The role of viscoelasticity in the mechanical modelling of rubbers

Abstract

Bipolar plates (BPPs) are the main component in proton exchange membrane fuel cells. In the last years, different manufacturing processes have been proposed as alternative to the traditional graphite BPPs, including the manufacture of thin stamped BPPs using the rubber pad forming process. In this context, the numerical simulation of the forming process is used to optimize of the process parameters. Thus, in addition to the modelling of the elastoplastic behavior of the metallic sheet, it is also necessary to describe the hyper-viscoelastic behavior of the rubber pad. The main objective of this study is to evaluate the importance of the viscous effect on the global behavior of two different polyurethanes, since the modelling of the viscoelastic behavior is significantly more complex than the hyperelastic one. Uniaxial compression and stress relaxation tests are carried out both experimentally and numerically, considering three loading/unloading velocities. The hyperelastic behavior is described by the Mooney-Rivlin model, while the viscoelasticity is modelled by a series of Maxwell elements. The results show that the viscous effect can be neglected in the numerical modelling of the rubber pad forming, if the rubber hardness value is low.