The harmonic excitation of simply supported Euler plates is performed experimentally using arrays of piezoceramic patch pair actuators bonded to the plate surface. The experimental techniques used are presented, and the effects of patch location, relative actuator phasing, and excitation frequency on modal excitation are demonstrated. In addition, experimental results are compared to a previously developed closed-form solution which predicts the modal distribution due to such excitation. Finally, a finite element model of a simpler 2-D case of beam actuation is employed to illustrate the effects of the adhesive layers between the patches and structure on modal excitation. Results show that the closed-form solution is capable of predicting both the relative modal distribution and absolute modal amplitudes for different experimental configurations and indicate that with knowledge of the system resonant frequencies and nodal lines, experimental parameters such as excitation frequency, patch location, and relative patch phasing can be logically manipulated to produce a desired vibrational response. The results of the finite element analysis reveal that the net effect of the finite adhesive layer depends on both the stiffness and thickness of the layer, and that increasing either of these parameters can result in multiple consequences, which can combine to positively or negatively affect modal excitation levels. / Master of Science

Actuator placement is a major concern in control system designs. Utilizing piezoelectric actuators increases the complexity of actuator designs, because both actuator location and dimensions need to be considered. A comprehensive study was conducted in this dissertation on the optimization of piezoelectric actuator designs for vibration suppression of flexible structures. The investigation on the optimal piezoelectric actuator designs were grouped into two parts. Part one covered actuator designs when the same number of actuators as the controlled modes are used. Approaches were formed to optimally design piezoelectric actuators which requires least control efforts. In part two of this dissertation, a method named the Weighted Pseudoinverse Method was introduced to deal with the cases in which fewer actuators than the controlled modes are utilized. The weighted pseudoinverse method yields a optimal transformation from modal control forces into the actuator-moments in physical space. Based on the Weighted pseudoinverse method, the piezoelectric actuator designs were optimized to ensure least-control-effort actuator designs. A simply-supported beam was used as an example to demonstrate the effectiveness of the design methods proposed in this dissertation. However, the design methods are applicable to general cases. / Ph. D.

Intelligent materials are a class of material systems usually consisting of a composite or hybrid material system with fibrous or distributed actuators, various sensors and a control system. One type of actuator being developed for intelligent material systems is made of nitinol or shape memory alloy wire. In order for nitinol and other actuators to be a reliable part of the system, the effect of composite manufacturing on the actuators’ performance and behavior must be determined. The results of a study investigating the effects of a "high temperature" thermoplastic composite processing cycle on the nitinol actuator’s performance is presented. A study of the interfacial strength between the actuators and APC-2 thermoplastic composite is also reported. The nitinol actuators were exposed to high temperature (400°C) composite processing cycles. Critical parameters of the processing cycles were varied to determine their effect on the actuators’ performance. After the processing cycles, the nitinol actuators demonstrated useable recovery stresses (σ_r^u) of 173-265 MPa. The σ_r^u of a nitinol actuator in the virgin state, subjected to a thermoset processing cycle, and embedded in a specimen of APC-2 thermoplastic composite was also tested to develop a basis for comparison. The quality of the actuator-composite interface bond was tested by pull-out testing and fatigue loading to determine if the actuator is adequately bonded with the host composite. Pull-out forces of 30-50 N could fracture the actuator-composite interface, but 1000 activation cycles of the actuator produced no damage in the bond between actuator and host composite. / Master of Science