Point and Line Source Laser Generation of Ultrasound for Inspection of Internal and Surface Flaws in Rail and Structural Materials

Laser-based ultrasound and air-coupled ultrasound test methods were used for the inspection of flowed rail, internal, and surface-breaking cracks in railroad tracks. Signals were generated with an infrared pulse laser and detected with a micromachined capacitive air-coupled transducer. A comparison is presented between point source and line source laser-generated signals and their effectiveness in detecting surface flaws. The experiments demonstrate the flexibility and capability of a laser-air hybrid ultrasonic technique to detect cracks using test procedures that are not possible with current contact inspection techniques. The noncontact and remote nature of these methods renders such tests suitable for in-service applications.