Nonlinear Interactions of Lamb Waves With a Delamination in Composite Laminates

Abstract

In view of their higher sensitivity in localizing an incipient damage, methods of non-destructive evaluation based on the nonlinear wave-damage interactions have been of continued interest in the recent past. In this paper, the propagation of guided waves through a delamination with contacting interfaces is studied numerically using a finite element-based framework. In particular, influence of the interlaminar location of the delamination on the nonlinear acoustic features in the response spectrum is investigated in detail. The numerical framework is validated by an in-house experimentation performed on a unidirectional glass fiber reinforced polymer (GFRP) laminate containing a through-width delamination. A parameter, referred to as the nonlinearity index (NI), is defined for quantifying the strength of the nonlinear wave-damage interactions and its dependence on the interlaminar location of the delamination is studied across a range of interrogation frequencies. The notion of contact energy intensity is introduced and further used for justifying the trends of variation of the NI obtained numerically and observed experimentally. Results indicate that two fundamental parameters govern the underlying contact phenomenon; they are the phase difference between the wave packets passing through the two sub-laminates and the flexural rigidities of the two sub-laminates present at the site of the delamination defect. While the former controls the relative displacement between the two sub-laminates, the latter governs the propensity of collisions between the two sub-laminates. Finally, a diametric effect of these two parameters on the generation of nonlinear harmonic signals with varying interlaminar locations of the delamination is brought out.