Elastic Brittle Damage Model of Ni-YSZ and Predicted Stress–Strain Relations as a Function of Temperature and Porosity

Abstract

Nickel-yttria stabilized zirconia (Ni-YSZ) is the most widely used material for solid oxide fuel cell (SOFC) anodes. Anode-supported SOFCs rely on the anode to provide mechanical strength to the positive–electrolyte–negative (PEN) structure. The stresses generated in the anode can result in the formation of microcracks that degrade its structural properties and electrochemical performance. In this paper, a brittle elastic damage model is developed for Ni-YSZ and implemented in finite element analysis with the help of a user-defined subroutine. The model is exploited to predict Ni-YSZ stress–strain relations at temperatures and porosities that are difficult to generate experimentally. It is observed that the anode material degradation depends on the level of strain regardless of the temperature at the same porosity: at higher temperature, lower load is required to produce a specified level of strain than at lower temperature. Conversely, the anode material degrades and fails at a lower level of strain at higher porosity at the same temperature. The information obtained from this research will be useful to establish material parameters to achieve optimal robustness of SOFC stacks.