13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- The Crack Growth Behavior in electrolyte membrane under Mechanical-electrochemical Loading Yun J Chen1, Yi Sun1,*, Yi Z Liu1, Chen Wang1 1 Department of Astronautic Science and Mechanics, Harbin Institute of Technology, Harbin 150001, PR China * Corresponding author: sunyi@hit.edu.cn Abstract As the key component of SOFC (solid oxide fuel cell), a theoretical framework has been built to illustrate the coupling effect between oxygen vacancy concentration and stress field in early works. Here, the coupling theory is expanded and more affecting factors are taken into consideration. An electrolyte membrane with a macro crack is studied by a modified multi-scale method under fully coupling effect. It can be observed that the crack propagates with the increase of remote loadings, and the fracture mode is brittle fracture. The local stress concentration at the crack tip influences significantly the electromechanical fields and the fracture toughness of the stoichiometric sample (Ce0.8Gd0.2O1.9) may be reduced from 0.9493MPa•m1/2 of uncoupled value to 0.5142MPa•m1/2. It can be concluded that the coupling effect is important for the electrolyte in the working environment; especially in the case of the existence of a crack. Keywords: electrolyte membrane, mechanical-electrochemical coupling, multi-scale simuation, fracture toughness 1. Introduction As an energy conversion device, solid oxide fuel cell (SOFC) can generate high efficiency electric power without environment pollution[1], and it has attracted more and more attention for its excellent property. Meanwhile, as the core component, considerable researches have been completed to study the performance of the electrolyte[2]. The GDC (Gadolinium (Gd2O3) doped ceria (CeO2)) is regarded as a promising candidate electrolyte material for its higher ionic conductivity[3]. When two cerium ions (Ce4+) are replaced by gadolinium ions (Gd3+), an oxygen vacancy is generated to maintain electrical neutrality. And oxygen ions can transport through the electrolyte at high temperature. In the working environment, the effects of temperature and stress are inevitable, the electrolyte actually works in a complicated coupling field[4-6]. In the present work, a modified multi-scale method is introduced and applied to simulate the electrolyte with a crack under the full coupling effect. Based on the simulation results, the reasons and the process of the electrolyte failure can be further revealed. 2. Framework of the coupling effect 2.1. The stress-induced diffusion potential When the electrolyte (GDC) is at low oxygen partial pressure, extra oxygen vacancies are generated owing to reduction reaction, and the elastic constants of the material can be assumed a function of the vacancy concentration: ( ) 0 ijkl ijkl ijkl C C C d α α α ρ ρ α ρ ρ = = + ∂ ∂ ∑ (1)
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