Ultrasonic and Acoustic Emission Detection of Fatigue Damage.

TLDR: In this paper, an ultrasonic pulse-echo system was used during fatigue cycling to record conventional A-scan waveforms as well as to monitor ultrasonic attenuation, and acoustic emission signals were recorded simultaneously with the ultrasonic measurements on each test specimen using two different acoustic emission systems.

Abstract: : The primary purpose of the research was to optimize existing ultrasonic and acoustic emission techniques and to investigate new ones for early detection of fatigue damage in aluminum alloys used in aircraft construction. Ultrasonic attenuation measurements made simultaneously with fatigue tests on aluminum alloy bar, and sheet specimens gave warning of crack formation and imminent fracture much earlier than conventional ultrasonic methods. An ultrasonic pulse-echo system was used during fatigue cycling to record conventional A-scan waveforms as well as to monitor ultrasonic attenuation. In addition, acoustic emission signals were recorded simultaneously with the ultrasonic measurements on each test specimen using two different acoustic emission systems. The correlation of evidence of cumulative fatigue damage and acoustic emission data was approached by the use of long term true-rms averaging of the system output and frequency domain analysis of acoustic emission signals recorded at selected intervals throughout the test. The integrity of the data was verified by independent electronic testing of the instrumentation. Visual and in situ eddy current inspection, and optical and scanning electron microscopy were used to correlate acoustic emission and ultrasonic attenuation data to the physically deformed microstructure.