Structural Health Monitoring of Composites Using Integrated and Flexible Piezoelectric Ultrasonic Transducers

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 12.7 mm. These piezoelectric film-based sensors are fabricated using a sol-gel spray technique. The center operation frequency of these sensors ranges from 1.3 MHz to 14.5 MHz. For the first sensor type, piezoelectric films of thickness >= 30 mu m 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 degrees and 90 degrees cross ply Gr/Ep composite is measured and delamination detected. For the second sensor type, piezoelectric films are coated onto a 50 mu m thick polyimide membrane as flexible sensors that may be attached to a host composite structure with planar or curved surfaces. An induction type non-contact method for the interrogation of the Gr/Ep composites using integrated sensors is also presented.