| ABSTRACT: | LASER-AIR HYBRID ULTRASONIC TECHNIQUE FOR DYNAMIC RAILROAD INSPECTION
APPLICATIONS
S. Kenderian1, B. B. Djordjevic1, D. Cerniglia2, G. Garcia3, and R. Morgan3
1the Johns Hopkins University, Baltimore, Maryland, USA; 2University of Palermo, Palermo, Italy,
3Transportation Technology Center, Inc., Pueblo, Colorado, USA.
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 meters 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.
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