Micromechanical Modelling of Cellular Ferroelectrets by Using Internal Variables

An internal variable model is used to investigate the charging and discharing behavior of a soft ferroelectret film. The model is able to describe electric breakdown in the polymer voids and takes into account the electrostatic forces between the interface charges. The bulk behavior is described by a Maxwell stress based electromechanical model which may account for finite deformations. The 2D finite element simulations focus on a cell of fluorinated ethylene propylene (FEP) containing lens-shaped porous expanded polytetrafluoroethylene (ePTFE). The simulations for a loading-unloading history show that, depending on the void size, breakdown in the ePTFE lenses takes place consecutively.