Fracture Properties of Fuel Cell Membranes
In a parallel study, a fracture mechanics-based model capable of simulating the in-situ crack initiation and propagation in the membrane during fuel cell operation is also developed. The elastic-viscoplastic nature of PFSA membranes is well-established in (2). A finite element method (FEM) based constitutive model that can simulate this behavior is used to relate the stress and strain at different environmental conditions (3). Numerical simulations reveal the presence of cyclic mechanical stresses within the membrane due to dynamic hygrothermal conditions present in a running fuel cell that can cause the initiation and propagation of cracks through mechanical membrane degradation. The dynamic stress-field thus obtained is coupled with the fracture mechanics model. In-situ test cases for various temperature, humidity and strain rate conditions are run to fully understand their effect on crack propagation rates and ultimate failure of the membranes.
This research is supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada through an Automotive Partnership Canada (APC) grant.
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2. M.A. Goulet, R.M.H. Khorasany, C. De Torres, M. Lauritzen, E. Kjeang, G.G. Wang, N. Rajapakse, J. Power Sources 234 38 (2013).