Structural health monitoring of composites using integrated ultrasonic transducers

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Structural health monitoring of composites using integrated ultrasonic transducers

Kobayashi, M. / Wu, K.T. / Song, L. / Jen, C.K. / Mrad, N.

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 1 mm to 27.9 mm. These piezoelectric film based sensors are fabricated using a sol-gel spray technique. The center operation frequency of these sensors ranged from 1.3 MHz to 10.5 MHz. For the first sensor type, piezoelectric films of thickness greater-than 60 micrometer were deposited directly onto planar and curved Gr/Ep composites surfaces as integrated sensors. Ultrasonic signals propagating in a distance of more than 300 mm have been obtained. Anisotropy of 0 deg and 90 deg cross ply Gr/Ep composite was measured. For the second sensor type, piezoelectric films were coated onto a 50 micrometer 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.