Dynamic Characteristics Of Laminated Piezoelectric Composite Structures

Piezoelectric materials are often used in the design of smart devices, such as sensors, actuators, ultrasonic transducers, energy harvesters due to their excellent electromechanical coupling properties. Nowadays, these devices have been widely applied in many engineering fields, such as health monitoring of concrete structures in civil engineering, detecting and locating underwater targets in underwater acoustic field, harvesting pavement deformation energy in traffic system, among others.Due to ease of use, high specific strength and rigidity, and excellent electromechanical performance, laminated piezoelectric composite structures have drawn more and more attention for the development of novel smart devices. However, for devices consisting of multilayer elastic layers and piezoelectric layers, the dynamic coupling effects between elastic and electric field within it are highly complicated, which make it is difficult to solve and analyze this kind of problem. Therefore, common layered piezoelectric smart devices used in the current engineering only include few piezoelectric layers and elastic layers. The method of establishing the reasonable model to obtain the dynamic solutions of the smart devices composed of piezoelectric layers and elastic layers of arbitrary layer numbers has an important significance for both development and design of these kinds of smart devices.Based on the piezoelasticity theory, theoretical analysis combined with ANSYS numerical simulation and experiment research were used in this dissertation to deeply investigate dynamic characteristics of radially polarized and axially polarized multilayer piezoelectric/elastic composite cylindrical structures with arbitrary layer numbers, radially layered novel cymbal energy harvesters, and piezoelectric stack generators. Through establishing analytical models, analytical solutions of these kinds of structures were obtained, and parametric analysis was completed. For specific cases, the present solutions present good consistency with those obtained from the related works, validating that the present solutions are correct. At the end of this dissertation, the application of piezoelectric stack generator in railway systems was explored.The main works are as follows:(1) Taking radially polarized piezoelectric tube as the basic unit, a kind of radially polarized piezoelectric/elastic composite cylindrical structure with arbitrary layer numbers was proposed, and its dynamic analytical model was established. The theoretical solution was given, and its validity was verified by the results obtained from the related works. The effects of polarization directions in piezoelectric layers, the inner radius of composite structure, the thickness of elastic layer and the number of piezoelectric layers on the dynamic characteristics of composite structure were discussed. The model can be used to guide the design of radially polarized structural elements with arbitrary layer numbers, which can replace the axially polarized piezoceramic disk in the traditional cymbal structure. The model provides a theoretical support for designing the novel cymbal transducer.(2) Taking axially polarized piezoelectric ring as the basic unit, an axially polarized piezoelectric/elastic composite cylindrical structure with arbitrary layer numbers was proposed, and its dynamic analytical model was established. The theoretical solution was given, and its correctness verification and parameter influence analysis were presented. Then, the model was extended as a new combined model included the actuator part and the sensor part, and its multifrequency characteristics were obtained through adjusting the ratio of piezoelectric layer numbers between the actuator part and the sensor part, the external electric resistance of sensor part. Furthermore, the matching electric resistance can be used for the optimal design of structural performance. The proposed models can be used to guide the design of axially polarized structural elements with arbitrary layer numbers, which can replace the axially polarized piezoceramic disk in the traditional cymbal structure. The models provide a theoretical support for designing the novel cymbal transducer and its performance optimization.(3) Two kinds of radially multilayer novel cymbal piezoelectric energy harvesters were designed and fabricated. One design includes a stepped metal ring to finish the mechanical coupling with cymbal metal caps by using epoxy; the other is a design of a drilled metal ring to finish the mechanical coupling with cymbal metal cap by using screw bolts. An experiment was then carried out to investigate their energy harvesting performance. ANSYS numerical simulation and theoretical analysis were also completed. The obtained results and the experiment data are in good agreement. Experiment results show that these two designs can work well when the harvesters are applied to a higher load, which provides a new design concept for further exploiting novel cymbal energy harvesters used in the high load environment, such as roadway systems and railway systems.(4) A theoretical model of piezoelectric stack generators was established, and its dynamic solution was given. The effects of electrodes were analyzed. The test specimens of energy harvester were fabricated and the experiment verification was performed. The work provides a theoretical basis for developing the novel piezoelectric stack generator.(5) A type of piezoelectric stack device was designed to harvest the mechanical energy of railway systems. The Winkler elastic foundation beam subjected to moving multi-loads was adopted to model the railway track. The dynamic model of the energy harvesting device coupling with track structure was established. The effects of axle loads, running velocity, load resistor and spring stiffness of the device on energy harvesting performance were discussed. The work provides a reference for exploiting piezoelectric energy harvesters used in railway systems.