Piezoelectric stack actuators are increasingly used in micropositioning applications due to their precision and responsiveness. Advanced automotive fuel injectors have recently been developed that utilize multilayer piezoelectric actuators. Since these injectors must operate under high dynamical excitations at high temperatures, understanding their thermo-electro-mechanical performance under such operating conditions is crucial to their proper design. In this thesis, the effect on soft Lead Zirconate Titanate (PZT) piezoelectric actuators of different controlling parameters relevant to fuel injection is studied experimentally. These parameters include electric-field magnitude and frequency, driving-field rise time, DC offset, duty-cycle percentage, and ambient temperature. Soft PZT actuators generate a significant amount of heat when driven under high electric-field magnitudes and/or high frequency, both of which occur in fuel injectors. They also exhibit hysteretic nonlinear behavior when driven under high electric-field magnitudes. Self-heating and hysteretic nonlinearity are interconnected, and both are undesirable in applications that require precise positioning, such as fuel injection. Self-heating in PZT stacks is considered to be caused by ferroelectric hysteretic nonlinearity, originating from domain-switching. Theoretical studies of self-heating and domain-switching in PZT materials are developed in this thesis. An analytical self-heating model based on the first law of thermodynamics is presented that accounts for different parameters such as geometry, magnitude and frequency of applied electric field, duty-cycle percentage, and surrounding properties. It also directly relates self-heating in PZT actuators to displacement-electric field loss (displacement hysteresis), which is found to increase linearly with increased temperature. The model shows reasonable agreement with experimental results at low and high electric-field magnitudes. A novel domain-switch.

Piezoelectric actuators are increasingly used for the electronic control of fuel injector opening valves. Hydrogen is considered an attractive clean alternative fuel for automobile and power generation applications. Current understanding of the performance of piezoelectric actuators in a hydrogen environment is very limited. This work is aimed at experimentally investigating the performance of hydrogen-exposed piezoelectric actuators under conditions directly relevant to a hydrogen-based fuel injector. The performance is assessed with both quasi-static and dynamic electric loads. It is found that up to 12 weeks of continuous exposure to hydrogen at 100°C and 10 MPa has a negligible effect on the actuator stroke when testing is conducted at temperatures of 5-80°C. Cyclic exposure and exposure done on fatigue cycled actuators also yields similar results. Microstructure and dielectric investigations confirm this behavior. The reason for a negligible effect of hydrogen is attributed to the presence of a protective ceramic insulation around the lateral surface of actuators which deactivates the hydrogen diffusion mechanism. A fully-coupled 3-D FEM-based numerical model of a Thermo-Electro-Mechanical continuum in hydrogen environment is developed using the 'Equation Based Modeling' feature of COMSOL Multiphysics. The model provides a useful tool for understanding the localized responses of the actuators in hydrogen environment and to predict their durability and applicability under different conditions.

Today, multi-functional materials such as piezoelectric/ferroelectric ceramics, magneto-strictive and shape memory alloys are gaining increasing applications as sensors, actuators or smart composite materials systems for emerging high tech areas. The stable performance and reliability of these smart components under complex service loads is of paramount practical importance. However, most multi-functional materials suffer from various mechanical and/or electro-magnetical degra-dation mechanisms as fatigue, damage and fracture. Therefore, this exciting topic has become a challenge to intensive international research, provoking the interdisciplinary approach between solid mechanics, materials science and physics. This book summarizes the outcome of the above mentioned IUTAM-symposium, assembling contributions by leading scientists in this area. Particularly, the following topics have been addressed: (1) Development of computational methods for coupled electromechanical field analysis, especially extended, adaptive and multi-level finite elements. (2) Constitutive modeling of non-linear smart material behavior with coupled electric, magnetic, thermal and mechanical fields, primarily based on micro-mechanical models. (3) Investigations of fracture and fatigue in piezoelectric and ferroelectric ceramics by means of process zone modeling, phase field simulation and configurational mechanics. (4) Reliability and durability of sensors and actuators under in service loading by alternating mechanical, electrical and thermal fields. (5) Experimental methods to measure fracture strength and to investigate fatigue crack growth in ferroelectric materials under electromechanical loading. (6) New ferroelectric materials, compounds and composites with enhanced strain capabilities.

The objective of this research was to analytically and experimentally study the capabilities of piezoelectric plate actuators for suppressing flutter. Piezoelectric materials are characterized by their ability to produce voltage when subjected to a mechanical strain. The converse piezoelectric effect can be utilized to actuate a structure by applying a voltage. For this investigation, a two-degree-of-freedom wind tunnel model was designed, analyzed, and tested. The model consisted of a rigid wing and a flexible mount system that permitted a translational and a rotational degree of freedom. The model was designed such that flutter was encountered within the testing envelope of the wind tunnel. Actuators made of piezoelectric material were affixed to leaf springs of the mount system. Command signals, applied to the piezoelectric actuators, exerted control over the damping and stiffness properties. A mathematical aeroservoelastic model was constructed by using finite element methods, laminated plate theory, and aeroelastic analysis tools. Plant characteristics were determined from this model and verified by open loop experimental tests. A flutter suppression control law was designed and implemented on a digital control computer. Closed loop flutter testing was conducted. The experimental results represent the first time that adaptive materials have been used to actively suppress flutter. They demonstrate that small, carefully placed actuating plates can be used effectively to control aeroelastic response. Heeg, Jennifer Langley Research Center RTOP 505-63-50-15...

Taking advantage of high resolution, rapid response, and compact structure, piezoelectric actuators are widely employed for achieving precision positioning in both scientific research and industrial application. With the development of science and technology, the requirements for precision positioning are increasing. Accordingly, great efforts have been made to improve the performances of piezoelectric actuators, and significant progress has been achieved. This book discusses some recent achievements and developments of piezoelectric actuators, in terms of piezoelectric material, driving principle, structural design, modeling, and control, as well as applications.