Pavel M. Chaplya

Dielectric and piezoelectric response of lead zirconate–lead titanate at high electric and mechanical loads in terms of non-180° domain wall motion

The effect of prestress on the nonlinear dielectric (polarization) and piezoelectric (strain) response of lead zirconate–lead titanate (PZT–5H) piezoelectric ceramic is studied. The response to bipolar (−2/+2 MV/m) and unipolar (0/+2 MV/m, −0.4/+2 MV/m) electric field under constant prestress (up to 175 MPa) is experimentally evaluated. In the bipolar regime, prestress mainly influences the first non-180° process. In the unipolar regime, the dielectric and piezoelectric response achieve maximum values near 50–60 MPa because the prestress increases the number of available non-180° domains. A detailed description of the effect of the prestress on electro–mechanical response is provided in terms of non-180° domain wall motion. Based on rule of mixtures formulation, an analytical model is developed to estimate the optimum prestress value for the unipolar electric loading condition. It is found that the dielectric and piezoelectric response of the material is proportional to the volume fraction of the non-180°...

Durability properties of piezoelectric stack actuators under combined electromechanical loading

This paper presents results on the electro-thermo-mechanical behavior of piezoelectric materials for use in actuator applications with an emphasis on durability performance. The objective of this study was to compare the performance of different commercially available actuator systems and to determine the properties necessary for the design of such actuator systems. Basic piezoelectric properties of five stack actuators were determined as a function of mechanical preload and temperature. Changes in these properties during ferroelectric fatigue up to 107cycles were determined from strain-field relations after a specified number of fatigue cycles. Experimental results indicate a strong dependence of piezoelectric properties and power requirements on mechanical loading conditions. Results indicate that the optimum operating conditions (i.e., mechanical preload) that will improve actuation capabilities of piezoelectric stack actuators can be determined. That is, strain output was found to increase by 60% for ...

Compression of piezoelectric ceramic at constant electric field: Energy absorption through non-180° domain-wall motion

The effect of bias electric field on the nonlinear stress–strain response of a lead zirconate–lead titanate piezoelectric ceramic is studied. The material is subjected to various compressive stress amplitudes (25–300 MPa) under constant electric field (from −0.5 to 2.0 MV/m) along the original poling direction. Application of a positive electric-field bias results in closed stress–strain hysteresis loops absorbing significant amounts of mechanical energy. Increasing the positive electric field increases the specific damping and decreases the elastic modulus. The trend is reversed when the electric field becomes sufficiently high to inhibit the domain-wall motion by the mechanical stresses. Measured specific damping values vary from 0.18 to 0.46 depending on the stress amplitude and bias electric field. The corresponding secant modulus varies from 79 to 24 GPa. The coercive stress is found to approach zero as the negative electric-field bias approaches the coercive field value. The coercive stress increase...

Compression of PZT-5H piezoelectric ceramic at constant electric field: investigation of energy absorption mechanism

This paper presents an experimental and analytical investigation into the mechanical behavior of PZT-5H piezoelectric ceramic. The materia is subjected to cyclic uniaxial compressive stress at a constant electric field bias. The damping characteristics such as fraction of energy absorbed and elastic modulus are evaluated as a function of bias electric field. Increasing the positive electric field increases the specific damping and decreases the elastic modulus. The trend is reversed when the electric field becomes sufficiently high to inhibit the domain wall motion by the mechanical stresses. Measured specific damping values vary form 0.18 to 0.46 depending on the stress amplitude and bias electric field. The corresponding secant modulus varies from 79 to 24 Gpz. The optimum electric field values increase as the stress amplitude increases because the positive electric field and the compressive stress counteract each other in terms of domain wall motion. An analytical model shows that the materials response is proportional to the volume fraction of the domains available for switching and the domain wall pressure difference between positive electric field and compressive stress.

Piezoelectric PVDF materials performance and operation limits in space environments.

Piezoelectric polymers based on polyvinylidene fluoride (PVDF) are of interest for large aperture space-based telescopes. Dimensional adjustments of adaptive polymer films are achieved via charge deposition and require a detailed understanding of the piezoelectric material responses which are expected to suffer due to strong vacuum UV, gamma, X-ray, energetic particles and atomic oxygen under low earth orbit exposure conditions. The degradation of PVDF and its copolymers under various stress environments has been investigated. Initial radiation aging studies using gamma- and e-beam irradiation have shown complex material changes with significant crosslinking, lowered melting and Curie points (where observable), effects on crystallinity, but little influence on overall piezoelectric properties. Surprisingly, complex aging processes have also been observed in elevated temperature environments with annealing phenomena and cyclic stresses resulting in thermal depoling of domains. Overall materials performance appears to be governed by a combination of chemical and physical degradation processes. Molecular changes are primarily induced via radiative damage, and physical damage from temperature and AO exposure is evident as depoling and surface erosion. Major differences between individual copolymers have been observed providing feedback on material selection strategies.

Investigation of energy absorption capabilities of piezoelectric ceramic

This paper presents an experimental investigation into the damping characteristics of piezoelectric ceramic PZT-5H. The material is subjected to cyclic uniaxial compressive stress (up to 200 MPa) at a constant electric field bias (from 0 to 2 MV/m). The experiments are conducted at 25 degree(s)C, 0 degree(s)C, and 50 degree(s)C. Fraction of energy absorbed (a specific damping capacity_ and elastic modulus are evaluated as a function of bias electric field. For investigated stress amplitudes, the specific damping capacity increases with increasing bias field, reaches a maximum (28-33%) at the optimum field level, and then decreases. The optimum electric field values increase as the stress amplitude increases because the positive electric field and the compressive stress counteract each other in terms of domain wall motion. The damping properties are stable in the investigated temperature range. The piezoceramic is found to have superior damping properties compared to common structural methods.

Relation of the cracking phenomena in piezoelectrics to domain wall motion

An ongoing investigation into understanding the nature and mechanics of damage in piezoelectric material under combined cyclic electrical and static mechanical loads is described. The piezoelectric is subjected to large field excursions that are sufficient to cause polarization switching at least around internal anomalies, as well as mechanical stresses with values well below ultimate strength of the material. Experimental work is conducted on PZT-5H with macroscopically engineered dissimilar (180°) domain structures. All samples contain a seed notch to introduce a stress concentration at a specified location and eliminate questions associated with electrode attachment. Results indicate that for specimens undergoing significant domain wall motion the crack initiation occurs after only 20 - 100 cycles while for specimens undergoing small domain wall motion cracks initiate after 800,000 cycles. Compressive mechanical loads are found to retard damage growth. Experimental results are explained with data obtained from a finite element model. The principal conclusion is that domain wall motion on both micro and macro levels is responsible for crack initiation and degradation of the material during cycling loading.

Analytical and Experimental Studies of Orthotropic Corner-Supported Plates With Segmented In-Plane Actuators

This paper outlines a model for a corner-supported, thin, rectangular bimorph actuated by a two-dimensional array of segmented, orthotropic PVDF laminates; it investigates the realization and measurement of such a bimorph. First, a model is derived to determine the deflected shape of an orthotropic laminate for a given distribution of voltages over the actuator array. Then, boundary conditions are realized in a laboratory setup to approach the theoretical corner-supported boundary condition. Finally, deflection measurements of actuated orthotropic PVDF laminates are performed with Electronic Speckle Pattern Interferometry and are compared to the model results.

Rechargeable Lithium Batteries for Powering Piezoelectric Devices

A new, rechargeable, thick-film, polymer electrolyte, lithium battery using a high-energy density cathode material (vanadium pentoxide aerogel, 350 mAh/g) has been tested in a pulse-discharge mode of operation. Three separate 12 volt batteries were pulse-discharged through a piezoelectric stack actuator. Since motion rectification devices such as linear motors operate at elevated frequencies, the batteries were pulse-discharged at 10, 100, and 500 Hz. Multiple cycle, charge/discharge data is presented for the three batteries tested in this study. Additionally, a 6 volt battery was fabricated and used to power a piezoelectric actuator patch (chirp source) that was part of a damage detection system.

Optomechanical Design for Cost Effective DEMVAL Systems.

Sticker shock for optomechanical hardware designed for advanced optical DEMVAL systems can lead to program loss. In optomechanical design it is important to manage this risk through easily manufacturable and inexpensive hardware to meet demands of lower budget programs. The optical and optomechanical design teams must work closely to optimize system design for ease of manufacture, and assembly, while at the same time minimizing the impacts to system performance. Effective teaming often results in unique/creative design solutions which enable future system development. Outlined are some novel optomechanical structure concepts, with 5 degrees of freedom (DOF), used to design a low cost DEMVAL optical system. The concepts discussed include inexpensive repeatable magnetic kinematic mounts, flexure rings for lens preloading, simplistic drop-in lens housing designs, and adjustable tooling ball metering rods which accommodate alignment in 5 DOF.