Application of piezoelectric paints to damage detection in structural materials

Piezoelectric paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were coated on aluminum plates and were cured at room temperature, thus forming the paint films having thicknesses of 25 to 300 mu m and a PZT volume fraction of 53 %. These films were then poled at room temperature, and were evaluated with regard to the sensitivity as an acoustic emission sensor in the frequency range of 0-1.2 MHz. The paint film sensitivity obtained at a given poling field depends on the film thickness, even after being normalized by dividing by the film thickness. The current-voltage characteristic of the paint film reveals that the film-thickness dependence of the normalized sensitivity is interpreted in terms of the space-charge buildup at the PZT/epoxy interface during the poling process of the paint film.