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Laser detects cracks in the tracks

MATERIALS Cutting Edge

SCIENTISTS at a university in the United States have developed a technique that can pick up defects in steel rail tracks.

Boffins at the University of California in San Diego claimed that a laser-based system they have developed can pick up cracks in tracks before the material fails.

The October 2000 Hatfield train crash was caused by a phenomenon called gauge corner cracking and the new method could pick up those sort of defects.

The technology uses a laser system to send out ultrasonic 'tapping' waves along the steel rails. The waves travel at almost 3 km/sec and are picked up by microphones set 25 cm away from the laser.

As the vehicle runs down the track, tapping out the laser pulses, the microphone detects any reductions in the strength of the ultrasonic signals and logs surface cuts, internal cracks and other defects.

The inspection vehicle can be used at speeds of over 100 kph, according to the research team, which is led by UCSD structural engineering professor Francesco Lanza di Scalea.

He said: 'The current generation of technology often doesn't detect interior cracks in rails that happen to lie under areas of superficial cracking. Our technique is much better able to find such defects and it can work in varying weather conditions.'