Localization of a Breathing Delamination Using Nonlinear Lamb Wave Mixing

A guided wave-based method for localization of breathing delamination is presented in this investigation. The proposed technique utilizes one-way mixing of a dual-frequency fundamental antisymmetric Lamb modes with judiciously selected central frequencies. The dual-frequency interrogation signal, upon interacting with a breathing delamination, leads to additional frequency sidebands in the frequency response spectrum, strength of which is quantified in terms of the combination tone index. The numerical predictions of these sidebands are validated using an in-house experimentation. It is further exposited that the combination tone index depends strongly on the extent of the temporal overlap that the two constituent wave envelopes have as they propagate through the breathing delamination. Accordingly, for a synchronous passage (with 100% temporal overlap), the combination tone index is maximum while it reduces with the decreasing temporal overlap. By utilizing the dispersive nature of the chosen Lamb mode, a relation is then developed correlating the temporal separation of the wave envelopes at the location of the actuator, the group speeds, and the distance between the actuator and the delamination. Based on these inferences, a technique for localizing a breathing delamination is proposed, which involves interrogating the component by systematically altering the temporal overlap in the input waveform and monitoring the combination tone index for its maxima. The efficacy of the localization technique (close to 90%) is demonstrated through an illustrative case analyzed numerically as well as experimentally.