P3E-5 Evaluation of Fatigue Specimens Using Emats For Nonlinear Ultrasonic Wave Detection

Abstract

Detection of a closed crack using a nonlinear ultrasonic wave method has been studied in recent years. This technique is based on the fact that the waveform of the received ultrasonic wave is slightly different from that of the incident ultrasonic wave, when the displacement of the ultrasonic wave and the opening width of a crack are almost the same. Therefore, regarding the incident ultrasonic wave, its harmonic frequency components change as it penetrates the crack. However, the nonlinearity of a solid material is very small compared to that when a liquid medium with a high nonlinear efficiency is to be used as the coupling medium. We then attempted to apply an electromagnetic acoustic transducer (EMAT), which does not require a coupling medium. In addition, we tried to develop the EMAT that could alternately drive the S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -Lamb wave and SH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -plate wave to detect any nonlinearity in the different ultrasonic wave modes. We actually tested the performance using fatigue specimens we had fabricated. As a result, we observed that the harmonic components changed when we used the specimen with a specific loading condition and a specific ultrasonic mode. This indicated that the trial system could also detect the degree of damage to any structures or any materials.