Computational Characterization of Mechanical Behavior of Polymer Electrolyte Membrane Based on Nonaffine Molecular Chain Model

In this paper, a computational model is constituted based on the microstructural features of polymer electrolyte membrane (PEM). Assuming that the interaction between the water molecular and PEM molecular is quite weak, the cluster inside PEM is considered as void and the homogenization method is applied to constitute a unit cell model in which several voids are contained to represent the periodic microstructure of PEM. On the other hand, to account for the nonaffine movement of the molecular chains of PEM, the number of segment in a single chain is proposed as a function of the local stretch of the molecular chain and the constitutive equation of the matrix of PEM is constituted based on the nonaffine molecular chain model. It is found that this proposed model can reproduce the strain softening deformation behavior of PEM very well. Furthermore, a series simulations based on this proposed model are performed to discuss the effect of the water content and that of the triaxiality of macroscopic loading condition on the mechanical behavior of PEM. The results show that a relative quick development of the number of segments in a single chain is observed in the case of high water content and high triaxiality loading condition.