Do you know that there are more than 2,200 annual train derailments in the U.S.? One third of these accidents can be attributed to hard-to-find defects in steel railroad tracks. Now researchers at University of California at San Diego (UCSD) have developed a new ultrasonic technology to find defects in these tracks which could help prevent many train derailments. This system uses laser beam ultrasonic pulses traveling on the steel rails. Microphones are installed behind the lasers to catch the reflecting waves indicating possible defects. It has already being successfully tested and could be soon used by the U.S. Department of Transportation (DoT). Read more...
Before going further, here is an illustration showing how the technology works (Credit: UCSD/DoT).
This technology has been developed by a UCSD team led by Francesco Lanza di Scalea who is the director of the Non-Destructive Evaluation/Structural Health Monitoring (NDE/SHM) Laboratory.
Here is a more thorough explanation of this defect-detection technique using lasers.
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 telltale reductions in the strength of the ultrasonic signals, pinpointing surface cuts, internal cracks, and other defects.
For more details, you can read this page about their project called "Development of a non-contact remote ultrasonic system for the non-destructive inspection of railroad tracks."
As you'll see in the UCSD news release, this technique has already been successfully tested with a prototype vehicle in Gettysburg, PA. And more tests are scheduled this fall.
This project was funded by the Federal Railroad Administration of the DoT. [Personal note: I love their URL, which ends in dot.gov]. Here is a link to an October 2005 report about this project, "On-line High-speed Rail Defect Detection – Phase III" (PDF format, 5 pages, 325 KB). The illustrations in this note have been extracted from this document.
Below is a screenshot of "the signal detection portion of the inspection software showing the detection of a transverse head crack in the 'transmission' mode" (Credit: UCSD/DoT).
This research work has been published by the Journal of Sound and Vibration under the name "Modeling wave propagation in damped waveguides of arbitrary cross-section" (Volume 295, Issues 3-5, Pages 685-707, August 22, 2006). Here is a link to the abstract.
Now, we have to hope that this technology will work better than current ones; But researchers are confident. As said Lanza di Scalea, "Our technique is much better able to find such [hard-to-find] defects, and it can work under varying weather conditions while the inspection vehicle is zipping along a track at speeds of up to 70 mph."
Sources: University of California at San Diego news release, August 21, 2006; and various web sites
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