Laser-Generated Acoustic Signal Interaction with Surface Flaws on Rail Wheels

Long- and short-range acoustic-signal interaction with surface-breaking cracks and geometric boundaries of the rail-wheel tread area are presented in this article. Ultrasonic signals are generated using a laser-line source of varying length and distance from a crack and are detected with a 1-MHz contact transducer to map the sound field behind the crack in the near, intermediate, and far fields of the insonified region. The factors that affect the behavior of a laser-generated surface acoustic wave propagating along the tread area of a rail wheel are discussed. A signal normalization method is proposed to help in sensing the presence of a crack from the transmitted signal unaffected by the …

Laser-air hybrid ultrasonic technique for dynamic railroad inspection applications

The 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 stand-off 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 detect…

Generation of narrowband antisymmetric lamb waves using a formed laser source in the ablative regime

A formed laser source, using a four-element lenticular array, is used in the ablative regime to generate select, narrowband, acoustic plate waves. The arrangement of the array produces acoustical signals that have frequencies compatible with the response of the broadband capacitive air-coupled transducer used in this study. A simplified concept is presented to explain the effect of a line array source on the frequency content of acoustic waves. The analytical model for a point pulse surface displacement is derived from the point load solution to Lamb's problem. The point pulse displacement elements of a line array source are summed mathematically, taking into account all applicable propagat…

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 a…

Laser-air hybrid ultrasonic technique for dynamic railroad inspeection applications

Dynamic railroad inspection using the laser-air hybrid ultrasonic technique

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 te…