Microcrack damage and nonlinear constitutive behavior of ferroelectric materials - a mesomechanical approach

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Microcracking accompanied with domain switching occurs in ferroelectric materials as a result of sufficiently high electric or mechanical loading. It also appears at relatively low load level during cyclic electrical loading. Nucleation, growth and coalescence of microcracks may not only lead to electric and mechanical fatigue and macroscopic cracking, but also degrade the effective properties of materials in the early stage of service. It is the aim of the project to establish a mesomechanically based macroscopic constitutive relation, taking into account domain switching and microcracking as interacting mechanisms. The analysis is based on the investigation of a ferroelectric multidomain unit cell with a single nucleating microcrack. The detailed electromechanical behaviour during electric loading and unloading is studied by analytical methods and numerically by the finite element method. For the meso-to-macro transition, Rice's concept of internal variables and the domain of microcrack growth theory (DMG) are used. The results of the theory will be compared with experimental findings from the literature for typical configurations.