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Description
This study presents a combined numerical and experimental investigation of nonlinear guided waves generation and propagation in weakly nonlinear isotropic elastic plates, with particular emphasis on their interaction with a crack-type defect. The analysis focuses on the second harmonic guided wave (SHGW) generated from the fundamental symmetric mode in an aluminium plate. Numerical simulations were conducted to evaluate the influence of excitation conditions and intrinsic material nonlinearity on SHGW generation while eliminating spurious nonlinear effects introduced by measurement instrumentation. Experimentally, guided waves were generated using a calibrated piezoelectric wafer transducer bonded to the surface. The resulting wave fields were measured using a three-dimensional scanning laser vibrometer, enabling full-field acquisition of both normal and tangential surface displacements. This methodology allows reliable isolation and characterization of the second harmonic component. A wavenumber analysis imaging technique is then implemented for damage localization. The results from both approaches confirm that the secondary mode generation is feasible using a narrowband excitation signal. However, the amplitude remains considerably weak in the pristine structure. In the presence of damage, the second and third harmonics are clearly identified. Their amplitudes increase significantly with the severity of the damage. This constitutes a very sensitive indicator for early detection and characterization of defects. The corresponding reconstructions successfully allowed the localisation of the damage.