Thermal stress intensity factors of crack in solid oxide fuel cells

Structural durability is the main focus of solid oxide fuel cells (SOFCs) development which is affected by the thermal stress caused by considerable CTE mismatch between components and thermal gradient. In this paper we investigate the thermal stress intensity factor for mode I, mode II and mode III of positive electrode-electrolyte-negative electrode (PEN) at room temperature and steady stage for an initial crack size of 10 μm. A commercial finite element analysis (FEA) was used to find the highly stressed regions in PENs and calculate the thermal stress intensity factors. The stress distributions are calculated at uniform room temperature and at steady stage with a non-uniform temperature profile. The thermal stress intensity factors are calculated for various principal directions at the location having the greatest maximum principal stress at room temperature and steady stage. The critical stress regions are identified based on the maximum principal stress at room temperature and steady stage. The maximum principal stress is of 53.45 MPa and 45.12 MPa in principal direction of -43.97° and -42.37° at room temperature and steady stage, respectively. The mixed-mode stress intensity factor including mode I, mode II, and mode III is calculated due to multi-axial thermal stresses. However, the stress intensity factor for mode I have a highest value compared to those for modes II and III. The principal direction has an effect on the thermal stress intensity factor for the critical region with the greatest maximum principal stress. All the calculated stress intensity factors in the present study are less than the corresponding fracture toughness given in the literature, ensuring the structural integrity for the given planar SOFC stack.