An FE model of a cellular polypropylene: exploring mechanical properties

Several analytical models have been suggested to describe the changes in the electromechanical properties of Cellular Polypropylene (Cell-PP) due to charging. However, there is a limited number of studies considering the non-linear dependence of the piezoelectric coefficient d₃₃ on the mechanical load applied. One of the main reasons for this nonlinearity is the stiffness of the film that increases proportionally to the applied mechanical load. Moreover the size and shape distribution of the enclosed voids is an important determinant of the electromechanical properties. In this work, the geometry of a 3D model of Cell-PP is designed on the basis of analytical Splines. Both the manufacturing procedure of Cell-PP films (bi-axial stretching) and the pressure expansion treatment were simulated in order to account for a realistic void distribution. The FEA is done on a 2D cross-section of the modelled film. The modelled mechanical response is analysed based on increasing mechanical load applied. The load-deflection curves obtained from the analysis are then compared to the experimental results acquired via Dynamical Mechanical Analyzer (DMA) to validate the model. Four types of Cell-PP films, expanded at different pressures, were used in this validation. The aim is to develop a model that describes the effect of morphological parameters on the stiffness of the films by simulating the manufacturing procedure.