Initial study of internally embedded shear-mode piezoelectric transducers for the detection of joint defects in laminate structures

There has been recent interest in embedding sensor networks into bondlines to create intelligent materials that can detect, report, and potentially respond to their state. This article presents an initial, large-scale investigation into embedding shear-mode (d₁₅) lead zirconate titanate piezoelectric transducers into the bondline of laminate structures, near the centerline, for the ultrasonic detection of joint defects. The study included analysis of dispersion curves, multiphysics numerical simulations, and experimental results for an aluminum–epoxy–aluminum laminate structure. Analysis of the time of flight and displacement profiles confirmed that antisymmetric waves were generated and propagated through the structure. Simulations were performed for models containing disbonds, through-thickness cracks, and voids with experimental validation of a specimen containing a void to evaluate the effectiveness of d₁₅ lead zirconate titanates embedded in a bondline as actuators and sensors for damage detection. The results were examined by looking at the cross-sectional deformation in simulations, and the signal changes were evaluated by calculating the root mean square deviation damage index and inspecting attenuation and phase shift in pristine and damaged structures. It was found that the d₁₅ shear-mode lead zirconate titanates actuated and sensed antisymmetric waves that were sensitive to all types of damages considered.