Multiscale modeling of the strain-induced α → ß phase transition and piezoelectric activity in semi-crystalline poly(vinylidene fluoride) over a large-strain range

The present contribution investigates within a hierarchical multi-scale approach the relation between the macroscopic properties of semi-crystalline poly (vinylidene fluoride) (PVDF) and the transition from the a-phase to the ss-phase crystalline structure in the course of a mechanical loading. A continuum-based constitutive model is proposed to capture the large-strain material behavior of PVDF, the amorphous molecular network orientation/ relaxation process, the strain-induced morphological anisotropy induced by the crystallographic texturing and the strain-induced alpha -> ss phase transition; the mechanical coupling between the deformation modes in alpha-PVDF, ss-PVDF and amorphous domains is obtained by considering the interfacial interactions in the micro-macro homogenization procedure. Fundamental parameters from molecular dynamics simulations, such as the amorphous, a crystalline and ss crystalline properties along with the onset of alpha -> ss phase transition caused by the straining of a-PVDF, are transferred to the continuum scale. By completing the scale bridging method by the identification of the other model parameters, the model outputs are found in good agreement with the existing tensile experiments of a PVDF upon large-strain plastic deformation. The profound influence of the straininduced alpha -> ss phase transition and the crystallographic texturing operated upon large-strain plastic deformation in the piezoelectric activity is finally investigated numerically.