Acoustic emission from spectrum fatigue cracks in 7075 aluminum

Abstract

The E-2C Hawkeye, a U.S. Navy aircraft, has experienced problems with fatigue cracks in its wings. This problem was studied in the laboratory using a representative specimen under simulated flight loading. Acoustic emission monitoring was used to detect the stress pulses emitted during cracking. A new wave analysis technique was applied in order to distinguish extraneous noise from crack growth. This technique distinguishes between the extensional and flexural waves in thin aluminum plates. Extensional waves were found to correlate experimentally with waves from crack growth, while noise sources show different waveforms with lower frequencies. It was shown that acoustic emission provided early (crack length less than 0.01 inch) detection of fatigue cracking. This show promise for use in monitoring aircraft fatigue life.