Analytical and experimental evaluation of piezoelectric wafer active sensors performances for lamb waves based structural health monitoring in composite laminates

Guided Lamb waves can be excited in composite materials through piezoelectric wafer active sensors (PWAS) to detect damage. PWAS are small, light-weight, inexpensive, and can be attached or embedded in composite structures. The proposed paper will present a parallel effort on two analytical approaches for predicting Lamb wave propagation in composite structures with surface attached PWAS. The first approach implements a layerwise mechanics theory and finite element for laminated composite beams with transducers and delaminations. The second approach uses a transfer matrix methodology (TM) and normal mode expansion (NME) to predict PWAS-plate interaction. Wave propagation predictions are performed using 2-D layerwise beam theory approximating the in-plane displacement, the through-thickness displacements and the electrical field as a continuous assembly of linear layerwise fields through the thickness. The effect of delamination cracks can be predicted by the introduction of additional degrees of freedom. Prediction of symmetric, antisymmetric and shear horizontal Lamb wave dispersion curves is done for composite material structures using TM methodology developed by Nayfeh. NME technique is applied to predict the PWAS tuning curves on composite plates; theoretical and experimental results are compared. Prediction of sensor signals and local displacement curves through the thickness will be presented for composite structure.