Piezoelectric PZT/epoxy Composites for Controlling Torsional Motion

Abstract

Thin layers of the piezoceramic PZT (Lead Zir conate/Titanate) have been used to actuate and sense bending mo tion of thin, flexible structures. However, because of its transverse isotropy (mm6 symmetry), a pure PZT piezoceramic is unable to generate or sense twisting motion for applications including beams, plates or shell panels. The use of a polyvinylidene fluoride (PVF₂) polymer possessing orthotropy (mm2 symmetry) allows sensing of twisting, but is not stiff enough to provide actuation because of its low modulus and typically low thickness. One possi ble method for generating a more powerful twisting actuation is to construct a piezoceramic/polymer composite element which is or thotropic in the plane and stiff enough to provide actuation. With the requirement of orthotropy in mind, composites have been fab ricated by cutting rods from a PZT plate and placing them in an epoxy matrix. The piezoelectric coupling coefficients d ₃₁ and d ₃₂ have been measured for these composites. The ratio (d ₃₁/d ₃₂) is ap proximately 2, which demonstrates the required orthotropy and thus demonstrates our ability to produce the desired twisting actua tion. A plate theory analysis provides information on the optimum orientation angle of the PZT/epoxy composite to provide twisting actuation and sensing. This theory predicts that the PZT/epoxy will demonstrate a factor of 40 improvement in actuation power over the PVF₂ for a sample geometry.