Sounding out track defects

Researchers at the University of California, San Diego have developed a new technique they said is better able than currently used technology to find defects in steel railroad tracks. They claim the technique can even reveal hard-to-find internal cracks that can break under the weight of passing trains.

Track defects account for about one-third of the 2,200 annual train derailments in the US, according to the Federal Railroad Administration (FRA), the federal agency charged with enforcing rail safety regulations.

A team led by UCSD structural engineering professor Francesco Lanza di Scalea described in the August 22 issue of the Journal of Sound and Vibration a defect-detection technique that uses laser beam pulses to gently “tap” on steel rails.

Each laser tap sends ultrasonic waves traveling 1,800 miles per second along the steel rails. Downward facing microphones are positioned a few inches above the rail and 12 inches from the downward pointed laser beam. As the prototype vehicle rolls down the test track delivering laser beams taps at one-foot intervals, the microphones detect any reductions in the strength of the ultrasonic signals, pinpointing surface cuts, internal cracks, and other defects.