Residual fatigue life modeling of fuel cell membranes

Abstract Fuel cell membranes operate in a dynamically varying humid environment that introduces detrimental mechanical stresses which may lead the membrane to fatigue failure. The damage caused by these stresses is investigated using a cumulative-damage model and the residual membrane fatigue life is determined. A time-temperature-humidity dependent constitutive model is first developed based on material data obtained from a range of tensile experiments conducted at different conditions. The constitutive model is then incorporated into a multi-physics fuel cell finite element model developed to characterize the material behavior and estimate the coupled hygro-thermo-mechanical stress field in the membrane during fuel cell operation. Using this modeling approach, and with the aid of experimentally obtained fatigue data, fail-safe regions are identified for a given load spectrum corresponding to accelerated stress test and simulated drive cycle conditions. For each load spectrum, the distribution of stress-reversals is calculated for the load history using rainflow counting algorithm. In addition to identifying the regions of membrane that are more susceptible to fatigue damage, it is found that high amplitude stress cycles with low occurrence percentage are more severe than high occurrence low-amplitude cycles.