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27 March 2018 A study on the detection of compressed micro-crack by nonlinear wave modulation technique
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We investigate the nonlinear wave propagation through micro-cracks that are compressed by external forces by means of nonlinear ultrasonic modulation technique. The nonlinear modulated waves are generated by the truncation of the waves passing through cracks due to the opening and closing of the cracks, and the nonlinear ultrasonic modulation technique has been known to be effective in detecting finer cracks in comparison with other linear ultrasonic methods since the technique utilizes the breathing of the cracks rather than wave reflections or refractions. However, if the cracks are strongly compressed, the crack opening is hindered due to the excessive initial stress and the nonlinearity does not show up.

In this study, the improvement of the nonlinear modulation wave technique for the detection of micro-cracks under compression is devised. By analyzing photomicrographs of the cracks with crack width measuring algorithm, a realistic crack model is generated, and a chirp signal is applied to find the resonant frequencies which are used as the excitation frequencies. Experimental tests are conducted to verify the numerical results. The aluminum plate is compressed in the direction normal to the cracks’ lateral surfaces and is excited using piezoelectric patches attached on the surface aluminum plate. The experimental and numerical results show good agreement for various excitation frequencies and different compressions.
Conference Presentation
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Sang Eon Lee, Hyung Jin Lim, Suyeong Jin, Hoon Sohn, and Jung-Wuk Hong "A study on the detection of compressed micro-crack by nonlinear wave modulation technique", Proc. SPIE 10598, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2018, 105982Z (27 March 2018);

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