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Large strain electrostriction in single-crystal ferroelectric materials is investigated. The mode of electrostriction is based on a combined electromechanical loading used to induce cyclic, 90°domain switching. Experiments have been performed on crystals of barium titanate with constant compressive stress and oscillating electric-field input. Induced strains of more than 0.8% have been measured. Strains as large as 5% are predicted for other materials of the same class. The results demonstrate a possible avenue for obtaining large actuation strains in electromechanical devices. © 2000 American Institute of Physics. ͓S0003-6951͑00͒01137-2͔Ferroelectric ceramics are used in a variety of sensor and actuator applications. In particular, they are one of the basic building blocks of smart structures which have been successfully used for active damping and damage detection. The behavior of conventional materials is characterized by good high-frequency response and low hysteresis, but unfortunately, very small strains ͑limited to about 0.1%͒. A variety of methods have been developed for creating large displacement actuators by using monomorph or bimorph benders, functionally graded ceramics, and single crystals. Research on single-crystal ferroelectric materials for sensor and actuator applications have recently focused on exotic relaxorbased systems, formulated near the morphotropic phase boundary, that take advantage of phase transition to produce large actuation strains. 1 The current investigation focuses on the use of domain reorientation to generate a large actuation strain in a ferroelectric single crystal of a simple perovskite structure. Experiments have been performed on barium titanate (BaTiO 3 ), a common ferroelectric, generating strains of more than 0.8%.The current study is motivated by the theoretical work of Shu and Bhattacharya who developed a model of a ferroelectric single crystal using the setting of finite deformations. 2 They assume the existence of a crystal free-energy density W, which is dependent on the deformation gradient (F), polarization ( P), and temperature ( ). For a flat plate configuration with electrodes on two faces, the total energy G can be expressed in three terms consisting of the crystal freeenergy density, and external mechanical and electrical work:where T o is stress and E o is the applied electric field. For a material such as barium titanate, there exist six possible ground states with the polarization vector in one of the six pseudocubic ͗100͘ directions. These ground states correspond to multiple energy wells of W. When considering a compressive stress and electric field across the ferroelectric plate, minimization of the total energy results in a phase diagram describing the exchange of stability of the different directions of polarization in the stress-electric-field space.The analysis further suggests that there exists a low-energy path for switching from one polarization to another. Thus, domain polarization can be switched by electric field or applied stress. Fur...

The internal shock loading of cylindrical shells can be represented as a step load advancing at constant speed. Several analytical models are available to calculate the structural response of shells to this type of loading. These models show that the speed of the shock wave is an important parameter. In fact, for a linear model of a shell of infinite length, the amplitude of the radial deflection becomes unbounded when the speed of the shock wave is equal to a critical velocity. It is evident that simple (static) design formulas are no longer accurate in this case. The present paper deals with a numerical and experimental study on the structural response of a thin aluminum cylindrical shell to shock loading. Transient finite element calculations were carried out for a range of shock speeds. The results were compared to experimental results obtained with the GALCIT 6-in. shock tube facility. Both the experimental and the numerical results show an increase in amplitude near the critical velocity, as predicted by simple steady-state models for shells of infinite length. However, the finite length of the shell results in some transient phenomena. These phenomena are related to the reflection of structural waves and the development of the deflection profile when the shock wave enters the shell.

A new mode of large electrostrictive actuation, based on 90°domain switching in ferroelectric crystals subjected to combined electromechanical loading, has recently been experimentally demonstrated. In this paper, we develop a model for this phenomenon by assuming a reasonable arrangement of domain walls and formulating equations of motion for these walls. The model captures most of the features observed in the experiments, reveals the significant role of friction at the interfaces between the loading frame and the crystal surfaces, and predicts that a reduction of friction will allow larger strains at lower mechanical loads.

The complex arrangement of domains observed in ferroelectric crystals is a consequence of multiple energy minima of the crystal free energy density. Since the total energy is a sum of the free energy, and electrical and mechanical work, switching between the different energetically equivalent domain states can be achieved by both electrical and mechanical means. For many ferroelectric materials, this results in an electrostrictive phenomenon resulting from domain switching. In the current study, the electrostrictive behavior of single crystal ferroelectric perovskites has been investigated experimentally. Experiments have been performed in which a crystal of barium titanate is exposed to a constant compressive stress and an oscillating electric field and global deformation is measured. The combined electromechanical loading results in a cycle of stress and electric field induced gO-degree domain switching. The domain switching cycle results in a measurable strain response theoretically limited by the crystallographic unit cell dimensions. Induced strains of more than 0.8% have been measured in barium titanate. Larger strains of up to 5% are predicted for other materials of the same class .