Spectral damage index for estimation of breathing crack depth in an aluminum plate using nonlinear Lamb wave

In the present study, generation of higher harmonics as a result of nonlinear interaction of Lamb wave with a transverse breathing crack in a thin aluminum plate is explored through experiments and finite element simulation. Piezoelectric wafer transducers are used for generating and sensing of Lamb wave in the experiments. In the finite element simulation, a breathing crack is modeled using contact elements. Augmented Lagrangian algorithm is used for solving the contact problem. The crack faces open and close as dilation and compression parts of the wave pass through it, causing local change of stiffness, which gives rise to contact nonlinearity. Results recorded in both experiments and simulation show presence of three higher harmonics. On the basis of the spectral information of these higher harmonics, a new spectral damage index is identified for quantifying the crack depth. The spectral damage index estimated from the results of both experiments and simulation for various crack depths is found to be in good agreement and follows increasing trend with increase in the crack depth. This shows that the nonlinear characteristics of Lamb wave can be effectively used for detecting and quantifying the breathing crack with a fair accuracy, with the proposed damage index. Copyright (c) 2013 John Wiley & Sons, Ltd