Railway Track & Structures - November 2008 - (Page 20)

TTCI R&D Update: advanced rail inspection system Researchers evaluate a prototype laser-based rail flaw inspection system. nder sponsorship of the Association of American Railroads’ Strategic Research Initiatives Program, Transportation Technology Center, Inc., and Tecnogamma SPA have developed a prototype system, called U-Rail, for noncontact rail flaw inspection. U-Rail is currently being evaluated at TTCI, Pueblo, Colo., and preliminary results show that the system is detecting transverse defects, TD, under shelling, vertical split heads, transverse defects on the rail base and horizontal web defects. This laser-based ultrasonic inspection system uses pulsed lasers to generate ultrasonic signals and air-coupled transducers to monitor the waves propagating U through the rail without physical contact. A laser pulse with high optical power density directed on the rail surface produces a reactive stress component in the ablative regime that acts as an ultrasonic source producing elastic perturbations (bulk and surface waves) that propagate through the rail material. The lasers have an average of 50 watts of power and a repetition rate, 120 Hz, sufficient to allow appropriate spatial resolution between laser pulses during dynamic inspection of the rail. Ultrasonic waves generated by the laser are monitored with air-coupled transducers that are oriented at specific angles, determined by applying Snell’s Law. Snell’s Law is a formula used to describe the relationship between the angles of incidence and refraction when referring to light or other waves; in this case, sound passing through a boundary between two different isotropic media. Figure 1, top, the laser-based ultrasound generation mechanism in the ablative regime. Figure 2 shows the carriage with the pneumatic cylinder for horizontal loading. The transducers are robust, provide excellent signal to noise ratio and have high sensitivity. They are capable of noncontact operation at remote distances of at least 2.75 inches (69.85 mm) above the top running surface of the railhead. This distance is in accordance with the minimum allowed by the AAR Car Construction Fundamentals and Details (AAR Manual of Standards and Recommended Practices, Standard S-2028 Plate C – Equipment Diagram for Limited Interchange Service, 2007). Laser-based technology can generate ultrasonic waves in every part of the rail by G. Garcia, Bill Larson and Semih Kalay, TTCI, D. Cerniglia and C. Cosenza, Tecnogamma SPA. www.rtands.com 20 Railway Track & Structures November 2008 http://www.aar.com http://www.rtands.com

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Railway Track and Structures Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D TrainingVvital in Shaping Future of Railroad Industry Switch Stands, Switch Machines Automation Offers Improvements in M/W Planning AREMA 2008 Conference Report Products and Literature People Calendar Advertisers Index Sales Representatives Website Directory Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - November 2008

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