UC assistant professor detects structural damage with lasers

Large structures like buildings and bridges constantly bear the elements. Whether it’s a steady flow of traffic, the rapid beating of tides or just the unforgiving nature of weather patterns, large structures undergo erosion and damage difficult to detect with the naked eye.

Engineers sometimes assess these large structures for damages by using a laser Doppler vibrometer, a tool that uses lasers to measure the vibration of a structure. This tool allows people to assess a structure’s condition and identify possible areas that need maintenance or repair from as far away as several hundred yards.

University of Cincinnati Assistant Professor Yongfeng Xu, Ph.D., recently received a $150,000 National Science Foundation (NSF) grant to improve the effectiveness of these laser Doppler vibrometers.

“Traditionally, when users of a scanning laser Doppler vibrometers direct lasers to a certain point, they keep it there and take a measurement for several seconds,” says Xu.

This method is called stepped scanning. A vibration shape is obtained by processing measurement data of multiple points. Stepped scanning, however, has its setbacks.

“An obtained vibration shape by step scanning is not incorrect,” adds Xu, “but when the number of measured points is small, the shape is not always detailed enough for damage detection.”

To achieve a detailed vibration shape, one needs to increase the number of measured points. Adding more points, though, means a longer measurement time, sometimes hours longer.

Xu and his collaborator, professor Weidong Zhu, Ph.D., at the University of Maryland, Baltimore County, are proposing new three-dimensional continuously scanning laser Doppler vibrometry capable of continuously scanning a structure.

Unlike stepped scanning, Xu’s vibrometer yields vibration shapes with tens or even hundreds of thousands of points in a few seconds. This continuous scanning is much faster than traditional stepped scanning, and it’s just as accurate.

The whole goal of continuously scanning laser Doppler vibrometry is to detect structural damage early on. For example, a crack in a structure, if caught in its infancy, can be prevented from spreading. Ultimately, this can increase national prosperity and defense by providing early warnings of damage and preventing failures of large structures.

Says Xu, “This research can reduce potential economic and human losses, in addition to advancing knowledge in the field of measurement science.”