As the aircraft fleet ages and the number of in-flight material fatigue incidents climbs, a professor at the University of Missouri-Columbia says he has found a new and reliable method of identifying potentially dangerous cracks in aging aircraft.
P. Frank Pai, professor of mechanical and aerospace engineering, has developed a vibration-based technique he calls the boundary effect evaluation method (BEEM) and a scanning laser vibrometer that can detect tiny cracks within various materials such as aluminum alloy and composite laminates.
The user attaches to the structure piezoceramic patches that produce small vibrations when electrical voltage is applied. The laser vibrometer scans the structure at various uniformly distributed points measuring vibration levels. The data is relayed to a computer and processed by a mathematical theory developed by Pai. The locations and sizes of the cracks are displayed on the computer’s monitor.
Pai said the simplicity of his technique sets it apart from others. “The traditional ultrasound method requires the structural component to be disassembled from the aircraft, placed in water for an ultrasound scan and then reassembled,” he said. “The BEEM method allows for inspection of the entire aircraft, especially critical sections near the fuel tank and wing and body junctions, while fully assembled.”
NASA, along with some private sector companies, is developing structural damage inspection methods using high-power lasers to induce and measure stress waves. According to Pai, that method produces high levels of heat that can potentially damage the structural surfaces.
Pai’s system, which can be transported to an airport or aircraft hangar, uses a mobile, low-power laser that causes no harm. He said it is also less expensive and quicker than other methods.