When disaster strikes, things fall to pieces. But scientists have found a way to detect cracks that can prevent buildings and bridges from crumbling.
Researchers at Los Alamos National Laboratories are using sound waves to detect structural weaknesses. The technique could allow engineers to monitor bridges, oil pipelines, aircraft, and engine parts for strength and durability without so much as a peek inside.
"The problem with testing concrete is that you need to know what its destruction point is, without destructing it," said Los Alamos researcher Eric Smith.
By applying different frequencies to a structure and analyzing the results, researchers can read its weaknesses. As sound waves pass through materials, they measure the changes in tone and resonance caused by structural flaws.
"With normal sound, you can tell the complexity of cracks," Smith said. "If we measure natural pitches of a piece of material at different sound levels, you can find out what its crack content is."
Called Nonlinear Resonant Ultrasound Spectroscopy, the technique is featured in the September issue of the journal Materials World.
When a sound wave passes through concrete, cracks in the material cause changes in frequency. The more flaws there are, the lower the frequency will be, much like a cracked bell that produces a dull tone.
Applications for the technique are endless: It could test the strength of bridges, highway supports, building foundations, and basements.
"It's testing to see how much these structures have aged," said James Ten Cate, a geophysicist and acoustician at Los Alamos. "It might look fine, but it would be nice to see how much longer it will be before you have to replace it."
Other applications might include the ability to monitor the quality of concrete as it flows, and detection of microcracks in metal structures such as oil pipelines, or small fractures in internal engine parts. Scientists are also developing a method that would not only diagnose damage inside a structure, but also pinpoint the exact location.
"It's a simple test, easy to do and you don't damage anything," Ten Cate said. "It's always nice to have another tool in the toolbox."
