A three dimensional, coupled computational fluid dynamics and finite element model of
a single, anode supported solid oxide fuel cell has been developed in order to predict
the probability of failure of the ceramic components subjected to an idealised operating
duty cycle. The duty cycle represents 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 StarCDTM computational fluid dynamics code provided the platform to determine
the temperature distribution throughout the operating fuel cell by solving the
conservation equations for energy, mass and momentum, with additional subroutines
written to account for species transport, electrochemical reactions and heat generation.
An AbaqusTM finite element model used the temperature distribution predicted by the
computational fluid dynamics model at low, medium and high power to solve for the
thermal stress distribution for individual cases and throughout the duty cycle. The
finite element model included the effects of thermal expansion, residual stress from manufacture,
material properties changes due to chemical reduction of the anode and viscoplastic
creep. The maximum principal stress in the anode support layer at 800◦C and
low, medium and high power was found to be 5.0, 26.5, 33.2 and 39.8 MPa respectively.
The stress analysis results were used to determine the time independent and time
dependent (accounting for sub-critical crack growth) probability of failure, and showed
that over the duty cycle sub-critical crack growth significantly increased the predicted
probability of failure in the anode support layer from less than 1 ×10−12 to 0.54, and in
the cathode layer from 1.28 × 10−5 to 1.24 × 10−3. The probability of failure of SOFC
ceramic components is thus shown to be both time and history dependent
