Dynamic tests are performed on parts with complex geometry, limited accessibility and curved surfaces. Also, dark and rough finish surfaces, which significantly reduce the efficiency of optical detection techniques, can be interrogated successfully. These characteristics make the LAHUT ideal for many industrial applications including the railroad industry. It was developed for railroad inspections targeting the most critical cracks in rails and wheels. State-of-the-art inspection techniques available to the railroad industry often miss Vertical Split Head (VSH) and Transverse Detail Defect (TDD), which lie in unfavourable positions and orientations in the rail head. No method exists to perform dynamic inspections of the rail base or any part of the railroad wheel. Laboratory experiments were performed for the detection of TDD and Proof Of Concept (POC)field tests were performed for VSH, rail base cracks, thermal fatigue cracks along the wheel flange and tread and subsurface Shattered Rim Cracks (SRC) along the wheel tread. The results were successful and highly repeatable. The technique lends itself for digital collection and automated processing of data making the LAHUT a very strong candidate,for next-generation railroad inspection technique

Non-contact ultrasonic guided wave inspection of rails: field test results and updates

“…Other drawbacks of the conventional rail inspection methods include speed limitations (typically less than 25 km/hour) as well as difficulties in detecting Vertical Split Head defects. In the last 20 years, efforts have been focused on non-contact rail inspection [6][7][8][9][10][11][12][13][14][15][16][17][18] . Theoretically, a non-contact method can lead to higher speed and can be less sensitive to surface-conditions or non-effective coupling.…”

Detection of Disbonds in Multi-layer Structures by Laser-Based Ultrasonic Technique

“…In the last years non-contact ultrasound within the NDE methods had further development thanks to innovative probes, made with new materials for acoustic devices and manufacturing technologies [8,9]. The use of a laser to generate acoustic waves is also an emerging approach, advantageous as inspection is remote, does not depend on contact conditions (pressure, coupling medium, contact area), allows development of automated systems, and operation in hostile environment is feasible by guiding the laser beam through proper delivery optics [10][11][12].…”

Inspection of rail track head surfaces using electromagnetic acoustic transducers (EMATs)

“…One of the reasons for slow inspection speeds using conventional NDT is the need for couplant between the transducer and the track, either liquid or dry couplant materials. EMATs have been used (2,3) or suggested (4) to measure both rail tracks and wheels by other workers and the use of non-contact ultrasonic measurements are still being investigated by a number of international research groups (5)(6)(7)(8) .…”