Mathieu Domenjoud

Modelling of hysteretic behavior of piezoceramic materials under electrical loading

The purpose of this study is to model the hysteretic behavior of piezoceramic materials under electrical loading. Remanent strain and remanent polarization are chosen as internal variables. A domain orientation distribution is used to describe the evolution of these variables by bridging the characteristics of microscopic domain distribution into macroscopic behaviors. This model is able to calculate electric displacement, longitudinal, and transversal strains as a function of uniaxial electrical field. Good quality of the formulation is demonstrated through comparison with experimental data of the literature. In addition, results confirm our hypothesis of isochoric deformation of piezoceramics under electrical loading.

Theoretical and experimental study of the electroacoustic behavior of lithium niobate under an initial mechanical stress

Recently, a second-order formalism of piezoelectric structures under an external mechanical stress was developed. Because the yield strength of lithium niobate was unknown, this study was not able to describe and evaluate realistic benefits of a prestress load on electromechanical properties. Therefore, in this study, experimental determination of the yield strength of lithium niobate sample is performed and shows that this limit is close to 110 MPa. Then, the nonlinearities and evolutions of electroacoustic parameters of this piezoelectric material under mechanical stress are numerically studied. By varying the initial prestress, as well as azimuthal and elevation angles, the cut planes in which a prestress induces significant benefits on velocities and coupling coefficient are identified. Finally, approximate relations describing changes between electroacoustic parameters defined in the two coordinate systems of the study are determined.

Exact second order formalism for the study of electro-acoustic properties in piezoelectric structures under an initial mechanical stress.

In this study we develop the exact second order formalism of piezoelectric structures under an external mechanical stress. Indeed, previous models are approximated since they consist in deriving all the equations in the natural coordinate system (corresponding to the pre-stress free case). Hence, our exact formalism proposes to obtain the whole of equations in the current coordinate system (which is the coordinate system after the pre-deformation). Then, this exact formalism is used to derive the modified Christoffel equations and the modified KLM model. Finally, we quantify the correction with the approximate formalism on several transfer functions and electro-mechanical parameters for a non hysteretic material (lithium niobate). In conclusion, we show that for this material, significant corrections are obtained when studying the plane wave velocities and the electrical input impedance (about 4%), whereas other parameters such as coupling coefficient and impulse response are less influenced by the choice of coordinate systems (corrections less than 0.5%).

Domain motion modeling for hysteresis in piezoceramic materials under mechanical loading

The purpose of this study is to model domain motions of piezoceramic materials under mechanical loading to reproduce their hysteretic behaviors. Evolutions of remanent strain and remanent polarization are described by bridging the characteristics of microscopic domain distribution into macroscopic behaviors. Taking into account hysteretic behavior in unpoled piezoceramics, this model calculates electric displacement and longitudinal strain as a function of uniaxial mechanical field. Good quality of the formulation is demonstrated through comparison with experimental data. In addition, results confirm our choice of one single domain evolution law to describe domain motion in piezoceramics under mechanical and electrical loading.

Integrated piezoelectric structures under external mechanical stress: Theory and experiments

The purpose of the study is to understand and predict the behavior of integrated structures when submitted to external or internal mechanical stress. This is of primary importance in the field of thick or thin film technology. In our laboratory, a modified KLM model that enables to compute the electro-acoustic behavior of piezoelectric materials under external mechanical stress has been developed. In this present work, we produce the first experimental results of electromechanical characterizations of reference materials under external mechanical stress in order to further validate our model. A static stress (with a stepper motor) and a superimposed dynamic wave (with PZT actuator) are applied to PZT type materials (PZ21 and PZ26). The hysteretic behavior and the evolution with the stress (0 to 100 MPa) of plane wave velocity are presented for the two samples. The evolution of ultrasonic wave velocities along the direction of stress are treated using conventional pulse echo technique. Results validate the acoustical and mechanical method but show high sensitivity of the mechanical aspect and reveal the need to enhance the experimental setup to obtain more accurate values.

Domain wall evolution laws of piezoceramic materials under mechanical loading

The purpose of this study is to model the nonlinear hysteretic behavior of piezoceramic materials under mechanical loading to determine associated domain wall evolution laws. The model is constructed by bridging the characteristics of microscopic domain distribution into the macroscopic behavior. Evolutions of the remanent strain and remanent polarization are described by a domain distribution evolution. These variables are used to develop a phenomenological model that is able to reproduce the longitudinal strain and electric displacement in function of uniaxial mechanical loading. Evolutions of domain walls induced by polarization and ferroelastic strain are characterized and discussed for two piezoceramic materials.

Determination of microscopic parameters of piezoceramic materials under electrical loading using genetic algorithm

The purpose of this study is the characterization of microscopic parameters of piezoceramic materials, such as spontaneous polarization and spontaneous strain. In previous works, a model has been developed by bridging characteristics of microscopic domain distribution into the macroscopic behavior. It reproduces longitudinal strain and electrical displacement as a function of uniaxial electrical loading, according to material parameters and applied electrical field. Optimization is performed between theoretical and experimental hysteresis curves. This method is based on a genetic algorithm procedure in order to ensure robust convergence even if the system is multimodal. Materials used in this study are PLZT8/65/35 and PZT-5A. After optimization, experimental curves are well fitted to theoretical curves and a good agreement has been shown between retrieved parameters and values reported in literature. This validates domain wall modeling and genetic algorithm as an efficient way to characterize piezoceramic materials under harsh operating conditions.

Modeling and numerical study of the electroacoustic behavior of lithium niobate under an initial electrical stress

Recently, we developed a second order formalism of piezoelectric structures under an external stress. In this work, this formalism is used to numerically study the nonlinearities and evolutions of electroacoustic behavior of lithium niobate under initial electrical stress. By varying the initial prestress, as well as azimuthal and elevation angles, the cut planes in which an electrical prestress induces significant changes on quasi-longitudinal velocity and benefits on coupling coefficient are identified.