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Smart Structures and Systems Volume 25, Number 3, March 2020 , pages 301-310 DOI: https://doi.org/10.12989/sss.2020.25.3.301 |
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Crack localization by laser-induced narrowband ultrasound and nonlinear ultrasonic modulation |
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Peipei Liu, Jinho Jang and Hoon Sohn
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| Abstract | ||
| The laser ultrasonic technique is gaining popularity for nondestructive evaluation (NDE) applications because it is a noncontact and couplant-free method and can inspect a target from a remote distance. For the conventional laser ultrasonic techniques, a pulsed laser is often used to generate broadband ultrasonic waves in a target structure. However, for crack detection using nonlinear ultrasonic modulation, it is necessary to generate narrowband ultrasonic waves. In this study, a pulsed laser is shaped into dual-line arrays using a spatial mask and used to simultaneously excite narrowband ultrasonic waves in the target structure at two distinct frequencies. Nonlinear ultrasonic modulation will occur between the two input frequencies when they encounter a fatigue crack existing in the target structure. Then, a nonlinear damage index (DI) is defined as a function of the magnitude of the modulation components and computed over the target structure by taking advantage of laser scanning. Finally, the fatigue crack is detected and localized by visualizing the nonlinear DI over the target structure. Numerical simulations and experimental tests are performed to examine the possibility of generating narrowband ultrasonic waves using the spatial mask. The performance of the proposed fatigue crack localization technique is validated by conducting an experiment with aluminum plates containing real fatigue cracks. | ||
| Key Words | ||
| fatigue crack localization; laser scanning; laser ultrasonic; narrowband excitation; nonlinear ultrasonic modulation; spatial mask | ||
| Address | ||
| Department of Civil and Environmental Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea. | ||