| The ability to control structural vibration and noise is of great importance in meeting the current standards for noise radiation, machinery reliability and structural fatigue life. One promising method for controlling low-frequency vibration, typically encountered in large, complex and lightweight structures, is to employ the rapidly growing technology of smart materials and structures, featuring embedded actuators and sensors that are designed and operated to enhance the dynamic behavior of the system.; The main goal of this work is to investigate the use of Active Piezoelectric Damping Composites (APDC), consisting of piezoelectric rods that are embedded in a polymer matrix, in structural vibration and noise control applications. While these composites have been extensively used as acoustic transducers, this work extends their use as actuators. A finite element model is developed to investigate the dynamic behavior of elastic plates, treated with discrete patches of APDC, and radiating sound into an acoustic enclosure. The effectiveness of the APDC in damping out plate vibration and attenuating sound radiation is presented. Considerable attenuation of vibration and noise are realized by proper selection of the design parameters of the APDC treatment. The theoretical predictions are supported experimentally by studying an elastic plate, clamped from all sides, and radiating sound into a rigid enclosure. The theoretical and experimental results, which are found to be in close agreement, demonstrate the effectiveness of APDC in controlling structural vibrations and noise.; The final part of this work deals with investigating some of the nonlinear phenomena exhibited by piezoelectric materials and extending the analysis to piezoelectric composites. To this end, a nonlinear piezoelectric model featuring quadratic terms in the constitutive equations was developed. The model was employed, together with supporting experimentation, to gain more insight into the behavior of piezoelectric stack actuators, as well as the piezocomposites. It is concluded that nonlinear effects are pronounced at high actuator drive levels and frequencies; conditions that are beyond the operating range of the structural vibration and noise control problem posed in the earlier part of the dissertation. |
