Current research in flexible, adaptive, space structures includes active vibration control required for stable operation. Theoretical and experimental research into the use of low mass, spatially distributed piezoelectric film actuators has demonstrated the possibilities of increasing the damping of resonant response of flexible space structures in bending.
This thesis describes a theoretical and experimental development of a laminated spatially distributed piezoelectric torsional vibration actuator for a clamped free cantilever beam. The strain energy transferred from a piezoelectric film actuator to a substructure is derived as a function of actuator strain only and is then used to calculate the induced strain in a substructure loaded in uniaxial extension/compression, bending and torsion. The induced strain calculated with this method agrees with published results for extension and bending and the result for torsion is verified by experiment. Since transferred strain energy is calculated for the actuators, this transferred energy can be maximised, by optimising the actuator/structure dimensions and material properties. Optimal beam sizes are proposed for given actuator properties for bending and torsion. The theoretical models are extended by deriving expressions for modal loss factor due to the presence of the actuators in bending and torsion. These loss factor expressions are used to generate free end displacement time histories and Energy Time Curve (ETC) histories associated with the fundamental mode decay which are compared with experimental results. The actuator damping characteristic is similar to Coulomb damping where the effective loss factor increases as displacement decreases.
Experimental cantilever beams were constructed to examine the first mode decay in bending and torsion under the influence of the actuators. The torsion beam consisted of a 6.5mm outside diameter, 0.125mm wall thickness nickel tube, 1 metre in length. This was covered with a laminated actuator manufactured from two layers of 28 micron piezoelectric film wrapped helically around the tube and excited by an applied voltage out of phase with the free end torsional velocity. First mode decays were recorded with an accelerometer fitted to a free end lumped inertia which was given an initial impulse.
Comparison of the theoretical and experimental ETC decay histories of the first torsion mode decay indicate a reduction in decay time for the actuator controlled beam of up to 10 times the uncontrolled beam for an excitation voltage of 225 V. It is shown by extrapolation of the validated theoretical model that critical damping can be achieved with optimal actuator/structure size ratios, typical of space structures.