Time independent and time dependent probability of failure of solid oxide fuel cells by stress analysis and the Weibull method

Abstract

A prediction of the probability of failure of the ceramic layers of a Solid Oxide Fuel Cell (SOFC) has been made by combining the weakest link theory and the Weibull method. Analytical and finite element models of a single, anode supported solid oxide fuel cell were developed in order to predict the stress levels in the ceramic components of an SOFC subjected to an idealised operating duty cycle representing cooling from sintering, warming to a uniform temperature of 800 °C where anode chemical reduction takes place, operation at low, medium and high power and finally cooling to room temperature. The results of this analysis are the basis of an analysis of the time independent probability of failure of the ceramic components using both an analytical approach and the CARES™ software. CARES was also used to determine time dependent probability of failure, which takes into account the degradation of ceramic bulk failure strength over time by the slow growth of inherent flaws. The results indicate that the probability of failure of the individual layer volumes of a solid oxide fuel cell increases significantly over time due to slow crack growth.