Structural health monitoring of composites using integrated ultrasonic transducers

Abstract

Two types of ultrasonic sensors are presented for structural health monitoring (SHM) and non-destructive testing (NDT) of graphite/epoxy (Gr/Ep) composites of thickness ranging from 1mm to 27.9mm. These piezoelectric film based sensors are fabricated using a sol-gel spray technique. The center operation frequency of these sensors ranged from 1.3MHz to 10.5MHz. For the first sensor type, piezoelectric films of thickness greater than 60μm were deposited directly onto planar and curved Gr/Ep composites surfaces as integrated sensors. Ultrasonic signals propagating in a distance of more than 300mm have been obtained. Anisotropy of 0° and 90° cross ply Gr/Ep composite was measured. For the second sensor type, piezoelectric films were coated onto a 50µm thick polyimide membrane as flexible sensors that could be attached to a host composite structure with planar or curved surfaces. The flexibility of such FUTs is achieved due to the thin polymide, porous PZT/PZT ceramics and electrodes. An induction type non-contact method for the interrogation of the Gr/Ep composites using integrated sensors is also presented. Such non-contact technique may be desired for NDT of rotating composite components.