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.

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.

This book presents new approaches to R&D of piezoelectric actuators and generators of different types based on established, original constructions and contemporary research into framework of theoretical, experimental, and numerical methods of physics, mechanics, and materials science. Improved technical solutions incorporated into the devices demonstrate high output values of voltage and power, allowing application of the goods in various areas of energy harvesting. The book is divided into seven chapters, each presenting main results of the chapter, along with a brief exposition of novel findings from around the world proving context for the author’s results. It presents particular results of the Soviet and Russian schools of Mechanics and Material Sciences not previously available outside of Russia.

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...