Effect of Time-Dependent Material Properties on the Mechanical Behavior of PFSA Membranes Subjected to Humidity Cycling
Journal of Power Sources
A viscoelastic-plastic constitutive model is developed to characterize the time-dependent mechanical response of perfluorosulphonic acid (PFSA) membranes. This model is then used in finite element simulations of a representative fuel cell unit, (consisting of electrodes, gas diffusion layer and bipolar plates) subjected to standardized relative humidity (RH) cycling test conditions. The effects of hold times at constant RH, the feed rate of humidified air and sorption rate of water into the membrane on the stress response are investigated. While the longer hold times at high and low humidity lead to considerable redistribution of the stresses, the lower feed and sorption rates were found to reduce the overall stress levels in the membrane. The redistribution and reduction in stress magnitudes along with inelastic deformation during hydration eventually lead to development of residual tensile stresses after dehydration. Simulations indicate that these tensile stresses can be on the order of 9–10 MPa which may lead to mechanical degradation of the membrane. The simulation results show that time-dependent properties can have a significant effect on the in-plane stress response of the membrane.
Khattra, N. S., Karlsson, A. M., Santare, M. H., 2012, "Effect of Time-Dependent Material Properties on the Mechanical Behavior of PFSA Membranes Subjected to Humidity Cycling," Journal of Power Sources, 214, pp. 365-376.
NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Power Sources. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Power Sources, 214, , (09-15-2012); 10.1016/j.jpowsour.2012.04.065
This research has been supported by DOE grant DE-FC36- 086018052 through a subcontract from W. L. Gore & Associates, Inc.