# Electromechanical Applications

## General Description

We have provided the electro-mechanical applications in KRATOS for the simulations of ferroelectric and piezoelectric materials. The code has been developed mainly to study the crack propagation in these materials but it can be effectively used for other purposes. Here we start from a brief theory of these materials and then we move to the numerical implementation in KRATOS. The theory of ferroelectric materials is presented in our published paper which can be accessed in the following link.

http://dx.doi.org/10.1016/j.actamat.2011.03.030

Abdollahi A, Arias I. Phase-field modeling of the coupled microstructure and fracture evolution in ferroelectric single crystals. Acta Mater (2011), doi:10.1016/j.actamat.2011.03.030

### Theory

The total electro-mechanical enthalpy for a ferroelectric body occupying a region is stated as:

where and ω are the tractions and surface charge density respectively, and and Γ_{N,φ} are the parts of the boundary of the domain where mechanical and electrical Neumann boundary conditions are applied. is the strain tensor associated with the mechanical displacement , , is the polarization, is the electric field defined as , where φ is the electric potential. *G*_{c} is the critical energy release rate or the surface energy density in Griffith's theory. The scalar field *v* provides a diffuse representation of the fracture zone, κ is a positive regularization constant to regulate the size of the fracture zone. The electro-mechanical enthalpy density *h* considering permeable and impermeable cracks follows

where the energy functions *U*, *W* and χ are stated as

where the combination of energy functions χ and *W* is the
total Landau-Devonshire energy density, *a*_{0} is the scaling
parameter of the domain wall energy, *b*_{i}(*i* = 1,2,3) are the
constants of the coupling terms between strain and polarization and
*c*_{i}(*i* = 1,2,3) are the elastic constants.

This model leads to to six degrees of freedom , , φ and *v* per node in the case of plane polarization and strain. NOTE that for the simulations of ferroelectric materials without considering a crack, the scalar field *v* should be fixed to 1 in all the domain. In this case, the degrees of freedom reduces to five.