Date of Completion

8-21-2013

Embargo Period

8-21-2013

Keywords

Finite element analysis, solid oxide fuel cell, microstructure, thermal stress, probability of failure, cohesive element

Major Advisor

Dr. Jeong-Ho Kim

Associate Advisor

Dr. Michael L. Accorsi

Associate Advisor

Dr. Ramesh B. Malla

Field of Study

Civil Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Finite element thermal stress analyses of solid oxide fuel cell (SOFC) electrode microstructure models are performed under various conditions to investigate mechanical integrity of electrodes under thermal loads. Image-based three-dimensional finite element models of electrode microstructures are generated from two-dimensional images of actual electrode cross-sections. Finite element thermal stress analyses of anode models under spatially uniform temperature fields of increasing magnitude are performed, and the effects of temperature-dependent material properties and plasticity on mechanical integrity are investigated. Linear elastic material models are found to underestimate the probability of failure of the anode at high temperatures. Analyses of cathode models are performed to study the effects of temperature-dependent material properties and varying phase volume fractions. An approximate heuristic scheme based on boundary pixel modification is developed, validated, and used to derive a microstructure of varying composition from the original microstructure. Limited variations in ceramic phase volume fractions are found to have limited effect on probability of failure of models having temperature-independent material properties, with higher pore volume fraction leading to higher probability of failure. Consideration of temperature-dependent material properties leads to lower probability of failure for the cathode models compared with temperature-independent material properties. Interface degradation under repeated thermal loading is simulated using cohesive elements. Effects of damage on mechanical integrity and electrochemical performance are studied. Three-phase boundary evolution due to mechanical interface damage is evaluated. Three-phase boundary density is found to decrease over a number of heating cycles, indicating that interface damage may be a major mechanism responsible for SOFC performance degradation over time.

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