Meso-scale stress response of thin ceramic membranes with honeycomb support
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Meso-scale stress response of thin ceramic membranes with honeycomb support Ryan B. Berke • Mark E. Walter
Received: 7 May 2013 / Accepted: 30 September 2013 / Published online: 11 October 2013 Springer Science+Business Media Dordrecht 2013
Abstract Planar solid oxide fuel cells are made up of repeating sequences of electrolytes, electrodes, seals, and current collectors. For electrochemical reasons it is best to keep the electrolyte as thin as possible. However, for electrolyte-supported cells, the thin electrolytes are susceptible to damage during production, assembly, and operation. One of the latest generation electrolytes employs a meso-scale honeycomb layer to support thin, electrochemically efficient membranes. Using finite element analysis, a two-scale model computes distributions of first principal stresses throughout a representative unit cell of the meso-scale structure. Displacement at the macro-scale is informed by meso-scale geometry via a homogenized equivalent stiffness, while the stresses at the two scales are related via a scalar magnification factor. The magnification factor is computed for a variety of geometries and loading conditions. Physical specimens are measured in tension to obtain an experimental magnification factor which agrees well with the simulations. When both the stiffness and magnification factor for a given meso-scale pattern are known, the macro-scale geometry can be analyzed without revisiting the mesoscale model, thus reducing computational time and costs.
R. B. Berke M. E. Walter (&) Department of Mechanical and Aerospace Engineering, The Ohio State University, 201 W. 19th Ave, Columbus, OH 43210, USA e-mail: [email protected]
Keywords Thin ceramic membranes Honeycomb support Solid oxide fuel cell Meso-scale finite element simulation Stress magnification
1 Introduction Fuel cells are electro-chemical devices which produce electricity from chemical reactions and are characterized by two electrodes separated by a solid electrolyte (Haile 2003; Ormerod 2003). The electrolyte in a solid oxide fuel cell (SOFC) is typically a stabilized zirconia (Sammes et al. 2005). Zirconia is an electrically insulating ceramic with good ionic conductivity. For maximum efficiency it is critical that oxygen ions produced at the cathode can easily move across the electrolyte to the anode. To increase ionic conductivity, either the operating temperature must be very high or the electrolyte must be made very thin (Minh 2004). To enable metal components to be used between cells, the operating temperatures must be kept in the 600–800 C range (Wu and Liu 2010). Therefore the only realistic way to have high ionic conductivity is by making the ceramic electrolytes as thin as possible. SOFCs are often categorized by which component in the assembly provides the primary mechanical support, usually the anode or the electrolyte. Electrolyte-supported cells are advantageous over anodesupported cells because they are less susceptible to
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Fig. 1 Geometry of th
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