An insight into high-order harmonic generation of lamb waves induced by a breathing crack using a spring model and a local interaction simulation approach

The study and use of high-order harmonic generation is the core of recent research conducted regarding Lamb wave-based identification of undersized damage. A numerical study was performed using a Local Interaction Simulation Approach (LISA) to explore the characteristics of high-order harmonic generation of Lamb waves propagating in a medium containing a “breathing” crack. In order to faithfully model the “breathing” pattern of the crack, a Spring Model (SM) was developed, as a spin-off of LISA. The SM substitutes the mechanism of local interaction between waves and the crack to an equivalent set of “tensorial springs”. Using LISA in conjunction with SM, a quantitative insight into the high-order harmonic generation induced by a “breathing” crack of various depths was achieved. It has been demonstrated that the developed model is capable of simulating the non-contact and flawed interface behavior of the “breathing” crack under dynamic loads. In addition, a damage index was established based on the high-order harmonic generation, showing dependence on the depth of the “breathing” crack at different excitation frequencies.