DOI:

Keywords:

Laser Ultrasonics, Nonlinear Ultrasonic Modulation, Finite Element Method, Fatigue Crack Detection, Structural Health Monitoring

Abstract

Laser ultrasonic technique is widely applied in non-destructive evaluation (NDE) and structural health monitoring (SHM) for the broadband generation of ultrasonic waves. However, controlling the spectral content of the laser-generated waves can enhance the sensitivity of damage detection. In this study, a finite element model is developed to investigate how laser beam diameter influences ultrasonic wave generation. A small beam diameter is used to produce a wide-spectrum (WS) response, while a larger beam generates a narrow-spectrum (NS) response. The two independent ultrasonic responses are then combined to form a dual-laser excitation approach. When a structure contains fatigue damage, nonlinear ultrasonic modulation occurs between the WS and NS responses, leading to the generation of sidebands. A spectral energy-based index is employed to quantify these sidebands and identify fatigue-induced nonlinearity. The results confirm that the proposed dual-laser ultrasonics method improves sensitivity to fatigue cracks compared to conventional single laser excitation.

References

Alnuaimi, H., Amjad, U., Alnuaimi, Y., & Kundu, T. (2025). Combining ultrasonic pulse velocity and nonlinear ultrasonic techniques to assess concrete strength. ASME Journal of Nondestructive Evaluation, 8(3).

Baldwin, K., Berndt, T., & Ehrlich, M. (1999). Narrowband laser generation/air coupled detection: Ultrasonic system for on-line process control of composites. Ultrasonics, 37(5), 329–334.

Dixon, S., Burrows, S., Dutton, B., & Fan, Y. (2010). Detection of cracks in metal sheets using pulsed laser generated ultrasound and EMAT detection. Ultrasonics, 51, 7–16.

Huang, J., Krishnaswamy, S., & Achenbach, D. (1992). Laser generation of narrow-band surface waves. Journal of the Acoustical Society of America, 92, 2527–2531.

Liu, P., & Sohn, H. (2017). Development of nonlinear spectral correlation between ultrasonic modulation components. NDT & E International, 91, 120–128.

Liu, P., Jang, J., & Sohn, H. (2018). Fatigue crack detection using dual laser induced nonlinear ultrasonic modulation. Optics and Lasers in Engineering.

Liu, P., Nazirah, A., & Sohn, H. (2016). Numerical simulation of damage detection using laser-generated ultrasound. Ultrasonics, 69, 248–258.

Liu, P., Sohn, H., & Park, B. (2015). Baseline-free damage visualization using noncontact laser nonlinear ultrasonics and state space geometrical changes. Smart Materials and Structures, 24(6), 065036.

Liu, P., Sohn, H., Kundu, T., & Yang, S. (2014). Noncontact detection of fatigue cracks by laser nonlinear wave modulation spectroscopy (LNWMS). NDT & E International, 66, 106–116.

Mezil, S., Chigarev, N., Tournat, V., & Gusev, V. (2016). Evaluation of crack parameters by a nonlinear frequency-mixing laser ultrasonics method. Ultrasonics, 69, 225–235.

Murray, T., Deaton, J., Jr., & Wagner, J. (1996). Experimental evaluation of enhanced generation of ultrasonic waves using an array of laser sources. Ultrasonics, 34(1), 69–77.

Park, B., An, Y., & Sohn, H. (2014). Visualization of hidden delamination and debonding in composites through noncontact laser ultrasonic scanning. Composites Science and Technology, 100, 10–18.

Ruzzene, M. (2007). Frequency-wavenumber domain filtering for improved damage visualization. Smart Materials and Structures, 16(6), 2116–2129.

Scruby, C., & Drain, L. (1990). Laser Ultrasonics: Techniques and Applications. London: Taylor & Francis.

Sohn, H., Dutta, D., Yang, J., Desimo, M., Olson, S., & Swenson, E. (2011). Automated detection of delamination and disbond from wavefield images obtained using a scanning laser vibrometer. Smart Materials and Structures, 20(4), 045017.

Wagner, J., Mckie, A., Spicer, J., & Deaton, J., Jr. (1990). Modulated laser array sources for generation of narrowband and directed ultrasound. Journal of Nondestructive Evaluation, 9, 263–370.

Yashiro, S., Takatsubo, J., Miyauchi, H., & Toyama, N. (2008). A novel technique for visualizing ultrasound waves in general solid media by pulsed laser scan. NDT & E International, 41, 137–144.

Zaitsev, V., Matveev, L., & Matveyev, A. (2009). On the ultimate sensitivity of nonlinear-modulation method of crack detection. NDT & E International, 42, 622–629.

Zhu, J., Zeng, S., Malone, C., Tu, J., & Sun, H. (2025). Thermal modulation of nonlinear ultrasonic waves for nondestructive evaluation of elastic materials. Nondestructive Testing and Evaluation.