Mismatch effect of material creep strength on creep damage and failure probability of planar solid oxide fuel cell

The creep and failure probability of a planar solid oxide fuel cell (SOFC) through a duty cycle is calculated by finite element method (FEM) and Weibull method, respectively. Two sealing methods, namely, rigid seal and bonded compliant seal (BCS), are compared. For the rigid seal, failure is predicted in the glass ceramic because of a failure probability of 1 and maximum creep strain. For the BCS design, the foil can absorb part of thermal stresses in the cell by its own elastoplastic deformation, which considerably decreases failure probability and creep strain in the SOFC. The creep strength of BCS method is achieved by sealing foil with excellent creep properties. Temperature fluctuation during the operating stage leads to the increase in thermal stress and failure probability. In particular, temperature change from low-power to high-power state results in a considerable increase in the creep strain, leading to creep failure for the rigid seal. A failure probability of 1 is generated during start-up and shut-down stages. Therefore, temperature fluctuation should be controlled to ensure structural integrity, and lowering the operating temperature can decrease failure probability and creep failure.

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Probabilistic-Based Design Methodology for Solid Oxide Fuel Cell Stacks

Journal of Fuel Cell Science and Technology ◽

10.1115/1.2971054 ◽

2009 ◽

Vol 6 (2) ◽

Author(s):

X. Sun ◽

A. M. Tartakovsky ◽

M. A. Khaleel

Keyword(s):

Fuel Cell ◽

Solid Oxide Fuel Cell ◽

Failure Probability ◽

Material Properties ◽

Design Methodology ◽

Operating Conditions ◽

Solid Oxide ◽

Utilization Rate ◽

Oxide Fuel ◽

Average Cell

A probabilistic-based component design methodology is developed for a solid oxide fuel cell (SOFC) stack. This method takes into account the randomness in SOFC material properties as well as the stresses arising from different manufacturing and operating conditions. The purpose of this work is to provide the SOFC designers a design methodology so that the desired level of component reliability can be achieved with deterministic design functions using an equivalent safety factor to account for the uncertainties in material properties and structural stresses. Multiphysics-based finite element analyses were used to predict the electrochemical and thermal mechanical responses of SOFC stacks with different geometric variations and under different operating conditions. Failures in the anode and the seal were used as design examples. The predicted maximum principal stresses in the anode and the seal were compared with the experimentally determined strength characteristics for the anode and the seal, respectively. Component failure probabilities for the current design were then calculated under different operating conditions. It was found that anode failure probability is very low under all conditions examined. The seal failure probability is relatively high, particularly for high fuel utilization rate under low average cell temperature. Next, the procedures for calculating the equivalent safety factors for the anode and seal were demonstrated so that a uniform failure probability of the anode and seal can be achieved. Analysis procedures were also included for non-normal distributed random variables so that more realistic distributions of strength and stress can be analyzed using the proposed design methodology.

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