Mechanical behavior of fuel cell membranes under humidity cycles and effect of swelling anisotropy on the fatigue stresses

The mechanical response of proton exchange membranes in a fuel cell assembly is investigated under humidity cycles at a constant temperature (85 degrees C). The behavior of the membrane under hydration-dehydration cycles is simulated by imposing a humidity gradient from the cathode to the anode. Linear elastic. plastic constitutive behavior with isotropic hardening and temperature and humidity dependent material properties are utilized in the simulations for the membrane. The evolution of the stresses and plastic deformation during the humidity cycles are determined using finite element analysis for two clamping methods and various levels of swelling anisotropy. The membrane response strongly depends on the swelling anisotropy where the stress amplitude decreases with increasing anisotropy. These results suggest that it may be possible to optimize a membrane with respect to swelling anisotropy to achieve better fatigue resistance, potentially enhancing the durability of fuel cell membranes. (c) 2007 Elsevier B.V. All rights reserved.