The electrochemical performance of solid oxide fuel cell (SOFC) is significantly influenced by three-phase boundary (TPB) zones in the microstructure. TPB zones are locations where all three phases comprising the microstructure such as the two solid phases and the pore phase are present. Electrochemical reactions such as oxygen reduction occur near TPBs, and TPB density is believed to affect the polarization resistance of the cathode. In this regard, the effect of interface degradation under repeated thermal loading on the mechanical integrity and electrochemical performance of solid oxide fuel cell (SOFC) electrodes is studied through finite element simulations. Image-based 3-D models are used in this study, with additional interface zones at the boundaries between dissimilar solid phases. These interface zones are composed of 3-D cohesive elements of small thickness. The effect of interface degradation on mechanical integrity is studied by subjecting 50:50 LSM:YSZ wt.% cathode models to increasing levels of thermal load from room temperature (20°C) up to operating temperature (820°C). Energy quantities (e.g., strain energy and damage dissipation) for cathode models with and without cohesive interface zones are obtained through finite element analysis (FEA). These quantities are compared using energy balance concepts from fracture mechanics to gain insight into the effects of interface degradation on mechanical integrity.
Part of the book: Selected Problems of Contemporary Thermomechanics
This chapter addresses the behavior of functionally graded solids under dynamic impact loading within the framework of linear elasticity using parallel explicit algorithm. Numerical examples are presented that verify the dynamic explicit finite element code and demonstrate the dynamic response of graded materials. A three-point bending beam made of epoxy and glass phases under low-velocity impact is studied. Bending stress history for beam with higher values of material properties at the loading edge is consistently higher than that of the homogeneous beam and the beam with lower values of material properties at the loading edge. Larger bending stresses for the former beam may indicate earlier crack initiation times, which were proven by experiments performed by other researchers. Wave propagation in a 3D bar is also investigated. Poisson’s ratio and thickness effects are observed in the dynamic behavior of the bar. Finite element modeling and simulation discussed herein can be a critical tool to help understand physics behind the dynamic events.
Part of the book: Computational Models in Engineering