Nov. 3, 1999 Cincinnati -- University of Cincinnati engineers have combined two technologies into a new method for detecting tiny cracks in aging aircraft parts before they reach the catastrophic stage.
Graduate student Zhongyu Yan and Peter Nagy, associate professor of aerospace engineering, presented their results Nov. 2 during the annual meeting of the Acoustical Society of America in Columbus.
Yan and Nagy combined laser heating and ultrasonic inspection to improve the detection of fatigue cracks by a factor of ten over previously known methods. That's significant considering how difficult it can be to locate early signs of cracking.
"The material is degrading on the microscopic level. You can't really see the cracks," explained Nagy, adding that cracks move through older aircraft parts much faster than cracks in newer aircraft.
The researchers tested their method using a series of aluminum and titanium specimens with cracks ranging from .5 to 1 millimeter in length and specimens with no cracks in them. Their results indicated that the method not only found the cracks, it could measure the difference in the severity of the cracking.
Nagy's previous work focused solely on aluminum alloys which are typically used in the aircraft fuselage. The current project expands that work to titanium alloys used in engine parts. Nagy said that was a challenge, because titanium behaves differently than aluminum. In short, titanium doesn't heat up as quickly.
"Basically, we had to slow down the inspection to accommodate the more sluggish response from titanium, but the detection sensitivity is almost as good as in aluminum alloys."
As a result, the new method is more time-consuming and more expensive. So, Nagy only expects it to be used for the most critical parts.
Nagy's research is funded under a $5 million federal program to improve inspections of aging aircraft in the military. A parallel program under the Federal Aviation Administration is working to improve the safety of commercial airliners.
Nagy will also be honored during the meeting as a newly elected Fellow of the Acoustical Society of America.
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