Department of Mechanical Engineering, Oita National College of Technology, 1666Maki, Oita, 870-0152, Japan

摘要

Non-linear ultrasonic and acoustic emission (AE) signals during ultrasonic fatiguetesting were analyzed by using Laser Doppler Vibrometer (LDV) and continuous AE waveform analysissystem (1MHz/12bit). Notched specimens of a high strength low alloy steel were prepared for theultrasonic fatigue test with exciting vibration frequency of 20 kHz. The detected surface velocity waslongitudinal direction on the end of specimen with frequency range from 100 Hz to 500 kHz. Duringthe waveform monitoring of the fatigue test, a distorted exciting waveform was observed in final stageof the test. Then the burst type noise mixed with the distorted exciting waveform was obtained justbefore the final failure. AE signal and upper harmonics of exciting frequency were analyzed by the FFTmethod. As the result, after the intensity of 2nd and 3rd harmonics increased rapidly, AE events weredetected continuously. It can be concluded that non-linear ultrasonic waveform analysis both ofharmonics and AE signal were effective monitoring tool for fatigue damage progression.