A. Arockiarajan

Modeling of dielectric and piezoelectric response of 1-3 type piezocomposites

A study is carried out to compare the non-linear behaviour of 1-3 piezocomposites with different volume fractions and bulk piezoceramics. Experiments are conducted to measure the electrical displacement and strain on piezocomposites and ceramics under high cyclic electrical loading. A thermodynamically consistent framework, combining the phenomenological and micromechanical models, is developed to predict the coupled behavior. Volume fractions of three distinct uni-axial variants (instead of six variants) are used as internal variables to describe the microscopic state of the material. In this model, the grain boundary effects are taken into account by introducing the back fields (electric field and stress) as non-linear kinematic hardening functions. In order to calculate the effective properties (elastic, piezoelectric, and dielectric constants) of piezocomposites for different volume fractions, an analytical model based on equivalent layered approach is proposed. The predicted effective properties are ...

Micromechanical Modeling of Switching Effects in Piezoelectric Materials - A Robust Coupled Finite Element Approach

A micromechanically motivated model for piezoelectric materials has been developed in this work. In particular, the nonlinear behavior of poly-crystalline specimens with tetragonal perovskite-type substructure are studied, and a robust three-dimensional coupled finite element formulation is elaborated. Differently oriented grains are taken into account within the proposed model, whereby representative dipole directions attached to each grain are randomly oriented. Furthermore, an energy reduction criterion applied to individual domains is adopted as a criterion for the initiation of domain switching processes. Based on this, macroscopic bulk response can be predicted by classical volume-averaging techniques. In practice, however, domain switching might occur even below the classical critical energy barrier which mainly stems from so-called intergranular effects. These effects are incorporated into the developed framework via a phenomenologically motivated probabilistic approach by relating the actual energy level to a critical energy level. In order to compare representative coupled finite element examples with experimental data reported in the literature, macroscopically uni-axial and quasi-static loading is applied to the bulk material: first, hysteresis and butterfly curves under purely electrical loading are discussed; secondly, additional mechanical loads in axial and lateral direction are applied to the specimen.

Two models to simulate rate-dependent domain switching effects—application to ferroelastic polycrystalline ceramics

The aim of this paper is to study rate-dependent switching in ferroelastic materials. More specifically, a micro-mechanically motivated model is embedded into an iterative three-dimensional and electromechanically coupled finite element framework. An established energy-based criterion serves for the initiation of domain switching processes as based on reduction in (local) Gibbs free energy. Subsequent nucleation and propagation of domain walls is captured via a linear kinetics theory with rate-dependent effects being incorporated in terms of a deformation-dependent limit-time-parameter. With this basic model in hand, two different switching formulations are elaborated in this work: on the one hand, a straightforward volume-fraction-ansatz is applied with the volume-fraction-value depending on the limit-time-parameter; on the other hand, a reorientation-transformation-formulation is proposed, whereby the orientation tensor itself is assumed to depend on the limit-time-parameter. Macroscopic behaviour such as stress versus strains curves or stress versus electrical displacements graphs are obtained by applying straightforward volume-averaging-techniques to the three-dimensional finite-element-based simulation results which provides important insights into the rate-dependent response of the investigated ferroelastic materials. (Less)

A thermodynamically motivated model for ferroelectric ceramics with grain boundary effects

The aim of this paper is to capture the grain boundary effects taking into consideration the nonlinear dissipative effects of ferroelectric polycrystals based on firm thermodynamic principles. The developed micromechanically motivated model is embedded into an electromechanically coupled finite element formulation in which each grain is represented by a single finite element. Initial dipole directions are assumed to be randomly oriented to mimic the virgin state of the unpoled ferroelectric polycrystal. An energy-based criterion using Gibbs free energy is adopted for the initiation of the domain switching process. The key aspect of the proposed model is the incorporation of effects of the constraint imposed by the surrounding grains on a switching grain. This is accomplished by the inclusion of an additional term in the domain switching criterion that is related to the gradient of the driving forces at the boundary of the grains. To study the overall bulk ceramics behavior, a simple volume-averaging technique is adopted. It turns out that the simulations based on the developed finite element formulation with grain boundary effects are consistent with the experimental data reported in the literature.

Thermo-electro-mechanical response of 1-3-2 type piezoelectric composites

A micromechanics-based analytical model is developed to evaluate the performance of 1-3-2 piezoelectric composite where both matrix and fiber materials are piezoelectrically active. A parametric study is conducted to investigate the influence of the ceramic base and the fiber volume fraction on the modified 1-3 composite. The performance of the 1-3-2 composite as a transducer for underwater acoustics and biomedical imaging applications has been analyzed. The proposed model is capable of predicting the effective properties of the composite subjected to thermoelectromechanical loading conditions. Simulated results of 1-3 type piezocomposite compare well with experimentally measured data reported in the literature (Taunaumang et al 1994 J. Appl. Phys. 76 484–9). The present study demonstrates that the low end ceramic base volume fraction of 1-3-2 composite yields comparative performance with 1-3 type composite. It is observed that the influence of thermal effects on the effective properties of the composite also induces the polarization in the composite.

A multi-surface model for ferroelectric ceramics - application to cyclic electric loading with changing maximum amplitude

Depending on the maximum amplitude of externally applied cyclic electric fields, ferroelectric ceramics show minor or major hysteresis. The materials also show asymmetric butterfly hysteresis in a prepoled material. Aiming at capturing these behaviour in a phenomenological constitutive model, a multi-surface modelling approach for ferroelectrics is introduced. In this paper, with the note on the motivation for a multi-surface model related to the results of new experimental investigations and also to experimental data reported in the literature, the constitutive relation for a rate dependent multi-surface ferroelectric model is developed. Following this, a brief graphical illustration shows how this model captures the objective phenomena. Consequently, the numerical implementation of the model to capture experimental results is demonstrated. Finally, the performance of this model to represent behaviour of decaying polarisation offset of electrically fatigued specimen is shown.

Experimental and theoretical investigation of temperature-dependent electrical fatigue studies on 1-3 type piezocomposites

1-3 type piezocomposites are very attractive materials for transducers and biomedical application, due to its high electromechanical coupling effects. Reliability study on 1-3 piezocomposites subjected to cyclic loading condition in transducer application is one of the primary concern. Hence, this study focuses on 1-3 piezocomposites for various PZT5A1 fiber volume fraction subjected to electrical fatigue loading up-to 106 cycles and at various elevated temperature. Initially experiments are performed on 1-3 piezocomposites, in order to understand the degradation phenomena due to various range in amplitude of electric fields (unipolar & bipolar), frequency of applied electric field and for various ambient temperature. Performing experiments for high cycle fatigue and for different fiber volume fraction of PZT5A1 is a time consuming process. Hence, a simplified macroscopic uni-axial model based on physical mechanisms of domain switching and continuum damage mechanics has been developed to predict the non-l...

Viscoelastic modeling and experimental characterization of thermo-electromechanical response of 1–3 piezocomposites

The viscoelastic behaviour of 1–3 piezocomposites with different volume fractions and bulk piezoceramics is studied under thermal environment subjected to electrical loading. Experiments are conducted to measure the temperature dependent effective properties based on IEEE standards and time dependent thermo-electromechanical response of 1–3 piezocomposites and piezoceramic subjected to high cyclic electrical loading under elevated thermal environment. The temperature dependent effective properties are predicted using the proposed numerical model based on unit cell approach and implemented into the viscoelastic model to predict the time dependent thermo-electro-elastic effective properties. The predicted effective properties are incorporated in a finite element based 3-D micromechanical model to predict the time dependent thermo-electro-mechanical performance behaviour of 1–3 piezocomposites. Comparison between the experiments and simulations shows that this model can reproduce the characteristics of time ...

Memory characteristics studies for large deflections in amorphous polymers: Experiments and numerical simulation:

In this work, the shape memory behaviour for large deflections in a ring-shaped epoxy-based shape memory polymer specimen is studied. A thermo-mechanical test setup was built to study the memory characteristics of ring shaped specimens with three different ratios of epoxy resin and hardener. Thermo-mechanical characterizations were also carried out to understand the material behaviour during shape fixing and recovery phases and also to obtain the material parameters for numerical simulations. Numerical simulations are carried out using a model proposed earlier by the authors based on the theory of multiple natural configurations and implemented using the VUMAT feature of ABAQUS commercial software. The simulation results for free shape recovery and constraint load recovery for large deflections confirm that the model performs well especially in relation to the memory dependent characteristics.

Effect of viscoelastic and dielectric relaxing matrix on ferroelastic behaviour of 1-3 piezocomposites

This work focuses on evaluating the time-dependent non-linear ferroelastic behaviour of 1-3 piezocomposites under pure uni-axial compressive stress loading condition. An experimental setup is developed to study the influence of high-stress levels on the stress-strain and stress-polarization behaviour of 1-3 piezocomposites. The electro-elastic effective properties of 1-3 piezocomposites are measured experimentally based on IEEE standard and compared with the proposed numerical model using finite-element software ABAQUS. The time-dependent effective properties are evaluated using viscoelastic model and it is incorporated into a 3D micromechanical model to predict the viscoelastic behaviour of 1-3 piezocomposites under mechanical loading. The simulated results are compared with the viscoelastic behaviour of 1-3 piezocomposites obtained from experiments.