Fatigue Process Evaluation of Ultrasonic Fatigue Testing in High Strength Steel Analyzed by Acoustic Emission and Non-Linear Ultrasonic

摘要

Non-linear ultrasonic and acoustic emission (AE) signals during ultrasonic fatigue testing were analyzed by using Laser Doppler Vibrometer (LDV) and continuous AE waveform analysis system (1 MHz/12 bit). Notched specimens of a high strength low alloy steel were prepared for the ultrasonic fatigue test with exciting vibration frequency of 20 kHz. The detected surface velocity was longitudinal direction at the end of specimen with frequency range from 200 Hz to 500kHz. During the waveform monitoring of the fatigue test, a distorted exciting waveform was observed in final stage of the test. Then the burst type noise mixed with the distorted exciting waveform was obtained just before the final failure in the case of failure specimens. Contrary, the distorted exciting waveform and AE were not observed in the case of non-failure specimens. AE signal and upper harmonics of exciting frequency were analyzed by the FFT method. As the result, after the intensity of 2nd and 3rd harmonics increased rapidly, AE events were detected continuously in the case of failure specimens. It can be concluded that nonlinear ultrasonic and AE analysis were effective monitoring tool for fatigue damage progression.