Time reversal health monitoring of composite plates using lamb waves

Abstract

In this work, the use of time reversal technique along with Lamb wave active sensing is investigated for health monitoring of composite plate structures. Piezoelectric wafer active sensors (PWAS) were used for the actuation and reception of the Lamb wave modes in the composite plates. Experiments were conducted on glass-epoxy composite plates with different lay-up sequences to study the time reversal behavior of A₀ and S₀ Lamb wave modes. Damage in the form of delamination was simulated by inserting a Teflon release film between the sixth and seventh layer of the glass-epoxy composite plate. The change in the shape of the broad band Gaussian pulse under time reversal in the presence of delamination was studied experimentally. Time reversal experiments were further carried out on carbon-epoxy composite t-pull specimen and the specimenwas subjected to a tensile loading in a universal testing machine. PWAS measurements were carried out for healthy and also during different stages of delamination due to tensile loading. Time reversal of A₀ and S₀ mode was applied for both healthy and delaminated composite specimens and change in shape of the time reversed Lamb wave was studied experimentally. This study aims in showing the effectiveness of Lamb wave time reversal as a baseline free technique for damage detection in composite plates.