Numerical and Experimental Investigation of Nonlinear Lamb Wave Mixing at Low Frequency

The nonlinear ultrasonic Lamb wave has attracted great attention recently due to its likelihood for microcrack detection in plate-like structures. Wave mixing technique has shown advantages over the conventional nonlinear ultrasonic technique. Most of the studies on wave mixing are based on bulk wave mixing. This paper presents a nonlinear Lamb wave mixing technique for enhanced damage detection in thin plate structures. Here, the analysis of the nonlinear interaction of the primary Lamb wave modes propagating in the opposite direction is performed using finite-element simulations and experiments. The results show that due to mutual interaction, additional combinational higher-order harmonics are generated due to nonlinearities. Experiments were conducted on a steel channel section with debond type damage. The results show that mixing of the fundamental Lamb wave modes at the defect zone increases the sensitivity of the damage detection procedure, thereby assisting in damage localization as well.